2. Global Warming


Rise in Atmospheric Carbon Dioxide

Rise in Atmospheric Carbon Dioxide

. The average monthly concentration of atmospheric carbon dioxide, or CO2 for short in parts per million (106), abbreviated ppm, of dry air plotted against time in years observed continuously since 1958 at the Mauna Loa Observatory, Hawaii. It shows that atmospheric amounts of the principal waste gas of industrial societies, carbon dioxide, have risen steadily for more than forty years. The up and down fluctuations, that are superimposed on the systematic increase, reflect a seasonal rise and fall in the absorption of carbon dioxide by trees and other vegetation. Summertime lows are caused by the uptake of carbon dioxide by plants, and the winter highs occur when the plants’ leaves fall and some of the gas is returned to the air. (Courtesy of Dave Keeling and Tim Whorf, Scripps Institution of Oceanography.)


Unusual Heat

Unusual Heat

. The temperature in the Northern Hemisphere (top curve, scale at left) has been warmer in the 20th centruy 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.)