调查发现：北极融冰有百分之七十是人为因素（英文）

　　调查发现：北极融冰有百分之七十是人为因素（英文）

　　Study finds only 30% of radical loss of summer sea ice is due to natural variability  in Atlantic —— and it will probably get worse.

　　The radical（激进的，根本的） decline  in sea ice around the Arctic is at least 70% due to human-induced climate change, according  to a new study, and may even be up to 95% down to humans —— rather higher than scientists  had previously thought.

　　The loss of ice around the Arctic has adverse effects on wildlife  and also opens up new northern sea routes and opportunities to drill for oil and gas under  the newly accessible sea bed.

　　The reduction has been accelerating since the 1990s and many  scientists believe the Arctic may become ice-free in the summers later this century,  possibly as early as the late 2020s.

　　“Since the 1970s, there's been a 40% decrease in the  summer sea ice extent,” said Jonny Day, a climate scientist at the National Centre for  Atmospheric Science at the University of Reading, who led the latest study.

　　“We were trying  to determine how much of this was due to natural variability and therefore imply what  aspect is due to man-made climate change as well.”

　　To test the ideas, Day carried out  several computer-based simulations of how the climate around the Arctic might have  fluctuated since 1979 without the input of greenhouse gases from human activity.

　　He found  that a climate system called the Atlantic multi-decadal oscillation（振荡，摆动） （AMO） was  a dominant source of variability in ice extent. The AMO is a cycle of warming and cooling  in the North Atlantic that repeats every 65 to 80 years —— it has been in a warming phase  since the mid-1970s.

　　Comparing the models with actual observations, Day was able to work out  what contribution the natural systems had made to what researchers have observed from  satellite data.

　　“We could only attribute as much as 30% [of the Arctic ice loss] to the  AMO,” he said. “Which implies that the rest is due to something else, and this is most  likely going to be man-made global change.”

　　Previous studies had indicated that around half  of the loss was due to man-made climate change and that the other half was due to natural  variability.

　　The research is published online in the journal Environmental Research Letters.

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