Simulation of the relative impact of land cover and carbon dioxide to climate change from 1700 to 2100

The contribution of land cover change (relative to increased CO₂) to climate change at the global scale is investigated using the Global Environmental and Ecological Simulations of Interactive Systems (GENESIS) climate model with an interactive BIOME vegetation model based on simulations at 1700 and 2100. Three 40-year model equilibrium simulations were performed. The first experiment specified carbon dioxide levels of 280 ppmv without human-induced land use (1700); the second experiment specified carbon dioxide levels of 690 ppmv without human-induced land use; the third experiment specified carbon dioxide levels of 690 ppmv and included patterns of extensive human land use (as projected for 2100). Data on the extent of human modification to the land at different times were obtained from the History Database of the Global Environment (HYDE) for 1700 and the Integrated Model to Assess the Global Environment (IMAGE2.2) for 2100. The IMAGE model projects land cover changes in response to demographic and economic activity. The projection based on the A1b scenario of the Intergovernmental Panel on Climate Change Special Report on Emission Scenarios was used for this work. As expected, statistically significant (95% level) climate changes in response to carbon dioxide levels were widespread. In contrast, the impact of the land cover change appears to reduce the spatial extent and sometimes magnitude of the changes in temperature due to increased carbon dioxide. Regions where land cover change explained more than 60% of the combined signal due to an increase in CO₂ and land cover change are confined to the Northern Hemisphere for near-surface temperature. Projected land cover changes produced warming (but smaller than that produced by CO₂) in some regions and cooling in other regions. The warming, which is about 4 K (seasonal) in some mid to high latitudes, is dominated by physiological factors altering the balance of latent to sensible heating rather than morphological mechanisms. The simulated changes in precipitation are more complex.