How to explain the unprecedented heat stroke in the polar regions?

Temperatures in Antarctica were up to 40°C above seasonal averages. © Mark Ralston, AP

How to explain the unprecedented heat stroke in the polar regions?

At the end of last week, temperatures broke all heat records in both Antarctica and the Arctic. Not far from the South Pole, they were up to 40°C above seasonal averages. Increases linked to the vagaries of “atmospheric rivers”.

At the end of last week, temperatures broke all heat records in both Antarctica and the Arctic. Not far from the South Pole, they were up to 40°C above seasonal averages. Increases linked to the vagaries of “atmospheric rivers”.
Temperatures up to 40°C above seasonal norms in Antarctica and between 20 and 30°C above normal in some places in the Arctic. The two polar regions simultaneously experienced an unprecedented heat wave around Friday, March 18. “Such a coincidence is very unusual”, recognizes Julienne Stroeve, polar climate specialist at University College London, contacted by France 24.

It was the soaring thermometer in Antarctica that first caught the attention of scientists. “The temperatures recorded, even on the Antarctic plateau [located at more than 2,000 meters above sea level on average], were absolutely absurd”, underlines Jonathan Wille, postdoctoral fellow and specialist in weather and climate in Antarctica at the Institute of environmental geosciences at the University of Grenoble Alpes, contacted by France 24.

At more than 3,000 m altitude, -11.5°C instead of -40°C

It was thus more than abnormally mild at Concordia station, which is more than 3,000 meters above sea level in eastern Antarctica. The temperature has, in fact, risen to -11.5°C whereas it is generally rather between – 40°C and – 50°C in this region at this time of the year.

“The topographic barrier formed by the elevation in eastern Antarctica means that the climate there is very stable and temperatures should never exceed -30 ° C”, explains to France 24 Martin Siegert, a glaciologist at the Imperial College in London who cannot believe the temperature readings taken in this part of the globe last week.

In 65 years of meteorological observations in this part near the South Pole – which is more than 4,000 km from Australia – such a heat peak had never occurred. But the thermometer remained below 0° C, which made it possible to avoid a melting of the ice “which would have been completely unprecedented”, notes Martin Siegert.

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On the other side of the globe, in the Arctic region, the thermometer has dangerously flirted with thawing temperatures even though “we are still at the end of the cold period”, underlines Martin Siegert. In some places, such as on the island of Hopen (north of Norway and south of the Svalbard archipelago), “a temperature of 3.9°C was recorded, which has never happened since. the beginning of the records in 1944”, said Ketil Isaksen, a Norwegian climatologist, on Twitter.

But the heat wave in the Arctic is “less unusual than that in Antarctica”, underlines Julienne Stroeve. This region of the world is the hardest hit by global warming – temperatures are rising three times faster than elsewhere on average – and extreme weather events are beginning to multiply.

The fact remains that “the magnitude of this heat peak is surprising,” said Martin Siegert. For him, the corollary could be an ice melting season that would start a little earlier than usual. In general, the thaw begins at the end of March and lasts until September in the Arctic region.

Hot air from Spain and New Zealand

If these historic records occurred at the same time in the two polar regions, “it’s a coincidence”, assures Julienne Stroeve. “There is almost no connection between the air movements that shape the weather in the Arctic and in Antarctica”, specifies Martin Siegert.

But in both cases, it is atmospheric rivers that are causing this sudden warming of the poles. These are air corridors which, like flying conveyor belts, transport large quantities of water vapor over long distances.

To explain the phenomenon in the Arctic region, it is necessary to go down “to the south-west of Spain and the north of Africa, from where the atmospheric river departed which transported all the humidity to the north and above all in the region of Siberia”, explains Jonathan Wille.

In Antarctica, the phenomenon was more complex. There was indeed an atmospheric river which originated “at the south-eastern end of Australia and in New Zealand”, notes the specialist from the University of Grenoble.

But that’s not all. On reaching the Antarctic coasts, this warmer air generated rain and, a little higher up, snow. Then, instead of dispersing and heading north again, this atmospheric current stayed put and even rushed ever further towards the South Pole. “It’s an atmospheric river that went faster, stayed longer over Antarctica and pushed further south than others” who reached this continent, summarizes Jonathan Wille.

A “weather oddity or a precursor event”?

“It would be tempting to put these anomalies on the account of global warming”, recognizes Martin Siegert. After all, one of the consequences of these human-induced changes is that extreme weather events – like heat spikes in the polar regions or hurricanes – are becoming more common.

But for now, it is still too early to attribute these temperature spikes to global warming. “The situation has returned to normal in the polar regions this week, and last week’s weather may remain an isolated phenomenon,” said Julienne Stroeve.

“This is the big question that will have to be answered: did we have to deal with a weather oddity or a precursor event [of the climate to come in these regions]?”, adds Jonathan Wille. The question is all the more important since “we were lucky this time in Antarctica”, considers Martin Siegert. If the atmospheric river had headed further west of the southern continent – where temperatures are already naturally milder in this season – the wave of hot air could have caused unprecedented melting of the ice. Which would be bad news for rising waters.




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