Arctic sea ice is headed toward a historic low

This summer, Arctic sea ice has retreated to near-record lows in the Northern Hemisphere, continuing the decades-long trend of shrinking and thinning ice cover in the Arctic Ocean.

This is the conclusion of researchers at NASA and the National Snow and Ice Data Center (NSIDC). 

More melting and less ice formation 

The amount of frozen seawater in the Arctic changes throughout the year as ice melts and refreezes between seasons. Scientists monitor these fluctuations to understand how the Arctic responds over time to rising air and sea temperatures and longer melting seasons.

Over the past several decades, satellites have consistently observed more melting during the summer and less ice formation in the winter. 

Tracking sea ice changes in real time has revealed wide-ranging impacts – from losses and changes in polar wildlife habitats to effects on local Arctic communities and international trade routes.

Minimal extent of Arctic sea ice 

This year, Arctic sea ice shrank to a minimal extent of about 1.65 million square miles (4.28 million square kilometers). 

That’s approximately 750,000 square miles (1.94 million square kilometers) below the 1981 to 2010 end-of-summer average of 2.4 million square miles (6.22 million square kilometers). 

To put it in perspective, the reduction in ice cover spans an area larger than the state of Alaska. Sea ice extent is defined as the total area of the ocean with at least 15% ice concentration.

Downward trend in Arctic sea ice 

While this year’s minimum remained above the all-time low of about 1.31 million square miles set in September 2012, the overall trend since the late 1970s has been a downward one. According to NSIDC, the Arctic has been losing about 30,000 square miles of sea ice per year.

Scientists measure sea ice extent using data from passive microwave sensors aboard satellites in the Defense Meteorological Satellite Program, along with historical data from the Nimbus-7 satellite, jointly operated by NASA and the National Oceanic and Atmospheric Administration (NOAA).

Sea ice is getting younger

Nathan Kurtz, lab chief of NASA’s Cryospheric Sciences Laboratory at the agency’s Goddard Space Flight Center, noted that sea ice isn’t just shrinking – it’s also getting younger. 

“Today, the overwhelming majority of ice in the Arctic Ocean is thinner, first-year ice, which is less able to survive the warmer months. There is far, far less ice that is three years or older now,” said Kurtz. 

Measurements collected with spaceborne altimeters, including NASA’s ICESat and ICESat-2 satellites, have found that much of the oldest, thickest ice has already been lost. 

New research from NASA’s Jet Propulsion Laboratory in Southern California shows that in the central Arctic, away from the coasts, fall sea ice now averages around 4.2 feet thick, down from a peak of 8.8 feet in 1980.

Downward trend in Antarctic sea ice

Meanwhile, sea ice in the southern polar regions has also been unusually low. Around Antarctica, scientists are tracking near-record-low sea ice at a time when it should have been expanding during the Southern Hemisphere’s darkest and coldest months. 

Ice around the continent is on track to be just over 6.6 million square miles (16.96 million square kilometers), compared to the average maximum extent of 7.22 million square miles (18.71 million square kilometers) between 1981 and 2010.

This meager growth prolongs a recent downward trend. Prior to 2014, Antarctic sea ice was increasing slightly by about 1% per decade. 

Shifting conditions in the Southern Ocean

However, following a spike in 2014, ice growth has declined dramatically. Scientists are working to understand the cause of this reversal. The recurring loss hints at a long-term shift in conditions in the Southern Ocean, likely resulting from global climate change.

“While changes in sea ice have been dramatic in the Arctic over several decades, Antarctic sea ice was relatively stable. But that has changed,” said Walt Meier, a sea ice scientist at NSIDC. “It appears that global warming has come to the Southern Ocean.”

Vicious cycle of sea ice loss

In both the Arctic and Antarctic, the loss of sea ice accelerates further ice loss. This happens because bright sea ice reflects most of the sun’s energy back into space, while open ocean water absorbs about 90% of it. 

With more ocean exposed to sunlight, water temperatures rise, further delaying sea ice growth – a cycle known as ice-albedo feedback.

Overall, the decline of sea ice contributes to increased heat in the Arctic, where temperatures have risen about four times the global average, Kurtz concluded.

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