The role of historical land-cover changes as a mechanism for global and regional climate change

Chase, Thomas N. (Thomas Newell), 1962-, author
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This paper describes the results from several modeling studies and an observational analysis as to the effect of historical land-cover change on regional and global climates. We discuss methods for determining historical vegetation change and present results from model simulations at the global and regional scale which compare climates generated using currently observed vegetation versus natural vegetation as a boundary condition. We also compare these modeling studies with recent observational data and with simulations of climate change resulting from increased greenhouse gases. We conclude from this research that vegetation change, as it has already occurred, globally and regionally, can have significant effects on both global and regional climates. These effects are not limited to the regions of direct land-cover change forcing. For example, as a result of tropical deforestation, the position and intensity of the ITCZ is affected by the change in land surface characteristics resulting in global-scale effects which are similar in nature to the climatic effects associated with El Niño Southern Oscillation (ENSO). These include changes in high-latitude circulations, the generation of low frequency waves which appear to propagate to the extratropics in well-defined teleconnection patterns, and reduced low-level easterlies over most of the topical Pacific basin under current vegetation. This implies an interaction mechanism between tropical deforestation and ENSO. The model simulations of climate change due to land-cover change compare favorably in spatial patterns and amplitude with recently observed temperature trends. Additionally, a comparison between simulations of climate changes due to land-cover disturbance and changes due to rising atmospheric CO2 concentration show that global land-cover changes as they have already occurred, are responsible for shifts in climate which are of similar amplitude and occur in the same regions as simulated climate changes resulting from increased CO2. A comparison of three independent observational datasets shows strong disagreement not only in the sign of recent globally-averaged temperature trends but also disagree as to regions where significant climate shifts are occurring. Unlike model simulations of greenhouse gas warming, warm anomalies do not occur preferentially over land during this period and do not increase with height in the tropics.
1999 Spring.
Includes bibliographical references (pages 99-117).
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Climatic changes
Vegetation and climate
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