Sea ice in the Arctic last month melted to its second lowest monthly minimum in the 29-year record of satellite measurements.
Scientists at the US National Snow and Ice Data Centre (NSIDC) in Colorado said the total surface area covered by sea ice during September was smaller than in any previous year apart from 2005, when it reached an all-time record minimum. And it was only a sudden change to cool and stormy weather in August that prevented another record low being set this September, they said.
"At this rate, the Arctic Ocean will have no ice in September by the year 2060," said Julienne Strove, one of the NSIDC's research scientists.
The Arctic sea ice floats on the ocean and its surface coverage varies naturally in line with seasonal temperature changes, with an absolute minimum in summer occurring around mid-September.
However, rising temperatures have seen a steady long-term decline in sea ice during the summer months, with little recovery during the Arctic winter.
Summer sea ice across the entire Arctic has been dwindling steadily since satellite measurements began in 1977. But since 2002 scientists have detected a noticeable acceleration in the rate of summer loss, which they believe is caused by global warming.
Mark Serreze, a senior research scientist at the NSIDC, said this summer could easily have surpassed last year's record loss if it had not been for the change in the weather.
"If fairly cool and stormy conditions hadn't appeared in August, slowing the rate of summer ice loss, I feel certain that 2006 would have surpassed last year's record low for September sea ice," Dr Serreze said.
"August broke the Arctic heatwave and slowed the melt, and storm conditions led to wind patterns that tend to spread the existing ice over a larger area."
Arctic sea ice acts like an insulating lid on the northernmost ocean, reflecting sunlight and preventing the water from absorbing heat and warming up.
Scientists fear that as more and more sea ice is lost, a "positive feedback" will kick in, with the Arctic Ocean absorbing more sunlight, which will in turn cause the loss of more sea ice.
"I'm not terribly optimistic about the future of the ice," Dr Serreze said. "Although it would come as no surprise to see some recovery of the sea ice in the next few years - such fluctuations are part of natural variability - the long-term trend seems increasingly clear. As greenhouse gases continue to rise, the Arctic will continue to lose its ice. You can't argue with the physics."
The Arctic has seen some of the largest increases in average temperatures in the world over the past few decades, and could be one of the places hardest hit by climate change.
"Arctic sea ice is an important climate indicator because it's so sensitive to this initial warming trend," said Ted Scambos, a senior scientist at the Snow and Ice Data Centre.Reuse content