SCI-TECH & AGRI

Climate change

THE PRIMARY cause for global warming, it is believed, is due to the greenhouse gases, as they perturb the radioactive balance of Earth.

Originally, carbon dioxide had been believed to be the main pollutant. The list of pollutants now include gases such as halocarbons methane, nitrous oxide and ozone as well as aerosols.

Aerosols are of two types, suspended such as black carbon (BC) and reflective such as sulphates and nitrates.

BC warms the atmosphere by absorbing sunlight and contributes to global warming. On the other hand, the other aerosols reflect sunlight to space and reduce the amount of heat reaching the earth. Thus they tend to cause local cooling.

BC emissions are a product of incomplete combustion from coal, diesel oil, biofuels and biomass; these are particularly very large in China and India. The study of the direct radiative effect of aerosols in this region is discussed below.

In a recent issue of the journal Science (2 September 2002), Surabi Menon et.al. report on climate model simulations, using the Goddard Institute for Space Studies (GISS) 12-layer climate model.

Unlike carbon dioxide emissions, BC emissions are the largest in the developing countries, as given by T. Bond and D. Streets.

USA UK CHINA INDIA

CO{-2} (Tg C) 5576 596 3749 991

BC (Tg C) 0.32 0.04 1.2 0.56

The authors conclude "if our interpretation is correct, reducing the amount of BC aerosols, in addition to having human health benefits, may actually help diminish the intensity of floods in South China and also drought in north China. Similar considerations may apply to India which has experienced recent droughts.''

R. Parthasarathy

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