Enhanced albedo feedback in North Africa from possible combined vegetation and soil-formation processes |
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Authors: | Wolfgang Knorr Karl-Georg Schnitzler |
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Institution: | (1) Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, BS8 1RJ Bristol, UK;(2) Max-Planck-Institut für Meteorologie, Bundesstr. 53, 20146 Hamburg, Germany |
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Abstract: | It has long been recognized that albedo related vegetation feedbacks amplify climate variability in North Africa. Recent studies
have revealed that areas of very high albedo associated with certain desert soil types contribute to the current dry climate
of the region. We construct three scenarios of North African albedo, one based on satellite measurements, one where the highest
albedo resembles that of soils in the desert transition zones, and one based on a vegetation map for the “green Sahara” state
of the middle Holocene, ca. 6,000 years ago. Using a series of climate model simulations, we find that the additional amplitude
of albedo change from the middle Holocene to the present caused by the very bright desert soils enhances the magnitude of
the June-to-August precipitation change in the region of the present Sahara from 0.6 to 1.0 mm/day on average. We also find
that albedo change has a larger effect on regional precipitation than changes in either the Earth’s orbit or sea surface temperatures
between 6,000 years ago and today. Simulated precipitation agrees rather well with present observations and mid Holocene reconstructions.
Our results suggest that there may exist an important climate feedback from soil formation processes that has so far not been
recognized. |
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