Antarctica’s shrinking sea ice hits record low

At its largest expanse, sea ice covered less than 17 million square kilometers (6.6 million square miles) of the Antarctic – an area that is almost 400,000 square miles smaller than the previous record low set in 1986, according to preliminary figures released by the National Snow and Ice Data Center at the University of Colorado, Boulder. The number represents the smallest peak extent in almost 45 years of satellite records.

Peak Antarctic ice coverage during the region’s winter – which is the northern hemisphere’s summer – likely occurred on Sept. 10. On that date, sea ice stretched over 16.96 million square kilometers, after which it began to shrink, the NSIDC said. This took place almost two weeks earlier than the median date of Sept. 23 between 1981 and 2010.

“There is some concern that this may be the beginning of a long-term trend of decline for Antarctic sea ice, since oceans are warming globally, and warm water mixing in the Southern Ocean polar layer could continue,” the NSIDC said in a news release.

While the drivers of the loss are complicated and not fully understood, scientists believe climate change plays a role, and continuing shrinking of the ice could exacerbate warming’s effects, as less ice means less sunlight is reflected back into space. Scientists who study Antarctica observed months ago that the ice was struggling to grow back from its February nadir, in a stark deviation from usual patterns.

If sea-ice coverage that is dramatically lower than usual continues, more of the coastline will be exposed to ocean waves, the effects of which are not yet clear, the NSIDC noted. Scientists have all sorts of ideas about how sea ice and oceans interact in the Antarctic, but most are theoretical and more study is needed.

In the Antarctic, sea ice typically covers the largest expanse of ocean at some point in September. After that, it begins a slow melt over the southern hemisphere’s summer, with the most open water typically seen in early March. The process is the same in the Arctic, though the winter-summer months are reversed.

The research center also released the latest summer sea-ice coverage estimates for the opposite side of the planet. They showed that sea ice covered just 4.23 million square kilometers of the Arctic Ocean at its lowest point this summer. That’s the sixth lowest figure recorded, and the 17 lowest were all posted in the past 17 years.

Scientists are interested in understanding why a given year may have more or less sea ice, even though the multidecade trend is clearly down, said Flavio Lehner, an assistant professor of Earth and atmospheric science at Cornell University who is also chief climate scientist for Polar Bears International.

“Was it because the air temperature was warmer, because certain weather patterns brought more warm air?” he asked. “Was it the ocean transporting more warm waters into the Arctic? Was it a big storm that broke up the sea ice and made it easier to be flushed out of the Arctic and melted? There’s different stories to every individual sea-ice-minimum year that help us better understand the vulnerability of the ice.”

Those variations can have a significant impact on those living in the region, from Indigenous communities to land and marine animals to the smallest flora and fauna. In the case of polar bears, for example, an earlier freeze in one area might mean an earlier hunting season, while a longer ice season might encourage the migration of bears from other areas. Understanding the variations, and the way animals are responding, is key to successful conservation.