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If there was a silver lining to the massive clouds of pollutants that hang over India, it was that this brown haze was keeping global warming in check in the region. Nevertheless, a new study shows that getting rid of it could actually help increase the rice harvests in the subcontinent.Between October and May, a 3-kilometre-thick brown haze sits over much of South Asia and the northern Indian Ocean. Caused mostly by urban pollution such as vehicle emissions, industrial soot and burning of wood and crops, this dirty cloud cools the region by reflecting sunlight back into space. But it also lessens the monsoon rainfall by reducing evaporation.Jeffrey Vincent at the University of California in San Diego, US, and colleagues combined a model containing historical data on India's rice harvest with a climate model. They found that historical rice harvests would have been up to 10.6% higher if the brown haze had not been there, and 14.4% higher if the detrimental effect of global warming was removed too."Pollution from predominantly urban sources has had an unrecognised negative impact on the rural economy," says Vincent.Existing technologyIt is not just Indian rice that might benefit from cleaner air. Rice is particularly sensitive to brown haze because it needs a lot of water to grow successfully, but other crops are likely to be suffering too, the researchers say. Brown haze occurs all over the globe, including significant blankets over parts of Europe, the US, the Amazon, Southeast Asia and southern Africa.Compared to the challenge of reducing greenhouse gas emissions, removing brown haze is far easier and the technology already exists. The Indian government is already taking steps to reduce air pollution from vehicles and many buses in Delhi now run on "clean" fuel."Any negative impacts of intensified warming on rice harvests would be outweighed by the positive impacts of greater rainfall due to a lessening of the brown cloud's drying effect," says Vincent&colon; "Who would have thought that reducing urban pollution could be a way to boost crop output?"Journal reference&colon; Proceedings of the National Academy of Sciences (DOI&colon; 10.1073/pnas.0609584104)

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Brown haze over India harming rice harvest