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Increasing Asian smog blocks out the Sun

发布时间:2019-03-06 02:13:01来源:未知点击:

By Fred Pearce, Amsterdam A year-round smog over the Indian Ocean and Asia is blotting out 10 to 15 per cent of the Sun’s rays, with potentially “very major consequences” for the atmosphere. The warning comes from the 1995 Nobel prize-winner for chemistry, Paul Crutzen, in a devastating analysis of the scale of air pollution in a once-pristine region of the tropics. He was speaking at a conference on global climate change in Amsterdam, a week before political talks resume on tackling the problem. The smog comes mostly from farmers using fire to clear fields across Asia and Africa. In field experiments last year, says Crutzen, “we found thick brown smog 4000 metres up in the Himalayas, over the Maldives in the Indian Ocean, and widely across south and east Asia. We were shocked.” Crutzen, from the Max Planck Institute for Chemistry in Mainz, Germany, won his Nobel prize for his pioneering investigations of the thinning ozone layer. He warned that biomass burning in the tropics had the potential to cause an unpleasant environmental “surprise” on a par with the discovery of the ozone hole 15 years ago. Crutzen says the theoretical cooling effect of the smoke blocking the Sun’s warmth is largely ignored in current climate models. He calculates it to be almost ten times greater than the warming from greenhouse gases. But there is no evidence that the region is in fact cooling. This could be because much of the pollution is black soot, which absorbs the sunlight and then itself radiates heat towards the ground. Even so, Crutzen warned that the tropical smogs could have “very major consequences” for the atmosphere. They could upset the hydrological cycle that maintains the Asian monsoon, for instance. They might also use up large amounts of the atmosphere’s main cleansing agent, the hydroxyl radical, so damaging the ability of the atmosphere to cleanse itself. The pollution is set to grow in coming decades. “In southern Africa we are very worried that the predicted decease in rainfall could cause an extreme increase in fires,” said Mary Scholes of Witwatersrand University, South Africa. Meinrat Andreae, also of the Max Planck Institute for Chemistry, said recent studies had found that more than seven billion tonnes of biomass was burned in the tropics each year, for farming our fuel. A typical rural inhabitant of the developing world consumes a tonne of biomass fuel a year. “Poverty pollutes, too,” said Crutzen. But the conference also heard that some rich nations are also burning. Mike Flannigan of the Canadian Forest Service said fires in its northern forests, mostly triggered by lightning,