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Southern Hemisphere Deglacial Warming and Atmospheric CO2 Increases
Reference
Stott, L., Timmermann, A. and Thunell, R. 2007. Southern Hemisphere and deep-sea warming led deglacial atmospheric CO2 rise and tropical warming. Science 318: 435-438.

Background
The authors write that establishing "the exact phasing of events during glacial terminations" is "a necessary step in understanding the physical relation between CO2 forcing and climate change."

What was done
Working with a marine sediment core from the western tropical Pacific Ocean, Stott et al. "determined the chronology of high- and low-latitude climate change at the last glacial termination by radiocarbon dating benthic and planktonic foraminiferal stable isotope and magnesium/calcium records," which provided a temporal resolution of 25 to 50 years for each sample over the period stretching from 10 to 22 thousand years before the present.

What was learned
The researchers report that "deep-sea temperatures warmed by ~2C between 19 and 17 thousand years before the present, leading the rise in atmospheric CO2 and tropical-surface-ocean warming by ~1000 years."

What it means
Stott et al. conclude that the cause of the deglacial deep-water warming "does not lie within the tropics, nor can its early onset between 19 and 17 thousand years before the present be attributed to CO2 forcing." And since the rate of deep-water warming after the start of the increase in the atmosphere's CO2 concentration did not increase (if anything, it declined), there is no compelling reason to believe that the deglacial increase in the air's CO2 content had anything at all to do with any of the warming that led to the ultimate development of the current interglacial.

Reviewed 13 August 2008