San Diego, CA, December 5, 2006-- New research from the University of California indicates that reductions of human-generated air pollution could create unexpected agricultural benefits in one of the world's poorest regions. These new findings appeared yesterday in the journal Proceedings of the National Academy of Sciences (PNAS). The research was co-authored by UCSD Scripps Institution of Oceanography professor V. Ramanathan, a participant in Calit2's India Initiative.
Rice harvests increased dramatically in India during the "Green Revolution" of the 1960s and 1970s, making the country self-sufficient in its staple food. Harvest growth has slowed since the mid-1980s, however, raising concerns that food shortages could recur in this densely populated and poor nation. Several explanations for the slowdown have been proposed, but until now, none took into account the complex interactions of two pollution-related sources of climate change: atmospheric brown clouds (ABCs), which form from soot and other fine particles in the air (collectively termed aerosols), and the better-known problem of global warming caused by greenhouse gases such as carbon dioxide.
In the PNAS paper, Maximilian Auffhammer at UC Berkeley's College of Natural Resources, as well as Scripps' Ramanathan and Jeffrey Vincent, analyze historical data on Indian rice harvests and examine the combined effects of atmospheric brown clouds and greenhouse gases on growing conditions. They find that the combined effects were negative and were greater after the mid-1980s than before, coinciding with the observed slowdown in harvest growth. They estimate that harvests would have been 20 to 25 percent higher during some years in the 1990s if the negative climate impacts had not occurred.
"Greenhouse gases and aerosols in brown clouds are known to be competing factors in global warming," said Ramanathan. "The major finding of this interdisciplinary study is that their effects on rice production are additive, which is clearly an unwelcome surprise."
Peter Timmer, senior fellow at the Center for Global Development, an independent, non-profit think tank in Washington, D.C., added that the study "links a sophisticated model of agricultural production in India to climate and pollution models, with the critical finding that 'brown cloud' pollution has already cost India millions of tons of food production."
The researchers noted that the impact of ABCs and greenhouse gases on agriculture provides another incentive for controlling air pollution in heavily polluted Asia. "Air pollution control measures in India have been motivated mainly by concern about the health of residents of the urban areas where most of the pollution is generated," said Vincent, an economist and environmental research director at the UC Institute on Global Conflict and Cooperation (IGCC). "Our study provides an additional motivation related to the economic health of poor rural areas."
Auffhammer, UC Berkeley assistant professor of agricultural and resource economics, added that "while this study focuses on India's rain-fed states, ABCs exist throughout Asia's main rice-producing countries, many of which have experienced decreasing growth rates in harvests, too. Furthering our understanding of how air pollution affects agricultural output is very important to ensure food security in the world's most populous region."
The paper is the result of a three-year collaboration between Auffhammer, Ramanathan and Vincent. Their work was supported in part by the Giannini Foundation, the National Science Foundation, the National Oceanic and Atmospheric Administration and IGCC.
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