Antarctic sea ice melts to all-time record low for winter. Here's why that's concerning.

Antarctic sea ice recently reached an all-time record wintertime low, scientists from the National Snow and Ice Data Center announced.

The mark was set "by a wide margin," the center said in a release, adding that the amount of ice was "far outside anything observed in the 45-year modern satellite record that began in 1979."

The amount of "missing" sea ice was some 386,000 square miles below the previous record low in 2022 – more than the size of Egypt.

“The drop in Antarctic sea ice this year has been really dramatic,” said Omar Baddour, chief of climate monitoring at the World Meteorological Organization. "What happens in Antarctica and the Arctic affects the entire globe,” he said.

What is sea ice? Why is it important?

Sea ice is frozen ocean water that melts each summer, then refreezes each winter. Antarctic sea ice is typically at its smallest in late February or early March, toward the end of summer in the Southern Hemisphere. It's at its largest in September as winter comes to an end.

At the top of the world, the Arctic's sea ice schedule is the opposite: largest in February/March, and smallest in September.

In the Arctic, sea ice fills a central role in the lives and customs of native Arctic people, the data center said, as indigenous people use it for hunting and traveling. Sea ice in the Arctic also affects wildlife such as polar bears, seals and walruses.

In Antarctica, it's penguins that rely on sea ice. Due to the dramatic loss of sea ice there, several colonies of emperor penguins face "quasi-extinction" in the decades to come, a study released in August reported.

In addition, sea ice also protects coastal areas from erosion by damping ocean waves. In areas with less sea ice, for example, storms on the Arctic Ocean can generate much larger waves, damaging shorelines and Arctic communities.

What happens in Antarctica doesn't stay in Antarctica

Sea ice also helps regulate the planet’s temperature by influencing the circulation of the planet's atmosphere and oceans.

“The 2023 Antarctic sea-ice deficit has direct impacts on the climate and ecosystems, both nearby as well as far field, including at lower latitudes, which are home to the majority of human population and their economic interests,” said Petra Heil of the Australia Antarctic Division and part of the World Meteorological Organization’s Global Cryosphere Watch.

Antarctica’s huge glacial ice expanse and the surrounding sea ice cover are critical to regulating the climate, because it reflects the sun’s energy back to the atmosphere and space. In contrast, the dark ocean surface absorbs most of the sun’s incoming energy.

So, less sea ice contributes to increasing temperatures – thus accelerating a vicious cycle.

NOAA's National Ocean Service said that changes in the amount of sea ice can disrupt normal ocean circulation, thereby leading to changes in global climate "Even a small increase in temperature can lead to greater warming over time, making the polar regions the most sensitive areas to climate change on Earth," the ocean service reports.

Why was Antarctic sea ice so small this year?

"It is still early to say all of the factors that might be involved, but warmer ocean waters reaching the Antarctic were a key factor in slowing the ice growth through the Antarctic winter and capping the maximum at the record low level," Walt Meier, a senior research scientist at the data center, told USA TODAY.

The Antarctic ocean warmth is a part of the overall globally warm oceans, he said, but it isn’t clear how much of the ocean heat that impacted the Antarctic was due to the extreme warm waters in other parts of the globe.

Overall, "there is growing evidence that the Antarctic sea ice system has entered a new regime, featuring a much stronger influence of warm ocean waters, limiting ice growth," the NSIDC said.

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

This article originally appeared on USA TODAY: Antarctic sea ice melts to all-time record low for winter