Impacts of carbon dioxide warming on climate and man in the semi-arid tropics |
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| Authors: | J A Mabbutt |
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| Institution: | (1) University of New South Wales, Australia;(2) Present address: RMB 218B Wattamolla Road, 2535 Berry, NSW, Australia |
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| Abstract: | Tropical semi-arid climates occur between 10 and 35 deg latitude and are characterised by highly variable summer rainfall of between 300 and 750 mm in a rainy season of at least 4 months, generally adequate for rainfed cropping but with considerable drought risk. They support a mesic savanna vegetation. They have a land extent of 4.5 million km2, mainly occupied by Third World nations with rapidly increasing populations which in the main are predominantly rural and largely agricultural with low per capita incomes, consequently vulnerable to climate change. A doubling of atmospheric CO2 by the year 2030 is predicted to cause a rise in equilibrium mean temperature of 1–3 °C; however there is continuing uncertainty regarding the consequences for rainfall amount, variability and intensity, length of rainy season or the frequency of extreme rainfall events. Two scenarios are considered, with reduction and increase in rainfall respectively, involving corresponding latitudinal shifts in present climatic boundaries of about 200 km. Because of their variability, a clear signal of the greenhouse effect on these climates may be delayed, whilst regional responses may differ. Vegetational and hydrological responses under the alternative scenarios are considered. The possible consequences for rainfed and irrigated agriculture, water and energy supplies and disease and pest ecology are discussed. Lands of the semi-arid tropics are already extensively desertified, with consequent lowered productivity and heightened vulnerability to drought, and the possible impacts of greenhouse warming on desertification processes and on measures for land rehabilition to the year 2030 are reviewed. Measures to conserve the biological diversity of savanna lands in face of greenhouse warming are discussed. |
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