record. The small town of Lytton in British Columbia, located in a basin at the foot of the Rocky Mountains, recorded a temperature of 49.6 °C on June 29, 2021. This is about 5 °C higher than the previous Canadian record of 45 °C, recorded in 1937. According to Meteo-France, this is also an absolute record for a station located above 50 degrees north latitude. This new mark is of course due to weather, but Lytton’s topography on a very dry valley floor also explains this extraordinary temperature. Values observed elsewhere in British Columbia are 40 °C, 20 °C above the mean seasonal temperature, and above the symbolic threshold for North Americans of 100 °F (38 °C). More than 500 people have died in Canada, 20 in the United States. The loss of material goods and damage to flora and fauna have not yet been estimated. Lytton was devastated by fire on 30 June. The village is more or less situated at the height of Lille. Météo-France thus calculated that a similar situation would cause a peak of 44 °C in the capital of Hauts-de-France.
A “heat dome” shaped like the Greek letter omega . exposes
This new mark is due to the blockage of a strong high pressure system over western Canada and the northwestern United States. “A hot air bubble remained blocked in this area, which was diverting the sediments to the north, Aurelian Ribes, a researcher at the National Center for Meteorological Research (CNRM), which relies on Meteo-France, explains. The temperature above was unusually high at the surface”.
This “heat dome” has the shape of the Greek letter omega . It is a combination of two different events. The heat comes from the rise in southern regions such as Mexico but it is the blockage of atmospheric circulation at high altitudes that amplifies and accelerates the phenomenon over time, with the higher warm layers of the atmosphere raising the temperature of the layers. Bass by compression. In this way the record climbed from Sunday to Tuesday. In Lytton, the temperature rose from 46.6 °C on Sunday 27 June to 49.6 °C on Tuesday, 29 June.
More and more intense heat waves by the end of the century
2003. If the event calls for its intensity, it is not exceptional. “This weather condition is repeated regularly throughout the Northern Hemisphere”. Specifies Aurelian Ribs. Thus the 2003 heatwave in France was caused by the same event of an anticyclone blocking, which lasted for more than ten days, preventing Atlantic sediments from entering the continent. Comparisons with the 2019 heat waves shed light on the conditions needed for the situation to become extraordinary. In 2019, on two occasions, an updraft caused by a depression in the Atlantic Ocean brought scorching heat from the Sahara to Europe and France. But the weather conditions did not block it and after three days of intense temperatures, the freshness was returned by the Atlantic. “In order for the 2003 heat wave to occur in France or Canada this year, it is necessary to connect these two episodes “, Aurelian Ribs says.
Now the question immediately arises: is climate change responsible for these heat records? “The sequence of atmospheric events is not directly affected by the increase in temperature, on the other hand its intensity may well be”, Aurelian reassures Ribs. The twenty or so climate models that operate around the world (including two in France, the Mateo-France and the Pierre-Simon-Laplace Institute) predict that by the end of the century these episodes of heat waves will increase in intensity and frequency. . According to Meteo-France, if we compare the temperature recorded at the end of June in Canada with the historical average of the region recorded since the XIX.I century, we go completely beyond the limits and the delay before the return of such an episode, without human intervention, would be several thousand years. Researchers gathered at the World Weather Attribution Program will now run their algorithms to try to specify the share of responsibility for human greenhouse gas emissions. This approach now applies to every extreme event. For the Canadian heatwave, the results should drop in a few weeks.