9. Juni 2010

184 Studien pro MWP

Im Folgenden werde ich 184 Studien anführen, in welchen die Studienautoren Evidenz für die Existenz einer MWP, im Gebiet der Studienuntersuchung,  aufweisen.
Genaueres siehe einleitend unten (Medieval Warm Period Project Table Describtions).

Diese Studien wurden von den Klimawissenschaftern Idso und deren Webpräsenz co2science.org übernommen, und dahingehend richtig zitiert.

Die Studiengebiete erstrecken sich auf alle Kontinente, Hemisphären und Ozeane im Vergleichszeitraum 2003-2010 incl.:

Afrika: 11 Studien
Antarktis: 5 Studien
Asien: 39 Studien
Australien/ Neuseeland: 3 Studien
Europa: 53 Studien
Nord Amerika: 46 Studien
Nördliche Hemisphäre: 2 Studien
Ozeane: 12 Studien
Süd Amerika: 13 Studien

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Medieval Warm Period Project Table Descriptions

Level 1 Studies
Studies that allow a quantitative comparison to be made between the temperatures of the Medieval Warm Period (MWP) and the Current Warm Period (CWP). These reports are very important, especially those that reveal the MWP to have been warmer than the CWP and that were published after the papers of Mann et al. (1998, 1999) appeared, because the authors of such Level 1 reports likely knew that their findings were not in harmony with the contemporary position of the Intergovernmental Panel on Climate Change, which strongly endorsed the Mann et al. papers that claimed the warmth of the latter part of the 20th century was unprecedented over the entire past millennium. Authors of more recent Level 1 papers have additionally had to contend with the contrary force of the paper of Mann and Jones (2003), which claimed that the warmth of the latter part of the 20th century was unprecedented over the past two millennia. Hence, it can be appreciated that the authors of many Level 1 papers were really "sticking their necks out" when reporting something considered by much of the scientific community to be incorrect, which would tend to give special credence to the sincerity of their belief in the validity of their data.

Level 2 Studies
Studies that allow a qualitative comparison to be made between the temperatures of the Medieval and Current Warm Periods. They enable one to determine if peak MWP temperatures were warmer than, equivalent to, or cooler than, peak CWP temperatures, but they do not enable one to determine how much warmer or cooler they may have been. Many of these studies, i.e., those that indicate the MWP was warmer than the CWP, were also published by scientists who likely knew their findings were not in harmony with the position of the scientific establishment, nor, for that matter, with the views of the political establishments of most of the world's nations, which again bears testimony to the strength of their faith in their findings.

Level 3 Studies
Studies that simply indicate the Medieval Warm Period did indeed occur in the studied regions. They may seem rather innocuous, but many of them may also be considered to be "politically incorrect," in that they contradict the climate-alarmist claim that the MWP, if it occurred at all, was only a regional phenomenon experienced by lands significantly influenced by the North Atlantic Ocean. In this level we include certain studies that are based on data related to parameters other than temperature, such as precipitation. These studies, however, are only used to help define the timeframe of the MWP; they are not employed to infer anything about either its quantitative or qualitative thermal strength.

References
Mann, M.E., Bradley, R.S. and Hughes, M.K. 1998. Global-scale temperature patterns and climate forcing over the past six centuries. Nature 392: 779-787.

Mann, M.E., Bradley, R.S. and Hughes, M.K. 1999. Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations. Geophysical Research Letters 26: 759-762.

Mann, M.E. and Jones, P.D. 2003. Global surface temperatures over the past two millennia. Geophysical Research Letters 30: 10.1029/2003GL017814.

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Africa
Level 2 Studies

High, Middle and Rif Atlas Mountains, Morocco, Northwest Africa

Reference
Esper, J., Frank, D., Buntgen, U., Verstege, A., Luterbacher, J. and Xoplaki, E. 2007. Long-term drought severity variations in Morocco. Geophysical Research Letters 34: 10.1029/2007GL030844.

Description
Esper et al. (2007) used Cedrus atlantica tree-ring width data to reconstruct long-term changes of the Palmer Drought Severity Index (PDSI) over nearly a full millennium in the part of Morocco (northwest Africa) centered on approximately 34 N, 5 W. This analysis revealed that "millennium-long temperature reconstructions from Europe (Bungten et al., 2006) and the Northern Hemisphere (Esper et al., 2002) indicate that Moroccan drought changes are broadly coherent with well-documented temperature fluctuations including warmth during medieval times, cold in the Little Ice Age, and recent anthropogenic warming." In addition, they report that the driest 20-year period of their reconstruction was 1237-1256 (with a PDSI of -4.2), while the driest 20-year period of the 20th century was 1981-2000 (with a less extreme PDSI of -3.9). Hence, a strict interpretation of the coherence that exists between Esper et al.'s (2007) PDSI history and European and Northern Hemispheric temperatures suggests that the peak warmth of the Medieval Warm Period was likely greater than the peak warmth of the 20th century over the entire Northern Hemisphere.

Additional References

Buntgen, U., Frank, D.C., Nievergelt, D. and Esper, J. 2006. Summer temperature variations in the European Alps, A.D. 755-2004. Journal of Climate 19: 5606-5623.

Esper, J., Cook, E.R. and Schweingruber, F.H. 2002. Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science 295: 2250-2253.



Level 3 Studies

Cold Air Cave, Makapansgat Valley of South Africa

Reference
Holmgren, K., Lee-Thorp, J.A., Cooper, G.R.J., Lundblad, K., Partridge, T.C., Scott, L., Sithaldeen, R., Talma, A.S. and Tyson, P.D. 2003. Persistent millennial-scale climatic variability over the past 25,000 years in Southern Africa. Quaternary Science Reviews 22: 2311-2326.

Description
General climatic conditions in the vicinity of Cold Air Cave (24 1'S, 29 11'E) in the Makapansgat Valley of South Africa were inferred from high-resolution oxygen and carbon stable isotope data obtained from two TIMS U-series dated stalagmites. Climate during the Medieval Warm Period was warm and wet between 800 and 1400 AD.



Crescent Island Crater Lake, Kenya

Reference
Lamb, H., Darbyshire, I. and Verschuren, D. 2003. Vegetation response to rainfall variation and human impact in central Kenya during the past 1100 years. The Holocene 13: 285-292.

Description
The authors present high-resolution pollen data from an 1100-year sediment core taken from Crescent Island Crater Lake (0.75 S, 36.37 E), a subbasin of Lake Naivasha, in the central Rift Valley of Kenya, which served as a proxy record of changes in the balance between regional precipitation and evaporation. The Medieval Warm Period (~ AD 900-1200) was identified as a prolonged period of drought in which the surrounding forest contracted and the lake level dropped. Furthermore, from the authors' Figure 3 it can be seen that the MWP drought was of greater magnitude and duration than recent 20th century drought.



Lake Edward, Uganda Congo

Reference
Russell, J.M. and Johnson, T.C. 2005. A high-resolution geochemical record from Lake Edward, Uganda Congo and the timing and causes of tropical African drought during the late Holocene. Quaternary Science Reviews 24: 1375-1389.

Description
The authors analyzed % biogenic silica (%BSi) from piston cores retrieved from Lake Edward (0 N, 30 E), Uganda Congo, equatorial East Africa. Correlation of %BSi with other climatologically-forced geochemical and lake level records from other equatorial African lakes further allowed them to develop a regional precipitation and drought history over the past 5400 years. Results indicated that drought affected "virtually all of tropical East Africa" between ~AD 1000 and 1200, which falls well within the era of the Medieval Warm Period.



Lake Hayq, North-central Highlands of South Wollo, Ethiopia

Reference
Lamb, H.F., Leng, M.J., Telford, R.J., Ayenew, T. and Umer, M. 2007. Oxygen and carbon isotope composition of authigenic carbonate from an Ethiopian lake: a climate record of the last 2000 years. The Holocene 17: 517-526.

Description
Lamb et al. developed a 2000-year history of effective precipitation based upon oxygen and carbon isotope and pollen stratigraphy data derived from a sediment core taken from Lake Hayq (11 21'N, 39 43'E) on the eastern margin of the north-central highlands in South Wollo, Ethiopia. This record revealed, in their words, that a "similar, but slightly moister climate than today, with high interdecadal variability, prevailed from AD 800 to AD 1200, equivalent to the European 'Mediaeval Warm Period'," and that "a period of high effective precipitation followed, from AD 1200 to AD 1700, during the 'Little Ice Age'."



Lake Kamalété , Central Gabon

Reference
Ngomanda, A., Chepstow-Lusty, A., Makaya, M., Schevin, P., Maley, J., Fontugne, M., Oslisly, R., Rabenkogo, N. and Jolly, D. 2005. Vegetation changes during the past 1300 years in western equatorial Africa: a high-resolution pollen record from Lake Kamal t , Lop  Reserve, Central Gabon. The Holocene 15: 1021-1031.

Description
Ngomanda et al. (2005) analyzed a high-resolution sediment core retrieved from Lake Kamal t  in the southeast corner of the Lop  Reserve of central Gabon (~ 0.72 S, 11.77 E), producing a record of vegetation changes over the past 1300 years. The results revealed a period of forest regression from ~AD 760-1450 in which the dry season was "more prolonged and more severe" than it is today, indicative of a "wider distribution" of the hydro-thermal "climatic anomaly" that was the MWP than just the mid-latitudes of the Northern Hemisphere.



Lake Kamalété, Gabon, Western Equatorial Africa

Reference
Ngomanda, A., Jolly, D., Bentaleb, I., Chepstow-Lusty, A., Makaya, M., Maley, J., Fontugne, M., Oslisly, R. and Rabenkogo, N. 2007. Lowland rainforest response to hydrological changes during the last 1500 years in Gabon, Western Equatorial Africa. Quaternary Research 67: 411-425.

Description
Based on analyses of pollen and total organic carbon δ13C derived from sediment cores extracted from Lake Kamal t  (0 43'S, 11 46'E) and Lake Ngu ne (0 12'S, 10 28'E) in Gabon, Africa, Ngomanda et al. detected "strong fluctuations of wet-dry conditions during the Northern Hemisphere 'Medieval Warm Period' (1100-800 cal yr BP)," which were notable for their contrast to the more consistently "dry conditions during the 'Little Ice Age' (500-300 cal yr BP)."



Lake Nguène, Gabon, Western Equatorial Africa

Reference
Ngomanda, A., Jolly, D., Bentaleb, I., Chepstow-Lusty, A., Makaya, M., Maley, J., Fontugne, M., Oslisly, R. and Rabenkogo, N. 2007. Lowland rainforest response to hydrological changes during the last 1500 years in Gabon, Western Equatorial Africa. Quaternary Research 67: 411-425.

Description
Based on analyses of pollen and total organic carbon δ13C derived from sediment cores extracted from Lake Kamal t  (0 43'S, 11 46'E) and Lake Ngu ne (0 12'S, 10 28'E) in Gabon, Africa, Ngomanda et al. detected "strong fluctuations of wet-dry conditions during the Northern Hemisphere 'Medieval Warm Period' (1100-800 cal yr BP)," which were notable for their contrast to the more consistently "dry conditions during the 'Little Ice Age' (500-300 cal yr BP)."



Nile River, Egypt

Reference
Kondrashov, D., Feliks, Y. and Ghil, M. 2005. Oscillatory modes of extended Nile River records (A.D. 622-1922). Geophysical Research Letters 32, L10702, doi:10.1029/2004GL022156, 2005.

Description
The authors applied advanced spectral methods (Singular-Spectrum Analysis and Multi-Taper Method) to historical records of low- and high-water levels of the Nile River (~30 N, 31.2 E) in an effort to better characterize their interannual and interdecadal periodicities. The results revealed that "drastic changes" occurred around AD 1000 in the dominant lower frequencies of all the Nile River records they analyzed, suggesting that a "fairly abrupt" shift in climate occurred near the beginning of the Medieval Warm Period. In addition, Singular-Spectrum Analysis of the 7.2-year mode in the Nile River records revealed a large increase in amplitude between AD 950 and 1450; and Kondrashov et al. cite "several authors, who used different analysis methods," who "all found evidence of climate shifts at the beginning and/or at the end of the Medieval Warm Period."



Pilkington Bay, Lake Victoria, East Africa

Reference
Stager, J.C., Cumming, B.F. and Meeker, L.D. 2003. A 10,000-year high-resolution diatom record from Pilkington Bay, Lake Victoria, East Africa. Quaternary Research 59: 172-181.

Description
The authors analyzed diatom types and abundances found in a sediment core retrieved from Pilkington Bay, Lake Victoria, East Africa (0 18'N, 33 20'E), relating them to the ratio of precipitation to evaporation (P/E) and/or lake depth. This work revealed, in their words, that "major droughts occurred ca. 1200-600 yr B.P. during Europe's Medieval Warm Period."



Sossusvlei, Namib Desert, Namibia

Reference
Vogel, J.C. 2003. The age of dead trees at Sossusvlei and Tsondabvlei, Namib Desert, Namibia. Cimbebasia 18: 247-251.

Description
The author radiocarbon dated stands of dead Acacia erioloba trees from locations within the central Namib Desert. Results indicated that trees growing near Sossusvlei (24.75 S, 15.28 E) started growing in the 11th-12th century "during the relatively humid conditions of the Medieval Warm Period and died out after the more arid conditions of the Little Ice Age set in during the 14th century."




Antarctica
Level 2 Studies

Amery Ice Shelf, Antarctica

Reference
Hemer, M.A. and Harris, P.T. 2003. Sediment core from beneath the Amery Ice Shelf, East Antarctica, suggests mid-Holocene ice-shelf retreat. Geology 31: 127-130.

Description
Changes in the location of the edge of the Amery Ice Shelf were inferred from measurements of biogenic opal, absolute diatom abundance and the abundance of Fragilariopsis curta found in sediments retrieved from beneath the ice shelf at a point that is currently 80 km from land's edge. The MWP at ca. 750 14C yr BP was likely warmer than at any time during the CWP.



Collins Ice Cap, King George Island, Antarctica

Reference
Hall, B.L. 2007. Late-Holocene advance of the Collins Ice Cap, King George Island, South Shetland Islands. The Holocene 17: 1253-1258.

Description
The author presents "radiocarbon and geomorphologic data that constrain [the] late-Holocene extent of the Collins Ice Cap on Fildes Peninsula (King George Island, South Shetland Islands: 62 10'51"S, 58 54'13"W)," based on field mapping of moraines and glacial deposits adjacent to the ice cap, as well as radiocarbon dates of associated organic materials. This work yielded, in Hall's words, "information on times in the past when climate in the South Shetland Islands must have been as warm as or warmer than today," with the specific period of this warmth indicated to stretch backwards in time from about AD 1300, which latter date would signify the end of this period of significant warmth, i.e., the Medieval Warm Period, with no date given as to its beginning.



Sombre Lake, Signy Island, Antarctica

Reference
Noon, P.E., Leng, M.J. and Jones, V.J.  2003.  Oxygen-isotope (δ18O) evidence of Holocene hydrological changes at Signy Island, maritime Antarctica.  The Holocene 13: 251-263.

Description
Primarily summer climatic conditions were inferred from a δ18O record preserved in authigenic carbonate retrieved from sediments of Sombre Lake (60 43'S, 45 38'W) on Signy Island, maritime Antarctica.  The Medieval Warm Period (AD 1130-1215) was warmer than the Current Warm Period.



Victoria Land Coast, Antarctica

Reference
Hall, B.L., Hoelzel, A.R., Baroni, C., Denton, G.H., Le Boeuf, B.J., Overturf, B. and Topf, A.L. 2006. Holocene elephant seal distribution implies warmer-than-present climate in the Ross Sea. Proceedings of the National Academy of Sciences USA 103: 10,213-10,217.

Description
The authors collected skin and hair - and even some whole-body mummified remains - from raised-beach excavations at various locations along Antarctica's Victoria Land Coast (~77 30'S, 163 30'E) that they identified by both visual inspection and DNA analysis as coming from southern elephant seals (Mirounga leonina) and which they analyzed for age by means of radiocarbon dating. Results from fourteen different locations - which they describe as being "well south" of the seals' current "core sub-Antarctic breeding and molting grounds" - indicate that what they call the Seal Optimum began about 600 BC and ended about AD1400, "broadly contemporaneous with the onset of Little Ice Age climatic conditions in the Northern Hemisphere and with glacier advance near [Victoria Land's] Terra Nova Bay." These findings, in their words, indicate "warmer-than-present climate conditions" over a period of time that encompassed both the Medieval and Roman Warm Periods, as well as the intervening Dark Ages Cold Period, and that "if, as proposed in the literature, the [Ross] ice shelf survived this period, it would have been exposed to environments substantially [our italics] warmer than present."



Level 3 Studies

Dome C, Antarctica

Reference
Castellano, E., Becagli, S., Hansson, M., Hutterli, M., Petit, J.R., Rampino, M.R., Severi, M., Steffensen, J.P., Traversi, R. and Udisti, R. 2005. Holocene volcanic history as recorded in the sulfate stratigraphy of the European Project for Ice Coring in Antarctica Dome C (EDC96) ice core. Journal of Geophysical Research 110: Do6114, doi:10.1029/2004JD005259.

Description
The authors analyzed sulfate ice core stratigraphy from Dome C, Antarctica (75.10 S, 123.40 E) to obtain a record of Holocene volcanic eruptions, which they compared with other volcanic indices throughout Antarctica. Sulfate depositional fluxes of individual volcanic events were found to vary greatly among the different sites, which variation was attributed to changes in atmospheric circulation driven by climate forcing; and the team of ten researchers concluded that "changes in the extent and intra-Antarctic variability of volcanic depositional fluxes may have been consequences of the establishment of a Medieval Warming-like period that lasted [from about 1000] until about 1500 AD."




Asia
Level 1 Studies

A Big Chunk of Eastern China

Reference
Ge, Q., Zheng, J., Fang, X., Man, Z., Zhang, X., Zhang, P. and Wang, W.-C. 2003. Winter half-year temperature reconstruction for the middle and lower reaches of the Yellow River and Yangtze River, China, during the past 2000 years. The Holocene 13: 933-940.

Description
Working with 200 different sets of phenological and meteorological records extracted from a number of historical sources, Ge et al. produced a 2000-year history of winter half-year temperature (October to April) for the region of China bounded by latitudes 27 and 40 N and longitudes 107 and 120 E. This effort revealed that following the Dark Ages Cold Period, "temperature entered a warm epoch from the AD 570s to 1310s," when peak warmth "was about 0.3-0.6 C higher than present for 30-year periods, but over 0.9 C warmer on a 10-year basis," after which the cooling that led to the Little Ice Age commenced. Most recently, Ge et al. report that "temperature has been rising rapidly during the twentieth century, especially for the period 1981-99." However, they find that the current mean temperature is only "0.5 C higher than for 1951-80." Hence, it can be appreciated that for the big chunk of China Ge et al. studied, the 10-year-mean peak MWP warmth was approximately 0.4 C higher than today's peak warmth.



Lake Qinghai, China

Reference
Liu, Z., Henderson, A.C.G. and Huang, Y. 2006. Alkenone-based reconstruction of late-Holocene surface temperature and salinity changes in Lake Qinghai, China. Geophysical Research Letters 33: 10.1029/2006GL026151.

Description
The authors developed a quantitative reconstruction of temperature changes over the past 3500 years based on alkenone distribution patterns in a sediment core retrieved from China's Lake Qinghai (37 N, 100 E), based on the alkenone unsaturation index that has been calibrated to the growth temperature of marine alkenone producers and "to temperature changes in lacustrine settings on a regional scale." This work revealed that the peak warmth of the Medieval Warm Period (AD 900-1500) exceeded the temperature of the latter part of the 20th century by about 0.5 C.



Lake Teletskoye, Altai Mountains, Southern Siberia, Russia

Reference
Kalugin, I., Daryin, A., Smolyaninova, L., Andreev, A., Diekmann, B. and Khlystov, O. 2007. 800-yr-long records of annual air temperature and precipitation over southern Siberia inferred from Teletskoye Lake sediments. Quaternary Research 67: 400-410.

Description
The authors collected several sediment cores from the deepest area of Teletskoye Lake (51 39'N, 87 40'E) in the Altai Mountains of southern Siberia, for which they measured the spectra of numerous elements - including Ba, Cd, Ce, I, La, Mo, Nb, Rb, Sb, Sn, Sr, Th, U, Y, Zr - after which "artificial neural networks were used for reconstruction of annual temperature and precipitation by sediment properties." This work revealed that the mean peak temperature of the latter part of the Medieval Warm Period was about 0.5 C higher than the mean peak temperature of the Current Warm Period.




Lake Teletskoye, Altai Mountains of Southern Siberia, Russia

Reference
Andreev, A.A., Pierau, R., Kalugin, I.A., Daryin, A.V., Smolyaninova, L.G. and Diekmann, B. 2007. Environmental changes in the northern Altai during the last millennium documented in Lake Teletskoye pollen record. Quaternary Research 67: 394-399.

Description
Working with a sediment core extracted from the central and deepest part of Lake Teletskoye in the northeastern part of the Altai Mountains in southern Siberia (51 43'N, 87 39'E), the authors analyzed pollen and charcoal stratigraphy to develop "the first detailed climate and vegetation reconstruction for the last millennium in the northern Altai Mountains." This work revealed the existence of a period "at least since ca. AD 1020" when "climate conditions were similar to modern [our italics]." Then, "around AD 1200, climate became more humid with the temperatures probably higher than today [our italics]," and this period "lasted until AD 1410."



Mixing Zone of the Kuroshio and Oyashio Currents, Off the Coast of Japan

Reference
Isono, D., Yamamoto, M., Irino, T., Oba, T., Murayama, M., Nakamura, T. and Kawahata, H. 2009. The 1500-year climate oscillation in the midlatitude North Pacific during the Holocene. Geology 37: 591-594.

Description
Working with three sediment cores retrieved off the coast of central Japan in the northwestern Pacific Ocean (36 02'N, 141 47'E), Isono et al. generated a multidecadal-resolution record of alkenone-derived sea surface temperature (SST) that covers the full expanse of the Holocene, which they then analyzed in a number of different ways. This record, in their words, "showed centennial and millennial variability with an amplitude of ~1 C throughout the entire Holocene," and they state that "spectral analysis for SST variation revealed a statistically significant peak with 1470-year periodicity." At the latter end of the record, Isono et al. report that "SST minima centered at ca. 0.3 ka and ca. 1.5 ka are correlated with the Little Ice Age and the Dark Ages Cold Period in Europe, respectively, whereas the SST maximum centered at ca. 1.0 ka is correlated with the Medieval Warm Period." From data presented in the authors' Figure 2, we estimate that the MWP was about 1 C warmer than the Current Warm Period.



Permafrost Regions of Qinghai-Tibet Plateau

Reference
Jin, H.J., Chang, X.L. and Wang, S.L. 2007. Evolution of permafrost on the Qinghai-Xizang (Tibet) Plateau since the end of the late Pleistocene. Journal of Geophysical Research 112: 10.1029/2006JF000521.

Description
The authors describe "the evolutionary history of permafrost in the central and eastern Qinghai-Tibetan Plateau since the end of the late Pleistocene, using relict permafrost and periglacial phenomena along the Qinghai-Tibet Highway from Gomud to Lhasa, the Qinghai-Kang (western Sichuan) Highway from Xi'ning to Yusu, adjacent areas, and the Xinjiang-Tibet Highway from Yecheng to Lhasa." Among their many findings they report that during "the warm period in the later Holocene (1000 to 500 years BP)," the "retreating of permafrost resulted in a total permafrost area of ~20-30% less than at present," while mean annual air temperatures were "1.5-2.0 C warmer than at present."



Polar Ural Mountains, Russia

Reference
Mazepa, V.S. 2005. Stand density in the last millennium at the upper tree-line ecotone in the Polar Ural Mountains. Canadian Journal of Forest Research 35: 2082-2091.

Description
Over the period 1999-2001, the author examined evidence related to historical tree growth dynamics along a continuous altitudinal transect 860 meters long and 40-80 meters wide on the eastern slope of the Polar Ural Mountains (66 48'57"N, 65 34'09"E). This work revealed that "a large number of well-preserved tree remains can be found up to 60-80 meters above the current tree line, some dating to as early as a maximum of 1300 years ago," and that "the earliest distinct maximum in stand density occurred in the 11th to 13th centuries, coincident with Medieval climatic warming." Since Marzepa cites many studies that conclude that "increases in tree-line elevation, and associated increases in tree abundance within the transient tree-line ecotone, are associated with extended warm periods," and that "the vertical gradient of summer air temperature in the Polar Urals is 0.7 C/100 m," we conclude that the Medieval Warm Period lasted from approximately AD 700 to 1300 and that significant portions of it were as much as 0.56 C warmer than the Current Warm Period.



Level 2 Studies

Bol'shoi Avam River, Putoran Plateau, North Central Siberia, Russia

Reference
Sidorova, O.V., Vaganov, E.A., Naurzbaev, M.M., Shishov, V.V. and Hughes, M.K. 2007. Regional features of the radial growth of larch in North Central Siberia according to millennial tree-ring chronologies. Russian Journal of Ecology 38: 90-93.

Description
The authors developed a history of trunk radial growth increment of larch (Larix gmelinii Rupr.) trees in the middle reaches of the Bol'shoi Avam River on the northern edge of the Putoran Plateau, central Taimyr (70 30'N, 93 01'E) for the period AD 886-2003, which they found to be correlated with summer air temperature. This work revealed a period of time from the start of the record to approximately AD 1200, when inferred temperatures were generally much greater than those of the final decades of the 20th century.



Buddha Cave, Qin Ling Mountains, Central China

Reference
Paulsen, D.E., Li, H.-C. and Ku, T.-L. 2003. Climate variability in central China over the last 1270 years revealed by high-resolution stalagmite records. Quaternary Science Reviews 22: 691-701.

Description
The authors used high-resolution records of δ13C and δ18O in stalagmite SF-1 from Buddha Cave (33 40'N, 109 05'E) to infer changes in climate in central China for the last 1270 years in terms of "warmer, colder, wetter and drier conditions," and among the climatic episodes evident in those data were, in the words of the three researchers, "those corresponding to the Medieval Warm Period, Little Ice Age and 20th-century warming, lending support to the global extent of these events." The MWP was further identified by them as having occurred over the period AD 965-1475, and according to the data presented in their Figure 6, the peak warmth of the MWP is below that of the Current Warm Period.



All of China

Reference
Ge, Q., Wang, S., Wen, X., Shen, C. and Hao, Z. 2007. Temperature and precipitation changes in China during the Holocene. Advances in Atmospheric Sciences 24: 1024-1036.

Description
Ge et al. reviewed proxy temperature records of China that span the entire Holocene, while providing greatest emphasis on the last 2000 years. Their evaluation of this prior work indicated that "during the past two millennia, a warming trend in the 20th century was clearly detected, but the warming magnitude was smaller than the maximum level of the Medieval Warm Period," which they describe as having occurred between AD 900 and 1300.



Duck Pond, Yangmingshan National Park, Northern Taiwan

Reference
Chen, S.-H., Wu, J.-T., Yang, T.-N., Chuang, P.-P., Huang, S.-Y. and Wang, Y.-S. 2009. Lat Holocene paleoenvironmental changes in subtropical Taiwan inferred from pollen and diatoms in lake sediments. Journal of Paleolimnology 41: 315-327.

Description
Working with a sediment core that "represents deposition from AD 650 to present" that was taken from a mountain lake (Duck Pond, 25 10.441'N, 121 33.013'E) in Northern Taiwan, the authors identified, measured and analyzed "pollen, spores, diatoms, organic carbon, nitrogen, and δ13C of organic matter in lake sediments to infer climate changes and reconstruct the paleo-environment of subtropical Taiwan over the past ~1300 years," temporally delineating five different climate zones in the process. Zone III (AD 1050-1250), as they describe it, was "wet and warmer; ~MWP [Medieval Warm Period]", Zone IV (AD 1250-1790) was "wetter and colder than in Zone III; corresponding to LIA [Little Ice Age]," and Zone V (AD 1790-2000) was "drier and warmer than in Zone IV." In commenting further on these delineations, they say that "in Europe and other regions, there was a short warm period (the medieval warm period, or MWP) prior to the LIA," and that their "Zones III and IV likely correspond to such warm and cold periods." In addition, they report that the ratio of arboreal pollen (AP) to non-arboreal pollen (NAP) "showed a positive correlation with temperature," and on the basis of this relationship, plus the fact that the peak AP/NAP ratio of the MWP was about three times greater than the peak AP/NAP ratio of the CWP, the peak warmth of the former period must have been considerably greater than the peak warmth of the latter period.



Dunde Ice Cap, Tibetan Plateau

Reference
Thompson, L.G., Mosley-Thompson, E., Davis, M.E., Lin, P.-N., Henderson, K. and Mashiotta, T.A. 2003. Tropical glacier and ice core evidence of climate change on annual to millennial time scales. Climatic Change 59: 137-155.

Description
The authors analyzed decadally-averaged δ18O records derived by them and their colleagues from three Andean and three Tibetan ice cores, demonstrating that "on centennial to millennial time scales atmospheric temperature is the principal control on the δ18Oice of the snowfall that sustains these high mountain ice fields," after which they produced "a low latitude δ18O history for the last millennium" that they use as a surrogate for air temperature. For the Dunde Ice Cap (38.1 N, 96.4 E), this work revealed several instances throughout prior centuries when average decadal temperatures were greater than those experienced over the last few decades of the 20th century.



East-Central Tibet, China

Reference
Brauning, A. and Griessinger, J. 2006. Late Holocene variations in monsoon intensity in the Tibetan-Himalayan region - Evidence from tree rings. Journal of the Geological Society of India 68: 485-493.

Description
The researchers analyzed δ13C data obtained from wood cellulose of annual growth rings of long-lived juniper (Juniperus tibetica) trees growing at a site in east-central Tibet at approximately 31.8 N, 92.4 E, which were significantly positively correlated with summer temperatures of the surrounding region. This exercise, in the words of Brauning and Griessinger, indicated "warm and dry conditions during the Medieval Warm Period between AD 1200 and 1400." In addition, their graph of the data revealed the peak temperature of the MWP to have been greater than the peak temperature of the CWP.



Guliya Ice Cap, Tibetan Plateau

Reference
Thompson, L.G., Mosley-Thompson, E., Davis, M.E., Lin, P.-N., Henderson, K. and Mashiotta, T.A. 2003. Tropical glacier and ice core evidence of climate change on annual to millennial time scales. Climatic Change 59: 137-155.

Description
The authors analyzed decadally-averaged δ18O records derived by them and their colleagues from three Andean and three Tibetan ice cores, demonstrating that "on centennial to millennial time scales atmospheric temperature is the principal control on the δ18Oice of the snowfall that sustains these high mountain ice fields," after which they produced "a low latitude δ18O history for the last millennium" that they use as a surrogate for air temperature. For the Guliya Ice Cap (35.28 N, 81.48 E), this work revealed several instances throughout prior centuries when average decadal temperatures were greater than that experienced over the last few decades of the 20th century.



Lake Chen Co, Southern Tibet, China

Reference
Zhu, L.-p., Zhang, P.-z., Xia, W.-l., Li, B.-y. and Chen, L. 2003. 1400-year cold/warm fluctuations reflected by environmental magnetism of a lake sediment core from the Chen Co, southern Tibet, China. Journal of Paleolimnology 29: 391-401.

Description
Working with magnetic particles of different grain size found in a sediment core covering the period AD 593-1998 that was extracted from Lake Chen Co in southern Tibet (China, 28 56'N, 90 36'E), the authors measured a number of magnetic properties, including "low-frequency dependent susceptibility, susceptibility of anhysteretic remanent magnetism, the saturation isothermal remanent magnetism [and] the isothermal remanent magnetism reverse." This work revealed three warm periods: one near the beginning of the record, one in the middle (1120-1370, which they call the "Middle Ages Warm-period"), and one at the end (1900-1998). Of these three, Zhu et al. concluded that "the warmest one occurred in ca. 1120-1370."



Lake Sugan, Northeastern Tibetan Plateau, China

Reference
Qiang, M., Chen, F., Zhang, J., Gao, S. and Zhou, A. 2005. Climatic changes documented by stable isotopes of sedimentary carbonate in Lake Sugan, northeastern Tibetan Plateau of China, since 2 kaBP. Chinese Science Bulletin 50: 1930-1939.

Description
Stable carbon isotope analyses were conducted on sediment cores taken from Lake Sugan (38 51.19'N, 93 54.09'E), located in the northeastern region of the Tibetan Plateau to produce a proxy of winter temperatures over the past 2,000 years. The results indicated a warm and dry period between 580 and 1200 AD, which they state "corresponds to the Medieval Warm Period." A view of the data in the author's Figure 3 reveals the MWP was probably at least as warm between ~AD 1100 and 1200 as it is presently .



Lake Teletskoye, Altai Mountains of Southern Siberia

Reference
Kalugin, I., Selegei, V., Goldberg, E. and Seret, G. 2005. Rhythmic fine-grained sediment deposition in Lake Teletskoye, Altai, Siberia, in relation to regional climate change. Quaternary International 136: 5-13.

Description
Sediment cores from Lake Teletskoye in the Altai Mountains of Southern Siberia (51 42.90'N, 87 39.50'E) were analyzed to produce a multi-proxy climate record spanning the past 800 years. The Medieval Warm Period was identifed as a climatic period evidenced between the start of the authors' record in 1210 AD and ending around 1480 AD that was "warmer and more humid than today."



Longxi Area of the Northeast Tibetan Plateau, China

Reference
Tan, L., Cai, Y., An, Z. and Ai, L. 2008. Precipitation variations of Longxi, northeast margin of Tibetan Plateau since AD 960 and their relationship with solar activity. Climate of the Past 4: 19-28.

Description
The authors developed a precipitation history of the Longxi area of the Tibetan Plateau's northeast margin (~34 30'N to 36 18'N, 103 25'E to 106 10'E) since AD 960, based on an analysis of Chinese historical records. This history correlated well with the Northern Hemisphere's temperature record, yielding high precipitation when temperatures were high and low precipitation when temperatures were low; and it revealed the existence of an MWP that stretched from about AD 960 to 1230, with precipitation peaks (which we assume can be used to infer temperature peaks) in the vicinity of AD 1000 and 1215 that clearly exceeded all precipitation levels (and, we assume, temperature levels) of the CWP through the end of the record, which looked to be just a few years shy of AD 2000.




Lop Nur, Tarim Basin, Xinjiang, China

Reference
Ma, C-M., Wang, F-B., Cao, Q-Y., Xia, X-C., Li, S-F. and Li, X-S. 2008. Climate and environment reconstruction during the Medieval Warm Period in Lop Nur of Xinjiang, China. Chinese Science Bulletin 53: 3016-3027.

Description
The authors analyzed multi-proxy data, including, in their words, "14C, grain size, microfossil, plant seeds, and geochemical elements" -- which they obtained from sediment retrieved from excavations made in the dry lake bed of Lop Nur China's West Lake (40 27'129" N, 90 20'083" E) -- in order "to amply discuss," as they describe it, "the climate and environment changes during the MWP," or Medieval Warm Period, which they identified as occurring between AD 900 and 1300. This work indicated that the peak temperature of the MWP was, in their estimation, "a little higher than nowadays."




Naychhudwari Bog, Himachal Pradesh, India

Reference
Chauhan, M.S. 2006. Late Holocene vegetation and climate change in the alpine belt of Himachal Pradesh. Current Science 91: 1562-1567.

Description
Chauhan analyzed pollen profiles derived from a 1-m-deep sediment core retrieved from Naychhudwari Bog (77 43'E, 32 30'N), Himachal Pradesh, northern India. Distributions of the different types of pollen revealed two broad climatic episodes of warm-moist and cold-dry conditions, the first covering the period AD 650 to 1200 and the second from AD 1500 onwards. "In the global perspective," to quote the author, the first period "is equivalent to the Medieval Warm Period, which has been witnessed in most parts of the world [our italics]," while the second period "falls within the time-limit of [the] Little Ice Age." In addition, Chauhan states that from AD 1500 onwards "the glaciers advanced and consequently the tree-line descended under the impact of [the] cold and dry climate in the region," which suggests that (1) the region has not yet become as warm as it was during medieval times, or (2) if such a level of warmth has been achieved, its temporal existence falls far short of that of the much longer sustained warmth of the Medieval Warm Period, or (3) both of the above.



Northeastern Tibetan Plateau

Reference
Liu, Y., An, Z., Ma, H., Cai, Q., Liu, Z., Kutzbach, J.K., Shi, J., Song, H., Sun, J., Yi, L., Li, Q., Yang, Y. and Wang, L. 2006. Precipitation variation in the northeastern Tibetan Plateau recorded by the tree rings since 850 AD and its relevance to the Northern Hemisphere temperature. Science in China: Series D Earth Sciences 49: 408-420.

Description
The authors used three well-dated Sabina Przewalskii ring-width chronologies derived from a total of 77 trees growing in three locations near Dulan, China, on the northeastern Tibetan Plateau (36.0-36.3 N, 98.2-98.6 E), to reconstruct annual precipitation variations in that region over the period AD 850-2002, after which they compared the results with instrumental temperature data for the same region over the period of temporal overlap. This protocol produced a 40-year moving average that was so well correlated with seven temperature curves of the Northern Hemisphere that they concluded it "could be regarded as the millenary temperature curve for the northeastern Tibetan Plateau," and this curve revealed that a group of 40-year-averaged temperature proxies in the vicinity of AD 915 were definitely greater than the highest such average at the end of the 20th century, which comprised the next highest peak of the record.



Northern Russian Treeline, Russia

Reference
MacDonald, G.M., Kremenetski, K.V. and Beilman, D.W. 2008. Climate change and the northern Russian treeline zone. Philosophical Transactions of the Royal Society B 363: 2285-2299.

Description
The authors conducted an analysis of past changes in the northern Russian treeline, as reconstructed from tree-ring data and radiocarbon-dated subfossil wood. This work revealed, in their words, that "temperature increases over the past century are already producing demonstrable changes in the population density of trees, but these changes have not yet generated an extension of conifer species' limits to or beyond the former positions occupied during the Medieval Warm Period (MWP: ca AD 800-1300)," indicative of the fact that "the impact of twentieth century warming has not yet compensated fully for the mortality and range constriction caused by the cold temperatures of the Little Ice Age," specifically mentioning, in this regard, the central Kola Peninsula and the northern Polar Urals.



Paradise Lake, Tawang District, Arunachal Pradesh, India

Reference
Bhattacharyya, A., Sharma, J., Shah, S.K. and Chaudhary, V. 2007. Climatic changes during the last 1800 yrs BP from Paradise Lake, Sela Pass, Arunachal Pradesh, Northeast Himalaya. Current Science 93: 983-987.

Description
The authors developed a history of atmospheric warmth and moisture covering the last 1800 years for Paradise Lake in the Northeastern Himalaya (27 30.324'N, 92 06.269'E), based on pollen and carbon isotopic (δ13C) analyses of a one-meter-long sediment profile they obtained from a pit "dug along the dry bed of the lakeshore." This work revealed a "warm and moist climate, similar to the prevailing present-day conditions," around AD 240, as well as another such period that turned out to be "more warmer [our italics] 1100 yrs BP (around AD 985) corresponding to the Medieval Warm Period".



Qilian Mountains, Tibetan Plateau, China

Reference
Liu, X., Shao, X., Zhao, L., Qin, D., Chen, T. and Ren, J. 2007. Dendroclimatic temperature record derived from tree-ring width and stable carbon isotope chronologies in the Middle Qilian Mountains, China. Arctic, Antarctic, and Alpine Research 39: 651-657.

Description
Based on ring-width and δ13C data derived from long-lived Qilian juniper trees in the middle Qilian Mountains of China (37-39 N, ~99-103 E), Liu et al. (2007) reconstructed a 1000-year temperature history of the region that captures approximately 75% of the temperature variance over the calibration period of 1960-2000 and correlates extremely well with a well-established Northern Hemisphere temperature reconstruction. The six researchers say the two warmest intervals of their new temperature history are 1060-1150 and 1900-2000, with peaks occurring around 1100 and 1999; and in viewing the graph of their results, the peak temperatures of these two times look identical. However, the new temperature history does not extend as far back in time as the hemispheric temperature history, which rises to its highest level prior to the time that Liu et al.'s history begins. As a result, Liu et al. conclude that their temperature reconstruction "has not included all of the Medieval Warm Period and, perhaps, not even its warmest period [our italics]." All we can report, therefore, is that the MWP of this study encompasses AD 1060-1150, and that the MWP = CWP at least, although the earlier portion of the MWP was probably warmer than the CWP at this location.



Song Hong (Red River) Delta, Vietnam

Reference
Li, Z., Saito, Y., Matsumoto, E., Wang, Y., Tanabe, S. and Vu, Q.L. 2006. Climate change and human impact on the Song Hong (Red River) Delta, Vietnam, during the Holocene. Quaternary International 144: 4-28.

Description
The authors conducted palynological analyses of two sediment cores taken from the Song Hong (Red River) Delta, Vietnam (~20.26 N, 106.52 E) in an effort to reconstruct climate variations there throughout the Holocene. As indicated by an abundance of taxa well adapted to tropical and subtropical environments, they concluded that the Medieval Warm Period (~AD 500-1330) was warmer than the present climate.



Western Slope of the Northern Okinawa Trough, East China Sea

Reference
Fengming, C., Tiegang, L., Lihua, Z. and Jun, Y. 2008. A Holocene paleotemperature record based on radiolaria from the northern Okinawa Trough (East China Sea). Quaternary International 183: 115-122.

Description
Using a well-established radiolarian-based transfer function, the authors developed a mean annual sea surface temperature (SST) history of the last 10,500 years based on data derived from the top 390 cm of a gravity core recovered from the western slope of the northern Okinawa Trough (29 13.93'N, 128 53'E) of the East China Sea. This effort indicated the existence of the MWP (~ AD 750-1250) and Little Ice Age (~ AD 300-600), after which it began to warm once again. However, the warming was short-lived, with the mean annual SST actually reversing its course and falling slightly below the coldest value of the entire Little Ice Age at about AD 1950, where the SST history terminates. Hence, we presume that current SSTs at this location are likely considerably lower than they were during the peak warmth of the MWP, having had insufficient time to once again reverse course and warm to such an elevated level from their lowest level of the past 1300 years.



Yangtze River Delta, China

Reference
Zhang, Q., Gemmer, M. and Chen, J. 2008. Climate changes and flood/drought risk in the Yangtze Delta, China, during the past millennium. Quaternary International 176-177: 62-69.

Description
Based on a study of historical documents covering the period AD 1000-1950 and actual instrumental data from meteorological stations for the period 1950-2003, Zhang et al. developed a millennial-scale temperature index for the Yangtze Delta region of China that revealed "three distinct climate periods" - the "Warm Medieval Period (AD 1000-1400), Little Ice Age (AD 1400-1920), and the ongoing well-established Global Warming Period (AD 1920-present)." Based on this record, it can readily be determined there was a continuous period from about AD 1200 to 1235 when it was significantly warmer than the peak warmth recorded during the "well-established Global Warming Period."



Level 3 Studies

Dandak Cave, Kanger Valley National Park, Chhattisgarh, India

Reference
Sinha, A., Cannariato, K.G., Stott, L.D., Cheng, H., Edwards, R.L., Yadava, M.G., Ramesh, R. and Singh, I.B. 2007. A 900-year (600 to 1500 A.D.) record of the Indian summer monsoon precipitation from the core monsoon zone of India. Geophysical Research Letters 34: 10.1029/2007GL030431.

Description
Working with data collected from India's Dandak Cave (19 00'N, 83 00'E), the authors derived a near-annually resolved record of Indian summer monsoon rainfall variations for the core monsoon region of India for the period 600-1500 AD, based on a 230Th-dated stalagmite δ18O record. This work revealed the existence of the Medieval Warm Period, which they designated as occurring between about AD 920 and 1340, and which they found to have been a much wetter regime than the subsequent Little Ice Age.



Dulan, Northeastern Qinghai-Tibetan Plateau, China

Reference
Zhang, Q.-B., Cheng, G., Yao, T., Kang, X. and Huang, J. 2003. A 2,326-year tree-ring record of climate variability on the northeastern Qinghai-Tibetan Plateau. Geophysical Research Letters 30: 10.1029/2003GL017425.

Description
Zhang et al. collected tree-ring samples from (1) well-preserved Sabina przewalskii tree trunks that had been used as building blocks in ancient tombs in the Dulan area (35 50' ~ 36 30'N, 97 40' ~ 98 20'E) of the Qinghai-Tibetan Plateau, (2) tree trunks employed in building local cabins, and (3) living sabina trees in the same area, in order to crossdate annual growth rings of the ancient tree trunks and establish a climate-growth relationship for the trees, which they accomplished using regional means of climatic data measured at three nearby meteorological stations over the period 1953-2000. This work allowed them to reconstruct an annually-resolved 2,326-year tree-ring chronology (stretching from 326 BC to AD 2000) that was "most strongly correlated with the spring precipitation (May-June, r = 0.58, p < 0.001)," which indicates, in their words, that "moisture stress in [the] growing season is a major limiting factor to tree-ring growth." In addition, they state that "this result is in general agreement with that observed in dendro-climatological studies of the same species in other areas of the Qinghai-Tibetan Plateau, suggesting that the annual growth rings mainly reflect variations in regional spring precipitation." As shown by the graphical representation of their data in the figure below, therefore, we conclude that the MWP in the Dulan area (as defined by spring precipitation) held sway from about AD 820 to AD 1100.



Lake Baikal, Russia

Reference
Mackay, A.W., Ryves, D.B., Battarbee, R.W., Flower, R.J., Jewson, D., Rioual, P. and Sturm, M.  2005.  1000 years of climate variability in central Asia: assessing the evidence using Lake Baikal (Russia) diatom assemblages and the application of a diatom-inferred model of snow cover on the lake.  Global and Planetary Change 46: 281-297.

Description
Based on diatom assemblage data obtained from a lake sediment core taken from the south basin of Lake Baikal, Russia (51 24'06"N, 104 31'43"E), the MWP (AD 880-1180) was described by the authors as "a relatively warm" period.



Lake Biwa, Central Japan

Reference
Goto, S., Hamamoto, H. and Yamano, M. 2005. Climatic and environmental changes at southeastern coast of Lake Biwa over past 3000 years, inferred from borehole temperature data. Physics of the Earth and Planetary Interiors 152: 314-325.

Description
The authors reconstructed the ground surface temperature history from a borehole off the southern coast of Lake Biwa, the largest and oldest lake in Japan, to produce a proxy climate record spanning the past 3000 years. The Medieval Warm Period was described as a period of warmth from the 8th to the 12th century A.D. Comparison of the magnitude of warmth during the Medieval and Current Warm Periods, however, could not be made because of anthropogenic and environmental factors influencing the record.



North-Central China

Reference
Porter, S.C. and Weijian, Z. 2006. Synchronism of Holocene East Asian monsoon variations and North Atlantic drift-ice tracers. Quaternary Research 65: 443-449.

Description
Eighteen radiocarbon-dated aeolian and paleosol profiles (some obtained by the authors and some by others) within a 1500-km-long belt along the arid to semi-arid transition zone of north-central China (35-44 N, 100-117 E) were used to identify, respectively, mild/moist summer conditions and cold/dry winter conditions throughout the Holocene. One of the mild/moist periods was sandwiched between a cold/dry interval (the Dark Ages Cold Period) that ended about AD 810 and a cold/dry period (the Little Ice Age) that began about AD 1370. Allowing 50 years of transition at the end and start of these cold/dry periods, we have a Medieval Warm Period that ran from approximately AD 860 to AD 1320.



Northwestern Arabian Sea

Reference
Gupta, A.K., Das, M. and Anderson, D.M. 2005. Solar influence on the Indian summer monsoon during the Holocene. Geophysical Research Letters 32: doi:10.1029/2005GL022685.

Description
A high-resolution record of variations in the Indian summer monsoon derived from relative abundances of the planktic foraminifer Globigerina bulloides obtained from a sediment core off the coast of Oman in the northwestern Arabian Sea (18 03.08'N, 57 36.56'E) indicated that southwest monsoon winds were stronger during the Medieval Warm Period (AD 800-1300), coincident with a period of high solar activity.



Pinder Valley, Kumaon Higher Himalaya of India

Reference
Phadtare, N.R. and Pant, R.K. 2006. A century-scale pollen record of vegetation and climate history during the past 3500 years in the Pinder Valley, Kumaon Higher Himalaya, India. Journal of the Geological Society of India 68: 495-506.

Description
Based on a study of the pollen and organic matter content and magnetic susceptibility of radiocarbon-dated samples from a peat deposit in the Kumaon Higher Himalaya of India (30 3'N, 70 56'E), the authors developed a 3500-year palaeoclimate record of the Late Holocene. In describing this record they say that "with an abrupt rise in temperature as well as moisture at ~AD 400, the climate suddenly turned warm and moist and remained so until ~AD 1260," which time interval, according to them, is "generally referred to as the Medieval Warm Period in the Northern Hemisphere."




Qinghai Lake, China

Reference
Ji, J., Shen, J., Balsam, W., Chen, J., Liu, L. and Liu, X. 2005. Asian monsoon oscillations in the northeastern Qinghai-Tibet Plateau since the late glacial as interpreted from visible reflectance of Qinghai Lake sediments. Earth and Planetary Science Letters 233: 61-70.

Description
Reflectance spectroscopy was applied to a sediment core taken from the southeastern basin of Qinghai Lake, China (36 32' to 37 15'N, 99 36' to 100 47'E). Sediment redness, which is related to iron oxide content, was judged to be an indicator of paleoclimatic changes in the core. Lower redness values were found to generally correlate with light, laminated sediments "associated with cold periods including the Little Ice Age (LIA)," whereas "warm periods, e.g., Medieval Warm Period (MWP), ... were marked by the accumulation of reddish-colored sediments." Based upon these findings we can judge the MWP to have been a long warm and wet period (AD 400-1200, the MWP) sandwiched between the cold and dry spells of the Dark Ages Cold Period (100 BC-200 AD) and Little Ice Age (AD 1220-1600).



Sugan Lake, Northwest China

Reference
Chen, J.H., Chen, F.H., Zhang, E.L., Brooks, S.J., Zhou, A.F. and Zhang, J.W. 2009. A 1000-year chironomid-based salinity reconstruction from varved sediments of Sugan Lake, Qaidam Basin, arid Northwest China, and its palaeoclimatic significance. Chinese Science Bulletin 54: 3749-3759.

Description
Studying varved sediments retrieved from cores extracted from Sugan Lake (38 51'N, 93 54'E) on the northern Tibetan Plateau, the authors developed a 1000-year high-resolution (~10 years) salinity history of the lake, based on the relative abundances of different chironomid species they identified via microscopic examination of head capsules found in the sediments. This work suggested, in their words, that "over the last millennium, the Sugan Lake catchment has alternated between contrasting climatic conditions, having a dry climate during the period AD 990-1550, a relative humid climate during the Little Ice Age (AD 1550-1840), and a dry climate again from AD 1840 onwards," and they associate the first of the three periods with "the Medieval Warm Period in China," which they describe as being "warm and dry."



Western Liaohe River Basin, Inner Mongolia, Northeastern China

Reference
Li, Y.Y., Willis, K.J., Zhou, L.P. and Cui, H.T. 2006. The impact of ancient civilization on the northeastern Chinese landscape: palaeoecological evidence from the Western Liaohe River Basin, Inner Mongolia. Holocene 16: 1109-1121.

Description
The authors conducted a number of proxy analyses, including palynology, microfossil charcoal, stable isotopes (δ13C and δ15N) and sediment geochemistry, on a 3.6-m sediment core taken from a relict oxbow lake in the Western Liaohe River Basin (42.07 N, 119.92 E) of northeastern China in an effort to reconstruct the environmental history of that region over the past 5400 years. The results indicated the existence of a period of enhanced warmth and wetness from about AD 800 to 1400, which they associated with the Medieval Warm Period. Since they did not discuss the degree of warmth, however, we classify this paper as a Level 3 study, which merely confirms the existence and timeframe of the MWP.



Yakushima Island, Southern Japan

Reference
Cini Castagnoli, G., Taricco, C. and Alessio, S.  2005.  Isotopic record in a marine shallow-water core: Imprint of solar centennial cycles in the past 2 millennia.  Advances in Space Research 35: 504-508.

Description
Based on δ13C data from a two-millennia-long tree-ring record of Japanese cedars growing on Yakushima Island, southern Japan (30 20'N, 130 30'E), the authors identify the Medieval Warm Period as an interval of high temperature between 800 and 1200 AD.



Yangtze River Delta, China

Reference
Yi, S., Saito, Y., Chen, Z. and Yang, D.Y. 2006. Palynological study on vegetation and climatic change in the subaqueous Changjian (Yangtze River) delta, China, during the past about 1600 years. Geosciences Journal 10: 17-22.

Description
The authors analyzed arboreal pollen, non-arboreal pollen and spores contained in a sediment core retrieved from the Changjiang prodelta (31 01.1'N, 122 47.0'E). This effort revealed, in their words, "relatively warm/wet conditions comparable to [the] Medieval Warm Period (AD 910-1085) with a strengthen[ed] summer monsoon." Based on the findings of others, they further state that "the mean temperature during this period was 1-2 C warmer than that of today." Since Yi et al.'s own work does not resolve actual temperature values, however, we classify this particular analysis as a Level 3 Study.




Australia/NewZealand
Level 2 Studies

Caves at Waitomo, on New Zealand's North Island

Reference
Williams, P.W., King, D.N.T., Zhao, J.-X. and Collerson, K.D.  2004.  Speleothem master chronologies: combined Holocene 18O and 13C records from the North Island of New Zealand and their palaeoenvironmental interpretation.  The Holocene 14: 194-208.

Description
Temperatures were inferred from δ18O data obtained from four stalagmites found in caves at Waitomo (38.3 S, 175.1 E) on New Zealand's North Island for which 19 TIMS uranium series ages were measured.  The Medieval Warm Period occurred between AD 1100 and 1400 and was warmer than the Current Warm Period.



Level 3 Studies


New Zealand's Eastern North Island

Reference
Lorrey, A., Williams, P., Salinger, J., Martin, T., Palmer, J., Fowler, A., Zhao, J.-X. and Neil, H. 2008. Speleothem stable isotope records interpreted within a multi-proxy framework and implications for New Zealand palaeoclimate reconstruction. Quaternary International 187: 52-75.

Description
A master speleothem δ18O record (which is a proxy for temperature) was developed for New Zealand's eastern North Island for the period 2000 BC to about AD 1660 from data acquired from three speleothems of Disbelief and Te Reinga caves. This record revealed that the warmest time interval of the nearly 4000 years occurred between about AD 900 and 1100. Because the record did not extend beyond AD 1660, however, we cannot compare peak MWP warmth with peak CWP warmth.



New Zealand's Western South Island

Reference
Lorrey, A., Williams, P., Salinger, J., Martin, T., Palmer, J., Fowler, A., Zhao, J.-X. and Neil, H. 2008. Speleothem stable isotope records interpreted within a multi-proxy framework and implications for New Zealand palaeoclimate reconstruction. Quaternary International 187: 52-75.

Description
A master speleothem δ18O record (which is a proxy for temperature) was developed for New Zealand's western South Island for the period 2000 BC to about AD 1825 from data acquired from four speleothems of Aurora, Calcite, Doubtful Xanadu and Waiau caves. This record revealed that the warmest time interval of the nearly 4000 years occurred between about AD 900 and 1100. Because the record did not extend beyond AD 1825, however, we cannot compare peak MWP warmth with peak CWP warmth.




Europe
Level 1 Studies

Apennines, Italy

Reference
Giraudi, C. 2005. Middle to Late Holocene glacial variations, periglacial processes and alluvial sedimentation on the higher Apennine massifs (Italy). Quaternary Research 64: 176-184.

Description
Based on current relationships between elevation and soil periglacial and glacial processes, Giraudi estimated that the mean annual temperature on higher Apennine massifs in Italy (42 23'N, 13 31'E) from approximately AD 700 to 1030 were "higher than at present," and that winter temperatures were "at least 0.9 C higher" than those of today.



Austrian Alps

Reference
Büntgen, U., Esper, J., Frank, D.C., Nicolussi, K. and Schmidhalter, M. 2005. A 1052-year tree-ring proxy for Alpine summer temperatures. Climate Dynamics 25: 141-153.

Description
A 1052-year summer (June-August) temperature proxy from high elevation Alpine environments in Switzerland and the western Austrian Alps (between 46 28' to 47 00'N and 7 49' to 11 30'E) was derived via regional curve standardization applied to ring-width measurements from living trees and relict wood. Described as a period of warmer temperatures preceding the Little Ice Age, the MWP was present from the beginning of the authors' record in AD 951 to ~ AD 1350. From their Figure 7a it can be estimated that the Medieval Warm Period was about 0.8 C cooler than the Current Warm Period, albeit the authors acknowledge that "the significance of this notion is limited, since the number of chronologies and samples is reduced in recent years."



Central Scandinavian Mountains, Sweden

Reference
Linderholm, H.W. and Gunnarson, B.E. 2005. Summer temperature variability in central Scandinavia during the last 3600 years. Geografiska Annaler 87A: 231-241.

Description
Summer temperatures were inferred from a tree-ring width chronology derived from living and subfossil Scots pines (Pinus sylvestris L.) sampled close to the present tree-line in the central Scandinavian Mountains (63 10'N, 12 25'-13 35'E) spanning the time period from 2893 BC to AD 2002. Between AD 900 and 1000, summer temperature anomalies were as much as 1.5 C warmer than the 1961-1990 base period.



Lake Korttajarvi, Central Finland

Reference
Tiljander, M., Saarnisto, M., Ojala, A.E.K. and Saarinen, T.  2003.  A 3000-year palaeoenvironmental record from annually laminated sediment of Lake Korttajarvi, central Finland.  Boreas 26: 566-577.

Description
Winter temperatures were inferred from analyses of varve thickness, relative X-ray density, pollen and diatom profiles and organic matter loss-on-ignition data obtained from annually-laminated sediments of Lake Korttajarvi (62 20'N, 25 41'E) in central Finland.  The Medieval Warm Period occurred between AD 980 and 1250 and was as much as 2 C warmer than the Current Warm Period.



Lake Redon, Central Pyrenees, Northeast Spain

Reference
Pla, S. and Catalan, J. 2005. Chrysophyte cysts from lake sediments reveal the submillennial winter/spring climate variability in the northwestern Mediterranean region throughout the Holocene. Climate Dynamics 24: 263-278.

Description
The authors analyzed chrysophyte cyst data collected from a sediment core obtained from Lake Redon (42.64 N, 0.77 E) in the Central and Eastern Pyrenees of northeast Spain, producing a history of winter/spring temperatures for this region throughout the Holocene. The Medieval Warm Period (~ AD 875 to 1000) was categorized as the "warmest period" of the record, with temperatures about 0.25 C warmer than it is currently.



Lake Stora Viöarvatn, Northeast Iceland

Reference
Axford, Y., Geirsdottir, A., Miller, G.H. and Langdon, P.G. 2009. Climate of the Little Ice Age and the past 2000 years in northeast Iceland inferred from chironomids and other lake sediment proxies. Journal of Paleolimnology 41: 7-24.

Description
The authors developed a regional climatic record from a sediment core retrieved from lake Stora Viöarvatn in northeast Iceland (66 14.232'N, 15 50.083'W) in the summer of 2005, based on chironomid assemblage data that were well correlated with nearby measured temperatures over the 170-year period of the instrumental record. With respect to the MWP, the four researchers report that their data indicated "warm temperatures in the tenth and eleventh centuries, with one data point suggesting temperatures slightly warmer than present," which -- as best we can determine from the graph of their results, reproduced below, -- yields a peak MWP temperature 0.4 C greater than the peak CWP temperature.



Lake Tsuolbmajavri, Finnish Lapland

Reference
Weckstrom, J., Korhola, A., Erasto, P. and Holmstrom, L. 2006. Temperature patterns over the past eight centuries in Northern Fennoscandia inferred from sedimentary diatoms. Quaternary Research 66: 78-86.

Description
The authors developed a high-resolution quantitative history of temperature variability over the past 800 years, based on analyses of diatoms found in a sediment core retrieved from a treeline lake - Lake Tsuolbmajavri (68 41'N, 22 05'E) - in Finnish Lapland. It revealed that what they call the "termination phase of the MWP" - which they indicate as having occurred between AD 1200 and 1300 - was 0.15 C warmer than the peak warmth of the Current Warm Period, which in their history occurred at the conclusion of the 20th century.



Lapland

Reference
Helama, S., Timonen, M., Holopainen, J., Ogurtsov, M.G., Mielikainen, K., Eronen, M., Lindholm, M. and Merilainen, J. 2009. Summer temperature variations in Lapland during the Medieval Warm Period and the Little Ice Age relative to natural instability of thermohaline circulation on multi-decadal and multi-centennial scales. Journal of Quaternary Science 24: 450-456.

Description
The authors employed tree-ring data obtained from living and subfossil wood of Scots pine (Pinus sylvestris L.) trees found in the northern limits of forests in Finland and Norway (68-70 N, 20-30 E), which they alternately calibrated and tested using mid-summer (July) temperature data from northern Norway for the two periods AD 1876-1937 and 1937-1998. This work revealed that the warmest 250-year period of their record, which began in AD 750, "occurred at AD 931-1180," which they describe as sharing "significant temporal overlap with the general hemispheric climate variability due to the Medieval Warm Period (MWP)."



Northern Fennoscandia

Reference
Bjune, A.E., Seppa, H. and Birks, H.J.B. 2009. Quantitative summer-temperature reconstructions for the last 2000 years based on pollen-stratigraphical data from northern Fennoscandia. Journal of Paleolimnology 41: 43-56.

Description
Working with mean July temperature reconstructions based on "pollen-stratigraphical data obtained from eleven small lakes located in the middle boreal, northern boreal, low-alpine, or low-arctic zones of northern Norway, northern Sweden, northern Finland and north-west Russia," the authors developed a mean quantitative temperature history of this Northern Fennoscandia region (66 25'-70 50'N, 14 03'-35 19'E) that spanned the past two millennia; and in describing their results, they say that "no consistent temperature peak is observed during the 'Medieval Warm Period'." Nevertheless, in viewing their final result (see figure below), it may readily be seen that what they describe as the present temperature (red vertical line) -- derived from the uppermost 1 cm of the sediment cores, which were collected at various times between AD 1994 and 2003 -- is colder than most all of the data points obtained by the authors over the past 2,000 years.

Focusing on the Medieval Warm Period, which most people generally define as the period of time between AD 800 and 1300, it is evident that temperatures were as much as 1.4 C warmer than what they were over the most recent decade or so. And that is the key point. Irrespective of whether or not a "consistent temperature peak" was observed during this period, temperatures of the most recent decade or so in Northern Fennoscandia have not been higher than they were back in medieval times. In fact, they were exceeded for most of the entire two thousand-year record. If there is anything unusual about temperatures of the most recent decades, therefore, it is that they are unusually cold!



Northern Icelandic Coast

Reference
Sicre, M.-A., Jacob, J., Ezat, U., Rousse, S., Kissel, C., Yiou, P., Eiriksson, J., Knudsen, K.L., Jansen, E. and Turon, J.-L. 2008. Decadal variability of sea surface temperatures off North Iceland over the last 2000 years. Earth and Planetary Science Letters 268: 137-142.

Description
The authors developed a unique 2000-year-long summer sea surface temperature (SST) record with unprecedented temporal resolution (2-5 years) from a sediment core retrieved off North Iceland (66 33'N, 17 42'W), based on their analyses of alkenones synthesized primarily in the summer by the marine alga Emiliania huxleyi that grew in the overlying ocean's surface waters, while dating of the SST data was provided by tephrochronology. The results, pictured below, indicate that the peak warmth of the Medieval Warm Period was about 1 C higher than the peak warmth of the Current Warm Period.



Northern Icelandic Shelf, North Atlantic Ocean

Reference
Justwan, A., Koc, N. and Jennings, A.E. 2008. Evolution of the Irminger and East Icelandic Current systems through the Holocene, revealed by diatom-based sea surface temperature reconstructions. Quaternary Science Reviews 27: 1571-1582.

Description
Based on analyses of diatoms found in a sediment core extracted from the northern Icelandic shelf (66 37'53"N, 20 51'16"W), the authors reconstructed August sea surface temperatures with a resolution of 40 years over the past 11,000-plus years. The figure below shows the most recent two millennia of this record. We have visually judged the period AD 800-1150 to represent the Medieval Warm Period, the peak warmth of which is essentially identical to the peak warmth of the Current Warm Period, albeit the peak warmth of the CWP does not appear at its current end-point, which would technically make the CWP's current temperature (which climate alarmists claim to be unprecedented over the past millennia or two) about 0.5 C less than the peak MWP temperature.



North Icelandic Shelf, North Atlantic Ocean

Reference
Jiang, H., Ren, J., Knudsen, K.L., Eiriksson, J. and Ran, L.-H. 2007. Summer sea-surface temperatures and climate events on the North Icelandic shelf through the last 3000 years. Chinese Science Bulletin 52: 789-796.

Description
The authors analyzed diatom data they obtained from core MD992271 (66 30'05"N, 19 30'20"W) on the North Icelandic shelf to derive summer sea surface temperatures (SSTs) for that location based on relative abundances of warm and cold water species, after which they compared the results they obtained with results of similar analyses of nearby cores HM107-03 (66 30'N, 19 04'W) and MD992275 (66 33"N, 17 42'W). In the words of Jiang et al., "the Medieval Warm Period and the Little Ice Age are identified in the record," which from our visual assessment of their SST history appears to have prevailed between approximately AD 950 and 1250. Unfortunately, the MD992271 record ends in the midst of the Little Ice Age and therefore does not reveal any 19th- or 20th-century warming. The HM107-03 record, on the other hand, extends to within about 50 years of the present; but it too shows no evidence of warming at its end. However, core MD992275 does extend to the present; and it suggests that the temperature at the end of the 20th century was at least three-quarters of a degree Centigrade cooler than the peak temperature of the Medieval Warm Period.



Spannagel Cave, Central Alps, Austria

Reference
Mangini, A., Spotl, C. and Verdes, P. 2005. Reconstruction of temperature in the Central Alps during the past 2000 yr from a δ18O stalagmite record. Earth and Planetary Science Letters 235: 741-751.

Description
Mangini et al. (2005) developed a highly-resolved 2000-year record of temperature with better than decadal resolution from a stalagmite recovered from Spannagel Cave in the Central Alps of Austria (47.09 N, 11.67 E). The highest temperatures of the past two millennia occurred during the Medieval Warm Period (AD 800-1300) and were "slightly higher than those of the top section of the stalagmite (1950) and higher than the present-day temperature." In fact, at three different points during the MWP, their data indicate temperature spikes in excess of 1 C above present (1995-1998) temperatures of 1.8 C.



Spannagel Cave, Central Alps, Austria

Reference
Mangini, A., Verdes, P., Spotl, C., Scholz, D., Vollweiler, N. and Kromer, B. 2007. Persistent influence of the North Atlantic hydrography on central European winter temperature during the last 9000 years. Geophysical Research Letters 34: 10.1029/2006GL028600.

Description
Based on an analysis of δ18O data obtained from three stalagmites (SPA 12, SPA 128, SPA 70) found within Austria's Spannagel Cave (47.09 N, 11.67 E), Mangini et al. (2007) developed what they demonstrated to be a regional δ18O history covering the last 9000 years; and applying the calibration curve derived for SPA 12 by Manginni et al. (2005) to the new δ18O curve, it can readily be determined that the peak temperature of the Medieval Warm Period (AD 800-1300) was approximately 1.5 C higher than the peak temperature of the Current Warm Period.



Swedish Scandes

Reference
Kullman, L. and Kjallgren, L. 2006. Holocene pine tree-line evolution in the Swedish Scandes: Recent tree-line rise and climate change in a long-term perspective. Boreas 35: 159-168.

Description
The authors created an 11,000-year Pinus sylvestris tree-line history for the central and southern Swedish Scandes (61-66 N, 12-15 E) by merging data from three batches of radiocarbon-dated megafossil tree-remains. Based on a lapse rate of -0.6 C per 100 m altitudinal rise, it may be inferred from their tree-line history (corrected for isostatic land uplift) that summer temperatures of that region during the 1940s may have been about 0.5 C warmer than those of the region's Medieval Warm Period peak of approximately AD 850.



Tagus River Estuary, off Lisbon, Portugal

Reference
Abrantes, F., Lebreiro, S., Rodrigues, T., Gil, I., Bartels-J nsd ttir, H., Oliveira, P., Kissel, C. and Grimalt, J.O. 2005. Shallow-marine sediment cores record climate variability and earthquake activity off Lisbon (Portugal) for the last 2000 years. Quaternary Science Reviews 24: 2477-2494.

Description
Sea surface temperatures, river discharge and biological productivity were reconstructed in a multi-proxy analysis of a high-resolution sediment core obtained from the Tagus River estuary near Lisbon, Portugal (~ 38.56 N, 9.35 W). The MWP was identified as occurring between AD 550 and 1300, during which time interval mean sea surface temperatures were between 1.5 and 2 C higher than the mean value of the past century, while peak MWP warmth was about 0.9 C greater than late 20th-century peak warmth.



Tornetrask Area of Northern Sweden

Reference
Grudd, H. 2008. Tornetrask tree-ring width and density AD 500-2004: a test of climatic sensitivity and a new 1500-year reconstruction of north Fennoscandian summers. Climate Dynamics: 10.1007/s00382-0358-2

Description
Working with an extensive pre-existing set of Scots pine (Pinus sylvestris L.) tree-ring maximum density (MXD) data from the Tornetrask area of northern Sweden (68.21-68.31 N, 19.45-19.80 E), which originally covered the period AD 441-1980, Grudd extended the record an additional 24 years to 2004 using new samples obtained from 35 relatively young trees, which had the effect of reducing the mean cambial age of the MXD data in the 20th century and thus eliminating, as he described it, a "loss of sensitivity to temperature, apparent in earlier versions of the Tornetrask MXD chronology." This work revealed, as shown in the figure below, and as stated in Grudd's own words, that "the warmest summers in this new reconstruction occur in a 200-year period centered on AD 1000," which he specifically calls the Medieval Warm Period.

Based on Grudd's findings, we estimate that the peak temperature of the MWP was approximately 1.2 C higher than the peak temperature of the CWP, which occurs at the very end of the record, and that the entire MWP, as we have defined it (AD 880-1110) was warmer than the peak warmth of the CWP.



Voring Plateau, Eastern Norwegian Sea

Reference
Andersson, C., Risebrobakken, B., Jansen, E. and Dahl, S.O.  2003.  Late Holocene surface ocean conditions of the Norwegian Sea (Voring Plateau).  Paleoceanography 18: 10.1029/2001PA000654.

Description
August surface temperatures of the eastern Norwegian Sea's Voring Plateau (66.97 N, 7.64 E) were derived from planktic stable isotopes and foraminiferal assemblage concentrations.  The Medieval Warm Period occurred between AD 1200 and 1500 and was as much as 3.3 C warmer than the Current Warm Period.



Level 2 Studies

Berre Lagoon, France

Reference
Robert, C., Degiovanni, C., Jaubert, R., Leroy, V., Reyss, J.L., Sali ge, J.F., Thouveny, N. and de Vernal, A. 2006. Variability of sedimentation and environment in the Berre coastal lagoon (SE France) since the first millennium: Natural and anthropogenic forcings. Journal of Geochemical Exploration 88: 440-444.

Description
Mineral and microfossil assemblages from a sediment core taken from the Berre coastal lagoon in southeast France (~ 43.44 N, 5.10 E) were analyzed in an effort to reconstruct environmental changes in the region over the past 1500 years. The MWP was identified as an interval of higher kaolinite content between AD 980 and 1370, which was judged to be indicative of "increased chemical weathering in relation to higher temperatures and/or precipitation." In addition, the concentration of microfossils of the thermophilic taxon Spiniferites bentorii peaked during this period, which combined evidence leads us to conclude that the MWP was warmer than the CWP at Bette lagoon.



Eastern Gotland Basin, Central Baltic Sea

Reference
Leipe, T., Dippner, J.W., Hille, S., Voss, M., Christiansen, C. and Bartholdy, J. 2008. Environmental changes in the central Baltic Sea during the past 1000 years: inferences from sedimentary records, hydrography and climate. Oceanologia 50: 23-41.

Description
The authors analyzed five 60-cm sediment cores that were retrieved from the eastern Gotland Basin of the central Baltic Sea (56 55'-57 15'N, 19 20'-20 00'E) for a variety of physical, chemical and biological properties. These analyses revealed, in their words, that "during the Medieval Warm Period, from about AD 900 to 1250, the hydrographic and environmental conditions were similar to those of the present time," although analyses of lignin compounds in the sediment cores -- which they say "can be used to characterize terrigenous organic matter from plants" -- pointed to the Medieval Warm Period possibly being warmer than the Current Warm Period.



European Alps, Switzerland

Reference
Buntgen, U., Frank, D.C., Nievergelt, D. and Esper, J. 2006. Summer temperature variations in the European Alps, A.D. 755-2004. Journal of Climate 19: 5606-5623.

Description
The authors developed an annually-resolved mean summer (June-September) temperature record for the European Alps (46.3 N, 7.8 E), covering the period AD 755-2004 and based on 180 recent and historic larch (Larix decidua Mill.) maximum latewood density series, using the regional curve standardization method that preserves interannual to multi-centennial temperature-related variations. In the words of the researchers, this work revealed "warmth during medieval and recent times, and cold in between." As best we can determine from the graphical presentation of their results, the MWP occurred between 1150 and 1275 AD. Peak warmth during this interval (~ 1200 AD) was approximately equivalent to that of the last few years of the record, which extended through 2004.



Gorner Glacier, Alps of Valais, Switzerland

Reference
Holzhauser, H., Magny, M. and Zumbuhl, H.J. 2005. Glacier and lake-level variations in west-central Europe over the last 3500 years. The Holocene 15: 789-801.

Description
Holzhauser et al. present a high-resolution record of glacial variation for Gorner glacier, in the Alps of Valis, Switzerland (~46.05 N, 7.62 E), as part of an effort to develop a 3500-year climate history of west-central Europe. In their estimation, "at no other glacier in the Swiss Alps ... [is] the Mediaeval Climatic Optimum so well documented as at the Gorner glacier," especially when the glacier retreated to levels beyond that of the present-day between AD 800 and 1100. Because glaciers in mountain areas are "highly sensitive to climate changes and thus provide one of nature's clearest signals of warming or cooling and/or dry and wet climate periods," as they describe it, "one can say that the quasi periodical fluctuations of Alpine glaciers were driven by glacier-hostile (warm/dry) and glacier-friendly (cool/wet) periods." On this basis, therefore, one can cautiously conclude that temperatures at Gorner Glacier were likely warmer during the Medieval Warm Period than they have been recently.



Great Aletsch Glacier, Alps of Valais, Switzerland

Reference
Holzhauser, H., Magny, M. and Zumbuhl, H.J. 2005. Glacier and lake-level variations in west-central Europe over the last 3500 years. The Holocene 15: 789-801.

Description
Holzhauser et al. present a high-resolution record of glacial variation for the Great Aletsch glacier in the Alps of Valis, Switzerland (~46.38 N, 7.75 E), as part of an effort to develop a 3500-year climate history of west-central Europe. As they describe it, the Medieval Warm Period occurred between AD 800 and 1300; and based on data presented in their Figure 2 (reproduced below), glacial extension between AD 800 and 1000 was at a level equal to that of today. Furthermore, because glaciers in mountain areas are "highly sensitive to climate changes and thus provide one of nature's clearest signals of warming or cooling and/or dry and wet climate periods," in their estimation, they state that "one can say that the quasi periodical fluctuations of Alpine glaciers were driven by glacier-hostile (warm/dry) and glacier-friendly (cool/wet) periods." On this basis one can logically, albeit cautiously, conclude that temperatures during the Medieval Warm Period were likely as warm as they are today at the Great Aletsch Glacier.



Korallgrottan, Caledonian Mountain Range, J mtland County, Sweden

Reference
Sundqvist, H.S., Holmgren, K., Moberg, A., Spotl, C. and Mangini, A. 2010. Stable isotopes in a stalagmite from NW Sweden document environmental changes over the past 4000 years. Boreas 39: 77-86.

Other Reference
Moberg, A., Sonechkin, D.M., Holmgren, K., Datsenko, N.M. and Karlen, W. 2005. Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature 433: 613-617.

Description
Working with a stalagmite (K11) that they collected in 2005 from Korallgrottan -- a cave in the Caledonian mountain range of Jamtland County, northwest Sweden (64 53'N, 14 E) -- Sundqvist et al. developed a 4000-year δ18O history, which they demonstrated to be well correlated with temperature, even that of the entire Northern Hemisphere, in fact, as may be seen in the figure below.

In describing the δ18O history, Sundqvist et al. write that "the stable isotope records show enriched isotopic values during the, for Scandinavia, comparatively cold period AD 1300-1700 [which they equate with the Little Ice Age] and depleted values during the warmer period AD 800-1000 [which they equate with the Medieval Warm Period]." And as can clearly be seen from the figure above, the two δ18O depletion "peaks" (actually inverted valleys) of the Medieval Warm Period are both more extreme than the "peak" value of the Current Warm Period, which appears at the end of the record.



Lake Haukadalsvatn, West Iceland

Reference
Geirsdottir, A., Miller, G.H., Thordarson, T. and Olafsdottir, K.B. 2009. A 2000-year record of climate variations reconstructed from Haukadalsvatn, West Iceland. Journal of Paleolimnology 41: 95-115.

Description
Working with biogenic silica (BSi) and total organic carbon (TOC) data obtained from two sediment cores retrieved from Haukadalsvatn (65 03.064'N, 21 37.830'W) -- a lake in northwest Iceland -- and a 170-year instrumental temperature history that was obtained from Stykkisholmur (50 km distant), the authors identified "a broad peak in BSI and lack of a trend in TOC between ca. 900 and 1200 AD," which they described as being indicative of "a broad interval of warmth" that was "coincident with the Medieval Warm Period," and which clearly exhibited much greater warmth than was observed at any time during the Current Warm Period.



Lake Korttajarvi, Central Finland

Reference
Tiljander, M., Karhu, J.A. and Kauppila, T. 2006. Holocene records of carbon and hydrogen isotope ratios of organic matter in annually laminated sediments of Lake Korttajarvi, central Finland. Journal of Paleolimnology 36: 233-243.

Description
The authors studied the isotopic composition of carbon (δ13C) and hydrogen (δD) in organic matter found in two sediment cores retrieved from the center of the southern basin of Lake Korttajarvi (62 20'N, 25 41'E). In doing so, they found that "the Medieval Warm Period in AD 980-1250 is associated with a local maximum in δD, lending support for a significant warming during that time," as can be seen in the figure below, since researchers generally find, in their words, "δD increasing at warmer environmental conditions."



Lake Lehmilampi, Eastern Finland

Reference
Haltia-Hovi, E., Saarinen, T. and Kukkonen, M. 2007. A 2000-year record of solar forcing on varved lake sediment in eastern Finland. Quaternary Science Reviews 26: 678-689.

Description
The authors extracted two sediment cores from Lake Lehmilampi (63 37'N, 29 06'E) in eastern Finland, after which they identified and counted the approximately 2000 annual varves contained in each core and measured their individual thicknesses and mineral and organic matter contents, which they found to be related to residual δ14C data derived from tree rings, which serve as a proxy for solar activity. Consequently, because they note that (1) "the thinnest varves of the last 2000 years were deposited during [the] solar activity maxima in the Middle Ages," specifically AD 1060-1280, that (2) the low deposition rate of mineral matter in that period "implies mild winters with a short ice cover period during that time with minor snow accumulation interrupted by thawing periods," and that (3) the concurrent "low accumulation of organic matter suggests a long open water season and a high decomposition rate of organic matter," it follows that the solar-induced Medieval Warm Period of AD 1060-1280 in that part of the world was likely the warmest period of the past two millennia.



Lomonosovfonna Ice Core, Svalbard, Norway

Reference
Grinsted, A., Moore, J.C., Pohjola, V., Martma, T. and Isaksson, E. 2006. Svalbard summer melting, continentality, and sea ice extent from the Lomonosovfonna ice core. Journal of Geophysical Research 111: 10.1029/2005JD006494.

Description
From data obtained from a 121-meter-long ice core they extracted from the highest ice field in Svalbard (Lomonosovfonna: 78 51'53"N, 17 25'30"E), Grinsted et al. developed "a model of chemical fractionation in ice based on differing elution rates for pairs of ions ... as a proxy for summer melt (1130-1990)," which was "validated against twentieth-century instrumental records and longer historical climate proxies." This work revealed, in their words, that "the Medieval Warm Period in Svalbard summer conditions [was] as warm (or warmer) as present-day," because "the degree of summer melt was significantly larger during the period 1130-1300 than in the 1990s."



Oberer Landschitzsee, an Alpine Lake in the Southern Austrian Alps

Reference
Schmidt, R., Kamenik, C. and Roth, M. 2007. Siliceous algae-based seasonal temperature inference and indicator pollen tracking ca. 4,000 years of climate/land use dependency in the southern Austrian Alps. Journal of Paleolimnology 38: 541-554.

Description
The authors combined spring and autumn temperature anomaly reconstructions based on siliceous algae and pollen tracers found in a sediment core extracted from an Alpine lake (Oberer Landschitzsee; 47 14'52" N, 13 51'40" E) located at the southern slopes of the Austrian Central Alps just slightly above the present tree-line. This work revealed that "spring-temperature anomalies during Roman and Medieval times equaled or slightly exceeded [our italics] the modern values and paralleled tree-line and glacier fluctuations," indicative of their broad range of applicability. As for the timing of the Medieval Warm Period, Schmidt et al. identified "warm phases similar to present between ca. 850-1000 AD and 1200-1300 AD," which they say were "followed by climate deterioration at ca. 1300 AD, which culminated during the Little Ice Age." Hence, their data place the Medieval Warm Period as occurring between AD 850 and 1300.



Svalbard, Norway

Reference
Berge, J., Johnsen, G., Nilsen, F., Gulliksen, B. and Slagstad, D. 2005. Ocean temperature oscillations enable reappearance of blue mussels Mytilus edulis in Svalbard after a 1000 year absence. Marine Ecology Progress Series 303: 167-175.

Description
A thermophilous mollusk community was detected in 2004 along the west coast of Svalbard (78 13'N, 14 E) that is believed to have been initiated by larvae transported "in unusually warm water" from the mainland of Norway during the summer of 2002, after a 1000-year absence from where the mussels were "abundant" during "warm intervals in the Holocene." The authors say the reappearance "suggests that recent water temperatures approach [our italics] those of the mediaeval warm period," which implies that it is not yet as warm at that high northern latitude as it was during the Medieval Warm Period (~AD 800-1200).



Level 3 Studies

Dosenmoor Bog, Northern Germany

Reference
Barber, K.E., Chambers, F.M. and Maddy, D. 2004. Late Holocene climatic history of northern Germany and Denmark: peat macrofossil investigations at Dosenmoor, Schleswig-Holstein, and Svanemose, Jutland. Boreas 33: 132-144.

Description
The authors analyzed the plant macrofossil remains from a sediment core obtained from a raised peat bog in northern Germany (Dosenmoor Bog, 54.17 N, 10.08 E) over the past 4000 years to extract records of changing bog surface wetness, which they interpreted as a proxy climate signal for precipitation and temperature. Results of the analysis revealed the climate of this region was dry and warm during the Medieval Warm Period (~ AD 600-1300), when there was an "almost complete domination of drier-indicating Sphagnum section Acutifolia" and "virtually no leaves at all of [wetter-indicating] S. papollosum and S. s. Cuspidata."



Estanya Gran Lake, Pre-Pyrenees, Spain

Reference
Riera, S., Wansard, G. and Julia, R. 2004. 2000-year environmental history of a karstic lake in the Mediterranean Pre-Pyrenees: the Estanya lakes (Spain). Catena 55: 293-324.

Description
Working with a sediment core retrieved from Estanya Gran Lake (42 02'N, 0 32'E) at mid-altitude in the Pre-Pyrenees, the authors employed sediment and biotic data, plus well-known historical events, to develop "a reliable history of environmental changes in this area during the last 2000 years." This work revealed that the period AD 1220-1360, which they describe as "being related to the Medieval Warm Period," was "the driest period recorded in the sequence." Conversely, they report that a high-water level that reached its maximum in AD 1550 coincided with "the first episode of the Little Ice Age."



Finland's Southern Boreal Forest, Near Savonlinna, Finland

Reference
Helama, S., Vartiainen, M., Kolstrom, T., Peltola, H. and Merilainen, J. 2008. X-ray microdensitometry applied to subfossil tree-rings: growth characteristics of ancient pines from the southern boreal forest zone in Finland at intra-annual to centennial time-scales. Vegetation History and Archaeobotany 17: 675-686.

Description
The authors applied x-ray microdensitometry to subfossil samples of Scots pine trees collected from the bottom sediments of six small lakes within the southern boreal forest zone near the city of Savonlinna in south-eastern Finland (61 55'-61 58'N, 28 50'-29 02'E), which covered the period AD 673-1788. This work revealed the occurrence of both the Medieval Warm Period (AD 975-1150) and the Little Ice Age (AD 1450-1625), between which periods there was a dramatic decline in tree-ring maximum density, indicative of a significant drop in summer growing-season temperature.



Gulf of Taranto, Ionian Sea

Reference
Cini Castagnoli, G., Taricco, C. and Alessio, S. 2005. Isotopic record in a marine shallow-water core: Imprint of solar centennial cycles in the past 2 millennia. Advances in Space Research 35: 504-508.

Description
A δ13C profile of Globigerinoides rubber extracted from a shallow-water core in the Gulf of Taranto (39 45'53"N, 17 53'33"E) was used to produce a high-precision record of climate variability over the past two millennia. The Medieval Warm Period was described as an interval of high illumination (low cloud coverage) and high temperature between 800 and 1200 AD.



Kaldbaksfjord, Faeroe Islands

Reference
Witon, E., Malmgren, B., Witkowski, A. and Kuijpers, A. 2006. Holocene marine diatoms from the Faeroe Islands and their paleoceanographic implications. Palaeogeography, Palaeoclimatology, Palaeoecology 239: 487-509.

Description
The authors studied the types and concentrations of diatoms found within four sediment cores extracted from Skalafjord and the mouth of the Kaldbaksfjord of the Faeroe Islands (62 02.895-62 10.707N, 06 45.033-06 47.870W). This work revealed, in their words, that "the freshwater diatom flora that occurred between 1200 and 700 cal. yr BP in all four cores suggests markedly increased freshwater discharge into the fjord," which in turn suggests that "during this time much higher precipitation occurred" and that "increased snowdrift and melt-water runoff from land ... played a major role for the increase in the freshwater flora in the Skalafjord." They also write that "this period represents the Medieval Warm Period (MWP), which coincides with the first human settlements on the Faeroe Islands."



Kongressvatnet, Svalbard, Western Spitsbergen, Norway

Reference
Guilizzoni, P., Marchetto, A., Lami, A., Brauer, A., Vigliotti, L., Musazzi, S., Langone, L., Manca, M., Lucchini, F., Calanchi, N., Dinelli, E. and Mordenti, A. 2006. Records of environmental and climatic changes during the last Holocene from Svalbard: palaeolimnology of Kongressvatnet. Journal of Paleolimnology 36: 325-351.

Description
The authors conducted "a multi-core, multidisciplinary palaeolimnological study of the partially varved sediment of a deep, meromictic, arctic lake, Kongressvatnet" (Svalbard, Western Spitsbergen, 78 01'N, 13 58'E), based on measurements and analyses of "sedimentation rates, magnetic properties, varve thickness, organic matter, geochemistry, pigments from algal and photosynthetic bacteria, mineralogy and biological assemblages (diatoms, Cladocera)," which were derived from three sediment cores taken from the deepest part of Kongressvatnet. These data revealed the existence of what they describe as "the Dark Age Cold Period, the Medieval Warm Period as well as the Little Ice Age."



Lake Anterne, Northern French Alps, France

Reference
Millet, L., Arnaud, F., Heiri, O., Magny, M., Verneaux, V. and Desmet, M. 2009. Late-Holocene summer temperature reconstruction from chironomid assemblages of Lake Anterne, northern French Alps. The Holocene 19: 317-328.

Description
Millet et al. developed "a new chironomid-based temperature record from Lake Anterne (northern French Alps) covering the past two millennia" with the help of a mean July air temperature transfer-function derived from the surface sediments of 114 lakes in northern Switzerland. Although the reconstructed data indicate the MWP was warmer than the CWP, the data were only considered valid up to the start of the 20th century. Subsequent to that time, human-induced environmental changes (fish introduction) in the lake likely contaminated the chironomid reconstruction, making a quantitative and/or qualitative comparison of MWP vs. CWP temperatures problematic. Given these potential inaccuracies, we have decided to classify this reconstruction as a Level 3 study and to only utilize it in further clarifying the time interval of the MWP, which the authors list as between AD 680 and 1350.



Marennes-Oléron Bay, France

Reference
Billeaud, I., Chaumillon, E. and Weber, O. 2005. Evidence of a major environmental change recorded in a macrotidal bay (Marennes-Ol ron Bay, France) by correlation between VHR seismic profiles and cores. Geo-Marine Letters 25: 1-10.

Description
Very high resolution seismic profiles were combined with sediment core data from Marennes-Ol ron Bay, France (~45.95 N, 1.20 E), in an investigation of major environmental change over the past few thousand years. The results indicated the presence of a major change in the amount and nature of sediment supplied to the bay, where fine-grained material increased during the Medieval Warm Period (AD 950-1450), which phenomenon, in the thinking of the authors, resulted from a combination of human activities (deforestation, farming, land reclamation) and climatic variations.



Lake Nautajarvi, Finland

Reference
Ojala, A.E.K. and Alenius, T. 2005. 10,000 years of interannual sedimentation recorded in the Lake Nautaj rvi (Finland) clastic-organic varves. Palaeogeography, Palaeoclimatology, Palaeoecology 219: 285-302.

Description
The authors examined the physical properties of varves over the past 10,000 years from Lake Nautaj rvi, Finland to produce a proxy record of winter precipitation and temperature. A period of very low catchment erosion and sediment transportation between 1000 and 1200 AD was interpreted by the authors as a period of attenuated spring floods caused by milder winters with considerably lower precipitation in the form of snow, which period they note "corresponds with the last historically recorded warm interval in Europe, known as the Medieval Climate Anomaly."



Las Tablas de Daimiel National Park, South Central Iberian Peninsula, Spain

Reference
Garcia, M.J.G., Zapata, M.B.R., Santisteban, J.I., Mediavilla, R., Lopez-Pamo, E. and Dabrio, C.J. 2007. Late Holocene environments in Las Tablas de Daimiel (south central Iberian peninsula, Spain). Vegetation History and Archaeobotany 16: 241-250.

Description
Working with a number of sediment cores retrieved from a river-fed wetland that is flooded for approximately seven months of each year in Las Tablas de Daimiel National Park (39.4 N, 3.8 W, south central Iberian Peninsula, Spain), Garcia et al. employed "a high resolution pollen record in combination with geochemical data from sediments composed mainly of layers of charophytes alternating with layers of vegetal remains plus some detrital beds" to reconstruct "the environmental evolution of the last 3000 years." Among other things, this endeavor revealed the existence of "the warmer and wetter Medieval Warm Period (A.D. 900-1400)."



Lower Grindelwald Glacier, Bernese Alps, Switzerland

Reference
Holzhauser, H., Magny, M. and Zumbuhl, H.J. 2005. Glacier and lake-level variations in west-central Europe over the last 3500 years. The Holocene 15: 789-801.

Description
Holzhauser et al. present a record of glacial variation for the Lower Grindelwald glacier, in the Bernese Alps, Switzerland (~46.58 N, 8.00 E), as part of an effort to develop a 3500-year climate history of west-central Europe. The Medieval Warm Period was identified in their Figure 2 as a period of significant glacial recession between AD 800 and 1300.



Mongan Bog, Central Ireland

Reference
Hall, V.A. and Mauquoy, D. 2005. Tephra-dated climate- and human-impact studies during the last 1500 years from a raised bog in central Ireland. The Holocene 15: 1086-1093.

Description
The authors conducted analyses on tephra, plant macrofossils and pollen from peat cored from Mongan Bog (53.33 N, 7.93 W), located on the east bank of the River Shannon in County Offaly in the Irish Midlands, to evaluate the effects of climatic and human impact in this region over the past 1500 years. They report that Zone C of their pollen diagram (~ AD 890-1270) "encompasses the time period during which the High Middle Ages occurred, therefore the reduction in local water-table depths may reflect warmer/drier conditions during this period of climatic amelioration."



Mt. Storsnasen, Southern Swedish Scandes, Sweden

Reference
Kullman, L. 2005. Pine (Pinus sylvestris) treeline dynamics during the past millennium - a population study in west-central Sweden. Annales Botanici Fennici 42: 95-106.

Description
The author reconstructed a 1000-year history of the dynamics of a fire-free treeline population of Scots pine (Pinus sylvestris) on the lower east-facing slope of Mt. Storsnasen (63.23 N, 12.43 E) near the mouth of Hand lan Valley in the southern Swedish Scandes. From the results of the analysis, Kullman infered that "a large proportion of the subfossil pines that died during the past millennium originated from a phase of relatively favorable climatic conditions during the Medieval period," adding that whether or not the current stand density and stature exceeded that of the Medieval optimum "cannot be judged by the data [in this study]."



Outer Hebrides, Scotland

Reference
Dawson, S., Smith, D.E., Jordan, J. and Dawson, A.G. 2004. Late Holocene coastal sand movements in the Outer Hebrides, N.W. Scotland. Marine Geology 210: 281-306.

Description
Dawson et al. (2004) conducted lithostratigraphical and biostratigraphical analyses of coastal marshes along the Atlantic coast of the Outer Hebrides (~58 N, 7 W) in order to create a proxy record of past coastal storminess in that region. Based on their findings, they concluded their "data appear to indicate that for the study sites investigated, the majority of the sand units were produced during episodes of climate deterioration both prior to and after the well-known period of Medieval warmth (MWP)," which period, based on information listed in their Table 1, occurred between AD 800 and 1400.



Ria de Vigo, Northwest Iberia, Spain

Reference
Desprat, S., Goni, M.F.S. and Loutre, M.-F. 2003. Revealing climatic variability of the last three millennia in northwestern Ibera using pollen influx data. Earth and Planetary Science Letters 213: 63-78.

Description
The authors studied the climatic variability of the last three millennia in northwest Iberia via a high-resolution pollen analysis of a sediment core retrieved from the central axis of the Ria de Vigo in the south of Galicia (42 14.07'N, 8 47.37'W). This work revealed "an alternation of three relatively cold periods with three relatively warm episodes." In order of their occurrence, these periods are described by Desprat et al. as the "first cold phase of the Subatlantic period (975-250 BC)," which was "followed by the Roman Warm Period (250 BC-450 AD)," which was followed by "a successive cold period (450-950 AD), the Dark Ages," which "was terminated by the onset of the Medieval Warm Period (950-1400 AD)," which was followed by "the Little Ice Age (1400-1850 AD), including the Maunder Minimum (at around 1700 AD)."



Russkaya Gavan' Fjord, Northwestern Coast of Novaya Zemlya, Barents Sea

Reference
Murdmaa, I., Polyak, L., Ivanova, E. and Khromova, N. 2004. Paleoenvironments in Russkaya Gavan' Fjord (NW Novaya Zemlya, Barents Sea) during the last millennium. Palaeogeography, Palaeoclimatology, Palaeoecology 209: 141-154.

Description
A sediment core retrieved from the deep part of glaciated Russkaya Gavan' Fjord (76 12.25'N, 62 29.19'E) on the northwestern coast of Novaya Zemlya, Barents Sea, was analyzed for lithology, grain size, coarse debris, organic carbon, foraminifera, macrobenthic remains and stable isotopes in foraminiferal tests, resulting in the production of a set of records that began at approximately AD 1170 in the midst of the Medieval Warm Period, which lasted until about AD 1400.



Saki Lake, Crimean Peninsula, Ukraine

Reference
Solomina, O., Davi, N., D'Arrigo, R. and Jacoby, G. 2005. Tree-ring reconstruction of Crimean drought and lake chronology correction. Geophysical Research Letters 32: L19704, doi:10.1029/2005GL023335.

Description
A sediment core from Saki Lake (~ 45.2 N, 33.5 E) on the Crimean Peninsula, Ukraine, revealed that "the wettest period of the past 1500 years (~AD 1050-1250) broadly coincides with the 'Medieval Warm Period' in Crimea."



Southern Finland

Reference
Helama, S., Merilainen, J. and Tuomenvirta, H. 2009. Multicentennial megadrought in northern Europe coincided with a global El Niño-Southern Oscillation drought pattern during the Medieval Climate Anomaly. Geology 37: 175-178.

Description
Helama et al. developed what they describe as "the first European dendroclimatic precipitation reconstruction," based on data obtained from hundreds of moisture-sensitive Scots pine tree-ring records originating in southern Finland (61-62 N, 28-29 E), using regional curve standardization (RCS) procedures. This work revealed, as they describe it, a "distinct and persistent drought, from the early ninth century AD to the early thirteenth century AD," which interval, in their words, "precisely overlaps the period commonly referred to as the Medieval Climate Anomaly, due to its geographically widespread climatic anomalies both in temperature and moisture [our italics]."



Spain

Reference
Thorndycraft, V.R. and Benito, G. 2006. The Holocene fluvial chronology of Spain: evidence from a newly compiled radiocarbon database. Quaternary Science Reviews 25: 223-234.

Description
The authors compiled and analyzed a database of Holocene radiocarbon dates from fluvial deposits throughout Spain (~ 40 N, 1 W) in an effort to identify episodes of increased fluvial activity. A period of increased frequency of large magnitude floods occurred between AD 700 and 1160 and "appear to coincide with the Medieval Warm Period."



Svanemose Bog, East Coast of Jutland, Denmark

Reference
Barber, K.E., Chambers, F.M. and Maddy, D. 2004. Late Holocene climatic history of northern Germany and Denmark: peat macrofossil investigations at Dosenmoor, Schleswig-Holstein, and Svanemose, Jutland. Boreas 33: 132-144.

Description
The authors analyzed the plant macrofossil remains from a sediment core obtained from a raised peat bog in northern Germany (Svanemose Bog, 55.37 N, 9.50 E) over the past 4000 years to extract records of changing bog surface wetness, which they interpreted as a proxy climate signal for precipitation and temperature. Results of the analysis revealed "an abrupt warming/drying trend" during the Medieval Warm Period and which peaked about A.D. 1200.



Taravilla Lake, Central Iberian Range, Spain

Reference
Moreno, A., Valero-Garces, B.L., Gonzalez-Samperiz, P. and Rico, M. 2008. Flood response to rainfall variability during the last 2000 years inferred from the Taravilla Lake record (Central Iberian Range, Spain). Journal of Paleolimnology 40: 943-961.

Description
Moreno et al. conducted a sedimentological, geochemical and palynological study of Spain's Taravilla Lake (40 39'N, 1 59'W) that revealed the presence of "allochthonous terrigenous layers that intercalate within the lacustrine sediments over the last 2000 years," which were formed "as the result of extreme hydrological events that caused higher clastic input to the basin." This work indicated that during the MWP, which they identify as occurring between AD 800 and 1300, "there is almost no evidence of flood deposits in the lake," in contrast to what was evident before and after it.



Temple Hill Moss, Southeast Scotland, United Kingdom

Reference
Langdon, P.G., Barber, K.E. and Hughes, P.D.M. 2003. A 7500-year peat-based palaeoclimatic reconstruction and evidence for an 1100-year cyclicity in bog surface wetness from Temple Hill Moss, Pentland Hills, southeast Scotland. Quaternary Science Reviews 22: 259-274.

Description
The authors analyzed plant macrofossils, peat humification and testate amoebae to reconstruct a proxy climate record spanning the last 7500 years of an ombrotrophic bog, Temple Hill Moss, in southeast Scotland. This work revealed, in their words, "a millennial scale periodicity of 1100 years" that provided "evidence for a drier/warmer phase between ca cal. 1000-800 BP, and a climatic deterioration between ca cal. 250-150 BP, which may relate to phases of warmer and then cooler climates such as the Medieval Warm Period and Little Ice Age, respectively."



Three Estuaries off the Atlantic Coast of France

Reference
Chaumillon, E., Tessier, B., Weber, N., Tesson, M. and Bertin, X. 2004. Buried sandbodies within present-day estuaries (Atlantic coast of France) revealed by very high resolution seismic surveys. Marine Geology 211: 189-214.

Description
The authors examined very high resolution seismic profiles from three estuary locations on the Atlantic coast of France (~ 48.95 N, 1.23 W; 45.2 N, 1.43 W; 46.25 N, 1.43 W). Common to all three locations was a "very sharp" sedimentary transition from basal sand to muddier sediments, from which two shells were recovered and radiocarbon dated to AD 720 and 1100. Speaking of this transition, they say "it could correspond to the transition between the cold period of the Dark Age (AD 400-900) and the Medieval warm period (AD 900-1400)," as warmer temperatures brought about higher rainfall and more frequent floods that resulted in an increase of estuarine mud supply to the region.




North America
Level 1 Studies

Boothia Peninsula, Nunavut, Canada

Reference
Zabenskie, S. and Gajewski, K. 2007. Post-glacial climatic change on Boothia Peninsula, Nunavut, Canada. Quaternary Research 68: 261-270.

Description
Sediment cores were extracted from Lake JR01 (69 54'N, 95 4.2'W) on the Boothia Peninsula, Nunavut, Canada, using a Livinstone corer, with the authors careful to note that "the uppermost part of the sediment was sampled in a plastic tube with piston to ensure that the sediment-water interface was collected," while further stating that "the upper 20 cm of sediment were sub-sampled into plastic bags at 0.5-cm intervals." Then, from the fossil pollen assemblages thereby derived, July temperatures were estimated "using the modern analog technique." Among other things, this work revealed "a short warming," which they say "could be interpreted as the Medieval Warm Period." Following this latter period of warmth, they found that "temperatures cooled during the Little Ice Age," as pollen percentages "returned to their values before the [MWP] warming." Last of all, during the final 150 years of the record, a "diverse and productive diatom flora" was observed. However, as the two researchers continue, "July temperatures reconstructed using the modern analog technique remained stable during this time," which suggests that this part of the world is currently not as warm as it was during the MWP. In fact, from data presented in their Figure 7, we calculate that peak MWP temperatures were fully 1.0 C warmer than it is currently, and that the MWP occurred between AD 1200 and 1500.



Chesapeake Bay, USA

Reference
Cronin, T.M., Dwyer, G.S., Kamiya, T., Schwede, S. and Willard, D.A. 2003. Medieval Warm Period, Little Ice Age and 20th century temperature variability from Chesapeake Bay. Global and Planetary Change 36: 17-29.

Description
Using the magnesium/calcium (Mg/Ca) proxy method as a paleothermometer, the authors reconstructed a 2200-year record of spring sea surface temperature from four sediment cores taken from Chesapeake Bay (~38.89 N, 76.40 W). Statistical analyses revealed mean 20th-century temperatures were 0.15 C cooler than mean temperatures during the first stage of the Medieval Warm Period, which they delineate as occurring between 450 and 900 AD.



Columbia Icefield, Canadian Rockies, Canada

Reference
Luckman, B.H. and Wilson, R.J.S. 2005. Summer temperatures in the Canadian Rockies during the last millennium: a revised record. Climate Dynamics 24: 131-144.

Description
Using new tree-ring data from the Columbia Icefield area of the Canadian Rockies (~52.13 N, 117.13 W), Luckman and Wilson present a significant update to a millennial temperature reconstruction published for this region in 1997. The new update produced two composite summer (May-August) maximum temperature reconstructions, one based on Regional Curve Standardization of maximum latewood density (MXD RCS) and another based on standardized ring widths (RW STD).

Results of the MXD RCS chronology revealed warm intervals "comparable to twentieth century values" during the MWP (~ AD 950-1200). In contrast, from the authors' Figure 4, we calculate the peak warmth of the MWP in the RW STD chronology to be about 0.20 C above that of the CWP, which warmth is further supported by the inclusion of a "critical" snag sample of Larixlyallii in the RW STD composite that was located approximately 30 km north of the present range limit of this species.



Eastern Sierra Nevada Range, California, USA

Reference
Millar, C.I., King, J.C., Westfall, R.D., Alden, H.A. and Delany, D.L. 2006. Late Holocene forest dynamics, volcanism, and climate change at Whitewing Mountain and San Joaquin Ridge, Mono County, Sierra Nevada, CA, USA. Quaternary Research 66: 273-287.

Description
Working with dead tree trunks located above the current treeline on tephra-covered slopes of Whitewing Mountain and San Joaquin Ridge south of Mono Lake just east of the Inyo Craters (37 38'N, 119 02'W) in the eastern Sierra Nevada range of California (USA), Millar et al. identified the species to which the tree remains belonged, dated them, and (using contemporary distributions of the species in relation to contemporary temperature and precipitation) reconstructed paleoclimate during the time they grew there. This work revealed that annual minimum temperatures during the Medieval Warm Period in the region they studied were "significantly warmer" (+3.2 C) "than present."



Hallet Lake, Alaska, USA

Reference
McKay, N.P., Kaufman, D.S. and Michelutti, N. 2008. Biogenic silica concentration as a high-resolution, quantitative temperature proxy at Hallet Lake, south-central Alaska. Geophysical Research Letters 35: 10.1029/2007GL032876.

Description
McKay et al. used biogenic silica concentrations preserved in lacustrine sediments from oligotrophic Hallet Lake (61.5 N, 146.2 W) in south-central Alaska (USA) to quantitatively reconstruct June-July-August air temperature there over the past 2000 years. Their work revealed a broad period of nearly constant substantial warmth over the interval AD 1280-1450, which was about 1.2 C cooler than the peak warmth at the end of what they call "the past 20 years." Prior to this almost vertical spike in modern summer air temperature, however, the Medieval Warm Period was consistently warmer; and they note that the magnitude and rate of change they recorded over the past 20 years "are greater than in other quantitative temperature proxies (Hu et al., 2001; Wilson et al., 2007)." Nevertheless, we report MWP-CWP = -1.2 C.



Great Bahama Bank, Straits of Florida

Reference
Lund, D.C. and Curry, W. 2006. Florida Current surface temperature and salinity variability during the last millennium. Paleoceanography 21: 10.1029/2005PA001218.

Description
Lund and Curry reconstructed surface temperatures of the Florida Current near the Great Bahama Bank (24 45.5'N, 79 17.5'W) from Mg/Ca measurements of the fossil shells of the surface-dwelling foraminifer Globigerinoides rubber found in a sediment core taken from a depth of approximately 700 meters. This work indicated that the peak surface temperature of the MWP (AD 740-880) was approximately 0.25 C greater than that of the upper segment of the core, which was deposited "primarily after AD 1950."



Iceberg Lake, Alaska, USA

Reference
Loso, M.G. 2009. Summer temperatures during the Medieval Warm Period and Little Ice Age inferred from varved proglacial lake sediments in southern Alaska. Journal of Paleolimnology 41: 117-128.

Description
Eleven outcrops of exposed lacustrine stratigraphy revealing continuous sediment deposition at southern Alaska's Iceberg Lake (60 47'N, 142 57'W) from AD 442 to 1998 were examined, photographed and sampled (for grain size, bulk density, organic-matter content, and for 14C and 137Cs dating), after which the authors developed a quantitative relationship between varve thickness and melt-season temperature that they used to construct a melt-season temperature history of the region. This work revealed a "strong steady pulse of medieval warming" between AD 1000 and 1100 that "overlaps with warming seen at other Alaskan sites," and it suggests that some of the later 20th-century temperature spikes were "slightly (0.1 C) warmer than the warmest part of the Medieval Warm Period." It should be noted, however, that the most recent temperature of the record (1998) is actually about 0.1 C cooler than the peak MWP temperature.



Lower Murray Lake, Ellesmere Island, Nunavut, Canada

Reference
Cook, T.L., Bradley, R.S., Stoner, J.S. and Francus, P. 2009. Five thousand years of sediment transfer in a high arctic watershed recorded in annually laminated sediments from Lower Murray Lake, Ellesmere Island, Nunavut, Canada. Journal of Paleolimnology 41: 77-94.

Description
Working with sediment cores extracted from Lower Murray Lake, Ellesmere Island, Nunavut, Canada (81 21'N, 69 32'W) in 2005 and 2006, the authors calculated annual mass accumulation rate (MAR) for the past five millennia, which they used to derive a relationship between MAR and July temperature at the two nearest permanent weather stations over the period of instrumental measurements. This work revealed there were several periods over the past 5000 years when the temperature of the region exceeded the peak temperature of the 20th century, the most recent of which was during the Medieval Warm Period, which we have delineated on the following figure as occurring between about AD 930 and 1400, and where the peak temperature of that period can be seen to have been about 0.6 C higher than the peak temperature of the Current Warm Period.



Level 2 Studies

Dog Lake, British Columbia, Canada

Reference
Hallett, D.J., Mathewes, R.W. and Walker, R.C. 2003. A 1000-year record of forest fire, drought and lake-level change in southeastern British Columbia, Canada. The Holocene 13: 751-761.

Description
The dendrochronological fire history of the forested area surrounding Dog Lake (50.77 N, 116.1 W) was compared with a high-resolution charcoal record derived from a sediment core extracted from the lake to reconstruct the region's fire history over the past 1000 years. In addition, the authors constructed a proxy record of lake-level change based on accumulation rates of Chara globularis-type oospores in the lake sediment core. These analyses revealed the presence of frequent forest fires and lowered lake levels during the Medieval Warm Period (AD 980-1270), which in the words of the authors support evidence of "warmer and drier climate than today."



Effingham Inlet, West Coast of Vancouver Island, British Columbia, Canada

Reference
Hay, M.B., Dallimore, A., Thomson, R.E., Calvert, S.E. and Pienitz, R. 2007. Siliceous microfossil record of late Holocene oceanography and climate along the west coast of Vancouver Island, British Columbia (Canada). Quaternary Research 67: 33-49.

Description
Diatoms, silicoflagellates and biogenic silica were analyzed from two ocean sediment cores obtained from Effingham Inlet (49.06 N, 125.15 W), a fjord on the western coast of Vancouver Island, British Columbia, in an effort to provide a palaeoceanographic perspective on modern ocean-climate patterns in this region. The 5,000-year record developed from this work revealed, in the researchers' words, "a period of warmer and drier climatic conditions and possibly increased coastal upwelling occurred offshore ca. 1440-1050 cal yr BP."



Greenland Ice Sheet Project Two (GISP2), Central Greenland

Reference
Dawson, A.G., Elliott, L., Mayewski, P., Lockett, P., Noone, S., Hickey, K., Holt, T., Wadhams, P. and Foster, I. 2003. Late-Holocene North Atlantic climate 'seesaws', storminess changes and Greenland ice sheet (GISP2) palaeoclimates. The Holocene 13: 381-392.

Description
The authors present palaeotemperature data derived from oxygen isotope stratigraphy of the Greenland Ice Sheet Project Two (GISP2) ice core, central Greenland (72.6 N, 38.5 W). Although they indicate that the "temperature warming of the 'Mediaeval Warm Period' (MWP) [is] not registered at GISP2," we believe that data presented in Figure 5 of their paper demonstrate otherwise. Reproduced below, this figure shows a period of above-average temperatures between approximately AD 1070 and 1140, during the time frame traditionally associated with the MWP. What is more, during what climate alarmists call the "unprecedented" warmth of the latter part of the 20th century, temperatures at GISP2 approach neither the magnitude nor the duration of warmth experienced during the MWP as we have identified it in the graph below. In fact, about the only thing unprecedented about central Greenland temperatures in the latter part of the 20th century is the presence of the coldest couple of years in the entire millennial record!



Hudson River Estuary, USA

Reference
Carbotte, S.M., Bell, R.E., Ryan, W.B.F., McHugh, C., Slagle, A., Nitsche, F., Rubenstone, J. 2004. Environmental change and oyster colonization within the Hudson River estuary linked to Holocene climate. Geo-Marine Letters 24: 212-224.

Description
The authors located fossil oyster beds within the Tappan Zee area of the Hudson River estuary, New York, USA (~ 41.13 N, 73.90 W), via chirp sub-bottom and side-scan sonar surveys, after which they retrieved sediment cores from the sites that provided shells for radiocarbon dating. Results of their analyses indicated that "oysters flourished during the mid-Holocene warm period," when "summertime temperatures were 2-4 C warmer than today." Thereafter, the oysters "disappeared with the onset of cooler climate at 4,000-5,000 cal. years BP," but "returned during warmer conditions of the late Holocene," which they specifically identified as the Roman and Medieval Warm Periods as delineated by Keigwin (1996) and McDermott et al. (2001), explicitly stating that "these warmer periods coincide with the return of oysters in the Tappan Zee." They further report that their shell dates suggest a final "major demise at ~500-900 years BP," which timing they describe as being "consistent with the onset of the Little Ice Age." Because the oyster beds of Tappan Zee have not been reestablished during the Current Warm Period, we conclude that temperatures in this region today are not as warm as they were during the MWP (~ AD 600-1250).

References
Keigwin, L.D. 1996. The Little Ice Age and Medieval Warm Period in the Sargasso Sea. Science 274: 1504-1508.

McDermott, F., Mattey, D.P. and Hawkesworth, C. 2001. Centennial-scale Holocene climate variability revealed by a high-resolution speleothem δ18O record from SW Ireland. Science 294: 1328-1331.



Iceberg Lake, Alaska

Reference
Loso, M.G., Anderson, R.S., Anderson, S.P. and Reimer, P.J. 2006. A 1500-year record of temperature and glacial response inferred from varved Iceberg Lake, southcentral Alaska. Quaternary Research 66: 12-24.

Description
The authors "present a varve thickness chronology from glacier-dammed Iceberg Lake [60 46'N, 142 57'W] in the southern Alaska icefields," where "radiogenic evidence confirms that laminations are annual and record continuous sediment deposition from AD 442 to AD 1998," and where "varve thickness increases in warm summers because of higher melt, runoff, and sediment transport." This work revealed that the highest varve thickness values of the entire record ("smoothed with a 40-year lowpass Butterworth filter") were observed in the mid-1970s of the Current Warm Period (CWP). Thereafter, varve thickness values declined to the present. We thus classify this paper as a Level 2 study in which peak warmth of the CWP was greater than peak warmth of Medieval times, although we note that the most recent 40-year filtered value is actually less than the peak 40-year filtered value of Medieval Times.



Igaliku Fjord, South Greenland

Reference
Lassen, S.J., Kuijpers, A., Kunzendorf, H., Hoffmann-Wieck, G., Mikkelsen, N. and Konradi, P. 2004. Late-Holocene Atlantic bottom-water variability in Igaliku Fjord, South Greenland, reconstructed from foraminifera faunas. The Holocene 14: 165-171.

Description
The authors conducted a foraminifera, magnetic susceptibility and oxygen isotope multiproxy analysis of an ocean sediment core retrieved from Igaliku Fjord (60.70 N, 46.03 W), south Greenland, to obtain a paleohydrographic record of this region during the late Holocene. According to Lassen et al.'s interpretation of the data, the Medieval Warm Period was a time of "relatively warm climate in terms of surface water temperature" between AD 885 and 1240, which was punctuated by enhanced mixing and wind stress that likely indicates sea ice was lacking during this time. Based upon data presented in their Figure 3 on % distribution of selected foraminiferal species, δ18O and magnetic susceptibility, plus the relationship inferred from these data with temperature, we can conclude that current warmth has not yet reached the level of Medieval warmth.



Kootenay Valley, Southern Canadian Rockies, Canada

Reference
Hallett, D.J. and Hills, L.V. 2006. Holocene vegetation dynamics, fire history, lake level and climate change in the Kootenay Valley, southeastern British Columbia, Canada. Journal of Paleolimnology 35: 351-371.

Description
Working with a sediment profile obtained from Dog Lake, British Columbia (50 46'N, 116 06'W), the authors reconstructed the Holocene environmental history of Kootenay Valley in the southern Canadian Rockies, based on data related to fire frequency, drought and forest type and cover, all of which are influenced by temperature and precipitation. This effort revealed that current global warming is only just beginning to orchestrate the return of the Valley landscape back to what it was like in medieval times (AD 800-1200).



Kuujjua River Region, Western Victoria Island, Northwest Territories, Canada

Reference
Podritske, B. and Gajewski, K. 2007. Diatom community response to multiple scales of Holocene climate variability in a small lake on Victoria Island, NWT, Canada. Quaternary Science Reviews 26: 3179-3196.

Description
Podritske and Gajewski evaluated the relationship that exists between diatoms and temperature by comparing a diatom stratigraphy based on high-resolution sampling with independent paleoclimatic records, after which they used a high-resolution diatom sequence of the past 9900 years that they developed from sediment-core data acquired from a small lake (unofficially named KR02) on Canada's Victoria Island (located at 71.34 N, 113.78 W) to place recent climatic change there "in an historical context." In doing so, they found "there is evidence of diatom community response to centennial-scale variations such as the 'Medieval Warm Period' (~1000-700 cal yr BP), 'Little Ice Age' (~800-150 cal yr BP) and recent warming." In addition, and most importantly, they discovered that recent warming-induced changes "are not exceptional when placed in the context of diatom community changes over the entire Holocene," stating that "although recent changes in diatom community composition, productivity, and species richness are apparent, they were surpassed at other periods throughout the Holocene." And they explicitly add, in this regard, that the most recent rate-of-change "was exceeded during the Medieval Warm Period."



Lake Mina, Minnesota, USA

Reference
St. Jacques, J.-M., Cumming, B.F. and Smol, J.P. 2008. A 900-year pollen-inferred temperature and effective moisture record from varved Lake Mina, west-central Minnesota, USA. Quaternary Science Reviews 27: 781-796.

Description
Working with sediment cores retrieved from Lake Mina (45 53.40'N, 95 28.68'W) in west-central Minnesota, USA, the authors derived mean February temperatures over the period AD 1116 to 2002 at a four-year resolution using "a pre-settlement pollen-climate calibration set." This work revealed, in their words, that "there was a cold Little Ice Age (AD 1500-1870) preceded by a warmer Medieval Climate Anomaly (AD 1100-1500) on the northeastern border of the Great Plains." From the peak temperature of the warmer of these two periods, which we call the Medieval Warm Period, to the coldest temperature of the Little Ice Age, their data indicate a temperature decline of 1.8 C, which is followed by a complete recovery by the year 1900, where their data terminate. Hence, since we know the planet warmed a good deal over the 20th century, we can conclude that the peak warmth of the MWP was less than that of the CWP for this study.



Lily Pond, General Creek Watershed, Sierra Nevada Mountains, California, USA

Reference
Beaty, R.M. and Taylor, A.H. 2009. A 14,000-year sedimentary charcoal record of fire from the northern Sierra Nevada, Lake Tahoe Basin, California, USA. The Holocene 19: 347-358.

Description
Based on high-resolution charcoal analysis of a 5.5-m-long sediment core extracted from Lily Pond (39 3'26"N, 120 7'21"W) in the General Creek Watershed on the west shore of Lake Tahoe in the northern Sierra Nevada in California (USA), as well as a 20-cm-long surface core that "preserved the sediment-water interface," the authors developed a 14,000-year record of fire frequency. This work revealed, in their words, that "fire episode frequency was low during the Lateglacial period but increased through the middle Holocene to a maximum frequency around 6500 cal. yr BP" that "corresponded with the Holocene temperature maximum (7000-4000 cal. yr BP)." Thereafter, as the temperature gradually declined, so too did fire frequency decline, except for a multi-century aberration the researchers describe as "a similar peak in fire episode frequency [that] occurred between c. 1000 and 600 cal. yr BP during the 'Medieval Warm Period'," which they say was followed by an interval "between c. 500 and 200 cal. yr BP with few charcoal peaks [that] corresponded with the so-called 'Little Ice Age'." Last of all, they found that the "current fire episode frequency on the west shore of Lake Tahoe is at one of its lowest points in at least the last 14,000 years." With respect to the future, Beaty and Taylor thus conclude that "given the strong relationship between climate and fire episode frequency, warming due to increased levels of greenhouse gases in the atmosphere may increase fire episode frequency to levels experienced during the 'Medieval Warm Period'." And since the part of the planet they studied is currently experiencing one of the lowest levels of fire frequency of the last 14,000 years, it is clear that it is currently nowhere near as warm there now as it was during the Medieval Warm Period.



Lower Murray Lake, Canada

Reference
Besonen, M.R., Patridge, W., Bradley, R.S., Francus, P., Stoner, J.S. and Abbott, M.B. 2008. A record of climate over the last millennium based on varved lake sediments from the Canadian High Arctic. The Holocene 18: 169-180.

Description
The authors derived thousand-year histories of varve thickness and sedimentation accumulation rate for Canada's Lower Murray Lake (81 20'N, 69 30'W), which parameters, in their words, "are related to temperatures during the short summer season that prevails in this region," according to the findings of several studies that had previously conducted similar field-work on other High Arctic lakes. These new data bases revealed that "the twelfth and thirteenth centuries were relatively warm," and their graphical representations indicate that Lower Murray Lake and its environs were often much warmer during this time period (AD 1080-1320) than they were at any time in the 20th century.



Nebraska Sand Hills, Western North America

Reference
Sridhar, V., Loope, D.B., Swinehart, J.B., Mason, J.A., Oglesby, R.J. and Rowe, C.M. 2006. Large wind shift on the Great Plains during the Medieval Warm Period. Science 313: 345-347.

Description
The authors studied the orientation, morphology and internal structure of dunes in the easternmost portion of the Nebraska Sand Hills (in about the center of the state), where shallow core and outcrop samples indicate the dunes were formed some 800 to 1000 years ago. Using a computer program, they then calculated what type of wind field had to have been operative during the MWP of AD 1000-1200 in order to produce the dunes, which are oriented quite differently from those that would form under today's wind regime (where air currents from the south in the spring and summer bring moist air from the Gulf of Mexico to the U.S. Great Plains) if the dune sand were free to move and not protected by prairie grasses. Their work revealed that the spring and summer winds of the MWP would have had to have come primarily from the southwest, bringing much drier and hotter-than-current air from the deserts of Mexico, along with greatly reduced opportunities for rain. In addition, they note that the drier and warmer conditions may have been even further "enhanced and prolonged by reduced soil moisture and related surface-heating effects," which, we might add, are not operative in our day to the degree they were 800 to 1000 years ago, as was demonstrated by still other of Sridhar et al.'s computer analyses. The overall effect of these phenomena was suggested by them to have impacted much of western North America and the U.S. Great Plains.



Northern Uinta Mountains, Northeastern Utah, USA

Reference
Carson, E.C., Knox, J.C. and Mickelson, D.M. 2007. Response of bankfull flood magnitudes to Holocene climate change, Uinta Mountains, northeastern Utah. Geological Society of America Bulletin 119: 1066-1078.

Description
Carson et al. developed a Holocene history of flood magnitudes in the northern Uinta Mountains of northeastern Utah (40 48'-40 58'N, 110 18'-110 48'W) from reconstructed cross-sectional areas of alluvial channels preserved within floodplain sediments and relationships relating channel cross-sections to flood magnitudes derived from modern stream gage and channel records. This work revealed that over the past 5,000 years, the record of flood discharges "corresponds well with independent paleoclimate data for the Uinta Mountains," and that "during this period, the magnitude of the modal flood is smaller than modern during warm dry intervals and greater than modern during cool wet intervals." In addition, the researchers found that "the decrease in flood magnitudes following 1000 cal yr B.P. corresponds to numerous local and regional records of warming during the Medieval Climatic Anomaly." The three largest such negative departures from modern flood magnitudes (indicating greater than modern warmth) occur between AD 1250 and 1400, as determined from radiocarbon dating of basal channel-fill sediments; and they range from -15 to -22%.



Northern Range of Yellowstone National Park, Wyoming, USA

Reference
Persico, L. and Meyer, G. 2009. Holocene beaver damming, fluvial geomorphology, and climate in Yellowstone National Park, Wyoming. Quaternary Research 71: 340-353.

Description
Persico and Meyer (2009) used beaver-pond deposits and geomorphic characteristics of small streams to assess long-term effects of beavers and climate change on Holocene fluvial activity in northern Yellowstone National Park, which feat was accomplished by comparing the distribution of beaver-pond deposit ages to paleoclimatic proxy records in the region (approximately 44.9 N, 110.5 W). This work revealed that gaps in the beaver-pond deposit record from AD 1000 to 1300 were "contemporaneous with increased charcoal accumulation rates in Yellowstone lakes and peaks in fire-related debris-flow activity, inferred to reflect severe drought and warmer temperatures [our italics]." They also report that the lack of evidence for beaver activity during this period "is concurrent with the Medieval Climatic Anomaly," and they say that the severe droughts of this period "likely caused low to ephemeral discharges in smaller streams, as in modern severe drought [our italics]," implying that the Medieval Warm Period was likely just as dry and warm as it has been throughout the last few decades.



North American Great Plains, USA

Reference
Nordt, L., von Fischer, J., Tieszen, L. and Tubbs, J. 2008. Coherent changes in relative C4 plant productivity and climate during the late Quaternary in the North American Great Plains. Quaternary Science Reviews 27: 1600-1611.

Description
Based on isotopic soil carbon measurements made on 24 modern and 30 buried soils scattered between latitudes 48 and 32 N and longitudes 106 and 98 W (average of 38.93 N, 101.99 W), Nordt et al. developed a time series of C4 vs. C3 plant dynamics for the past 12,000 14C years in the mixed and shortgrass prairie of the U.S. Great Plains; and because the percent soil carbon derived from C4 plants "corresponds strongly with summer temperatures as reflected in the soil carbon pool," as they describe it, they were able to derive a history of the relative warmth of the region that indicates that the peak warmth of the Medieval Warm Period was slightly greater than it has yet to be during the Current Warm Period.



Owens Valley, White Mountains, California, USA

Reference
Ababneh, L. 2008. Bristlecone pine paleoclimatic model for archeological patters in the White Mountains of California. Quaternary International 188: 59-78.

Description
The author derived a history of temperature-related tree-ring width indices from both whole-bark and strip-bark bristlecone pine trees from both Patriarch Grove and Sheep Mountain in California, USA, which commenced at AD 1171 and extended all the way to AD 2002. This history began in the midst of the Medieval Warm Period, which extended, in our estimation, to approximately AD 1430. During this interval there were several periods when tree-ring width indices were more than double those experienced over the final decades of the 20th century; and in a couple of instances they were even three times greater.



Southern California, USA

Reference
MacDonald, G.M., Kremenetski, K.V. and Hidalgo, H.G. 2008. Southern California and the perfect drought: Simultaneous prolonged drought in Southern California and the Sacramento and Colorado River systems. Quaternary International 188: 11-23.

Description
The authors developed dendrochronological reconstructions of the winter Palmer Drought Severity Index (PDSI) for southern California over the past one thousand years (first figure below), plus concomitant annual discharges of the Sacramento and Colorado Rivers (second figure below). This work revealed, in their words, that "prolonged perfect droughts (~30-60 years), which produced arid conditions in all three regions simultaneously, developed in the mid-11th century and the mid-12th century during the period of the so-called 'Medieval Climate Anomaly'," which is also widely known as the Medieval Warm Period, leading them to conclude that "prolonged perfect droughts due to natural or anthropogenic changes in radiative forcing, are a clear possibility for the near future." Consequently, since the perfect droughts of the 20th century "generally persist[ed] for less than five years," while those of the MWP lasted 5 to 12 times longer, one could reasonably conclude that late 20th-century warmth was significantly less than that of the central portion of the Medieval Warm Period.



Southern Alaska, USA

Reference
Wiles, G.C., Barclay, D.J., Calkin, P.E. and Lowell, T.V. 2008. Century to millennial-scale temperature variations for the last two thousand years indicated from glacial geologic records of Southern Alaska. Global and Planetary Change 60: 115-125.

Description
Wiles et al. used temperature-sensitive climate proxy records with tree-ring, lichen and radiocarbon dated histories from five land-terminating non-surging glaciers located just above the Gulf of Alaska (about 60 N between 140 and 150 W) for the last two millennia to "identify summer temperature as a primary driver of glacial expansions." This work provided evidence for the Medieval Warm Period that consisted of "soil formation and forest growth on many forefields in areas that today are only just emerging from beneath retreating termini," which suggests that the Medieval Warm Period was likely both warmer and longer-lived than what we have so far experienced during the Current Warm Period. They also report that "tree-ring chronologies show that forest growth on these forefields was continuous between the 900s and 1200s" at the Sheridan, Tebenkof and Princeton glaciers.



South Fork Payette River Area, Central Idaho

Reference
Pierce, J.L., Meyer, G.A. and Jull, A.J.T. 2004. Fire-induced erosion and millennial-scale climate change in northern ponderosa pine forests. Nature 432: 87-90.

Description
Pierce et al. (2004) dated fire-related sediment deposits in alluvial fans in central Idaho, USA, in a research program designed to reconstruct Holocene fire history in xeric ponderosa pine forests and to look for links to past climate change. Their work centered on tributary alluvial fans of the South Fork Payette (SFP) River area (~44 N, 115.6 W), where fans receive sediment from small but steep basins that are conducive to post-fire erosion. Altogether, they obtained 133 AMS 14C-derived dates from 33 stratigraphic sites in 32 different alluvial fans. The results suggested that the size and severity of large-event stand-replacing fires in this region tend to increase with temperature and that intervals of stand-replacing fires and large debris-flow events are largely coincident in SFP ponderosa pine forests "most notably during the 'Medieval Climatic Anomaly' (MCA), ~1,050-650 cal. yr BP." Based on these findings, the Medieval Warm Period was likely warmer than the Current Warm Period.



Rawson Lake, Northwestern Ontario, Canada

Reference
Laird, K.R. and Cumming, B.F. 2009. Diatom-inferred lake level from near-shore cores in a drainage lake from the Experimental Lakes Area, northwestern Ontario, Canada. Journal of Paleolimnology 42: 65-80.

Description
The authors developed a history of changes in the level of Lake 259 (Rawson Lake, 49 40'N, 93 44'W) within the Experimental Lakes Area of northwestern Ontario, Canada, based on a suite of near-shore gravity cores they analyzed for diatom species identity and concentration, as well as organic matter content. This work revealed "a distinct decline in lake level of ~2.5 to 3.0 m from ~800 to 1130 AD." This interval, in their words, "corresponds to an epic drought recorded in many regions of North America from ~800 to 1400 AD," which they say "is often referred to as the Medieval Climatic Anomaly or the Medieval Warm Period." They also note that the Canadian prairies are currently "experiencing reductions in surface-water availability due to climate warming and human withdrawals" and that "many regions in the western U.S. have experienced water supply deficits in reservoir storage with the recent multi-year drought," but they say that "these severe multi-year drought conditions pale in comparison [our italics] to the many widespread megadroughts [our italics] that persisted for decades and sometimes centuries [our italics] in many parts of North America over the last millennium." Thus, the close association between the severity and duration of drought and warmth within the affected region of North America suggests that the degree of warmth during the Medieval Warm Period in the Experimental Lakes Area of Canada was likely much greater than the degree of warmth so far experienced there during the Current Warm Period.



Tebenkof Glacier, Northern Kenai Mountains, Southern Alaska, USA

Reference
Barclay, D.J., Wiles, G.C. and Calkin, P.E. 2009. Tree-ring crossdates for a first millennium AD advance of Tebenkof Glacier, southern Alaska. Quaternary Research 71: 22-26.

Description
Noting that "tree-ring crossdates of glacially killed logs have provided a precisely dated and detailed picture of Little Ice Age (LIA) glacier fluctuations in southern Alaska," the authors extended this history back into the First Millennium AD (FMA) by integrating similar data obtained from additional log collections made in 1999 with the prior data to produce a "new-and-improved" history of advances and retreats of the Tebenkof Glacier (located in the northern Kenai Mountains on the western edge of Prince William Sound) that spans the entire past two millennia. This work revealed that between the FMA and LIA extensions of the Tebenkof Glacier terminus, there was a period between about AD 950 and 1230 when the terminus dropped further than two kilometers back from the maximum LIA extension that occurred near the end of the 19th century. It also suggests that this warmer/drier period of glacier terminus retreat had to have been much more extreme than what was experienced at any time during the 20th century, because at the century's end the glacier's terminus had still not retreated more than two kilometers back from the line of its maximum LIA extension.



Level 3 Studies

Aleutian Islands

Reference
Causey, D., Corbett, D.G., Lef vre, C., West, D.L., Savinetsky, A.B., Kiseleva, N.K. and Khassanov, B.F. 2005. The palaeoenvironment of humans and marine birds of the Aleutian Islands: three millennia of change. Fisheries Oceanography 14 (Suppl. 1): 259-276.

Description
The authors analyzed data pertaining to the paleoavifauna hunted by early Aleuts inhabiting the central Aleutian Islands of Amchitka (51.38 N, 179.27 E), Buldir (51.37 N, 176.92 E) and Shemya (52.72 N, 174.12 E), developing a relationship between bird abundance and climate in this region over the past few thousand years. Nearshore foragers such as cormorants and parakeet auklets were shown to have increased in abundance during periods of increased temperature, such as during the Medieval Warm Period (AD 900-1350), whereas piscivorous birds feeding offshore, such as murres and kittiwakes, predominated during colder times.



Amargosa Canyon, Death Valley, California, USA

Reference
Anderson, D.E. 2005. Holocene fluvial geomorphology of the Amargosa River through Amargosa Canyon, California. Earth-Science Reviews 73: 291-307.

Description
The author examined the fluvial geomorphology of the Amargosa River, located in Death Valley, California (~35.75 N, 116.25 W), in an attempt to reconstruct a Holocene history of the hydroclimatology of the region. Results indicated that two major aggradational periods, likely associated with wetter climates, were separated by a substantial erosional period that occurred between ~ AD 800 and 1400, which was likely the product of an era of low-frequency, high-magnitude floods that occurred during an overall drier climatic regime associated with the Medieval Warm Period.



Disko Bugt, West Greenland

Reference
Lloyd, J.M. 2006. Late Holocene environmental change in Disko Bugt, west Greenland: interaction between climate, ocean circulation and Jakobshavn Isbrae. Boreas 35: 35-49.

Description
Two marine sediment cores from Disko Bugt (69.17 N, 51.33 W), a large marine embayment along the west coast of Greenland, were analyzed to produce a proxy record of water temperature and salinity over the Holocene. Sedimentary and foraminiferal analyses revealed an increasing influence of Atlantic waters on the ocean temperature that culminated in "peak relatively warm and saline hydrographic conditions from c. 1664 to 474 cal. yr BP." Such peak warmth is noted by the authors to coincide with the well-known Medieval Warm Period.



Crevice Lake, Yellowstone National Park, USA

Reference
Whitlock, C., Dean, W., Rosenbaum, J., Stevens, L., Fritz, S., Bracht, B. and Power, M. 2008. A 2650-year-long record of environmental change from northern Yellowstone National Park based on a comparison of multiple proxy data. Quaternary International 188: 126-138.

Description
The authors state that "geochemical, stable-isotope, pollen, charcoal, and diatom records were analyzed at high-resolution in cores obtained from Crevice Lake" -- located at 45.000 N, 110.578 W -- with the goal of reconstructing "the ecohydrologic, vegetation, and fire history of the watershed for the last 2650 years to better understand past climate variations at the forest-steppe transition" in "the canyon of the Yellowstone River in northern Yellowstone National Park." This work revealed, in their words, that "the Crevice Lake data suggest a warm interval with dry winters between AD 600 and 850, followed by less dry but still warm conditions between AD 850 and 1100." MWP: AD 600-1100.



Southern Vancouver Island, Canada

Reference
Zhang, Q.-B. and Hebda, R.J. 2005. Abrupt climate change and variability in the past four millennia of the southern Vancouver Island, Canada. Geophysical Research Letters 32 L16708, doi:10.1029/2005GL022913.

Description
The authors constructed an ~4,000-year spring precipitation history from hundreds of well-preserved subfossil logs discovered at the bottom of Heal Lake (48 32'N, 123 28'W) near the city of Victoria, Vancouver Island, Canada. In contrast with the rest of the record, in the words of Zhang and Hebda, precipitation was "relatively stable around its mean condition" during the 10th-14th centuries, "corresponding to the North Atlantic Medieval Warm Period."



Mexican Highlands

Reference
Almeida-Lenero, L., Hooghiemstra, H., Cleef, A.M. and Van Geel, B. 2005. Holocene climatic and environmental change from pollen records of Lakes Zempoala and Quila, central Mexican highlands. Review of Palaeobotany and Palynology 136: 63-92.

Description
The authors analyzed Holocene pollen profiles derived from sediment cores retrieved from Lake Zempoala (19 03'N, 99 18'W) and nearby Lake Quila (19 04'N, 99 19'W) in the central Mexican highlands about 65 km southwest of Mexico City. This work revealed that the period AD 700-900 was the "driest and represents an extreme since the mid-Holocene." In addition, the researchers note that climatic conditions near the end of this 200-year period (~AD 900) were similar to those of today, in particular as recorded in data from Lake Zempoala.



Hole Bog, Minnesota and Minden Bog, Michigan

Reference
Booth, R.K., Notaro, M., Jackson, S.T. and Kutzbach, J.E. 2006. Widespread drought episodes in the western Great Lakes region during the past 2000 years: Geographic extent and potential mechanisms. Earth and Planetary Science Letters 242: 415-427.

Description
Booth et al. (2006) constructed a high-resolution history of water-table depth (drought) at two ombrotrophic peatlands separated by about 1000 km - Hole Bog in Minnesota, USA (47 18' N, 94 15' W) and Minden Bog in Michigan, USA (46 37' N, 82 50' W) - based on analyses of sediment-core-derived testate amoeba profiles and radiocarbon dates. This work revealed, in their words, that "the highest-magnitude moisture fluctuations in both regions occurred during an interval roughly overlapping with the Medieval Warm Period, with individual drought events centered on 1000 BP, 800 BP, and 700 BP." In addition, they report that "the droughts between 1000 and 700 BP were widespread in the western United States and mid-continent, and they may have extended well into eastern North America."



Lake Chichancanab, Mexico

Reference
Hodell, D.A., Brenner, M. and Curtis, J.H. 2005. Terminal Classic drought in the northern Maya lowlands inferred from multiple sediment cores in Lake Chichancanab (Mexico). Quaternary Science Reviews 24: 1413-1427.

Description
Depth profiles of bulk density data were obtained by means of gamma-ray attenuation from sediment cores retrieved from Lake Chichanacanab in the center of the northern Yucatan Peninsula of Mexico (19 50'-19 57'N, 88 45'-88 46'W) and used as proxies for drought over the past several thousand years. These data revealed the existence of several massive droughts of unprecedented magnitude between AD 770 and 1100 that coincided with the demise of the Maya civilization, which we interpret to have occurred coincident with the MWP.



Igaliku Fjord, South Greenland

Reference
Jensen, K.G., Kuijpers, A., Ko , N. and Heinemeier, J. 2004. Diatom evidence of hydrographic changes and ice concentrations in Igaliku Fjord, South Greenland, during the past 1500 years. The Holocene 14: 152-164.

Description
The authors conducted biostratigraphic diatom analyses on two ocean sediment cores retrieved from Igaliku Fjord (~60.95 N, 45.37 W), south Greenland, to obtain a record of changes in the hydrography and sea ice of the region during the late Holocene. Major cold and warm periods were evidenced in the subfossil diatom assemblages of the two cores, including a cold and presumably moist regime between AD 500 and 700 (Dark Ages Cold Period), a warm period with higher water temperatures and reduced sea ice between AD 800 and 1250 (Medieval Warm Period), a cold Little Ice Age between 1580 and 1850, and the Current Warm Period from 1850 to the present.



Naja Lake, Lacandon Forest, Chiapas, Mexico

Reference
Dominguez-Vazquez, G. and Islebe, G.A. 2008. Protracted drought during the late Holocene in the Lacandon rain forest, Mexico. Vegetation History and Archaeobotany 17: 327-333.

Description
Based on radiocarbon dating and pollen analyses of a sediment core retrieved from the shore of Naja Lake (16 59'27.6"N, 91 35'29.6"W), which is located near the Lacandon Forest Region in the state of Chiapas in southeastern Mexico, the authors found evidence for "a strong, protracted drought from 1260 to 730 years BP," which they characterize as "the most severe" of the record. In fact, they write that "the drought coincides with the Maya classic collapse and represents the most pronounced dry period of the last 2,000 years in the Lacandon area."



Narsaq Sound, Southern Greenland

Reference
Norgaard-Pedersen, N. and Mikkelsen, N. 2009. 8000 year marine record of climate variability and fjord dynamics from Southern Greenland. Marine Geology 264: 177-189.

Description
Working with a sediment core retrieved from the deepest basin of Narsaq Sound (60 56.200'N, 46 09.300'W) in southern Greenland, the authors were able to infer various "glacio-marine environmental and climatic changes" that had occurred over the prior 8,000 years. This work revealed the existence of two periods (2.3-1.5 ka and 1.2-0.8 ka) that, as they describe it, "appear to coincide roughly with the 'Medieval Warm Period' and 'Roman Warm Period'," while they identified the colder period that followed the Medieval Warm Period as the Little Ice Age and the colder period that preceded it as the Dark Ages Cold Period.



Sierra Nevada and White Mountains of California

Reference
Bunn, A.G., Graumlich, L.J. and Urban, D.L. 2005. Trends in twentieth-century tree growth at high elevations in the Sierra Nevada and White Mountains, USA. The Holocene 15: 481-488.

Description
Approximate 1000-year tree-ring chronologies for five species of high-elevation conifers at 13 sites in the Sierra Nevada and White Mountains of western North America indicated the existence of the MWP (a period with temperatures slightly higher than the long-term average) at the start of the records around AD 1000 and lasting until AD 1150.



Republican River, Southwest Nebraska, USA

Reference
Daniels, J.M. and Knox, J.C.  2005.  Alluvial stratigraphic evidence for channel incision during the Mediaeval Warm Period on the central Great plains, USA.  The Holocene 15: 736-747.

Description
Alluvial stratigraphic data from the upper Republican River, southwest Nebraska, USA, provided evidence for major channel incision between c. 1100 and 800 14C yr BP that correlates with a multicentennial episode of common, widespread drought, which the authors state is associated with the Medieval Warm Period, which occurred between AD 900 and 1200.



Piermont Marsh, New York, USA

Reference
Pederson, D.C., Peteet, D.M., Kurdyla, D., Guilderson, T. 2005. Medieval Warming, Little Ice Age, and European impact on the environment during the last millennium in the lower Hudson Valley, New York, USA. Quaternary Research 63: 238-249.

Description
A warmer and drier interval identified from the type and amount of pollen found in a sediment core with bi-decadal resolution retrieved from Piermont Marsh (41 00'N, 73 55'W) on the western shore of the Hudson River, New York, USA, revealed the MWP to have held sway in that area from AD 795 to 1290.




South Bay, Near San Francisco, California, USA

Reference
McGann, M. 2008. High-resolution foraminiferal, isotopic, and trace element records from Holocene estuarine deposits of San Francisco Bay, California. Journal of Coastal Research 24: 1092-1109.

Description
The author analyzed a sediment core retrieved from the western portion of South Bay near San Francisco International Airport (37 37.83'N, 122 21.99'W) for the presence and abundance of various foraminifers, as well as oxygen and carbon stable isotopes and numerous trace elements found in the tests of Elphidium excavatum. This work revealed, in her words, the presence of "warm and dry conditions, representative of the Medieval Warm Period," which she identified as occurring from AD 743 to 1343. Although a temperature reconstruction was provided, the uppermost core segment was considered to be "contaminated," so that no valid temperature was presented for the past century, and no comparison could be made between the level of warmth during the past two decades and the peak warmth of the MWP.



Upper Gunnison Basin, Colorado, USA

Reference
Emslie, S.D., Stiger, M. and Wambach, E. 2005. Packrat middens and late Holocene environmental change in southwestern Colorado. The Southwestern Naturalist 50: 209-215.

Description
Analyses of subfossil macrobotanical remains of 17 bushy-tailed packrat (Neotoma cinerea) middens in the Upper Gunnison Basin of Colorado revealed a period of warmer conditions between AD 500 and 1050.



Steel Lake, North-Central Minnesota, USA

Reference
Tian, J., Nelson, D.M. and Hu, F.S. 2006. Possible linkages of late-Holocene drought in the North American mid-continent to Pacific Decadal Oscillation and solar activity. Geophysical Research Letters 33: 10.1029/2006GL028169.

Description
The authors derived a high-resolution δ18O record of endogenic calcite, which they obtained from sediments extracted from Steel Lake (46 58'N, 94 41'W) in north-central Minnesota, USA. After demonstrating that evaporative 18O enrichment related to aridity was the "dominant control" of calcite δ18O at that location, they determined that the surrounding region was "relatively dry" from AD 1100 to 1400 compared to the periods that preceded and followed it, which drier time interval they referred to as the "Medieval Climate Anomaly."




Northern Hemisphere
Level 1 Studies

Northern Hemisphere (20-90 N)

Reference
D'Arrigo, R., Wilson, R. and Jacoby, G. 2006. On the long-term context for late twentieth century warming. Journal of Geophysical Research 111: 10.1029/2005JD006352.

Description
D'Arrigo et al. (2006) assembled mostly tree-ring width (but some density) data from living and subfossil wood of coniferous tree species found at 66 high-elevation and latitudinal treeline North American and Eurasian sites, after which they analyzed the data via the Regional Curve Standardization detrending technique to reconstruct a history of annual temperature for the Northern Hemisphere between 20 and 90 N for the period AD 713-1995. In comparing the temperatures of the Medieval Warm Period (MWP, 950-1100 A.D.) with those of the Current Warm Period (CWP), based on the six longest chronologies they analyzed, they concluded that "the recent period does not look particularly warmer compared to the MWP." However, the mean of the six series did depict a warmer CWP; but they describe this relationship as "a bias/artifact in the full RCS reconstruction where the MWP, because it is expressed at different times in the six long records, is 'averaged out' (i.e., flattened) compared to the recent period which shows a much more globally consistent signal." Nevertheless, the data are what they are; and for the period covered only by the proxy data (so that "apples and oranges" are not compared), they found that peak twentieth century warmth (which occurred between 1937 and 1946) exceeded peak MWP warmth by 0.29 C.



Northern Hemisphere, After Moberg et al. (2005)

Reference
Moberg, A., Sonechkin, D.M., Holmgren, K., Datsenko, N.M. and Karlen, W. 2005. Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature 433: 613-617.

Description
The authors present a temperature history of the Northern Hemisphere that spans the past two millennia. It was produced from two different sources of paleoclimatic data: tree-rings, which capture very high frequency climate variations, and lake and ocean sediments, which Moberg et al. say "provide climate information at multicentennial timescales that may not be captured by tree-ring data." Using data provided by the authors, we have produced a graph of average decadal temperature anomalies, shown below, in which the Medieval Warm Period peaks just prior to AD 900 and is strongly expressed between about AD 650 and 1250. Peak temperatures during this time period are about 0.22 C higher than those at the end of the Moberg et al. record. Instrumental data suggest significant subsequent warming; but the directly-measured temperatures cannot be validly compared with the reconstructed ones. Hence, it is not possible to determine if current temperatures have eclipsed those of a thousand years ago or whether they still fall below them; and the fairest thing to do, in our estimation, is to tentatively conclude (for this data set only) that the peak temperatures of both periods are approximately equivalent.




Oceans
Level 1 Studies

Indo-Pacific Warm Pool

Reference
Newton, A., Thunell, R. and Stott, L. 2006. Climate and hydrographic variability in the Indo-Pacific Warm Pool during the last millennium. Geophysical Research Letters 33: 10.1029/2006GL027234.

Description
Working with a sediment core collected at 5 12.07'S, 117 29.20'E in the Indo-Pacific Warm Pool (one of the warmest regions in the modern oceans), Newton et al. analyzed planktonic foraminiferal (Globigerinoides ruber) Mg/Ca and δ18O data to derive high-resolution summer sea surface temperature (SST) and salinity histories extending back in time about a thousand years. This work revealed, in their words, that "the warmest temperatures and highest salinities occurred during the Medieval Warm Period," which lasted from about AD 1020 to 1260. Over this period, summer SSTs averaged about 29.7 C, as best we can determine from their graph of the data, with a peak of about 30.9 C in the vicinity of AD 1080, which values are to be compared with "the average modern summer SST [of] 29 C." Consequently, modern summer temperatures still average about 0.7 C less than those of the Medieval Warm Period.



Makassar Strait, Sulawesi Margin, Indo-Pacific Warm Pool

Reference
Oppo, D.W., Rosenthal, Y. and Linsley, B.K. 2009. 2,000-year-long temperature and hydrology reconstructions from the Indo-Pacific warm pool. Nature 460: 1113-1116.

Description
Oppo et al. derived a continuous sea surface temperature (SST) reconstruction from the Indo-Pacific Warm Pool (IPWP), which they describe as "the largest reservoir of warm surface water on the earth and the main source of heat for the global atmosphere." This history -- which was based on δ18O and Mg/Ca data obtained from samples of the planktonic foraminifera Globigerinoides ruber found in two gravity cores, a nearby multi-core (all at 3 53'S, 119 27'E), and a piston core (at 5 12'S, 117 29'E) that were recovered from the Makassar Strait on the Sulawesi margin -- spans the past two millennia and, as they describe it, "overlaps the instrumental record, enabling both a direct comparison of proxy data to the instrumental record and an evaluation of past changes in the context of twentieth century trends." Reconstructed SSTs were, in their words, "warmest from AD 1000 to AD 1250 and during short periods of first millennium." From the authors' Figure 2b, adapted below, we calculate that the Medieval Warm Period was about 0.4 C warmer than the Current Warm Period.



Pigmy Basin, Northern Gulf of Mexico

Reference
Richey, J.N., Poore, R.Z., Flower, B.P. and Quinn, T.M. 2007. 1400 yr multiproxy record of climate variability from the northern Gulf of Mexico. Geology 35: 423-426.

Description
In the words of the authors, "a continuous decadal-scale resolution record of climate variability over the past 1400 years in the northern Gulf of Mexico was constructed from a box core recovered in the Pigmy Basin, northern Gulf of Mexico [27 11.61'N, 91 24.54'W]," based on climate proxies derived from "paired analyses of Mg/Ca and δ18O in the white variety of the planktic foraminifer Globigerinoides ruber and relative abundance variations of G. sacculifer in the foraminifer assemblages." This work revealed that "two multi-decadal intervals of sustained high Mg/Ca indicate that Gulf of Mexico sea surface temperatures were as warm or warmer than [our italics] near-modern conditions between 1000 and 1400 yr B.P." From the author's Figure 1 (adapted below), we calculate the peak warmth during this time to have been about 1.5 C warmer than present-day temperatures.



Level 2 Studies

Carmen Basin, Gulf of California, Mexico

Reference
Barron, J.A. and Bukry, D. 2007. Solar forcing of Gulf of California climate during the past 2000 yr suggested by diatoms and silicoflagellates. Marine Micropaleontology 62: 115-139.

Description
Barron and Bukry (2007) developed high-resolution records of diatoms and silicoflagellate assemblages spanning the past 2000 years from analyses of a sediment core extracted from Carmen Basin in the Gulf of California (26 17.39'N, 109 55.24'W). Results indicated that the relative abundance of Azpeitia nodulifera (a tropical diatom whose presence suggests the occurrence of higher sea surface temperatures), was found to be far greater during the Medieval Warm Period than at any other time over the 2000-year period studied, while during the Modern Warm Period its relative abundance was actually lower than the 2000-year mean.



Tropical Pacific Ocean

Reference
Cook, E.R., Seager, R., Cane, M.A. and Stahle, D.W. 2007. North American drought: Reconstructions, causes, and consequences. Earth-Science Reviews 81: 93-134.

Description
In a review of multiple long tree-ring reconstructions of past drought (Palmer Drought Severity Index) conditions in North America, Cook et al. find evidence of "a number of unprecedented megadroughts over the past millennium that clearly exceed any found in the instrumental records," including an amazing "epoch of significantly elevated aridity that persisted for almost 400 years over the AD 900-1300 period." They also report that all major historical droughts of North America were caused by "the development of cool 'La Ni a-like' SSTs in the eastern tropical Pacific," and that both "model and data agree" that "if there is a heating over the entire tropics [our italics] then the Pacific will warm more in the west than in the east because the strong upwelling and surface divergence in the east moves some of the heat poleward," so "the east-west temperature gradient will strengthen, so the winds will also strengthen, so the temperature gradient will increase further ... leading to a more La Ni a-like state," which in turn leads to drought in North America. Also, they report that "La Ni a-like conditions were apparently the norm [our italics] during much of the Medieval period," during which time the truly unprecedented 400-year megadrought held sway. Consequently, because the AD 900-1300 time interval (representing the core of the Medieval Warm Period) was host to the most severe and long-lasting drought of the last eleven centuries, that period must also have experienced the warmest tropical temperatures of the last 1100 years.



Southeastern Shelf of the Laptev Sea, Arctic Ocean

Reference
Matul, A.G., Khusid, T.A., Mukhina, V.V., Chekhovskaya, M.P. and Safarova, S.A. 2007. Recent and late Holocene environments on the southeastern shelf of the Laptev Sea as inferred from microfossil data. Oceanology 47: 80-90.

Description
Matul et al. studied the distributions of different species of siliceous microflora (diatoms), calcareous microfauna (foraminifers) and spore-pollen assemblages found in sediment cores retrieved from 21 sites on the inner shelf of the southern and eastern Laptev Sea, starting from the Lena River delta and moving seaward between about 130 and 134 E and stretching from approximately 71 to 78 N, which cores were acquired by a Russian-French Expedition during the cruise of R/V Yakov Smirnitsky in 1991. This endeavor indicated the existence of "the Medieval Warm Period, ~600-1100 years BP; the Little Ice Age, ~100-600 years BP, with the cooling maximum, ~150-450 years BP; and the 'industrial' warming during the last 100 years." In addition, "judging from the increased diversity and abundance of the benthic foraminifers, the appearance of moderately thermophilic diatom species, and the presence of forest tundra (instead of tundra) pollen," they write that "the Medieval warming exceeded the recent 'industrial' one."



Guaymas Basin, Gulf of California, Mexico

Reference
Barron, J.A. and Bukry, D. 2007. Solar forcing of Gulf of California climate during the past 2000 yr suggested by diatoms and silicoflagellates. Marine Micropaleontology 62: 115-139.

Description
Barron and Bukry (2007) developed high-resolution records of diatoms and silicoflagellate assemblages spanning the past 2000 years from analyses of a sediment core extracted from Guaymas Basin in the Gulf of California (27.92 N, 111.61 W). Results indicated that the relative abundance of Azpeitia nodulifera (a tropical diatom whose presence suggests the occurrence of higher sea surface temperatures), was found to be far greater during the Medieval Warm Period than at any other time over the 2000-year period studied, while during the Modern Warm Period its relative abundance was actually lower than the 2000-year mean.



Pescadero Basin, Gulf of California, Mexico

Reference
Barron, J.A. and Bukry, D. 2007. Solar forcing of Gulf of California climate during the past 2000 yr suggested by diatoms and silicoflagellates. Marine Micropaleontology 62: 115-139.

Description
Barron and Bukry (2007) developed high-resolution records of diatoms and silicoflagellate assemblages spanning the past 2000 years from analyses of a sediment core extracted from Pescadero Basin in the Gulf of California (24 16.78'N, 108 11.65W). Results indicated that the relative abundance of Azpeitia nodulifera (a tropical diatom whose presence suggests the occurrence of higher sea surface temperatures), was found to be far greater during the Medieval Warm Period than at any other time over the 2000-year period studied, while during the Modern Warm Period its relative abundance was actually lower than the 2000-year mean.



Level 3 Studies

Alfonso Basin, Gulf of California, Mexico

Reference
Perez-Cruz, L. 2006. Climate and ocean variability during the middle and late Holocene recorded in laminated sediments from Alfonso Basin, Gulf of California, Mexico. Quaternary Research 65: 401-410.

Description
Working with a laminated sediment core recovered from the Alfonso Basin in the Bay of La Paz (24 38.12'N, 110 33.24'W), the author studied the population history of the "equatorial" radiolarian Tetrapyle octacantha, which "is closely associated with warm subtropical and equatorial waters." This effort revealed, in the words of Perez-Cruz, that "two conspicuous intervals at AD ~910 and 1000 may be correlated to the 'Medieval Warm Period' ... that is consistent with the global pattern."



South China Sea

Reference
Zicheng, P., Xuexian, H., Xiaozhong, L., Jianfeng, H., Guijian, L. and Baofu, N. 2003. Thermal ionization mass spectrometry (TIMS)-U-series ages of corals from the South China Sea and Holocene high sea level. Chinese Journal of Geochemistry 22: 133-139.

Description
The authors utilized the technique of thermal ionization mass spectrometry on several coral samples obtained across the South China Sea (Huayang Reef ~8.86 N, 112.86 E, Parcel Islands ~16.3 N, 112 E, Hainan Island ~19 N, 110 E and the Lizhou Peninsula ~21 N, 110 E) in an effort to precisely date and determine historical sea level changes throughout the Holocene. Results indicated there were three phases of high sea level in this region over the past 7,000 years, the third of which took place between ~AD 720 and 1000 and corresponds with the "warm environments ... [of] the Medieval Warm Period" that the authors say were experienced in China during this time interval.



Skalafjord, Faroe Islands

Reference
Roncaglia, L.  2004.  Palynofacies analysis and organic-walled dinoflagellate cysts as indicators of palaeo-hydrographic changes: an example from Holocene sediments in Skalafjord, Faroe Islands.  Marine Micropaleontology 50: 21-42

Description
A temperature reconstruction based upon the dinoflagellate cyst and acritarch distribution within a sediment core extracted from Skalafjord, Faroe Islands (62 10.54'N, 6 47.94'W) was developed for the period 6350 BC to AD 1430.  The author says that an "amelioration of climate conditions" with warmer sea surface temperatures prevailed between AD 830-1090, which "may encompass the Medieval Warm Period in the Faroe region."



Lake Caveiro, Pico Island, Azores

Reference
Bjorck, S., Rittenour, T., Rosen, P., Franca, Z., Moller, P., Snowball, I., Wastegard, S., Bennike, O. and Kromer, B. 2006. A Holocene lacustrine record in the central North Atlantic: proxies for volcanic activity, short-term NAO mode variability, and long-term precipitation changes. Quaternary Science Reviews 25: 9-32.

Description
General climatic conditions were inferred from "sedimentology, geochemistry, diatom analyses, magnetic properties, and multivariate statistics, together with 14C and 210Pb dating techniques" applied to a core obtained from the center of a small crater lake on the Azores island of Pico (38 26'N, 28 12'W). The MWP was broadly characterized by the adjoining "cooler/drier periods" of 400-800 and 1300-1800 cal yr BP, but was said by the authors to be most strongly expressed between AD 1000 and 1100, which is where we have located it.




South America
Level 1 Studies

Cariaco Basin off the Venezuelan Coast

Reference
Goni, M.A., Woodworth, M.P., Aceves, H.L., Thunell, R.C., Tappa, E., Black, D., Muller-Karger, F., Astor, Y. and Varela, R. 2004. Generation, transport, and preservation of the alkenone-based U37K' sea surface temperature index in the water column and sediments of the Cariaco Basin (Venezuela). Global Biogeochemical Cycles 18: 10.1029/2003GB002132.

Description
Based on the degree of unsaturation of certain long-chain alkenones synthesized by haptophyte algae contained in a sediment core retrieved from the eastern sub-basin of the Cariaco Basin (10 30'N, 64 40'W) on the continental shelf off the Venezuelan central coast, Goni et al. determined that the highest sea surface temperatures at that location over the past 6000 years "were measured during the Medieval Warm Period (MWP)," which they identified as occurring between AD 800 and 1400. From the graph of their results reconstructed below, it is further evident that peak MWP temperatures were approximately 0.35 C warmer than peak Current Warm Period temperatures, and that they were fully 0.95 C warmer than the mean temperature of the last few years of the 20th century.



Jacaf Fjord, Northern Patagonia, Chile

Reference
Sepulveda, J., Pantoja, S., Hughen, K.A., Bertrand, S., Figueroa, D., Leon, T., Drenzek, N.J. and Lange, C. 2009. Late Holocene sea-surface temperature and precipitation variability in northern Patagonia, Chile (Jacaf Fjord, 44 S). Quaternary Research 72: 400-409.

Description
The authors derived alkenone-based spring/summer sea-surface temperatures (SSTs) from a marine sedimentary record obtained from Jacaf Fjord in northern Chilean Patagonia (44 20.00'S, 72 58.15'W) that spanned the last 1750 years; and in doing so they observed two different regimes of climate variability in their record: "a relatively dry/warm period before 900 cal yr BP (higher runoff and average SST 1 C warmer than present day) and a wet/cold period after 750 cal yr BP (higher runoff and average SST 1 C colder than present day)," which they associated with the Medieval Warm Period and Little Ice Age, respectively.



Northeastern Slope of the Cariaco Basin, Venezuela Coast

Reference
Black, D. E., Thunell, R. C., Kaplan, A., Peterson, L. C. and Tappa, E. J. 2004. A 2000-year record of Caribbean and tropical North Atlantic hydrographic variability. Paleoceanography 19, PA2022, doi:10.1029/2003PA000982.

Description
High-resolution δ18O records generated from seasonally representative planktic foraminifera were obtained from two ocean sediment cores extracted from the Cariaco Basin off the coast of Venezuela (~ 10.65 N, 64.66 W) to produce a temperature/salinity reconstruction in this region of the Caribbean/tropical North Atlantic over the last 2000 years. Results indicate a general trend toward cooler and perhaps more saline waters over the length of the record. Because of this trend, the authors describe discussion of the Medieval Warm Period and Little Ice Age as "complicated," but they nonetheless acknowledge their record reveals "an interval of warmer [sea surface temperatures] prior to ~ A.D. 1600-1900" where the δ18O data "correctly sequence the relative temperature change between the so-called MWP and LIA." In viewing the authors' graph of G. bulloides δ18O (25-year mean, reproduced below), and their stated relationship that a δ18O change of 1.0  is equivalent to a 4.2 C change in temperature, we calculate the difference in peak warmth between the MWP and CWP to be 1.05 C, with the MWP being the warmer of the two periods.



Peruvian Shelf

Reference
Rein B., Lückge, A., Reinhardt, L., Sirocko, F., Wolf, A. and Dullo, W.-C. 2005. El Ni o variability off Peru during the last 20,000 years. Paleoceanography 20: 10.1029/2004PA001099.

Description
The authors derived sea surface temperatures from alkenones extracted from a high-resolution marine sediment core retrieved off the coast of Peru (12.05 S, 77.66 W), spanning the past 20,000 years and ending in the 1960s. From their Figure 11, adapted below, it can be seen that the warmest temperatures of this 20,000 year period (~23.2 C) occurred during the late Medieval time (AD 800-1250). Taking this value, 23.2 C, and comparing it with the modern monthly long-term means in sea surface temperature, which the authors characterize as between 15 C and 22 C, we estimate the peak warmth of the Medieval Warm Period for this region was about 1.2 C above that of the Current Warm Period.



Level 2 Studies

Bragan a Peninsula, Eastern Amazon Region, Brazil

Reference
Cohen, M.C.L., Behling, H. and Lara, R.J. 2005. Amazonian mangrove dynamics during the last millennium: The relative sea-level and the Little Ice Age. Review of Palaeobotany and Palynology 136: 93-108.

Description
Cohen et al. (2005) used stratigraphy, pollen analysis and radiocarbon dating to reconstruct the environmental history of the Bragan a Peninsula (0.88 S, 46.67 W) over the past 1000 years, focusing on vegetation development in the central part of the peninsula, where boundaries of mangrove and salt marshes occur, and where sensitive vegetation changes related to relative sea-level changes could be expected. Their results indicated a broad period between AD 1150 and the late 1800s characterized by low inundation frequency (lower sea levels), with the exception of a brief interval of higher sea levels during the Little Medieval Warm Period. Higher sea levels were also observed from the start of the record until around 1130 and during the 20th century. With regard to the cause of these fluctuations, the authors note that the data "strongly point" to global climatic changes that have occurred during the last 1000 years, specifically mentioning the Little Ice Age. Of the present mangrove migration, they further note that it is likely associated "with the global tendency of an eustatic sea-level rise, due to the increase in temperature and glaciers melting around the world during the last 150 years." Given this interpretation and their additional statement that "for the period between 1000 and 1150 AD, relative sea-level was similar to the current sea-level," we can infer that temperatures during this latter stage of the Medieval Warm Period were likely similar to temperatures of the Current Warm Period.



Huascaran Glacier, Peru

Reference
Thompson, L.G., Mosley-Thompson, E., Davis, M.E., Lin, P.-N., Henderson, K. and Mashiotta, T.A. 2003. Tropical glacier and ice core evidence of climate change on annual to millennial time scales. Climatic Change 59: 137-155.

Description
The authors analyzed decadally-averaged δ18O records derived by them and their colleagues from three Andean and three Tibetan ice cores, demonstrating that "on centennial to millennial time scales atmospheric temperature is the principal control on the δ18Oice of the snowfall that sustains these high mountain ice fields," after which they produced "a low latitude δ18O history for the last millennium" that they use as a surrogate for air temperature. For the Huascaran Glacier (9.11 S, 77.62 W), this work suggests that the MWP was not as warm as the CWP.



Tropical Andes

Reference
Polissar, P.J., Abbott, M.B., Wolfe, A.P., Bezada, M., Rull, V. and Bradley, R.S. 2006. Solar modulation of Little Ice Age climate in the tropical Andes. Proceedings of the National Academy of Sciences: 10.1073/pnas.0603118103.

Description
Among other things, the authors derived a 1500-year history of Andean biome elevation changes from analyses of pollen identified in cores removed from the Piedras Blancas peat bog (8 47'N, 70 50'W). This work revealed that from at least AD 500 to about AD 1000, temperatures were generally higher than they were during the late 20th century.



Quelccaya Ice Cap, Peru

Reference
Thompson, L.G., Mosley-Thompson, E., Davis, M.E., Lin, P.-N., Henderson, K. and Mashiotta, T.A. 2003. Tropical glacier and ice core evidence of climate change on annual to millennial time scales. Climatic Change 59: 137-155.

Description
The authors analyzed decadally-averaged δ18O records derived by them and their colleagues from three Andean and three Tibetan ice cores, demonstrating that "on centennial to millennial time scales atmospheric temperature is the principal control on the δ18Oice of the snowfall that sustains these high mountain ice fields," after which they produced "a low latitude δ18O history for the last millennium" that they use as a surrogate for air temperature. For the Quelccaya Ice Cap (13.93 S, 70.83 W), this work revealed that peak temperatures of the MWP were warmer than those of the last few decades of the 20th century.



Sajama Glacier, Bolivia

Reference
Thompson, L.G., Mosley-Thompson, E., Davis, M.E., Lin, P.-N., Henderson, K. and Mashiotta, T.A. 2003. Tropical glacier and ice core evidence of climate change on annual to millennial time scales. Climatic Change 59: 137-155.

Description
The authors analyzed decadally-averaged δ18O records derived by them and their colleagues from three Andean and three Tibetan ice cores, demonstrating that "on centennial to millennial time scales atmospheric temperature is the principal control on the δ18Oice of the snowfall that sustains these high mountain ice fields," after which they produced "a low latitude δ18O history for the last millennium" that they use as a surrogate for air temperature. For the Sajama Glacier (18 S, 68 W), this work revealed that peak temperatures of the MWP were warmer than those of the last few decades of the 20th century.



Level 3 Studies

Marcacocha Lake, South Central Andes, Peru

Reference
Sterken, M., Sabbe, K., Chepstow-Lusty, A., Frogley, M., Vanhoutte, K., Verleyen, E., Cundy, A. and Vyverman, W. 2006. Hydrological and land-use changes in the Cuzco region (Cordillera Oriental, South East Peru) during the last 1200 years: a diatom-based reconstruction. Archiv f r Hydrobiologie 165: 289-312.

Description
The authors conducted a quantitative diatom analysis on a sediment core obtained from the small infilled lake basin of Marcacocha, in the Cuzco region of the south central Andes mountains of Peru (13.22 S, 72.2 W), in an effort to reconstruct environmental changes during the past 1200 years. Results indicated a major climate transition around AD 1070, representing "the most prominent change in the diatom record with a marked shift towards higher temperatures."



Peruvian Shelf

Reference
Rein B., Luckge, A. and Sirocko, F. 2004. A major Holocene ENSO anomaly during the Medieval period. Geophysical Research Letters 31: 10.1029/2004GL020161.

Description
Rein et al. analyzed a high-resolution sediment core retrieved from a sheltered basin situated on the edge of the Peruvian shelf about 80 km west of Lima, Peru (12.05 S, 77.66 W) to produce a proxy record of El Ni o flooding over the past 12,000 years. Results indicated the presence of a significant dry episode during the late Medieval period in which lithic concentrations - a proxy for El Ni o events - were "very low for about 450 years during the Medieval climatic anomaly from A.D. 800 to 1250." Because heavy winter rainfalls along and off coastal Peru only occur during times of maximum El Ni o strength, and because El Ni os are typically much more prevalent and stronger during cooler as opposed to warmer periods [see El Ni o (Relationship to Global Warming) in our Subject Index], the implied lack of strong El Ni os during the period of time from A.D. 800-1250 suggests that this period was truly a Medieval Warm Period.



Palpa-Nasca Basin, Northern Atacama Desert, Peru

Reference
Unkel, I., Kadereit, A., Machtle, B., Eitel, B., Kromer, B., Wagner, G. and Wacker, L. 2007. Dating methods and geomorphic evidence of paleoenvironmental changes at the eastern margin of the South Peruvian coastal desert (14 30'S) before and during the Little Ice Age. Quaternary International 175: 3-28.

Description
Working in the hyper-arid zone of the northern Atacama Desert of Peru between Pisco/Ica and Nazca/San Juan (~14.3 S, 75.3 W), Unkel et al. employed "geomorphological field-work" and "chronometric analyses" -- consisting of conventional 14C-dating of charcoal, wood and root samples and optical-stimulated luminescence dating of feldspar and quartz -- while investigating "alluvial archives and debris flow deposits." This work, together with that of others, indicated the existence of a period of "fluvial silence" for "the time of the 9th-13th centuries," due to "increased aridification," which they associated with the Medieval Warm Period (~AD 800-1250).



Tierra del Fuego, Argentina

Reference
Mauquoy, D., Blaauw, M., van, Geel, B., Borromei, A., Quattrocchio, M., Chambers, F.M. and Possnert, G.  2004.  Late Holocene climatic changes in Tierra del Fuego based on multiproxy analyses of peat deposits. Quaternary Research 61: 148-158.

Description
Changes in temperature and/or precipitation were inferred from plant macrofossils, pollen, fungal spores, testate amebae and peat humification in peat monoliths collected from the Valle de Andorra about 10 km to the northeast of Ushuaia, Tierra del Fuego, Argentina (54.75 S, 68.4 W).  Mauquoy et al. report finding evidence for a period of warming-induced drier conditions from AD 960-1020 that "seems to correspond to the Medieval Warm period (MWP, as defined in the Northern Hemisphere)" and "shows that the MWP was possibly synchronous in both hemispheres."