CLIMATOLOGY: Putting a Lid on CO2?

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Science  01 Feb 2002:
Vol. 295, Issue 5556, pp. 767d-769d
DOI: 10.1126/science.295.5556.767d

The concentration of atmospheric CO2 increased during the last deglaciation from about 190 parts per million (ppm) 17,000 years ago to about 265 ppm 11,000 years ago. A variety of hypotheses have tried to explain this observation, but none can account for the entire observed difference. One recent proposal [B. B. Stephens, R. F. Keeling, Nature 404, 171 (2000)] suggested that wintertime expansion and compaction of sea ice around Antarctica during the last glacial period may have inhibited the outgassing of CO2 from the ocean around the time of the Last Glacial Maximum.

Morales and Rahmsdorf present results from a coupled sea ice-upper ocean model, which show that ice-area fractions large enough to cause the observed difference might not have prevailed even under extreme glacial conditions. This mechanism could only account for 15 to 50% of the total glacial CO2 depression. Thus, Antarctic sea ice expansion needs to be considered in conjunction with other mechanisms to solve the persistent puzzle of why atmospheric CO2 levels were so low during glacial episodes. — HJS

Geophys. Res. Lett. 10.1029/2001GL013240.

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