Floating ice around Antarctica has hit a record low

The amount of floating sea ice encircling Antarctica reached the lowest level ever recorded, scientists reported this week, a sign that one of the most remote and mysterious facets of the climate system may, at last, be responding to the overall planetary warming trend.

The latest measurements represent the lowest reading for overall Antarctic sea ice extent since satellite monitoring began in late 1978. This marks the second year in a row that, as the Antarctic summer wears on and the Southern Ocean’s blanket of sea ice shrinks to its yearly minimum extent, a record low has been recorded.

The extent of ice around Antarctica dwindled to roughly 737,000 square miles as of Feb. 13, based on data from the National Snow and Ice Data Center in Colorado; it measured roughly 741,000 square miles during the previous low, on Feb. 25, 2022.

The ice is likely to decline even further throughout much of February, before beginning its seasonal climb as summer ends in the Antarctic.

“This will not just be a ‘barely made it’ record, it is looking like it will be another substantial jump downward on top of last year’s record,” said Ted Scambos, an expert on sea ice and glaciers at the University of Colorado at Boulder.

Scambos and other scientists determine sea ice extent at both poles from satellite data, and their figures count all areas where there is at least a 15 percent concentration of floating sea ice. Because individual daily readings can jump up and down, researchers use a five day average of the satellite data to assess whether a record has been broken.

Separately, a research group based in Germany called the Sea Ice Portal, which includes scientists from the Alfred Wegener Institute and other institutions, declared Friday that a record low had occurred for summer Antarctic sea ice.

The back-to-back record lows could begin to reassure scientists that Antarctic sea ice is finally starting to behave as expected as the planet warms.

[Warming seas are carving into massive Antarctic glacier that could boost sea level rise]

The National Oceanic and Atmospheric Administration (NOAA) also announced Tuesday that global sea ice reached a record low in January, driven in large part by diminished Antarctic ice.

In the Arctic, the downtrend in the extent of floating sea ice has been clear and pronounced since the late 1970s. Based on annual averages of the ice’s extent, the Arctic has lost a little over 20,000 square miles of ice per year since 1979.

In the Antarctic, no clear downtrend in overall sea ice extent has yet emerged. It has even appeared as if ice extent might be rising slightly - despite general expectations that a warmer Earth should feature less ice at both poles.

During the Southern Hemisphere winter of 2014, Antarctic sea ice actually grew to a record high of more than 7,782,275 square miles. The record set off massive chatter about the Antarctic’s apparent thwarting of climate predictions.

But scientists have cautioned that there are many differences between the Arctic and Antarctic, and our satellite records are still relatively short - meaning that Antarctic declines could manifest themselves soon enough.

In the Arctic, the pole is covered by an ocean overlain by ice that spreads outward, but soon encounters and freezes onto land masses including the coasts of Alaska, Russia and Canada’s Arctic Islands.

In the Antarctic, the pole is covered by a vast landmass. It is only at its edge, beyond the Antarctic glaciers and their great floating ice shelves, that thinner sea ice forms. Once the ice grows outward, it encounters no hindrances in the vast Southern Ocean, and eventually extends for hundreds of miles. It is usually thinner than sea ice in the Arctic.

Antarctic ice also declines more steeply when summer comes. The floating ice climbs to an annual peak of more than 7 million square miles in September - but then subtracts an area nearly the size of Russia by the following February. In the each of the last two years, the minimal extent has fallen well under 1 million square miles.

Scientists say that these vast seasonal swings have made it tough to detect trends in the Antarctic. But with two record lows for Antarctic ice in 2022 and 2023 - and before that a record low in 2017 - it could be that a signal is beginning to emerge, at least in the summer.

If so, that also could make some physical sense - recent research has suggested that the broad warming of the planet’s oceans is now reaching the Antarctic, and affecting trends in sea ice.

“The level of Antarctic sea ice variability exhibited in 2016-2017 (extreme sea ice low), 2021-2022 (extreme sea ice low), 2023 (extreme sea ice low) is unprecedented in the satellite record and might signal a change in the Antarctic sea ice regime as a response to anthropogenic warming,” said Liping Zhang, a researcher at the Geophysical Fluid Dynamics Laboratory at NOAA, who has studied how warming oceans could be affecting the ice.

“However, further data and analysis are required to evaluate and verify any claims for a changing Antarctic climate,” Zhang cautioned.

Scientists with the National Snow and Ice Data Center, which provides the data, also sounded a cautionary note in their announcement.

“Antarctic sea ice extent has been highly variable over the last several years,” they noted. “While 2022 and 2023 have had record low minimum extent, four out of the five highest minimums have occurred since 2008.”

The significance of a decline in Antarctic sea ice, if it begins to emerge more clearly, would be different in some ways than for the Arctic.

At the top of Earth, Arctic sea ice is a main player in a crucial feedback that determines how much, and how rapidly, the Earth warms. Every time an area of ice melts and gets swapped out for an area of ocean, the Arctic absorbs more solar heat (because bright ice reflects much more radiation than dark ocean does). This unleashes a feedback in which warming shrinks sea ice, which enhances warming - one that is already afoot.

In the Antarctic, loss of sea ice also affects Earth’s reflectivity. But it has other, different potential consequences. One of them, Scambos said, could be exposing the great Antarctic ice shelves to more pounding by waves - which in turn, if those shelves have already been weakened by surface melting or warm ocean waters underneath, could further destabilize them.

Antarctic ice shelves are the seaward extension of the world’s largest army of glaciers, and provide a stabilizing function. If damaged or lost, glaciers will flow faster and sea levels will rise more rapidly.

Scientists at the National Snow and Ice Data Center said the steep recent drop in sea ice around Antarctica has driven research on its potential causes and “whether sea ice loss in the Southern Hemisphere is developing a significant downward trend.”

- - -

The Washington Post’s Naema Ahmed contributed to this report.