Arctic satellite view - HO / NASA / AMSRE-E / AFP

  • Mercury soared to 38 ° C in Verkhoyansk on Saturday. A record for this small town in eastern Siberia, best known for its cold temperature records.
  • This heat wave is explained by the installation in this region "of a dome of very powerful highs, with a lot of hot air at altitude and in the low layers", explains François Jobard, forecaster at Météo-France.
  • But this meteorological phenomenon is part of a disturbing underlying trend. That of global warming more and more visible beyond the polar circle, and which has already resulted in very mild temperatures since the beginning of the year.

Verkhoyansk, a small town of 1,000 inhabitants in eastern Siberia, slightly above the Arctic Circle and 4,600 km northeast of Moscow, is usually better known for its extremely low temperatures in winter. "It is one of the coldest stations in the northern hemisphere," said François Jobard, a forecaster at Météo-France. Until - 67.8 ° C in February 1892. "A record for the northern hemisphere," says the meteorologist. And down to - 57 ° C last January.

On Saturday, Verkhoyansk distinguished itself in a completely different register, with a mercury which climbed to 38 ° C. Enough to win some new lines in the Guinness World Records. The highest temperature ever recorded above the polar circle. That, also, of the greatest amplitude between its coldest temperature ever recorded - the - 67.8 ° C of February 1892 - and the hottest - that of last Saturday. “Between the two, there is a difference of 105.8 ° C, continues François Jobard. It is unprecedented on a global scale. "

A sprayed record of 4 ° C, "it's considerable"

This differential is not so surprising for Verkhoyansk and its hypercontinental climate, marked by very cold winters and relatively hot summers. "The average minimum temperature in January, the coldest month of the year, is - 48 ° C, recalls François Jobard. And in summer, the average temperature is close to 20 ° C. Typically, at the end of June, in Verkhoyansk, we are around 21 ° C. "

However, there is a chasm between the seasonal average and the temperatures recorded last Saturday. It's rare, but it's not the first time that mercury has climbed so high in this corner of Siberia. "The previous record was 37.3 ° C, a temperature reached on July 25, 1988", continues the meteorologist. A slightly more normal period for such a record, "the seasonal peak is rather reached in July in this region".

This is also what surprises in the 38 ° C recorded on Saturday: this high temperature is reached early in the year. The previous record for a month in June in Verkhoyansk was 34 ° C. "Having sprayed 4 ° C on Saturday is considerable," comments François Jobard.

"A dome of hot air" blocked on the region

How to explain it? First by a meteorological phenomenon. For several days and certainly for those to come again, a zone of high pressures has settled on this part of Siberia to keep moving. François Jobard speaks of a "hot air dome" made up of "very powerful highs, with a lot of hot air at altitude and in the lower layers".

This situation corresponds to an anticyclone typical of heat waves that we observe more frequently at our latitudes. Eastern Siberia is not the only region to be crossed by a dome of hot air at the moment. François Jobard observes two others on a global scale. "One is currently in Scandinavia and Europe and should result in very hot weather this week, especially in France," he explains. Another stationed in northern Canada, again with high temperatures noted. "In addition to these heat waves, the Météo-France forecaster notes" much cooler poles, linked to depressions ". “We currently find it on another part of Siberia, western this time, but also in Alaska or in the middle of the Atlantic. "

So much for the economic phenomenon. François Jobard adds a background of global warming which is not without aggravating the situation. “There have always been blocking anticyclones of this type; what changes today is the mass of air that they carry, which is hotter than before. "

After 6 exceptionally hot winter months & stock of snow melted very early, the Siberian heat wave now starts hundreds of fires. These images are reminiscent of those of Australia in 2019. Tragic ... but unfortunately consistent with climate projections🙄!

- Christophe Cassou (@ cassouman40) June 22, 2020

Already six months particularly sweet

That's the problem, then, for Gerhard Krinner. The research director at the Laboratory of Glaciology and Environmental Geophysics in Grenoble (CNRS) sees in these many records of heat fallen in recent years, almost everywhere in the world, "a clear sign of global warming". "This dome of hot air in Siberia is not a completely isolated meteorological phenomenon," he says. It follows a six-month period during which temperatures were excessively mild in the region. "The winter 2019-2020 has been the warmest in Siberia since the surveys began 130 years ago, with average temperatures up to 6 ° C above seasonal norms," ​​recalled in early June 'AFP Marina Makarova, chief meteorologist at Guidrometsentr, the Russian weather agency. "Spring also came much earlier, in April, with temperatures easily (sometimes) exceeding 30 ° C," she continued.

Worried? “In any case, consistent with the models of global warming described by researchers for forty years, retorts Gerhard Krinner. Not only does the likelihood of such extreme events recurring increase with global warming, but we know the Arctic is particularly exposed, he explains. In these high northern latitudes, global warming is twice as great as the global average ”. Several mechanisms explain this, including that of feedback from the albedo. "In this region, there is a lot of snow, white therefore, which has the effect of reflecting the heat," explains Gerhard Krinner. As temperatures rise, it tends to melt and gives way to darker areas, be it the ocean or vegetation on the mainland bordering the Arctic. These darker areas intercept solar radiation more, and thus heat up more easily. "

Forest fires that multiply in Siberia

This underlying trend, which is worsened by cyclical weather phenomena, is not without consequences in this region of the globe. One of them is the spread of forest fires. In total, from January to mid-May, the flames ravaged 4.8 million hectares in Siberia, including 1.1 million boreal forests, according to a study published in early June by the Russian antenna of the NGO Greenpeace.

Gerhard Krinner adds peat fires in the Arctic region. "In the north of Siberia, beyond the forest line, you have the tundra, a vast area of ​​more level vegetation," he explains. In particular, there are a lot of peat bogs, very dry organic matter that can burn slowly even below the surface. That is to say covered with snow or vegetation ”. When the snow and ice gradually disappear in the spring, these fires may resume.

Farther north, the fear of "zombie fires"

Researchers at Copernicus, the European atmospheric monitoring service, call these tundra fires “zombie fires” and make them one of the serious fears looming over the Arctic this summer again. On May 27, they were worried about temperature anomalies in the Arctic regions, spotted during satellite observations, which could be explained by the reactivation of fires which would have subsisted under the surface since the unprecedented fires of summer 2019. A hypothesis that remains to be verified in the field. If confirmed, then the fear would be to have another dramatic summer in the region.


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