Combined effects of deforestation and doubled atmospheric CO2 concentrations on the climate of Amazonia

It is generally expected that the Amazon basin will experience at least two major environmental changes during the next few decades and centuries: 1) increasing areas of forest will be converted to pasture and cropland, and 2 ) concentrations of atmospheric CO2 will continue to rise. In this study, t he authors use the National Center for Atmospheric Research GENESIS atmosph eric general circulation model, coupled to the integrated Biosphere Simulat or, to determine the combined effects of large-scale deforestation and incr eased CO2 concentrations (including both physiological and radiative effect s) on Amazonian climate. In these simulations, deforestation decreases basin-average precipitation b y 0.73 mm day(-1) over the basin, as it consequence of the general reductio n in vertical motion above the deforested area (although there are some sma ll regions with increased vertical motion). The overall effect of doubled C O2 concentrations in Amazonia is an increase in basin-average precipitation of 0.28 mm day(-1). The combined effect of deforestation and doubled CO2, including the interactions among the processes, is a decrease in the basin- average precipitation of 0.42 mm day(-1). While the effects of deforestatio n and increasing CO2 concentrations on precipitation tend to counteract one another. both processes work to warm the Amazon basin. The effect of defor estation and increasing CO2 concentrations both tend to increase surface te mperature, mainly because of decreases in evapotranspiration and the radiat ive effect of CO2. The combined effect of deforestation and doubled CO2, in cluding the interactions among the processes, increases the basin-average t emperature by roughly 3.5 degrees C.