By Will Dunham WASHINGTON, Dec 4 (Reuters) - Air pollution caused by the burning of fossil fuels like coal and diesel has contributed to a worrisome slowdown in rice harvest growth in India in the past two decades, scientists said on Monday. The researchers said the findings suggest reducing so-called atmospheric brown clouds, formed from soot and other tiny airborne particles belched into the air when fossil fuels are burned, would help improve rice harvests to feed India's 1 billion people. India has an acute problem with this type of pollution, which previous research showed can cut rainfall and lower temperatures. Writing in the Proceedings of the National Academy of Sciences, the researchers said harm from this air pollution has combined with broader global warming effects from greenhouse gases such as carbon dioxide to squeeze India's rice harvest. "If we let air pollution levels get worse, these effects are going to get larger," University of California-Berkeley scientist Maximilian Auffhammer, one of the researchers, said in a telephone interview. "If we don't do anything about this, things are not going to get better." India is one of the world's major producers of rice. Broad agricultural improvements boosted India's rice harvests in the 1960s and 1970s, making it self-sufficient in its staple food. The annual growth rate peaked at 2.7 percent in the mid-1980s. Growth has eroded since then, prompting worry about potential food shortages in the densely populated and poor country. DIMINISHED HARVEST India's rice harvest would have been more than 14 percent better from 1985 to 1998 without the negative combined effects from the burning of fossil fuels and broader climate warming, the researchers said. "I don't think it forecasts immediate doom and mass starvation or anything like that," Auffhammer said. But he warned India's rice self-sufficiency could be threatened even as some experts forecast that its population will top China's by the middle of the century. There have been other explanations offered for the slowing rice harvest growth, including falling rice prices, deteriorating irrigation infrastructure and soil degradation. Auffhammer and University of California-San Diego scientists V. "Ram" Ramanathan and Jeffrey Vincent examined historical data on India's rice harvests and gauged the combined effects of atmospheric brown clouds and greenhouse gases on growing conditions. The combined effects of the two types of pollution were decidedly negative. The research indicated that the cooling effect of the brown clouds actually helped rice harvests by partially offsetting the warming effects of greenhouse gases, but not nearly as much as the drying effect from these clouds hurt the harvests. Some climate scientists have worried that reducing brown clouds and their cooling effect could harm crops by intensifying the warming caused by greenhouse gases. But this study indicated any negative impacts of intensified warming would be outweighed by positive effects of greater rainfall. "I don't want to start some big stink, pointing fingers at the Indian government saying air pollution policy is something that should have been done," Auffhammer said. "But (I'd) rather say, 'Here's the effect,' and this presents an incredible opportunity to (make) policy."
