Does polluted air keep the Artic cool?

日期:2019-03-01 01:01:18 作者:冯咬擎 阅读:

By FRED PEARCE AIR pollution is acting like a giant sunshade over the Arctic, cancelling out the expected global warming in the region, according to research results presented last week in London. But this conclusion was questioned by scientists who say the Arctic is actually becoming warmer. Arctic haze is created as polluted air drifting north from Russia, Europe and North America is trapped close to the ice. In the past 40 years the haze has become a near permanent feature of the far north. Over this period, sunlight has decreased by 15 per cent, according to data from 22 monitoring sites in the Arctic presented by Gerald Stanhill from Israel’s Agricultural Research Organisation. He was speaking at a meeting organised by the Royal Society. Stanhill believes that the shade provided by the haze explains why the Arctic has warmed much less than the Antarctic in the past few decades. The amount of solar heat reaching the Arctic surface has fallen each year since 1950 by an average of 0.36 watts per square metre. The drop is most marked in spring and has occurred in areas where the haze is densest, said Stanhill. But despite the drop in direct solar heating, the amount of heat staying at the surface has hardly changed – presumably, he said, because the build-up of greenhouse gases such as carbon dioxide was trapping more of solar heat reaching the surface. By contrast, over the Antarctic, where there is no haze, the radiation balance has changed dramatically. Over the past 40 years, this has led to a rise in average temperatures at the British Antarctic Survey’s Faraday research station of 2.5 °C, dramatic melting of the giant Wardie ice shelf and the spread of flowering grasses, all reported earlier this year by the survey. Stephen Schneider of Stanford University in California admitted at the meeting that Stanhill’s work was important, but questioned whether Stanhill had enough data to reach his conclusions. Schneider warned that the soot in Arctic haze might not shade the surface, but have the opposite effect. “It could reflect heat back down to the surface, trapping it,” he said. “We need to look at the optical properties of the haze.” There was confusion at the conference over whether the Arctic was warming or not. Howard Cattle of Britain’s Meteorological Office said parts of the Arctic had warmed by 0.75 °C a decade since the 1950s, and there was evidence that the Arctic Ocean contained less sea ice than in the past. Cattle presented new modelling studies showing that air pollution could have held up global warming in the Arctic for about 20 years,