Antarctic sea ice near historic low; Arctic ice continues to decline

Sea ice at the top and bottom of the planet will continue to shrink by 2024. In the waters around Antarctica, ice cover fell to a near-historic low for the third year in a row. The recurring loss indicates a long-term shift in conditions in the Southern Ocean, likely due to global climate change, according to scientists at NASA and the National Snow and Ice Data Center. Meanwhile, the 46-year trend of shrinking and thinning ice in the Arctic Ocean shows no sign of reversing.

“Sea ice acts as a buffer between the ocean and the atmosphere,” says ice scientist Linette Boisvert of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Sea ice prevents much of the exchange of heat and moisture from the relatively warm ocean to the atmosphere above.” Less ice cover causes the ocean to warm the atmosphere above the poles, leading to more melting ice in a vicious cycle of rising temperatures. In the past, the extent of sea ice around the Antarctic continent fluctuated dramatically from year to year, while averages were relatively stable over decades. However, in recent years, the sea ice around Antarctica has decreased significantly.

“In 2016, we saw what some call a regime shift,” says sea ice scientist Walt Meier of the National Snow and Ice Data Center at the University of Colorado Boulder. “Antarctic sea ice cover declined and has largely remained lower than normal. In the last seven years we have had three record lows.” This year, Antarctic sea ice reached its lowest annual extent on February 20, totaling 768,000 square miles (1.99 million square kilometers). That’s 30% below the late summer average from 1981 to 2010. The difference in ice cover covers an area the size of Texas. Sea ice extent is defined as the total area of ​​the ocean with at least 15% ice cover.

This year’s minimum ties that of February 2022 for the second-lowest ice cover around Antarctica and is close to the 2023 record low of 691,000 square miles (1.79 million square kilometers). With the latest ice loss, this year marks the lowest three-year average for ice cover around the Antarctic continent in more than four decades. The changes were observed in data collected by microwave sensors aboard the Nimbus-7 satellite, which is jointly operated by NASA and the National Oceanic and Atmospheric Administration (NOAA), along with satellites in the Defense Meteorological Satellite Program.

Arctic sea ice reached its annual maximum on March 14, marking the long-term decline
of the ice at the poles continues. Graph by Lauren Dauphin/NASA Earth Observatory
with data from the National Snow and Ice Data Center.

Antarctic sea ice at near historic lows

Meanwhile, on the other side of the planet, maximum winter ice cover in the Arctic Ocean is consistent with an ongoing 46-year decline. Satellite images show that the total area of ​​the Arctic Ocean covered by sea ice as of March 14 was 15.65 million square kilometers. That’s 247,000 square miles (640,000 square kilometers) less ice than the average between 1981 and 2010. Overall, maximum winter ice cover in the Arctic has shrunk since 1979 by an area equivalent to the size of Alaska. This year, the maximum ice at the North Pole is the 14th lowest on record. Complex weather patterns make it difficult to predict what will happen in any given year.

Shrinking ice makes the Earth more sensitive to solar heating. “The sea ice and the snow on it are very reflective,” says Boisvert. “In the summer, when we have more sea ice, it reflects the sun’s radiation and helps keep the planet cooler.” On the other hand, the ocean is darker and easily absorbs solar radiation, trapping that energy and ultimately contributing to the warming of the planet’s oceans and atmosphere. The sea ice around the poles is more sensitive to the weather than it was a decade ago. Ice thickness measurements with laser altimeters aboard NASA’s ICESat-2 satellite show that less ice has managed to survive the warmer months. This means that new ice must form anew every year, rather than building on old ice to create thicker layers.

Thinner ice, in turn, is more prone to melting than multi-year accumulations. “The thinking is that in a few decades we will have ice-free summers,” Boisvert said, with ice cover less than 1 million square kilometers and most of the Arctic Ocean exposed to the sun’s warming rays. It’s too early to know whether the recent low in Antarctic sea ice indicates a long-term change rather than a statistical fluctuation, but Meier believes a long-term decline is inevitable. “It’s only a matter of time,” he said. “After six, seven, eight years, it’s starting to look like it might be happening. The only question is whether there’s enough data to say for sure.”

Source: NASA