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Drought in African Sahel Not of Anthropogenic Origin
Holmes, J.A., Street-Perrott, F.A., Allen, M.J., Fothergill, P.A., Harkness, D.D., Kroon, D. and Perrott, R.A.  1997.  Holocene palaeolimnology of Kajemarum Oasis, Northern Nigeria: An isotopic study of ostracodes, bulk carbonate and organic carbon.  Journal of the Geological Society, London 154: 311-319.

Since the late 1960s, the African Sahel has experienced, in the words of the authors, "one of the most persistent droughts recorded by the entire global meteorological record."  Consequently, it is not surprising that several different mechanisms have been proposed to explain this situation, and it is little wonder that the recent historical increase in greenhouse gas concentrations is one of the leading contenders.

What was done
The authors conducted a high-resolution palaeolimnological study of a 5500-year lake sediment sequence extracted from Kajemarum Oasis in the Manga Grasslands of northeast Nigeria, focusing on stable oxygen and carbon isotope ratios in the carbonate-carbon and the organic-carbon fractions of the lake sediments.

What was learned
Quoting the authors, their results "show convincingly that the present drought is not unique and that drought has recurred on a centennial to interdecadal timescale during the last 1500 years."

What it means
On the basis of these findings, the authors conclude that this worst drought of the modern meteorological record "is not likely to be purely anthropogenic in origin."  And if it is no different from what has been occurring over and over again for the past 1500 years, it is surely not the result of anthropogenic greenhouse gas emissions.

Reviewed 13 September 2000