February 13, 2005
Our Variable Climate
A recent letter to Nature outlines what people have been saying all along -- there is a several hundred year cycle of warming and cooling periods. Hat tip to Envirospin Watch Here is the first paragraph and contact info (you can get the entire letter for free through most inter-library loans but the Nature website wants you to buy it if you want more than this synopsis) bq. Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy dataANDERS MOBERG, DMITRY M. SONECHKIN, KARIN HOLMGREN, NINA M. DATSENKO & WIBJÖRN KARLÉN bq. A number of reconstructions of millennial-scale climate variability have been carried out in order to understand patterns of natural climate variability, on decade to century timescales, and the role of anthropogenic forcing. These reconstructions have mainly used tree-ring data and other data sets of annual to decadal resolution. Lake and ocean sediments have a lower time resolution, but provide climate information at multicentennial timescales that may not be captured by tree-ring data. Here we reconstruct Northern Hemisphere temperatures for the past 2,000 years by combining low-resolution proxies with tree-ring data, using a wavelet transform technique to achieve timescale-dependent processing of the data. Our reconstruction shows larger multicentennial variability than most previous multi-proxy reconstructions, but agrees well with temperatures reconstructed from borehole measurements and with temperatures obtained with a general circulation model. According to our reconstruction, high temperatures—similar to those observed in the twentieth century before 1990—occurred around AD 1000 to 1100, and minimum temperatures that are about 0.7 K below the average of 1961–90 occurred around AD 1600. This large natural variability in the past suggests an important role of natural multicentennial variability that is likely to continue. To summarize: high temperatures... ...around AD 1000 to 1100, minimum temperatures... ...around AD 1600 Ties right in with the wine grapes growing in Greenland around 900 and people ice skating on the canals of Europe in the 1500's.
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