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The Relationship between CO2 and Temperature in Glacial-Interglacial Transitions of the past 800,000 Years

Flower, Benjamin P.1
1 College of Marine Science, University of South Florida, St. Petersburg, FL.

Past changes in CO2 and temperature can illuminate the potential future effect of continuing CO2 rise on global mean temperatures. Data from Antarctic ice cores have provided records of surface air temperature and inferred global CO2 concentrations back to about 740,000 years ago. Surface air temperatures based on the H and O isotopic composition of ice have varied by about 8-12°C on orbital timescales (10,0000 to 100,000 years); the longest current records indicate eight glacial-interglacial cycles back to about 740 ka (kiloyears B.P.). Associated with these cycles are ~80-120 ppmv changes in CO2 concentrations based on measurements of trapped air bubbles. The most rapid changes occurred in less than 10,000 years at glacial terminations, termed Terminations 1-8 at ca. 15, 130, 240, 325, 420, 515, 625, and 730 ka, respectively. These sharp Terminations provide an important test of potential relationships between Antarctic air temperature and global CO2 concentrations. However, determination of lead-lag relationships is complicated by the fact that air diffuses in compacting snow long after the snow is deposited, leading to significant age differences between air and ice at a given level in an ice core. The so-called “gas age - ice age difference” ranges from about 500 to 6000 years, depending on snow accumulation and compaction rates, with uncertainty on the order of 1000 years. Specifically, this complicates determining the timing of air temperature increase and CO2 rise because the former is derived from measurements on ice and the latter from trapped air. After constraining the “gas age - ice age difference” several studies have determined that initial Antarctic air temperature increase preceded CO2 rise on glacial terminations, typically by about 600 to 3000 years. One study used the ∂40Ar isotopic temperature proxy, measured on the same air samples as CO2, and found a lead of 800+200 years at Termination 3. These observations suggest that CO2 rise did not trigger temperature increase. However, these same studies show that approximately 80% of deglacial warming was synchronous with CO2 rise. Furthermore, sensitivity studies indicate that the magnitude of deglacial warming in response to orbital insolation changes requires substantial feedback from greenhouse gases. Scaling these results to make predictions about the next century is difficult, but past climate change is consistent with CO2 exerting a strong positive feedback on surface temperature.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009