A green planet versus a desert world: Estimating the maximum effect of vegetation on the land surface climate

We quantify the maximum possible influence of vegetation on the global climate by conducting two extreme climate model simulations: in a first simulation ('desert world'), values representative of a desert are used for the land surface parameters for all non glaciated land regions. At the other extreme, a second simulation is performed ('green planet') in which values are used which are most beneficial for the biosphere's productivity. Land surface evapotranspiration more than triples in the presence of the 'green planet', land precipitation doubles (as a second order effect) and near surface temperatures are lower by as much as 8 K in the seasonal mean resulting from the increase in latent heat flux. The differences can be understood in terms of more absorbed radiation at the surface and increased recycling of water. Most of the increase in net surface radiation originates from less thermal radiative loss and not from increases in solar radiation which would be expected from the albedo change. To illustrate the differences in climatic character and what it would imply for the vegetation type, we use the Koppen climate classification. Both cases lead to similar classifications in the extra tropics and South America indicating that the character of the climate is not substantially altered in these regions. Fundamental changes occur over Africa, South Asia and Australia, where large regions are classified as arid (grassland/desert) climate in the 'desert world' simulation while classified as a forest climate in the 'green planet' simulation as a result of the strong influence of maximum vegetation on the climate. This implies that these regions are especially sensitive to biosphere-atmosphere interaction.