What’s causing Antarctica’s deep-winter heatwave, what could be its fallout?

While even these elevated temperatures would be difficult to imagine for most people, they are alarmingly high for the permanently frozen continent at the bottom of the world. What is happening in Antarctica?

Reasons for heatwave

Scientists believe that the higher temperatures are mainly a consequence of the weakening of the polar vortex, the band of cold air and low pressure systems that spins around the poles of the Earth in the stratosphere.

The vortex usually remains strong and stable during winter in the southern hemisphere — keeping cold air trapped over Antarctica and not letting hot air come in — but it has been disturbed this year by large-scale atmospheric waves (periodic disturbances in the fields of atmospheric variables).

Due to this, the vortex released trapped cold air, and opened the door for warmer air to enter the region. As this warmer air travelled downwards from the upper atmosphere, it caused an increase in temperatures.

A weakened southern hemisphere vortex is a rare event that is only expected to occur once every two decades on average, Thomas Bracegirdle, the deputy science leader of the British Antarctic Survey’s Atmosphere, Ice and Climate team, told CNN in an interview. “This is a very unusual event, from that perspective,” Bracegirdle said.

Several other factors — including the reduction of the extent of the Antarctic sea ice — could also be at play.

In June, the extent of Antarctic sea ice was the second-lowest ever for that time of year — a little more than the extent recorded in June 2023, the lowest ever. Sea ice plays a crucial role in keeping temperatures down in the polar regions, as its bright, white surface reflects more sunlight (solar energy) back to space than liquid water.

Sea ice also ensures that the air remains cool by acting as a barrier between the cold air and the relatively warmer water below.

Edward Blanchard, an atmospheric scientist at the University of Washington, told The Washington Post: “It is likely that having less sea ice and a warmer Southern Ocean around the Antarctic continent loads the dice for warmer winter weather over Antarctica… From this perspective, it might be a bit less surprising to see large heat waves in Antarctica this year”.

Global warming has hit Antarctica harder than elsewhere on the planet. According to a 2023 study published in the journal Nature Climate Change, the continent is likely warming at a rate of 0.22 degrees Celsius to 0.32 degrees Celsius per decade — almost twice as fast as the rest of the world. The Intergovernmental Panel on Climate Change (IPCC), the United Nations body that advances scientific knowledge about climate change, has estimated that the Earth as a whole is warming at the rate of 0.14-0.18 degrees Celsius per decade.

The possible fallouts

Antarctica’s hot winter will likely lead to further losses of the Antarctic Ice Sheet (the world’s other major ice sheet is the Greenland Ice Sheet) that can potentially raise global sea levels by hundreds of feet. Antarctica has already lost 280% more ice mass in the 2000s and 2010s than it lost in the 1980s and 1990s, according to a 2019 study published in the journal PNAS.

In March 2022, when the continent witnessed its largest heatwave, and temperatures in East Antarctica soared to 39 degrees Celsius above normal, a portion of the ice sheet the size of Rome collapsed.

The Antarctic Ice Sheet, a glacier covering 98% of the Antarctic continent, holds more than 60% of the world’s total freshwater. If entirely melted, it can submerge coastal cities and reshape the world’s map. A sea level rise of only a few feet will displace the roughly 230 million people who live within about 3 feet of the high tide line today, according to a report by the environmental organisation Antarctic and Southern Ocean Coalition.

Rising temperatures will also impact the global ocean circulation system, which regulates climate by storing and transporting heat, carbon, nutrients, and freshwater around the world. A 2023 study published in the journal Nature showed that the melting ice in Antarctica is slowing down this circulation. The freshwater from melting ice reduces the salinity and density of the surface water and diminishes the downward flow to the ocean’s bottom, the analysis said.

A slower global ocean circulation system will lead to oceans absorbing less heat and CO2, intensify global warming, and increase the frequency and intensity of extreme weather events like floods and droughts.