Barely a week after the massive heat wave that hit British Columbia in western Canada and the entire northwestern United States, 27 scientists from leading climate research organizations (including universities in British Columbia, Princeton University, Columbia, Cornell, Berkeley and Washington). in Canada, the Royal Meteorological Institute of the Netherlands, Oxford for the United Kingdom, Pierre-Simon Laplace Institute for France) publish on the program website “Attribution of world time” a “quick analysis” of the links between this extreme weather event and current climate change. Their conclusion is clear: such an episode would not have had this intensity without an increase in global temperatures of 1.2 ° C since the beginning of the industrial era.
Since June 27, the west coast of Canada and the northwestern United States have experienced extreme heat that the region has never experienced in vivid memory. A record 49.6 ° C was recorded on June 29 at the foot of the Rocky Mountains chain. This is almost 5 ° C higher than the previous Canadian record of 45 ° C recorded in 1937. It is also an all-time record for a station above 50 degrees north latitude, according to Weather France. Values observed elsewhere in British Columbia exceed 40 ° C, 20 degrees above average seasonal temperatures and well above the symbolic threshold for North Americans of 100 degrees Fahrenheit (38 ° C). This event is a consequence of the connection of two different phenomena. The heat coming from Mexico was blocked by a powerful high-pressure system, creating a hot air bubble located very high at altitude. A “heat dome” was created that diverted the depressions from the Pacific Ocean to the North Pole for several days.
An exceptional weather event due to its intensity
This series of meteorological events is not exceptional. Intensity is what examines researchers. They very quickly retrieved measurements from stations located between 45 and 52 degrees north latitude near the cities of Vancouver, Seattle and Portland. They compared these data with their numerical models to compare the climate as it is with 1.2 ° C added human activity since the beginning of the 19th century.e century and the climate of the past.
The test area and measuring station (the redder the point, the higher the temperature) were selected to conduct a study on attributing Canadian heat to climate change. Copyright World time attribution
The extreme temperatures recorded have been shown to be well above the average range recorded in previous centuries, making any comparison difficult. But researchers have come to the conclusion that without a recent rise in temperatures, such a heat wave would not be possible at these latitudes. According to the most realistic statistical estimates, such temperatures could occur only once in 1000 years in the climate of this early 21e century.
Fear of crossing the irreversible threshold
According to researchers, there are two possible causes of this event. The first, most convincing, is that this is an episode that has a very low probability of happening and that could be compared to a series of “bad luck” in a series of phases leading to this extreme heat. Worsened, however, by global warming. Another – worrying – is that interactions within the climate system cause us to cross irreversible thresholds by increasing the likelihood of such events beginning to be observed. Researchers recognize this: they must explore this second possibility in order to gain certainty.
According to this hypothesis, a heat wave of this magnitude would be 150 times rarer in a less hot climate by 1.2 ° C. In addition, the temperatures recorded in June 2021 would be 2 ° C lower at the beginning of the industrial era. And if we look to the future, a world with a rise of 2 ° C, in line with the limit it sets Paris Agreement, which could be achieved in 2040, such heat waves would return every five to ten years. France experienced a similar event in 2003. This exceptional heat wave could be repeated twice in a decade.