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20th-Century Global Warming and Central African Climate
Reference
Russell, J.M. and Johnson, T.C. 2007. Little Ice Age drought in equatorial Africa: Intertropical Convergence Zone migrations and El Niņo-Southern Oscillation variability. Geology 35: 21-24.

What was done
The authors conducted high-resolution analyses of Mg concentrations in authigenic calcite found in five sediment cores retrieved from Lake Edward in central equatorial Africa to develop a water balance history of the region that spans the past 1400 years.

What was learned
Russell and Johnson report that their work reveals the occurrence of "strong droughts in central Africa during the Little Ice Age (AD 1400-1750), in contrast to records from Lake Naivasha, Kenya, which suggest a wet Little Ice Age." In analyzing this differential behavior between the eastern and western parts of the continent, they argue that "the key factor linking high-latitude cooling, the Intertropical Convergence Zone (ITCZ), and moisture gradients within Africa is the El Niņo-Southern Oscillation (ENSO)." Citing numerous studies that indicate "a shift toward El Niņo-like conditions during the Little Ice Age," they thus conclude that "interactions between the ITCZ and the ENSO system during the Little Ice Age could have triggered a shift toward El Niņo-like conditions and increased rainfall in easternmost Africa, while southward ITCZ migration triggered drought in the west."

What it means
Noting that the region around Lake Edward is currently "experiencing an unusually prolonged period of stable, wet conditions in comparison to previous centuries of the past millennium," the two researchers say that "unless global warming is a mitigating factor," which they in fact imply it is, "central Africa is overdue for a return to decades-long drought that exceeds anything observed in the past century." Hence, they conclude that "the patterns and variability of twentieth-century rainfall in central Africa have been unusually conducive to human welfare in the context of the past 1400 years," which is but one more example of the important fact that for most people in most places, the global warming of the past century has been a significant positive development.

Reviewed 28 March 2007