It’s a remarkable summer that Antarctica has just come through. In February, the sea ice around the continent shrank to 1.9 million square kilometers, the smallest area since 1978, when satellite measurements began. And in March, various temperature records were broken in East Antarctica. At the Russian research station Vostok, minus 17.7 degrees Celsius were measured, more than 30 degrees above the usual temperatures at this time of year.
One Study in the journal Advances in Atmospheric Sciences now gets to the bottom of the causes of one of those extremes, the record low in summer sea ice extent hit on February 25. It is important to know that, unlike in the Arctic, where a negative trend has been observed for decades, the average area covered by ice around Antarctica has so far increased slightly, by around one percent per decade. However, the sea ice is subject to strong fluctuations over the course of the year. Roughly speaking, it melts from September to February, and then grows again the rest of the year.
Maximum annual extent of Antarctic sea ice in September 2021. The yellow line indicates the mean from 1981 to 2010.
(Photo: NSIDC/NOAA)
According to the researchers led by Jinfei Wang from the Sun Yat-sen University in Zhuhai, China, this year’s melt clearly stands out. The retreat of the sea ice probably began at the beginning of September and thus earlier than usual in the year and then proceeded a lot faster. The losses were particularly massive in the western Amundsen Sea and the eastern Ross Sea, where there was finally no sea ice at all on February 25.
Absolute low of Antarctic sea ice in February 2022. The yellow line shows the long-term mean.
(Photo: NSIDC/NOAA)
The climatologists attribute this development, among other things, to record sea temperatures last year in the southern hemisphere. In the Amundsen Sea in particular, the sea ice was thinner as a result and melted correspondingly faster. This in turn leads to a negative feedback: the darker sea surface absorbs more heat than the lighter ice, causing water temperatures to rise and melting to accelerate – a kind of vicious circle.
In addition, the low extent of sea ice coincided with the La Niña climate phenomenon and a positive state of the Antarctic Oscillation (AAO). The latter refers to a belt of strong westerly winds around Antarctica. La Niña influences wind and water temperatures in the Pacific. And both phenomena affect the air masses around Antarctica, which may partly explain this year’s strong melt. Therefore, the US Atmosphere Agency NOAA speaks of the fact that the low value from early February “probably can be attributed to a natural fluctuation rather than a long-term trend”.
in one Commentary in the specialist magazine Nature Reviews Earth & Environment However, Marilyn Raphael and Mark Handcock of the University of California Los Angeles point out that summer sea ice extent around Antarctica had already reached a record low in 2017. The fluctuations five years ago and this year are unprecedented. “They could signal a change in the Antarctic sea-ice system in response to human-caused warming,” the climate researchers write. This does not necessarily mean that the sea ice will retreat more and more from now on. Rather, significant fluctuations in one direction or the other could increase. A record extent of sea ice was only measured in 2014 during the Antarctic winter. “These record fluctuations,” write Raphael and Handcock, “point to a new period of extremes.”