Unusual Heat

Unusual Heat

. The temperature in the Northern Hemisphere (top curve, scale at left) has been warmer in the 20th century than in any other century of the last one thousand years, and the 1990s were the hottest decade during all that time. The sharp upward jump in temperature during the past 100 years was recorded by thermometers near the Earth's surface; earlier temperature fluctuations were inferred from tree rings, lake and ocean sediments, coral reefs, and ice cores. There has been an exponential rise in the amount of atmospheric carbon dioxide over the past two and a half centuries (bottom curve, scale at right). (Courtesy of Michael E. Mann, top curve, and Charles D. Keeling, bottom curve.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University