Worldwide Expansion of agriculture and global warming and regional precipitation anomalies in past half century

Land use and land cover (LULC) change affects regional and global climate through both biochemical and biophysical impacts. The IPCC report indicates the LULC change (albedo only) would cause global cooling. A recently compiled global land evolution data (LUHa.V1, Hurtt et al., 2006) provides the global gridded estimates of the underlying land use transitions, wood harvesting, and resulting secondary lands annually for 1700-2005.

To comprehensively investigate LULC change's biophysical impacts on global climate for last half century, we conducted two experiments using the NCEP-GCM/SSiB from 1948 to 2010. Control experiment is conducted using a potential vegetation map. The LULC change experiment uses a series of land cover change evolution maps from 1948-2005 which is based on historical LULC change LUHa.V1, and updates the vegetation conditions annually. The results indicate that the degradation in Mexico, West Africa, South and East Asia and South America produce negative precipitation anomalies, most of which are consistent with observed regional decadal precipitation anomalies. Meanwhile, it has also been found that the land degradation based on relative realistic LULC change information enhances the global warming in past century. There are two competing processes influence the surface temperature. Firstly, degradation increases albedo, reduces surface net short wave radiation, and causes a cooling effect, which is consistent with IPCC report; on the other hand, degradation decreases evapotranspiration into air, resulting in lower latent heat fluxes, and warmer surface temperature over global land, which is a dominate factor, that enhances the global warming.