At least 70 percent, and as much as 95 percent, of sea ice loss in the Arctic is the result of human activities such as the burning of greenhouse gases, according to a new study.
According to the National Snow and Ice Data Center (NSIDC), summer sea ice extent in the Arctic is declining by approximately 12 percent per decade; 2007 and 2011 experienced the lowest summer sea ice levels on record, and NSIDC director Mark Serreze has said that this year's ice is in a "sorry state", at the extreme low end of the satellite record for this time of year and on track to be similar to 2007.
But how much of that change is the result of global warming, and how much can be attributed to natural cycles? The new study, published in the journal Environmental Research Letters, set out to answer that very question.
Scientists at the University of Reading and the Japan Agency for Marine Earth Science and Technology (JAMSTEC) used advanced statistical techniques to compare satellite data obtained since 1979 with computer simulations on supercomputers, and found the natural cycles in winds over the Arctic (the Arctic Oscillation, or AO), which can cause ice to thin in some areas and pile up in others, had surprisingly little influence on the loss of sea ice.
The Atlantic Multi-decadal Oscillation (AMO), a cycle of warming and cooling in the North Atlantic, which repeats every 65-80 years and has been in a warming phase since the mid 1970s, did, however, play a role – but, the researchers found, a relatively minor one in comparison to human activities: responsible for no more than 30 percent, and perhaps as little as 5 percent, of sea ice decline.
According to study lead author Jonny Day of the University of Reading, "The debate over how much the change observed in Arctic sea ice can be attributed to humans and how much is due to natural variability in the climate is an important one. Our study shows that while natural changes play a significant role, the majority of sea ice loss – between 70% and 95% – is likely to be due to man-made greenhouse gas emissions."
IMAGE: Inuit hunter walking on summer ice floe in midnight sun. (Rob Howard, Corbis)