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Going under

发布时间:2019-03-07 10:20:09来源:未知点击:

By Fred Pearce THE whole of the Amazon rainforest will be lost if the level of carbon dioxide in the atmosphere rises by more than 50 per cent. But whatever action the world takes to halt global warming, sea levels are set to rise and wipe out several island nations. These stark predictions come from a three-year study by the Hadley Centre, part of Britain’s Meteorological Office in Bracknell. Its report is being launched in Bonn this week, where environment ministers are meeting to devise rules for implementing the cuts to greenhouse gas emissions agreed two years ago in Kyoto. The study uses climate models to predict three possible futures: an unchecked increase in emissions, and atmospheric CO2 concentrations that stabilise at 750 and 550 parts per million. An unchecked increase in emissions would kill many of the world’s forests by late next century, including the entire Amazon rainforest. A 750 ppm ceiling would still destroy the Amazon, but delay its loss until the 22nd century. A limit of 550 ppm—which is twice preindustrial levels and 50 per cent above today’s—would probably save it. The worst news is that whatever governments do to cut emissions, sea levels will rise by at least 2 metres over the next few hundred years. This will flood hundreds of islands, devastating Tuvalu and Kiribati in the Pacific and the Maldives in the Indian Ocean. Low-lying farmland and cities occupied by hundreds of millions of people will also be inundated. “Thermal expansion of the ocean will continue for many hundreds of years after CO2 is stabilised, due to the gradual penetration of heat deeper and deeper into the ocean,” notes Robert Nicholls of Middlesex University in London, one of the authors of the report. European environment ministers have agreed to push for a global strategy to ensure that CO2 concentrations in the air never exceed the 550 ppm limit. As it takes a century or more for CO2 to be removed from the atmosphere by natural processes, staying below a 550 ppm ceiling will require emissions to rise by no more than 25 per cent of current levels and to be falling fast by the end of the next century (see Figure). The 550 ppm ceiling would save 2 billion people from water shortages, dramatic falls in crop yields and increased coastal flooding, especially in Africa and India. The models also reveal unexpected benefits from global warming. All three futures show increased river flows in some places, mostly from melting glaciers,