labs_title

Caldeira Lab Research:Land Plants, Carbon, and Climate

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

G. Bala, K. Caldeira, M. Wickett, T.J. Phillips, D.B. Lobell, C. Delire, & A. Marin

Generally, the reduction of deforestation has been championed as a way to combat the effects of global warming, due to its role in releasing CO2 into the atmosphere. However, the effects of deforestation other than CO2 release such as changing rates of evapotranspiration, changing amounts of cloud cover, and changes in land surface albedo have not been widely studied. Here, the effects of these changes are observed, revealing the interesting result of a net cooling effect of deforestation.


Bala G, Caldeira, K., Wickett M, et al. Combined climate and carbon-cycle effects of large-scale deforestation, Proceedings of the National Academy of Sciences of the United States of America 104 (16): 6550-6555, 2007.

The effect of deforestation on climate: When global deforestation is implemented in the model, temperatures are raised only in the Tropical regions of the world, are changed by a negligibly small amount in Temperate regions, and are decreased in Boreal regions. This leads to an overall decrease in temperature due to global deforestation, implying that afforestation projects would only be useful to combat global warming if implemented in the Tropics.

Location specific effects of deforestation: The global temperature effects of deforestation when implemented in Boreal (C), Temperate (D) and Tropical (E) regions. Again, deforestation creates an overall warming effect when implemented in the tropics only.

Abstract

The prevention of deforestation and promotion of afforestation have often been cited as strategies to slow global warming. Deforestation releases CO2 to the atmosphere, which exerts a warming influence on Earth’s climate. However, biophysical effects of deforestation, which include changes in land surface albedo, evapotranspiration, and cloud cover also affect climate. Here we present results from several large-scale deforestation experiments performed with a three-dimensional coupled global carbon cycle and climate model. These simulations were performed by using a fully three dimensional model representing physical and biogeochemical interactions among land, atmosphere, and ocean. We find that global-scale deforestation has a net cooling influence on Earth’s climate, because the warming carbon-cycle effects of deforestation are overwhelmed by the net cooling associated with changes in albedo and evapotranspiration. Latitude-specific deforestation experiments indicate that afforestation projects in the tropics would be clearly beneficial in mitigating global-scale warming, but would be counterproductive if implemented at high latitudes and would offer only marginal benefits in temperate regions. Although these results question the efficacy of mid- and high-latitude afforestation projects for climate mitigation, forests remain environmentally valuable resources for many reasons unrelated to climate.