Brown clouds, greenhouse gas emission key sources

Vinson Kurian

Thiruvananthapuram, Dec. 5

Negative climate impacts have put back rice harvests in India by at least 20 to 25 per cent during the 1990s, according to latest research findings from the University of California.

There is a need to reduce human-generated air pollution, which could create unexpected agricultural benefits, said a research team that included Prof V. Ramanathan of the Scripps Institution of Oceanography.

A cutback in aerosols would enhance rainfall, while a drop in greenhouse gas emission would reduce the higher night temperatures that negatively affect the growth of the rice plant.

The combined effects of atmospheric brown clouds (ABCs) and greenhouse gases were negative and were greater after the mid-1980s than before, coinciding with the observed slowdown in harvest growth.

Complex matrix

Several explanations for the slowdown have been proposed, but until now, none took into account the complex interactions of these two pollution-related sources of climate change.

ABCs form from soot and other fine particles in the air (collectively termed aerosols), while the better-known problem of global warming is caused by greenhouse gases such as carbon dioxide.

ABCs exist throughout Asia's main rice-producing countries, many of which have experienced decreasing growth rates in harvests.

Previous research by a scientific team led by Prof Ramanathan had found that brown clouds have made the Indian subcontinent "drier and cooler''. Greenhouse gases and aerosols in brown clouds are known to be competing factors in global warming.

Rice harvests increased dramatically in India during the Green Revolution, making the country self-sufficient in its staple food.

Harvest growth has slowed since the mid-1980s, raising concerns that food shortages could recur.

(This article was published in the Business Line print edition dated December 6, 2006)
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