NEW YORK • Sea ice in the Arctic Ocean has reached its minimum extent following the summer melt season, and coverage is not as low as it has been in recent years, scientists have said.
The National Snow and Ice Data Centre at the University of Colorado said that the minimum had most likely been reached on Sept 16 and estimated this year's total ice extent at 4.72 million sq km.
That is the 12th lowest total since satellite sensing of the Arctic began in 1979 and is about 25 per cent higher than last year.
In a statement, Mr Mark Serreze, director of the centre, described this year as a "reprieve" for Arctic sea ice, as colder and stormier conditions led to less melting.
In particular, a persistent zone of colder, low pressure air over the Beaufort Sea north of Alaska slowed the rate of melting there.
The total is a reminder that the climate is naturally variable and that variability can sometimes outweigh the effects of climate change. But the overall downward trend of Arctic sea ice continues, as the region warms more than twice as fast as other parts of the world.
The record minimum was set in 2012, and this year's results are about 40 per cent higher than that. But this year's total is still nearly 1.55 million sq km below the average minimum for 1981 to 2010. And including this year, the minimums for the last 15 years are the lowest 15 since 1979.
What is more, the relatively high minimum appears to have been gained at the expense of thicker, multi-year ice, which remains near its lowest totals in the satellite record.
Thinning or complete melting of thicker Arctic sea ice (there is now about one-fourth as much as there was four decades ago) is troubling.
The thinner sea ice gets, the more sunlight it lets through to the water underneath, which can affect marine ecosystems and generate even more warmth as more of the sun's energy is absorbed and re-emitted as heat. And since first-year ice, being thinner, is more prone to melting completely as it replaces older ice, the region overall becomes more susceptible to melting.
Many scientists expect that the Arctic may become ice-free in summers within a decade or two.
The westward blowing of older ice from north of Greenland last winter may be a continuation of a troubling pattern that was noticed last year.
The area is normally so full of persistent, multi-year ice that it is known as the "last ice area" where, even as ice disappears completely in Arctic summers, it has been thought that enough ice will remain to serve as a refuge for polar bears and other ice-dependent wildlife.
But last year, a German research icebreaker on a year-long expedition encountered little thick ice while travelling through the area.
And a study suggested that variable wind patterns, coupled with warming-induced thinning and the melting of ice, had led to much of the thicker ice being blown out of the area.