Satellite data show the Arctic sea ice minimum extent of the year 2015 is the fourth lowest recorded since the beginning of the observations from space.
Researchers from NASA and the National Snow and Ice Data Center (NSIDC) at the University of Colorado at Boulder have observed the annual minimum extent of 4.41 million square kilometers (1.7 million square miles) on September 11, 2015. This number makes the minimum of 2015 about 1.81 million square kilometers (699 000 square miles) lower than the minimum average in the period between 1981 - 2010.
The sea-ice covering the surface of Arctic is made of frozen seawater floating on top of the ocean water mass. It's vital to regulating Earth's temperature, as its high albedo is responsible for reflecting significant amounts of solar energy back into space. Sea ice caps grow and shrink back again with the change of seasons. The data show the minimum summertime extent has been decreasing since the late 1970s.
Video credit: NASA
Usually the low minimum ice extent is related to meteorological impact, however, this years it seems this was not the reason behind it: "This year is the fourth lowest, and yet we haven’t seen any major weather event or persistent weather pattern in the Arctic this summer that helped push the extent lower as often happens. It was a bit warmer in some areas than last year, but it was cooler in other places, too,” said Walt Meier, a sea ice scientist with NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
2012, the lowest year on record so far, was under the influence of a strong August cyclone that fractured the ice cover, accelerating its decline.
Generally speaking, decline of the sea ice coverage has accelerated since 1996. 10 lowest minimum extents have been observed during the last 11 years. Changing winds and late season melts still hold the possibility of decreasing the Arctic sea ice minimum extent over the next couple of days.
“The ice cover becomes less and less resilient, and it doesn’t take as much to melt it as it used to. The sea ice cap, which used to be a solid sheet of ice, now is fragmented into smaller floes that are more exposed to warm ocean waters. In the past, Arctic sea ice was like a fortress. The ocean could only attack it from the sides. Now it’s like the invaders have tunneled in from underneath and the ice pack melts from within,” Meier explained.
Some observations have given an indication that the Arctic's oldest and thickest ice which survives beyond the summer melt season, partially recuperated since the record low of 2012. However, it appears the recovery has leveled out during last winter, and will most probably reverse again following this melt season.
“The thicker ice will likely continue to decline. There might be some recoveries during some years, especially when the winter is unusually cold, but it is expected to go down again because the surface temperature in the region continues to increase,” Joey Comiso, a sea ice scientist from Goddard concluded.
The Arctic area receives most of its solar energy during June. However, the June of 2015 experienced quite slow melt rates which picked up again during July. Ice continued to melt throughout August at a faster than usual pace, although by that time the ice loss typically begins to slow. The ice pack in the Beaufort and Chukchi seas suffered a big "hole", as the thinner seasonal ice melted. This opening enabled the surrounding ocean to absorb more solar energy, which again accelerated the melt, in return.
It's still uncertain if this year's El Niño influenced the sea ice melting in the Arctic sea, although the research has established a strong link between.El Niño event and the sea ice cover extent around Antarctica. This is likely a good explanation why the growth of the Antarctic sea ice cover, which was climbing toward its yearly maximum extent through most of the 2015, has rapidly fallen below its normal levels during mid-August.
“Historically, the Arctic had a thicker, more rigid sea ice that covered more of the Arctic basin, so it was difficult to tell whether El Niño had any effect on it. Although we haven’t been able to detect a strong El Niño impact on Arctic sea ice yet, now that the ice is thinner and more mobile, we should begin to see a larger response to atmospheric events from lower latitudes,” said Richard Cullather, a climate modeler at Goddard.
To validate current satellite measurements, NASA's Operation IceBridge, an airborne survey of polar ice, will be carrying flights over sea ice across Arctic, as of September 21.
Featured image:Yearly minimum of the Arctic sea ice cover, September 11, 2015. Image credit: NASA