The Role of Land Cover Change in Long-Term Climate Change

Open Access
Author:
Lamptey, Benjamin Lantei
Graduate Program:
Geosciences
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 28, 2005
Committee Members:
  • Eric James Barron, Committee Chair
  • Richard B Alley, Committee Member
  • David Pollard, Committee Member
  • Toby Nahum Carlson, Committee Member
  • Paul Plassmann, Committee Member
Keywords:
  • urbanization
  • global and regional climate modeling
  • climate change
  • vegetation
  • land-use/land-cover change
Abstract:
Three studies involving global and regional climate models were conducted to investigate the relative effects of increased CO${}_2$, 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 CO${}_2$) 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 CO${}_{2}$ levels were widespread. In contrast, the impact of the land cover changes appears to reduce the spatial extent and sometimes t he magnitude of the changes in temperature due to increased CO${}_2$. Regions where land cover change explained more than 60\% of the combined signal due to an increase in CO${}_2$ 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 northeastern 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. The increase in summer temperature due to urbanization was more widespread than that due to the effect of agricultural land use. The conversion of forest to agricultural land resulted in a decre ase in temperature of more than 0.5 K during winter and an increase of more than 1 K during summer over th e sites of perturbation. The reduced temperature during winter is related to snow cover; agricultural lands are covered by snow while the trees in non-agricultural areas protrude through the snow, reducing the albedo of the surface. The warming due to agriculture during summer reflects reduced evaporation.