Extreme “heat”, about +104°F above normal, fell on Antarctica as the cold continent plunged into the darkness of the southern winter in mid-March. This humid heat was accompanied by 4 in of snowfall, the equivalent of the year’s total precipitation.
“Unthinkable, an event that we don’t want to see at this time of year,” exclaims Vincent Favier, from the CNRS laboratory of glaciology and geophysics of the environment in Grenoble. On the far side of the Earth, the thermometer at the Franco-Italian Concordia station (perched at an altitude of 10,826 ft, in Dome C, on the Antarctic ice cap) showed 11°F on 18 March.
A record “heat” of 95 to 104 °F above the seasonal normal, at a time when the cold continent sinks into the darkness of the endless southern winter. “Absolute record all months combined, beating the 7,34 °F of December 17, 2016,” recalled Etienne Kapikian, from Meteo France. On the coast of Adelie Land, the base of Dumont-d’Urville has shown an exceptional mildness of +41 °F.
Repeated extreme events
In Concordia, the average annual temperature is -67°F. The temperature oscillates between -22 and -58°F in summer, and the mercury can plunge to -112°F in winter. “We think that Antarctica, a very cold and dry continent, is relatively spared from global warming, but extreme events have been recurring for the past seven years,” says Vincent Favier.
This incredible hot spell over Antarctica is due to an atmospheric river. “This is an intense and very rapid transport of a mass of moist air, like a bed in the atmosphere, when the air situation is blocked,” explains Gerhard Krinner, a polar climate specialist at the CNRS. These rivers occur in other seasons and at other latitudes. A similar phenomenon occurred in the Arctic at the same time, causing an exceptional mildness of + 39 °F in Svalbard (Norway) between mainland Norway and the North Pole.
The surprise in Antarctica comes from the power of the event at this time of year. “When an atmospheric river occurs during the brief summer period on the western side of the continent, it accelerates the melting process at work,” continues Gerhard Krinner.
But at the end of March, the cold weather quickly returned to the ice continent. This brief record of wet heat was accompanied by a record of precipitation. A 10 cm layer of snow piled up on the continent. That’s the equivalent of the year’s total precipitation,” says Vincent Favier, “Usually it snows very little. And that’s the positive part of the event. “The snow has a role of delaying the rise in sea level, he explains, it is the only way to compensate, in part, the loss of ice due to melting.