Both poles are being warmed by unusually hot air currents, but scientists think the extreme temperatures in Antarctica are a result of natural variability not climate change
Abnormally hot air has hit both of the world’s poles at once, while the extent of Arctic sea ice appears to have been historically low this winter.
Temperature records were broken in Antarctica as warm air swept unusually far into the heart of the continent. Concordia station, which is high above sea level and has an annual average temperature of -50°C, reached an all-time high of -12.2°C on 18 March, beating the -13.7°C record set in December 2016. Another research station, Vostok, also saw record high temperatures.
“The Antarctic [heat] is really extreme. I haven’t seen anything like that. Colleagues haven’t seen anything this extreme,” says Walt Meier at the US National Snow and Ice Data Center (NSIDC) in Boulder, Colorado.
A band of westerly winds around Antarctica usually isolates the continent from other weather systems. But in the past week, an “atmospheric river” of hot air, originating in the mid-latitudes, travelled down from Tasmania and South Australia, breaching those winds to travel far across the ice, says John Turner at the British Antarctic Survey.
Although such events aren’t unprecedented, the temperatures this time are very high. Turner says while it is undoubtedly an “extreme event”, he thinks the Antarctic heat looks like natural variability rather than climate change. Past research by Turner has found no discernible trend in extreme temperatures in Antarctica, where the hole in the ozone layer appears to have cancelled out the impact of global warming so far.
The recent highs won’t have any consequences such as impacts on landing strips for scientists stationed on the continent either, says Ted Scambos at the University of Colorado, Boulder, because most have already departed ahead of the Antarctic winter and those remaining are hunkered down with supplies.
The record temperatures come shortly after Antarctic sea ice declined to a record low minimum extent, at 1.92 million square kilometres on 25 February. “It was quite a lot lower than anything else in the 40-plus year record,” says Scambos.
However, he says Antarctic sea ice extent is highly variable from year to year and no downward trend has emerged yet because of climate change. The record sea ice low and recent temperatures are unconnected, he says, though he thinks if there was more ice this year, it may have blunted the impact of the warm air by drawing more moisture out of it.
Temperatures have also been unusually high in the Arctic recently, with some areas 30°C warmer than usual and the region as a whole 3.3°C hotter than the long-term average.
The cause of the heat is a pulse of warm, moist air being sent northwards from the North Atlantic, says Meier. Such pulses of heat in the Arctic have been seen a few times in recent years, most notably in January 2016 when temperatures were up to 8°C above average.
“So this is not unprecedented, but it’s certainly a strong event, and it’s something that was quite rare until recent years,” says Meier. There may be some surface melt at the North Pole, but the effect will be relatively small, he says.
The heat in the far north comes as Arctic sea ice has settled at its 10th lowest winter maximum on record, at just under 15 million square kilometres. Though the ranking hasn’t been officially confirmed yet, Meier says it is unlikely to change. “In light of the last 15 years, it’s not particularly extreme. [It is] extreme compared to the 1980s,” he says.
Unlike Antarctica, the Arctic has seen two very clear signals of climate change: the long-term decline of sea ice and temperatures rising three times faster than global increases.
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