Jul 12 2007
Impact of Land Cover Change on Surface Climate
Davin, E. L., N. de Noblet-Ducoudre, and P. Friedlingstein (2007), Impact of land cover change on surface climate: Relevance of the radiative forcing concept, Geophys. Res. Lett., 34, L13702, doi:10.1029/2007GL029678.
Abstract: We use the IPSL climate model to investigate biophysical impacts of Anthropogenic Land Cover Change (ALCC) on surface climate. Including both the changes in surface albedo and evapotranspiration, we find that ALCC represents a radiative forcing of -0.29 W/m2 from 1860 to 1992 and of -0.7 W/m2 from 1992 to 2100. The simulated surface temperature response to ALCC indicates a historical cooling of 0.05 K and an additional cooling due to future changes of 0.14 K, which is consistent with the sign of the radiative forcing. However, this cooling is substantially lower than the one we would have obtained if it was caused by a radiatively equivalent change in CO2 concentration. These results thus question the relevance of the radiative forcing framework in the context of land use change, since the radiative forcing due to ALCC may not be comparable to the one exerted by other anthropogenic perturbations.
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I’ll draw your attention to the figure above. On the left is the radiative forcing due to anthropogenic land cover change (ALCC) from 1860 to 1992, and on the right is the modelled forcing from 1992 to 2100. As can be seen, the effects of land cover change are extremely heterogeneous. Over much of North and South America, there is expected to be a large cooling due to ALCC. However, some parts of Europe and Asia - in particular, the Iraq, Iran, Pakistan area - are going to see increases in temperature. This rise in temperature is in addition to the warming caused by anthropogenic CO2.
The extreme negative radiative forcing in northern South America is due to the expected continuation of deforestation of the Amazon rainforest in Brazil - I think. The paper doesn’t explicitly comment on that, but it’s the only plausible reason I could think of. I guess this is because of the change in albedo from a dark forest to a lighter soil underneath. Of coarse, even if deforestation of the Amazon will lead to a regional cooling, it’s still a environmental catastrophe.
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