16. Februar 2011

Ein Blick zurück - 1966

This epoch appears to show most of the same characteristics as the post-glacial epoch both in the Northern Hemisphere and in the Antarctic, only in less degree, perhaps because of its shorter duration.
The Arctic pack ice had melted so far back that appearences of drift ice in waters near Iceland and Greenland south of 70° N. were rare in the 800s and 900s and apparently unknown between 1020 and 1200, when a rapid increase of frequency began. This evidence hardly supports Brooks' suggeston that the Arctic Ocean again became ice-free during this epoch, though "permanent" ice was probably limited to inner Arctic areas north of 80° N. and possibly not including the Canadian Archipelago (to judge from occasional exploits there by the Old Norse Greenland colonist).[1] From the evidence of early Norse burials and plant roots in ground now permanently frozen in southern Greenland, annual mean temperatures there must have been 2°-4°C. above present values. It seems probable that sea temperatures in the northernmost Atlantic were up by a similar amount.
In western and mittle Europe vineyards extended generally 4°-5° latitude farther north and 100-200 metres higher above sea level than at present (Lamb, 1959). Estimates of the upper limits of the forests and of tree species on the Alps and more northern hills in central Europe range from 70 to 200 metres above where they now stand (Gams, 1937; Firbas and Losert, 1949). These figures suggest mean summer temperatures about 1° C., or a little more, above those now normal.
In North America archaeological studies in the upper Missisippi valley (approx. 45° N.) suggest a warm dry epoch, followed by a change to cooler, wetter conditions after A.D. 1300 (Griffin, 1961).
In lower latitudes Brooks (1949, p. 327, 355) names this as a wet period in central America (Yucatan) and probably in Indo-China (Cambodia). there is evidence of greater rainfall and larger rivers in the Mediterranean and the Near East (Butzer, 1958, p. 12). There is some evidence of a moister period in the Sahara from 1200 or earlier, lasting until 1550 (Brooks, 1949, pp. 330-8).
In southernmost South America the forest was receding rapidly to western aspects only, indicating a drier climate than in the previous epoch and more predominant westerly winds.
On the coast of east Antarctica, at Cape Hallett, a great modern penguin rookery appears from radiocarbon tests to have been first colonized between about A.D. 400 and 700, presumably during a phase of improving climate, and to have been occupied ever since (Harrington and McKellar, 1958). this tends to confirm the earlier assumption of explorers of the Bunger Oasis in east Antarctica of a period of marked climatic improvement about a thousand years ago, since which there has been only a modest reversion.
  Lamb, H. H.: SECONDARY CLIMATIC OPTIMUM (CIRCA A.D. 1000 to 1200),
in: The nature of certain climatic variations, in: Lamb, H. H. (editor):
The changing climate, selected papers,
London: Methuen 1966, 64f.


Es bleibt den Lesern überlassen, zu überprüfen, welche Aussagen mittlerweile als bestätigt gelten können und welche nicht. 

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[1] Glaciological and other studies of Arctic ice islands, and their presumed growth when formerly part of the Ellesmere Land ice shelf, have not so far been reduced to an agreed time scale (Crary, 1960, p. 34; Stoiber et al., 1960, p. 71). It seems most probable, however, that the ablation period in progress in the early 1950s began only about 40 years ago and that the total age of the ice is 620 years of less, implying growth during the Little Ice Age epoch and that net ablation prevailed before that, during the secondary climatic epoch, in the Canadian Archipelago.


Literatur
Brooks, C. E. P. 1949. Climate through the ages. 2nd ed. London, Ernest Benn.
Butzer, K. W. 1958. Studien zum vor- und frühgeschichtlichen Landschaftswandel der Sahara, Abh. math.-nat. Kl. Akad. Wiss. Mainz, no. 1.
Crary, A. P. 1960. Arctic ice island and ice shelf studies, Scientific studies at Fletcher's Ice Island, T-3: 1952-1955. Geophysical Research Papers (no. 63), vol. III, p. 1-37. Boston, Air Force Cambridge Research Center. (AFCRC-TR-59-232(3) ASTIA document no. AD-216815.)
Firbas, F.; Losert, H. 1949. Untersuchungen über die Entstehung der heutigen Waldstufen in den Sudeten, Planta (Berlin), vol. 36, p. 478-506.
Gams, H. 1937. Aus der Geschichte der Alpenwalder, Zeitschrift des deutsch. und österreich. Alpenvereins (Stuttgart), vol. 68, p. 157-170.
Griffin, J.B. 1961. Some correlations of climatic and cultural change in eastern North American prehistory, New York Academy of Sciences, Symposium on solar variations, climatic changes and related geophysical problems (Publication pending).
Harrington, H. J.; McKellar, I. C. 1958. A radio-carbon date for penguin colonization of Cape Hallett, Antarctica, N.Z. J. Geol. Geophys., vol. 1, p. 571-576.
Lamb, H. H. 1959. Our changing climate, past and present, Weather, vol. 14, p. 299-318.
Stoiber, R. E.; Lyons, J. B.; Elberty, W. T.; McCreahan, R. H. 1960. Petrographic evidence on the source area and age of T-3, Scientific studies at Fletcher's Ice Island, T-3: 1952-1955. Geophysical Research Papers (no. 63), vol. III, p. 78, Boston, Air Force Cambridge Research Center. (AFCRC-TR-59-232(3) ASTIA document no. AD-216815.)