Paris - Natural changes in the environment are responsible for about 40% of Arctic sea ice loss, while humans are to blame for the rest, says a climate study.
The paper, based on model simulations of different climate conditions, was a rare attempt to quantify the relative contributions of humans and Nature to the dramatic decline and could have a major impact on future research into Arctic ice lost.
Understanding all causes of the sea ice retreat is crucial for accurately projecting the rate of future loss and trying to slow it.
Scientists have long accepted that natural changes in the environment, such as atmospheric air circulation, were at least partly responsible.
But its relative contribution, and that of human-induced global warming, has been fiercely debate.
Summer circulation trend
The new study concluded that up to 60% of sea ice decline since 1979 was caused by summertime changes in atmospheric circulation.
About 70% of the air flow changes, in turn, were the result of natural variability, not human-caused climate change.
Taken together, this meant that between half and two-thirds the sea ice decline was attributable to climate change, said the American team.
Natural variability, on the other hand, "dominates the Arctic summer circulation trend and may be responsible for about 30-50% of the overall decline in September sea ice since 1979," they said.
Chris Rapley, a professor of climate science at University College London, said the study helped explain why Arctic sea ice was disappearing faster than most climate models predict - they underestimated the contribution of natural drivers.