The role of land cover change in long-term climate change

Three studies involving global and regional climate models were conducted to investigate the relative effects of increased CO2, agricultural land cover change, and urbanization at the global to regional scales.; 1. The GENESIS 2.2 global climate model was used to assess the contribution of land cover change (relative to CO2) to climate change from 1700 to 2100. The 1700 simulation used a distribution of natural land cover. One of the 2100 simulations used a distribution of natural land cover and the second incorporated changes due to agricultural land use. As expected, statistically significant (95% level) climate changes in response to increased CO2 levels were widespread. In contrast; the impact of the land cover changes appears to reduce the spatial extent and sometimes the magnitude of the changes in temperature due to increased CO2. 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 temperature. For rainfall, the effect was scattered over both Northern and Southern Hemispheres and mostly not statistically significant. Projected land cover changes produced warming in some regions and cooling in other regions. The seasonal warming in many mid to high latitude areas was governed by physiological rather than morphological mechanisms.; 2. The effects of present-day (1990) global land use change (i.e. agriculture) on the regional climates of northeastern United States and West Africa were investigated. The GENESIS 2.2 global model and a climate version of the MM5 Mesoscale model were used for this study. The forcing due to global agriculture has a small but appreciable impact on the winter climate over the northeastern United States. The summer climate was dominated by regional scale processes. The global forcing of agriculture does not have an appreciable impact in either winter or summer over West Africa.; 3. The climate sensitivity to the specification of 1990 agricultural and urban land cover was investigated using a climate version of MM5 over the north-eastern United States. Urbanization resulted in near-surface temperature increases of more than 1 K over the urban sites during both winter and summer. Urbanization also reduced the diurnal temperature range by about 0.4 K. (Abstract shortened by UMI.)...