NASA Says 2019 Arctic Sea Ice Minimum Ties for Second Lowest on Record: 'There Is No Sign That the Sea Ice Cover Is Rebounding'

The 2019 Arctic sea ice minimum was the second lowest on record, tying with 2007 and 2016, NASA has said. On September 18, sea ice coverage measured 1.6 million square miles, satellite data from NASA and the National Snow and Ice Data Center (NSIDC) showed. The lowest Arctic sea ice minimum ever recorded took place in 2012, when it shrunk to 1.32 million square miles.

Arctic sea ice—a vast area of frozen seawater in the Arctic Ocean—expands and shrinks with the seasons. In March this year, at the end of the long, cold Arctic winter, it covered 5.71 million square miles. Over summer, the sea ice melts, normally falling to its lowest levels at some point in September.

Sea ice extent has been measured for the last 40 years—and over recent years both the sea ice maximum and minimum have reached record lows. NSIDC said that the 13 lowest extents of Arctic sea ice recorded have all taken place in the last 13 years.

"This year's minimum sea ice extent shows that there is no sign that the sea ice cover is rebounding,"

Arctic sea ice maximum extent is also falling. NSIDC research scientist Walt Meier said the last four years have been some of the lowest on record, "reflecting a downward trend in winter sea ice extent." He continued: "This is just another indicator of the rapid changes that are occurring in the Arctic due to climate change.

It is thought that increasing global temperatures are behind the decline in Arctic sea ice. Since the start of the Industrial Revolution, temperatures have increased by around 1 degree Celsius. It is thought that if greenhouse gas emissions continue at current levels, warming could reach over 4 degrees Celsius by the end of the century.

Tom Rippeth, Professor of Physical Oceanography at the U.K.'s Bangor University, said 2019's sea ice minimum was initially tracking below the 2012 record. The August sea ice extent was the lowest ever recorded. "The decline in summer sea ice extent is something we have been observing for well over a decade," he told Newsweek. "Furthermore, there is a growing body of evidence that the decline is not just due to warming from the atmosphere above, but that it also linked to the warming of inflowing Atlantic Water which enters the Arctic Ocean through the Fram Strait, and flows anticlockwise around the basin. This is particularly apparent in the Barents Sea where sea ice rarely even forms in the winter these days."

arctic sea ice
The Arctic sea ice minimum on September 18, 2019. The extent tied with 2007 and 2016 to be the second lowest ever recorded. NASA Goddard

The impact of of consistently low sea ice minimums means it is less likely a large volume of seawater will freeze over the winter. "Once sea ice forms, it insulates the sea water below the ice from the atmosphere, and so the thickening of the ice is a very slow process," Rippeth explained. "As a result it normally takes several years for sea ice to reach a thickness of a few meters. Newly formed—and thinner—sea ice (first year ice) is thus much more susceptible to melting than the older ice.

"The more the sea ice melts back, the greater the proportion of the first year ice at the end of the winter, and so the more easily the ice is melted, and the earlier it melts. This causes the ocean to absorb more heat, which it must be got rid of to the atmosphere in the fall in order for the ocean surface to cool sufficiently to allow sea ice to reform. The result is the ice forms later and so the ice free season is longer where ice is lost."

Rippeth said sea ice is particularly effective at reflecting the sun's rays back into space—which helps limit warming. When there is less ice, less light—and heat—is reflected back, which causes more warming to the water and atmosphere above. This may then impact weather systems across the northern Hemisphere, he said. "While there is still some debate as to the roll of reducing sea ice on our weather, I would be very surprised if it wasn't having some impact."

NASA Says 2019 Arctic Sea Ice Minimum Ties for Second Lowest on Record: 'There Is No Sign That the Sea Ice Cover Is Rebounding' | Tech & Science