Climatic effects of land cover change at different carbon dioxide levels

Land cover change (LCC) simulations were performed at 3 different carbon dioxide levels (280, 355 and 430 ppmv) using the standard version of the NCAR CCM3 at T42 resolution coupled with the Biosphere-Atmosphere Transfer Scheme (BATS) and a mixed-layer ocean model. We follow the evolution of the initial temperature perturbation within the horizontal and vertical structure of the atmosphere and then examine the 15 yr average of near-surface air temperature and meridional stream function differences between current and natural land cover at the 3 different CO2 levels. Results show that LCC caused temperature perturbations which initially affected only those regions where the land cover was modified. After a short period, however, the effects of LCC propagated to remote regions. While the remote effects of LCC were generally different at each CO2 level, 4 common remote regions of sensitivity were identified in these simulations (North Pacific, North America, northeast Asia and the Indian Ocean). The main factor in explaining the differing remote responses was the change in the zonally averaged background circulation resulting from circulation changes caused by LCC, CO2 level, and the interaction between these 2 forcings. The 15 yr average seasonal results indicate that LCC may have impacts on surface air temperature which vary in sign between seasons, depending on the character of the initial land cover perturbation as well as local meteorological conditions. We find no evidence that the impacts of LCC decrease with increasing CO2, rather we show that LCC does appear to affect regional climate at a statistically significant level.