Faced with the proliferation of extreme events like those that Quebec has been experiencing since the beginning of the summer, one might wonder whether these phenomena, which are exceptional today, risk becoming the norm in the future. THE Duty met with several experts to take stock of this subject.
What is meant by “extreme weather event”?
Forest fires, thunderstorms, high temperatures: already today, these phenomena are quite common in summer. But to qualify as extreme, they must meet certain criteria.
For example, a heat wave is particularly worrisome when it exceeds 31°C to 33°C for more than three days in a row, with nighttime lows of 16°C to 20°C or higher. A violent thunderstorm is severe when the rains are very heavy (50 millimeters or more in less than an hour), when gusts exceed 90 km/h or when hailstones more than 2 centimeters in diameter fall, after Environment and Climate Change Canada.
Other phenomena, such as forest fires, can be qualified as exceptional when they burn very large areas, such as those experienced at the beginning of summer, but there is no threshold to strictly speaking.
Have we observed climate change in recent years?
In Quebec, since 1950, the average temperature has warmed by 1 to 3°C depending on the region, according to data from the Ouranos group, a consortium that models different possible climate scenarios in Quebec and Canada for the decades to come. .
This increase in average temperatures is already accompanied by a multiplication of certain extreme events. For forest fires, for example, there has been an increase in the number of fires and the area burned in Canada over the past 60 years or so, according to a study published in 2019 in the Canadian Journal of Forest Research.
But if we already see on a global scale an “upward trend in extreme precipitation”, this is however “less clear” in Quebec and Canada, underlines Nathan Gillett, researcher at Environment and Climate Change Canada.
As for thunderstorms and tornadoes, it is also “more complicated” to quantify, according to Angelica Alberti-Dufort, adaptation specialist at Ouranos. “Counting tornadoes is difficult because they often occur in remote areas,” she explains. A summary by the National Institute of Public Health (INSPQ) thus shows that, although Quebec experienced nearly 200 tornadoes between 1985 and 2018, there is no clear trend that emerges as to their frequency and their intensity.
What to expect for the years to come?
According to data from the Ouranos group, if greenhouse gas emissions continue to rise, the trends of recent years should continue with a rise in summer temperatures of 2 to 6°C by 2100.
Extreme episodes will also be more numerous. “In the Montreal region, for example, it is expected that by 2100, we will have 30 to 50 days more than today during which the temperature will exceed 30°C, specifies Angelica Alberti-Dufort. . We will certainly have summers with several heat waves, which will start earlier than before. As for forest fires, specialists predict that they will probably intensify in the years to come.
“We also expect there to be more extreme precipitation in the future,” according to the Ouranos specialist. These could certainly cause flooding in the city due to the saturation of the sewers, as in recent days in Montreal. On the other hand, with regard to spring floods, “there are a lot of uncertainties”, she specifies.
The researcher explains that, on the other hand, it is quite difficult to make reliable projections for thunderstorms and tornadoes, due to the lack of past data and the (very local) scale at which they can occur.
Are we likely to have more tornado or severe thunderstorm warnings in Montreal?
For a scale as local as a city, forecasts are more uncertain. “We have to look at these changes on a larger scale than Montreal,” underlines André Monette, meteorologist at MétéoMédia.
The meteorologist explains that the risk is predicted on the scale of a fairly large territory and that it is not possible to predict whether a storm or tornado alert will occur more often in Montreal in particular. Likewise, due to natural variability, it is possible for one summer to be cooler than another, even in 2050.
Can an extreme event be attributed to climate change?
“We must not make the mistake of saying that a particular event confirms climate change,” warns André Monette. For each exceptional meteorological episode, it is indeed necessary to carry out studies and advanced modeling to assess whether it is part of natural variations, or whether it is an extreme event induced by climate change.
This is why, before these studies could be made, the experts are cautious. “We say that a particular event is part of a more global trend,” explains Angelica Alberti-Dufort.
With Clara Descurninges