Nonlocal Effects Dominate the Global Mean Surface Temperature Response to the Biogeophysical Effects of Deforestation

Deforestation influences surface temperature locally ("local effects"), but also at neighboring or remote regions ("nonlocal effects"). Observations indicate that local effects induce a warming in most locations, while many climate models show a global mean cooling when simulating global deforestation. We show that a nonlocal cooling in models, which is excluded from observations, may strongly contribute to these conflicting results. For the MPI-ESM, the globally averaged nonlocal cooling exceeds the globally averaged local warming by a factor of three, for global deforestation but also for realistic areal extents and spatial distributions of deforestation. Furthermore, the globally averaged nonlocal effects dominate the local effects in realistic scenarios across a range of climate models. We conclude that observations alone are not sufficient to capture the full biogeophysical effects, and climate models are needed to better understand and quantify the full effects of deforestation before they are considered in strategies for climate mitigation. Plain Language Summary Deforestation influences surface temperature at the location of deforestation (local effects) and elsewhere (nonlocal effects). Only the local effects are included in observation-based data sets, but in reality surface temperature may in addition be substantially influenced by the nonlocal effects. Using simulations in a climate model, we show that deforestation-induced changes in the brightness of the surface influence surface temperature mainly nonlocally and thus may be largely overlooked in observation-based data sets. The simulations show that the nonlocal effects have a larger impact on global average surface temperature than the local effects, independent of how much area is deforested and at which latitude the deforestation takes place. A better understanding of the nonlocal effects is essential before the full climate effects of deforestation can be included into international climate policies that aim at mitigating global climate warming.