Climate Change 2001:
Working Group I: The Scientific Basis
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Figure 8.13: Annual mean precipitation changes (mm/yr) over Africa (20°W to 30°E) for the mid-Holocene climate: (upper panel) Biome distributions (desert, steppe, xerophytic and dry tropical forest/savannah (DTF/S)) as a function of latitude for present (red circles) and 6,000 yr BP (green triangles), showing that steppe vegetation replaces desert at 6,000 yr BP as far north as 23°N (vertical blue dashed line); (middle panel) 6000 yr BP minus present changes as simulated by the PMIP models. The black hatched lines are estimated upper and lower bounds for the excess precipitation required to support grassland, based on present climatic limits of desert and grassland taxa in palaeo-ecological records, the intersection with the blue vertical line indicates that an increase of 200 to 300 mm/yr is required to sustain steppe vegetation at 23°N at 6,000 yr BP (redrawn from Joussaume et al., 1999); (lower panel) same changes for the IPSL atmosphere-alone (A), i.e., PMIP simulation, the coupled atmosphere-ocean (OA), the atmosphere-alone with vegetation changes from OA (AV) and the coupled atmosphere-ocean-vegetation (OAV) simulations performed with the IPSL coupled climate model. The comparison between AV and OAV emphasises the synergism between ocean and land feedbacks (redrawn from Braconnot et al., 1999).

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