Sensitivity of Mid Holocene Global Climate to Changes in Vegetation Reconstructed From the Geologic Record (original) (raw)

2001

Abstract

The influence of land surface changes upon global and regional climate has been shown both for anthropogenic and non-anthropogenic changes in land surface distribution. Because validation of global climate models (GCMs) is dependent upon the use of accurate boundary conditions, and because changes in land surface distribution have been shown to have effects on climate in areas remote from those changes, we have tested the sensitivity of a GCM to a global Mid Holocene vegetation distribution reconstructed from the fossil record, a first for a 6 ka GCM run. Large areas of the globe exhibit statistically significant seasonal warming of 2 to 4 ° C, with peak warming of 10 ° C over the Middle East in June-July-August (JJA). The patterns of maximum warming over both Northern Asia and the Middle East strongly coincide with the patterns of maximum decrease in albedo in all seasons. Likewise, cooling of up to 4 ° C over Northern Africa associated with the expansion of savanna and broadleaf evergreen forest also coincides with increases in surface heat flux of up to 35 W/m2 in March-April-May (MAM) and 60 W/m2 in JJA. At both the regional and global scale, the magnitude of vegetation forcing is equal to that of 6 ka orbital forcing, emphasizing the importance of accurate land surface distribution for both model validation and future climate prediction.

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