Global climate sensitivity to tropical deforestation

Abstract Regional to global-scale climate sensitivity to tropical deforestation is simulated using a modified version of the NCAR Community Climate Model (CCM1-Oz) which includes a mixed-layer ocean model, a 3-layer sea-ice model and BATS (the Biosphere-Atmosphere Transfer Scheme). A fourteen-year control integration is followed by a six year deforestation experiment in which the tropical moist forest throughout the Amazon Basin, S.E. Asia and tropical Africa is replaced by scrub grassland. The three deforested regions sustain different impacts on their regional climates. The largest disturbances occur in the Amazon Basin where total precipitation decreases by −437 mm yr −1 , evaporation decreases by −231 mm yr −1 and a marked decrease in moisture convergence is clear, although the surface temperature increases by 0.3 K. In S.E. Asia, surface temperature decreases in 11 months with an annual average cooling of −0.7 K; total evaporation decreases all the year by 130 mm yr −1 ; while the sign of the precipitation changes is strongly seasonal. The African region is least affected by deforestation, although surface net radiation decreases year-round and there is a detectable decrease in moisture convergence in the dry season. Regional responses to deforestation differ because regional circulation patterns are affected differently. For example, while ground surface temperatures increase in the Southern Amazon and over this basin as a whole, the northern Amazon, S.E. Asia and Africa all exhibit decreases in ground surface temperatures. The modification of atmospheric circulation patterns over deforested tropical regions prompts climate responses distant from the disturbance. Impacts of tropical deforestation include a disturbance of the Asian monsoon and small but statistically significant changes in climate in the middle and high latitudes.