British Antarctic Survey Scientist Dr. Louise Sime On Antarctic Tipping Points, 2023's 5-Sigma Sea Ice Loss
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When and why did scientists become concerned about tipping points in Antarctica?
It has become a major talking point in the past five to 10 years, though the possibility has been known for much longer. Up until 2016, the sea ice in Antarctica seemed relatively stable. Then everything started to change. At first, the decline was mostly in line with climate models. But suddenly, in 2023, there was an enormous drop. About 2.5 million sq km of Antarctic sea ice went missing relative to the average before 2023. The anomaly was of such a magnitude that it’s quite hard for scientists to know what to make of it. It has been described as a five sigma event.
What is a five sigma event?
Something that may only happen once in 10,000 years, or higher, possibly once in several million years. It was so far outside of expectations that the statistics became really hard to handle. It was very startling.
What was the cause?
It’s still not absolutely clear but it is probably associated with global warming and circulation changes in the oceans. In that year, there was an enormous atmospheric river event over East Antarctica, which was also a five sigma event. This coincided with the biggest heatwave on record, where we had a temperature anomaly in excess of 40C.
What effect did this have on the region?
When that much sea ice is lost, there are substantial knock-on impacts. While the ocean is covered by ice, the temperature above the surface can easily be -20C, -30C. But as soon as the water is exposed, then the surface temperature cannot go below -2C. And once the surface is opened to the atmosphere, then you start to get evaporation of water vapour. That means a sudden and substantial change of weather around Antarctica.
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https://www.theguardian.com/environment/ng-interactive/2025/jun/27/tipping-points-antarctica-arctic-sea-ice-polar-scientist