The sea ice cap of the Arctic appeared to reach its annual maximum winter extent on Feb. 25, according to data from the NASA-supported National Snow and Ice Data Center (NSIDC) at the University of Colorado, Boulder. At 5.61 million square miles (14.54 million square kilometers), this year’s maximum extent was the smallest on the satellite record and also one of the earliest.
Arctic sea ice likely reached its annual maximum winter extent on Feb. 25, barring a late season surge. At 5.61 million square miles, this year's winter peak extent is the lowest and one of the earliest on the satellite record that began in 1979.
Credits: NASA's Goddard Space Flight Center
Arctic sea ice, frozen seawater floating on top of the Arctic Ocean and its neighboring seas, is in constant change: it grows in the fall and winter, reaching its annual maximum between late February and early April, and then it shrinks in the spring and summer until it hits its annual minimum extent in September. The past decades have seen a downward trend in Arctic sea ice extent during both the growing and melting season, though the decline is steeper in the latter.
This year’s maximum was reached 15 days earlier than the 1981 to 2010 average date of March 12, according to NSIDC. Only in 1996 did it occur earlier, on Feb. 24. However, the sun is just beginning to rise on the Arctic Ocean and a late spurt of ice growth is still possible, though unlikely.
This short video shows the bulk of the Arctic sea ice freeze cycle from October through this year's apparent winter maximum on Feb. 25.
Credits: NASA's Goddard Space Flight Center
If the maximum were to remain at 5.61 million square miles, it would be about 50,000 square miles below the previous lowest peak wintertime extent, reached in 2011 at 5.66 million square miles — in percentages, that’s less than a 1 percent difference between the two record low maximums. In comparison, the swings between record lows for the Arctic summertime minimum extent have been much wider: the lowest minimum extent on record, in 2012, was 1.31 million square miles, about 300,000 square miles, or 18.6 percent smaller than the previous record low one, which happened in 2007 and clocked at 1.61 million square miles.
A record low sea ice maximum extent does not necessarily lead to a record low summertime minimum extent.
“The winter maximum gives you a head start, but the minimum is so much more dependent on what happens in the summer that it seems to wash out anything that happens in the winter,” said Walt Meier, a sea ice scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “If the summer is cool, the melt rate will slow down. And the opposite is true, too: even if you start from a fairly high point, warm summer conditions make ice melt fast. This was highlighted by 2012, when we had one of the later maximums on record and extent was near-normal early in the melt season, but still the 2012 minimum was by far the lowest minimum we’ve seen.”
Here the 2015 maximum is compared to the 1979-2014 average maximum shown in yellow. A distance indicator shows the difference between the two in the Sea of Okhotsk north of Japan.
Credits: NASA's Goddard Space Flight Center
The main player in the wintertime maximum extent is the seasonal ice at the edges of the ice pack. This type of ice is thin and at the mercy of which direction the wind blows: warm winds from the south compact the ice northward and also bring heat that makes the ice melt, while cold winds from the north allow more sea ice to form and spread the ice edge southward.
“Scientifically, the yearly maximum extent is not as interesting as the minimum. It is highly influenced by weather and we’re looking at the loss of thin, seasonal ice that is going to melt anyway in the summer and won’t become part of the permanent ice cover,” Meier said. “With the summertime minimum, when the extent decreases it’s because we’re losing the thick ice component, and that is a better indicator of warming temperatures.”
Sea ice increases in Antarctica do not make up for the accelerated Arctic sea ice loss of the last decades, a new NASA study finds. As a whole, the planet has been shedding sea ice at an average annual rate of 13,500 square miles (35,000 square kilometers) since 1979, the equivalent of losing an area of sea ice larger than the state of Maryland every year.
“Even though Antarctic sea ice reached a new record maximum this past September, global sea ice is still decreasing,” said Claire Parkinson, author of the study and climate scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “That’s because the decreases in Arctic sea ice far exceed the increases in Antarctic sea ice.”
Parkinson used microwave data collected by NASA and Department of Defense satellites for her study, which was published last December in the Journal of Climate. She added Arctic and Antarctic sea ice extents month by month from November 1978 to December 2013 to determine the global ice extent for each month. Her analysis shows that over the 35-year period, the trend in ice extents was downward in all months of the year, even those corresponding to the Arctic and Antarctic sea ice maximum extents.
Comparing Arctic sea ice loss to Antarctic sea ice gain shows that the planet has-been shedding sea ice at an average annual rate of 13,500 square miles since 1979, the equivalent of losing an area of sea ice larger than the state of Maryland every year.
Credits: NASA's Earth Observatory/Joshua Stevens and Jesse Allen
Furthermore, the global ice decrease has accelerated: in the first half of the record (1979-96), the sea ice loss was about 8,300 square miles (21,500 square kilometers) per year. This rate more than doubled for the second half of the period (1996 to 2013), when there was an average loss of 19,500 square miles (50,500 square kilometers) per year – an average yearly loss larger than the states of Vermont and New Hampshire combined.
“This doesn’t mean the sea ice loss will continue to accelerate,” Parkinson said. “After all, there are limits. For instance, once all the Arctic ice is gone in the summer, the Arctic summertime ice loss can’t accelerate any further.”
Sea ice has diminished in almost all regions of the Arctic, whereas the sea ice increases in the Antarctic are less widespread geographically. Although the sea ice cover expanded in most of the Southern Ocean between 1979 and 2013, it decreased substantially in the Bellingshausen and Amundsen seas. These two seas are close to the Antarctic Peninsula, a region that has warmed significantly over the last decades.
In her study, Parkinson also shows that the annual cycle of global ice extents is more similar to the annual cycle of the Antarctic ice than the Arctic ice. The global minimum ice extent occurs in February of each year, as does the Antarctic minimum extent, and the global maximum sea ice extent occurs in either October or November, one or two months after the Antarctic maximum. This contrasts with the Arctic minimum occurring in September and the Arctic maximum occurring in March. Averaged over the 35 years of the satellite record, the planet’s monthly ice extents range from a minimum of 7.03 million square miles (18.2 million square kilometers) in February to a maximum of 10.27 million square miles (26.6 million square kilometers) in November.
“One of the reasons people care about sea ice decreases is that sea ice is highly reflective whereas the liquid ocean is very absorptive,” Parkinson said. “So when the area of sea ice coverage is reduced, there is a smaller sea ice area reflecting the sun’s radiation back to space. This means more retention of the sun’s radiation within the Earth system and further heating.”
Parkinson doesn’t find it likely that the Antarctic sea ice expansion will accelerate and overturn the global sea ice negative trend in the future.
“I think that the expectation is that, if anything, in the long-term the Antarctic sea ice growth is more likely to slow down or even reverse,” she said.
Parkinson calculated and published the global results after witnessing the public’s confusion about whether Antarctic sea ice gain might be cancelling out Arctic sea ice loss.
“When I give public lectures or talk with random people interested in the topic, often somebody will say something in the order of ‘well, the ice is decreasing in the Arctic but it’s increasing in the Antarctic, so don’t they cancel out?’” Parkinson said. “The answer is no, they don’t cancel out.”
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Maria-José Viñas
NASA's Earth Science News Team
NASA's Earth Science News Team
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