Progressive Mid-latitude Afforestation: Impacts on Clouds, Circulation, and the Global Energy Budget

Abstract:

Vegetation influences the atmosphere in complex and non-linear ways. Large-scale changes in vegetation can drive changes in climate on both local and global scales. Interactions between the land and atmosphere are controlled by shifts between terms controlling the surface energy budget. Depending on the magnitude and location of land surface changes, imbalances in energy at large spatial scales can be introduced which shift atmospheric circulation on a global scale. Various studies have explored the impacts of large area changes in vegetation, but how the climate response scales with the area of vegetation change has not been demonstrated. Here, we systematically evaluate the response of climate to linearly increasing the area of forest cover over the northern mid-latitudes. We show that global circulation changes the atmospheric cross-equatorial energy transport in a linear fashion with respect to the area of afforestation (a relationship which has not previously been demonstrated). We also identify how vegetation-induced changes in cloud cover further feedback on changes in the global energy balance - a concept that has been largely ignored in most large-scale vegetation manipulation experiments. The changes in atmospheric energy transport induced by vegetation changes result in remote shifts in precipitation; the relationship between the change in energy transport and the shift in tropical precipitation is shown to be model dependent. Our results highlight the importance of considering both local and remote effects of large-scale vegetation change, and explore how the effects of vegetation change on climate scale with the area of land surface changed. We demonstrate how vegetation changes can modify the surface energy budget both directly and through impacts on cloud cover through land-atmosphere interactions.