Forests affect climate in two ways: by absorbing carbon dioxide and storing large carbon pools in tree biomass and forest soils, and by modulating the biophysical surface properties and affecting the land-atmosphere fluxes of energy. This research focuses on the biophysical effects and is based on joint Earth observations of global changes in forest cover and of surface temperature performed during the decade 2003-2012.
Results show the key role of evapotranspiration (the sum of evaporation and plant transpiration from the Earth‘s land surface to the atmosphere) on the biophysical impacts of forest on local climate. Forest clearing produces a marked increase of mean annual maximum air surface temperatures, slight changes in minimum temperatures and an overall increase of mean temperatures. But these effects vary according to the climate zone, with the arid areas showing the strongest effects, followed by the temperate, the tropical and the boreal zones.
So far, climate policies and treaties have only taken into account land-based mitigation options like afforestation, reforestation and avoided deforestation or forest degradation, because of the key role played by forests in the global carbon cycle. On the contrary the climate impacts of biophysical processes, such as the surface exchange of energy and water vapour, have so far been neglected.
This study aims to fill this knowledge gap by providing a robust assessment of the biophysical climate impacts of observed forest gains and losses. It may support the idea that, in the future, the effects of land biophysics should be taken into consideration in climate negotiations. Ultimately, it also helps the definition of new protocols for the measurement, reporting, and verification of these relevant effects at global scale.