The severe decline in sea ice around Antarctica has been making headlines for months. In February 2023, the peak of the summer thaw, sea ice was lower than ever across Antarctica. But even when it became colder again, the ice surface did not return to normal. On the contrary, the anomaly has now reached such proportions that statistically it only occurs once every million years under normal conditions.
But conditions in Antarctica are no longer normal. That’s the conclusion reached by Australian Antarctic researchers Ariane Buric and Edward W. Doddridge in a recent publication. Scientists also write in the specialized journal “Nature, Earth and Environment Communications”.The reduced sea ice cover indicates that Antarctica has transitioned to a fundamentally new state.
Antarctic sea ice has behaved unpredictably for a long time. Until about 2016, its area had actually increased somewhat, contrary to the warming trend – and climate model predictions. However, since then, ice surfaces have shown a radical downward trend. There are currently no satisfactory explanations for the increasing trend until 2016 or the significant decline since then.
Burish and Doddridge support one of the existing hypotheses in their work. Accordingly, the previously identified atmospheric influences become less important; Instead, warm ocean waters now determine the southern direction of sea ice. The amount of surface area covered by Antarctic sea ice each year has always fluctuated greatly and has so far depended mainly on the state of the atmosphere and the strength of the winds around Antarctica. Stronger westerly winds and higher pressure differences in mid-latitudes caused sea ice to expand. Weaker westerly winds, strong oscillations of the westerly wind belt to the north and south, and strong low pressure areas bringing warm air from the north caused the ice to retreat.
This no longer applies now. Last year and this year, the westerly winds around Antarctica were very strong. However, both years had record lows. A new factor identified by the two experts in their study may be responsible for this: unusually warm seawater at depths of about 100 metres. This trend toward warmer subsurface waters began around 2015, Burish and Doddridge said – A year before Antarctica’s sea ice began to decline significantly. This layer of water had previously been unusually cold for ten years, and sea ice had reached unusually large proportions.
Warmer sea water, in turn, is likely a direct result of global warming. Most of the additional heat from greenhouse gases has ended up in the oceans, and the consequences are slowly beginning to appear. Globally, sea surface temperatures are much higher than normal, and a recent study shows that ocean heatwaves, previously felt primarily at the surface, are more intense at great depths. The new state of Antarctic sea ice that the study posits is one in which climate change has become the determining factor in sea ice expansion. If this is true, this year’s sea ice minimum will not be the lowest point, but just the beginning.
“Alcohol buff. Troublemaker. Introvert. Student. Social media lover. Web ninja. Bacon fan. Reader.”