Changes in the concentration of atmospheric CO_2 and surface air temperature are closely related. However, temperature can influence atmospheric CO_2 as well as be influenced by it. Studies of polar ice cores have concluded that temperature increases during periods of rapid warming have preceded increases in CO_2 by hundreds of years. Parrenin et al. (p. 1060; see the Perspective by Brook) present a revised age scale for the atmospheric component of Antarctic ice cores, based on the isotopic composition of the N_2 that they contain, and suggest that temperature and CO_2 changed synchronously over four intervals of rapid warming during the last deglaciation.
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