The response of the regional longwave radiation balance and climate system in Europe to an idealized afforestation experiment

Afforestation is an important mitigation strategy for climate change due to its carbon sequestration potential. Besides this favorable biogeochemical effect on global COinline-formula₂ concentrations, afforestation also affects the regional climate by changing the biogeophysical land surface characteristics. In this study, we investigate the effects of an idealized global COinline-formula₂ reduction to pre-industrial conditions by a Europe-wide afforestation experiment on the regional longwave radiation balance, starting in the year 1986 on a continent entirely covered with grassland. Results show that the impact of biogeophysical processes on the surface temperatures is much stronger than that of biogeochemical processes. Furthermore, biogeophysically induced changes of the surface temperatures, atmospheric temperatures, and moisture concentrations are as important for the regional longwave radiation balance as the global COinline-formula₂ reduction. While the outgoing longwave radiation is increased in winter, it is reduced in summer. In terms of annual total, a Europe-wide afforestation has a regional warming effect despite reduced COinline-formula₂ concentrations. Thus, even for an idealized reduction of the global COinline-formula₂ concentrations to pre-industrial levels, the European climate response to afforestation would still be dominated by its biogeophysical effects.