Forcings and feedbacks by land ecosystem changes on climate change

Abstract
Vegetation change is involved in climate change through both forcing and feedback processes. Emissions of CO₂ from past net deforestation are estimated to have contributed approximately 0.22 - 0.51 Wm ^{- 2} to the overall 1.46 Wm ^{- 2} radiative forcing by anthropogenic increases in CO₂ up to the year 2000. Deforestation-induced increases in global mean surface albedo are estimated to exert a radiative forcing of 0 to -0.2 Wm ^{- 2}, and dust emissions from land use may exert a radiative forcing of between approximately +0.1 and -0.2 Wm ^{- 2}. Changes in the fluxes of latent and sensible heat due to tropical deforestation are simulated to have exerted other local warming effects which cannot be quantified in terms of a Wm ^{- 2} radiative forcing, with the potential for remote effects through changes in atmospheric circulation. With tropical deforestation continuing rapidly, radiative forcing by surface albedo change may become less useful as a measure of the forcing of climate change by changes in the physical properties of the land surface. Although net global deforestation is continuing, future scenarios used for climate change prediction suggest that fossil fuel emissions of CO₂ may continue to increase at a greater rate than land use emissions and therefore continue to increase in dominance as the main radiative forcing. The CO₂ rise may be accelerated by up to 66% by feedbacks arising from global soil carbon loss and forest dieback in Amazonia as a consequence of climate change, and Amazon forest dieback may also exert feedbacks through changes in the local water cycle and increases in dust emissions.