47.9 ° C near Vancouver, 46.1 ° C in Portland… What is the “heat dome” affecting Canada and the United States?



47.9 ° C near Vancouver, 41.6 ° C in Seattle or 46.1 ° C in Portland… In recent days, a “dome of heat” has descended on Canada and the United States. If the phenomenon is not exceptional, its intensity is.

Western Canada and the United States, where the climate is usually temperate at this time of year, suffocates due to an unprecedented heat wave, which has even claimed the lives of hundreds of people in the region of Vancouver. What is a “heat dome”? Can such a phenomenon occur in France? Is it linked to global warming? 20 minutes make the point.

What is a “heat dome”?

A “heat dome” is a mass of very hot air that is stagnant. This phenomenon results “from a situation of atmospheric blockage”, explained Aurélien Ribes, researcher at the National Meteorological Research Center (CNRM), during a Meteo France press conference on the subject, this Wednesday afternoon.

In addition to this mass of hot air, rising from Mexico to western Canada and the United States, “anticyclonic conditions favor what is called subsidence, that is to say that a wind blowing vertically, like a column, came to compress the air mass, increasing its temperature ”. In other words, this atmospheric blockage situation forms a bubble of hot air, on the surface and in altitude, which stagnates and heats up, allowing to reach record temperatures.

Is this phenomenon exceptional?

If the “heat dome” phenomenon has been known to specialists for a long time and can occur anywhere in the world, it is its intensity and stability which are exceptional in this case. In Portland (Oregon) and Seattle (Washington State), known for their temperate and humid climates, the temperature reached record levels unmatched since the archives began in 1940. It was 46.1 ° C at the airport in Portland on Monday and 41.6 ° C compared to Seattle, according to US Meteorological Service (NWS) readings.

On Tuesday, mercury easily crossed 30 degrees in Vancouver, well above the normal of 21 this season, while inland the temperature was unbearable. Lytton, 250 km northeast of Vancouver, set a new all-time Canadian heat record, with 49.5 degrees Celsius, according to the Canadian Weather Service. The mercury also reached 42 degrees in the ski resort of Whistler, north of Vancouver, according to this service. “It is the stability of this phenomenon that increases its intensity. The temperature records were broken by around 4-5 degrees, that’s unprecedented, ”added Samuel Morin, director of the National Meteorological Research Center.

How long will this episode last?

According to Météo France forecasts, the “heat dome” should persist until the end of the week. “We should have westerly winds that will move this air mass eastward at the end of the week,” explained Samuel Morin, who estimates that the phenomenon will gradually diminish within a week. In the meantime, with the air mass still stuck, new temperature records could be broken in Canada or the United States in the coming days.

Can we have a similar episode in France?

According to the two specialists, this phenomenon took place in Europe, and particularly in France, during the 2003 heat wave. “In terms of length, intensity and stability, it is comparable to the 2003 heat wave in France” , warned Aurélien Ribes, who believes that this phenomenon could recur in the future.

But the temperatures being higher than in 2003, a “heat dome” could significantly increase the thermometer in France. “To beat a record of 4 degrees in the south of France, that would bring us close to 50 degrees. It is quite possible, but we cannot know if it will happen in 5, 10, 15 or 50 years, ”warned Samuel Morin. In France, the last temperature record recorded was 46 degrees in Hérault, in June 2019.

Is this phenomenon linked to global warming?

If global warming is not the very cause of this “heat dome”, it clearly contributes to its intensity, according to the two researchers: “Studies show that heat waves are influenced by global warming, with high temperatures. higher and more frequent heat waves ”. “For every additional degree of global warming, we increase the frequency and intensity of these temperature events,” they cautioned.

Climate change is causing record temperatures set to become more frequent. Globally, the decade that ended in 2019 was the hottest on record and the hottest five years in the past five years. An opinion visibly shared by US President Joe Biden: “Did anyone imagine that one day looking at the news, they would say it is over 46 degrees in Portland, Oregon?” 46 degrees, but don’t worry, there is no global warming. There is no such thing. It is the fruit of our imagination, ”he replied to climate skeptics.





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