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Comparisons of Climate and Atmospheric CO2 Changes During the Last Glacial Period
Reference
Staufer, B., Blunier, T., Dallenbach, A., Indermuhle, A., Schwander, J., Stocker, T.F., Tschumi, J., Chappellaz, J., Raynaud, D., Hammer, C.U. and Clausen, H.B.  1998.  Atmospheric CO2 concentration and millennial-scale climate change during the last glacial period.  Nature 392: 59-62.

Background
Because of various impurities it contains, Greenland ice is now believed to have produced air-bubble CO2 concentrations that, in the words of the authors of this paper, "do not represent the atmospheric concentration but are caused by an acid-carbonate reaction or by oxidation of organic material in the ice."  Consequently, to compare climate oscillations inferred from studies of Greenland ice cores with concurrent atmospheric CO2 concentrations, it is necessary to use air-bubble CO2 concentrations inferred from Antarctic ice cores.  Hence, it is necessary to have an accurate common timescale for ice-core-derived data from both polar regions; and this paper broaches that subject.

What was done
The authors derived a common timescale for earth's last glacial period based on records of atmospheric methane concentrations from Greenland and Antarctica.  They then used their findings to compare millennial-scale climate oscillations inferred from Greenland ice cores with concurrent variations in atmospheric CO2 concentration inferred from Antarctic ice cores.

What was learned
During large rapid warmings over Greenland of several degrees Centigrade, which were followed by slower cooling regimes that returned the climate to full glacial conditions, atmospheric CO2 concentrations typically varied by less than 10 ppm.  Furthermore, the weak correspondence between the two parameters was considered to have been caused by the change in climate, rather than by the change in CO2.

What it means
Climate can, and does, change significantly without any help from atmospheric CO2.  Hence, there is no compelling reason to believe that the modest warming of the last century has necessarily been influenced by the concommitant rise in the air's CO2 content.  Even when correlations between these two parameters have been observed in the past, as in some of the longer-term variations in this study, the climate change is believed to have been the independent variable, with atmospheric CO2 concentation following its lead.

Reviewed 1 December 1998