Late last week, temperatures broke all records in both Antarctica and the Arctic, with temperatures up to 40°C above the seasonal average not far from the South Pole. According to experts, these high-levels could be linked to the variations of 'atmospheric rivers', as the role of climate change still has to be measured.
The world’s two polar regions simultaneously experienced unprecedented heat waves on Friday, March 18: temperatures up to 40°C above seasonal norms in Antarctica, and between 20°C and 30°C above normal in some places in the Arctic.
"Such a coincidence is very unusual," Julienne Stroeve, a polar climate specialist at University College London, told FRANCE 24.
It was the soaring temperatures in Antarctica that first caught the scientists' attention. "The temperatures recorded, even on the Antarctic plateau [located at over 2,000 metres of altitude], were absolutely absurd," Jonathan Wille, a postdoctoral researcher and specialist in Antarctic weather and climate at the Institute of Environmental Geosciences at the University of Grenoble Alpes, told FRANCE 24.
At over 3,000 metres high, -11.5°C instead of -40°C
It was more than unusually mild at the Concordia station, located at over 3,000 metres of altitude, in East Antarctica: the thermometer rose up to -11.5°C, instead of keeping between -40°C and -50°C, the region’s average temperature at this time of year.
"The topographical barrier formed by the difference of altitude in East Antarctica means that the climate is very stable there and temperatures usually never exceed -30°C," Martin Siegert, a glaciologist at Imperial College London, told FRANCE 24.
In 65 years of meteorological observations in this part of the world, near the South Pole, which is more than 4,000 kilometres away from Australia, such a heat spike had never been recorded. The thermometer remained nevertheless well below 0°C. A positive temperature would have caused a "completely unprecedented" ice melt, Siegert added.
On the other side of the globe, in the Northern Arctic region, the thermometer flirted dangerously with thawing temperatures even though "we are still at the end of the cold season", Siegert insisted. In some places, such as the Hopen Island (in northern Norway and the southern Svalbard archipelago), "a temperature of 3.9°C was recorded, what had never happened since records began in 1944", Ketil Isaksen, a Norwegian climatologist, wrote on Twitter.
But a heatwave in the Arctic is "less unusual than one in Antarctica", Julienne Stroeve explained. The Northern polar region is the world’s hardest hit by climate change. Temperatures there are rising three times faster than elsewhere on average, and extreme weather events are beginning to multiply.
Nevertheless, "the magnitude of this heat spike is surprising", Martin Siegert noted. He believes that it could lead to a slightly earlier-than-usual start to the ice melt season, whereas the Arctic’s thaw usually starts at the very end of March and lasts until September.
Warm breezes from Spain and New Zealand
Even though these historical records occurred at the same time in both polar regions, "it's a coincidence", Julienne Stroeves said. "There is almost no connection between the air movements that shape the weather in the Arctic and the ones that shape the Antarctic’s," Siegert explained.
But in both cases, 'atmospheric rivers' are responsible for the sudden warming of the poles. The phenomenon consists of air corridors transporting large quantities of steam over long distances, like a flying conveyor belt.
To explain the phenomenon in the Arctic region, we have to go down "to south-western Spain and northern Africa, where the atmospheric river that carried all the moisture northwards, and especially to the Siberian region, came from", Jonathan Wille explained.
In Antarctica, it is a more complex event: there was indeed an atmospheric river that originated "at the south-eastern end of Australia and in New Zealand", the specialist from the University of Grenoble noted, but that's not all of it.
When it reached the coast of Antarctica, this warmer air generated rain, then snow, a little further higher. Then, instead of dispersing and moving northwards as usual, this atmospheric current stayed put and even rushed further towards the South Pole. "It's an atmospheric river that went faster, stayed longer over Antarctica and pushed further south than others" that have reached the continent, Wille summed up.
'Weather quirk or unprecedented event'?
"It would be tempting to blame these anomalies on global warming," Martin Siegert admitted. After all, one of the consequences of these human-induced changes is that extreme weather events - such as heat spikes in polar regions, or hurricanes - are becoming more common.
But for now, it is still too early to point to climate change as the main culprit for the temperature spikes, the experts insisted. "The situation has returned to normal in the polar regions this week, and it is possible that last week's weather was an isolated phenomenon," Julienne Stroeve nuanced.
"That's the big question we need to answer: was it a weather quirk or a unpredented event" pointing to the future climate in these regions, Wille said. The question is all the more important because "we were lucky this time in Antarctica", Siegert added. If the atmospheric river had been directed further west of the southern continent - where temperatures are already naturally milder this time of year - the warm air wave could have led to unprecedented ice melt, he explained.
Given the current rate of rising sea levels, such melt would only add to the chorus of bad climate news.
This story was translated from the original in French by Henrique VALADARES.
