29. Februar 2012

2012 und die MWP

Vor kurzem haben Ljungqvist et al. ihr Paper Northern Hemisphere temperature patterns in the last 12 centuries veröffentlicht.

Aus dem Abstract:
We analyse the spatio-temporal patterns of temperature variability over Northern Hemisphere land areas, on centennial time-scales, for the last 12 centuries using an unprecedentedly large network of temperature-sensitive proxy records

Sie kommen dabei auf Seite 231f zum Schluss:
Temperatures from the 9th to 12th centuries are generally above the long-term mean, gradually cooling to below the mean in teh 16th to 19th centuries and reaching a maximum cooling in the 17th century. ... The dominance of warm anomalies during the MWP and cold anomalies during the LIA is substantiated by results from the sign test (Fig. B1) that shows where and when there is significant aggreemant between the sign, positive or negatvie,o f the proxies within their search radius (for more details see Appendix B).

Wiederum wenig überraschend. Überraschend für mich ist eher die Aussage, dass es keine Proxyabdeckung "non-existent" für den Mittleren Osten gäbe (232). 

Folgende Studien, lokalisiert im Mittleren Osten, sprechen eine andere Sprache:
M. S. Chauhan:  Late Holocene vegetation and climate change in the alpine belt of Himachal Pradesh, in: Current Science, Vol. 91, No. 11, 10. Dezember 2006.

A. Bhattacharyya et al.: Climatic changes during the last 1800 yrs BP from Paradise Lake, Sela Pass, Arunachal Pradesh, Northeast Himalaya, in: Current Science, Vol. 93, No. 7, 10. October 2007.

Es sind mittlerweile weitere Studien zur MWP erschienen:
Xuhui Dong, Helen Bennion, Richard W. Battarbee, and Carl D. Sayer: A multiproxy palaeolimnological study of climate and nutrient impacts on Esthwaite Water, England over the past 1200 years, in: The Holocene January 2012 22: 107-118, first published on August 22, 2011 doi:10.1177/0959683611409780

Aus dem Abstract:
Two climatic phases, namely the ‘Medieval Warm Period’ (MWP) and the ‘Little Ice Age’ (LIA), were apparent. According to shifts in the diatom assemblages and other proxies, it was proposed that the MWP was initiated from ~ad 880 and was terminated by the LIA at ~ad 1350.

Longbin Sha, Hui Jiang, and Karen Luise Knudsen: Diatom evidence of climatic change in Holsteinsborg Dyb, west of Greenland, during the last 1200 years, in: The Holocene March 2012 22: 347-358, first published on October 12, 2011 doi:10.1177/0959683611423684

Aus dem Abstract:
A relatively warm period with increased influence of Atlantic water masses of the Irminger Current (IC) is found at ad 750–1330, although with some oceanographic variability after ad 1000. A pronounced oceanographic shift occurred at ad 1330, corresponding in time to the transition from the so-called ‘Medieval Warm Period’ (MWP) to the ‘Little Ice Age’ (LIA).

Sofia Ribeiro, Matthias Moros, Marianne Ellegaard, Antoon Kuijpers: Climate variability in West Greenland during the past 1500 years: evidence from a high-resolution marine palynological record from Disko Bay, in: Boreas, Vol. 41, pp. 68–83. 10.1111/j.1502-3885.2011.00216.x. ISSN 0300-9483.

Aus dem Abstract:
After c. AD 1050, the marine climate in Disko Bay becomes in-phase with trends described for the NE Atlantic, reflected in the warmer interval for the remainder of the MCA (c. AD 1050–1250), followed by cooling towards the onset of the Little Ice Age at c. AD 1400.

Eugene R. Wahl, Henry F. Diaz, Christian Ohlwein: A pollen-based reconstruction of summer temperature in central North America and implications for circulation patterns during medieval times, in: Global and Planetary Change, Volumes 84–85, March 2012, Pages 66-74.

Aus dem Abstract:
The results suggest a relatively warm period during the earlier part of the record (~ 1200–1500 CE) followed by a cooler Little Ice Age (~ 1500–1900) and a subsequent warming to modern conditions.

A.E. Viau, M. Ladd, K. Gajewski: The climate of North America during the past 2000 years reconstructed from pollen data, in: Global and Planetary Change, Volumes 84-85, March 2012, Pages 75-83.

Aus dem Abstract:
The MWP was warmer than the LIA over at least the boreal and eastern portions of the continent and perhaps across the continent.