The local and global effects of Amazon deforestation

Abstract

[1] To quantify the effects of land cover changes in the Amazon on local and global climate, numerical simulation experiments using the Goddard Institute for Space Studies Model II global climate model are conducted. An ensemble approach is adopted, in which a group of six control simulations is compared with a group of six deforested simulations. The deforestation effect in the Amazon is strong, with reductions in precipitation, evapotranspiration, and cloudiness. We also detect a noticeable impact in several other regions of the world, several of which show a reduction in rainy season precipitation that exhibits a high signal-to-noise ratio (determined by the t statistic). To determine the significance of the deforestation signal, we create several ''false'' ensembles, combining control and deforested members randomly, for comparison with the actual ''true'' ensemble. Such an analysis has not been used previously in deforestation studies and is useful for verifying the significance of a purported effect. The globally averaged precipitation deficits for the true ensemble are generally high in comparison with the false ensembles. Furthermore, changes in the Amazon due to the deforestation correlate significantly with remote changes in several areas. This suggests that the Amazon deforestation is producing a detectable signal throughout the Earth, and this finding underscores the importance of human activity in that region.

Combined climate and carbon-cycle effects of large-scale deforestation

“…Temperate deforestation produces local cooling due to dominant albedo change and remote warming due to carbon-cycle effect; these effects cancel each other on a global-mean basis. Boreal deforestation, in addition to causing strong local cooling, produces cooling everywhere, suggesting remote cooling effects through circulation (28)(29)(30)(31).…”

Mechanisms of water supply and vegetation demand govern the seasonality and magnitude of evapotranspiration in Amazonia and Cerrado

“…Such a coupling presents an opportunity for a positive feedback under climate change: should future rainfall in the Amazon decrease and forests downregulate metabolism via stomatal closure, rainfall reductions basin-wide could be exacerbated and further threaten forest integrity (Betts et al, 2004). Loss of a significant area of Amazon forest due to climate change, deforestation, or a combination of both can have further impacts globally due to hydrometerological teleconnections (Werth and Avissar, 2002) or carbon cycle feedbacks (Cox et al, 2000). However, much uncertainty remains surrounding modeling forest response to climate anomalies, due to both to model process differences/parameters or due to uncertainty in climate projections (Huntingford et al, 2008;Sitch et al, 2008;Galbraith et al, 2010;Poulter et al, 2012).…”

Impact of Congo Basin deforestation on the African monsoon

“…The increase in albedo leads to a reduction of radiation absorbed by surface and thus to a reduction of energy available for sensible and latent heat fluxes, while the decrease in leaf area index leads to a decrease of surface evapotranspiration. These changes in surface fluxes may exert a forcing on climate not only locally but also remotely through teleconnection patterns (Werth and Avissar, 2002;Avissar and Werth, 2005;Hasler et al ., 2009) and, for example, the equatorial and sub-equatorial Africa regions have been identified as being among the regions of the globe where the effects of land surface conditions on regional climate and dynamics are most pronounced (Koster et al ., 2004).…”