... for some, and earlier arrival of migratory birds. In addition, several other data support that conclusion, the report says. Part of the debate over global warming centers on disparities between the surface temperature and upper-air temperature. While the Earth's surface temperature has risen, data collected by satellites and balloon-borne instruments since 1979 indicate little if any warming of the low-to mid- troposphere. The report concurs with a previous Research Council report that said despite these differences, "The warming trend in the global mean surface temperature observations during the past 20 years is undoubtedly real and is substantially greater than the average rate of warming in the 20th century." Read about a scientist's efforts to study disappearing glaciers in Alaska. Learn how scientists use data from tree rings, ice cores, and other sources to reconstruct climate and temperature before the advent of climate-observing networks from the National Oceanic and Atmospheric Administration's ...

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