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Warmer Temperatures at Lower CO2 Concentrations
Reference
Cheddadi, R., Lamb, H.F., Guiot, J. and van der Kaars, S. 1998. Holocene climatic change in Morocco: a quantitative reconstruction from pollen data. Climate Dynamics 14: 883-890.

What was done
The authors of this paper provide quantitative estimates of Holocene climate change using proxy data from a lake-sediment core in the Middle Atlas of Morocco. Specifically, they reconstructed January and July temperature and annual precipitation values over the past 10,000 years.

What was learned
Three main climate intervals were apparent in the data: (1) a warm and dry phase from 6.5 to 10 thousand years ago, where January and July temperatures were found to be about 4C higher than present, (2) an intermediate phase characterized by relatively high mean January temperatures, and (3) a cooler and moist most recent phase. In addition, the authors note that "superimposed on the longer-term trends are short-term variations in all three climatic parameters," lasting in some cases a century or more.

What it means
This paper adds to a growing body of research that clearly shows that over a period in earth's climatic history when atmospheric carbon dioxide concentration varied but little and was approximately 100 ppm less than today's value, mean annual temperatures in some locations were as much as "4C warmer than the present." Therefore, even major future warming would not be proof of the claim that it is CO2-induced. History often repeats itself; and climatic history is no exception.


Reviewed 15 January 1999