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Past decade is warmest in at least 1,300 years Rhett A. Butler, mongabay.com September 1, 2008
Analyzing proxy data including marine and lake sediment cores, ice cores, coral cores and tree rings, Michael Mann and colleagues show that the past 10 years have been unusually warm compared with the previous two millennia. "Our results extend previous conclusions that recent Northern Hemisphere surface temperature increases are likely anomalous in a long-term context," the authors write. "Recent warmth appears anomalous for at least the past 1,300 years whether or not tree-ring data are used. If tree-ring data are used, the conclusion can be extended to at least the past 1,700 years."
"Ten years ago, we could not simply eliminate all the tree-ring data from our network because we did not have enough other proxy climate records to piece together a reliable global record," said Michael Mann, associate professor of meteorology and geosciences and director of Penn State's Earth System Science Center. "With the considerably expanded networks of data now available, we can indeed obtain a reliable long-term record without using tree rings." The results confirm that temperatures today in the Northern Hemisphere are higher than those of the Medieval warm period, a time when the Vikings colonized Greenland are are believed to have become the first Europeans to visit North America. Mann et al. (2008). Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia. PNAS September 9, 2008 vol. 105 no. 36.
Related article War of words over new climate change report, 'hockey stick' model Leading scientist says House climate report is "politicized"July 16, 2006 Paleoclimatologist Michael Mann criticized a report challenging the familiar "hockey stick" temperature record of the past thousand years. The report, commissioned by Texas Representative Joe Barton, chairman of the House Energy Committee, and championed in an op-ed piece appearing in last Friday's issue of The Wall Street Journal said that there is no evidence that the 1990s were the warmest decade in a millennium or that 1998 was the warmest year in the last 1,000.
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