Now that the year 2024 is behind us, it is time for climate assessments.
Globally, the temperature has reached a new high. In the coming days, several climatological institutes will announce their assessment of global warming, calculated from all weather stations on Earth. We already know that the increase will be around 1.5°C compared to pre-industrial temperatures.
And in Montreal? According to data from Environment Canada, the year 2024 will have been 3.9°C warmer than the historical average for the metropolis.
“Unfortunately, this is not a surprise,” says Philippe Lucas-Picher, a professor in the Department of Earth and Atmospheric Sciences at the University of Quebec in Montreal.
Data comes from the Montreal McGill station (1872-1993) and the McTavish station (1994-2024). It was Florian Knoll, an intern of Mr. Lucas-Picher, who provided them to the Duty.
The average warming in Montreal (+3.9°C) is therefore 2.6 times higher than that of the planet as a whole (+1.5°C). Different phenomena explain this major difference.
First, in general, the atmosphere warms faster over continents than over oceans. This is true in Montreal, but also everywhere on dry land. The reason: the oceans absorb heat. Evaporation from their surface also dissipates a lot of energy.
Then, we note an effect of amplification of warming at the poles. Because the Arctic sea ice, as it melts, gives way to a black sea. This region then becomes less white and reflects less and less solar radiation towards space. Montreal is feeling its influence from a distance, and is also seeing its own snow cover diminishing.
“The warming in Canada is approximately double that observed on a global scale,” recalls Damon Matthews, climatologist at Concordia University.
Finally, an “urban heat island” effect also comes into play. In Montreal, as in other large cities, buildings and roads absorb solar radiation rather than reflecting it. This raises the temperature. Added to this is the heat released by automobiles and the heating of buildings.
Record year globally
The record increase observed in Montreal is part of exceptional global warming since 2023. This warming (+1.5°C) exceeds the trend over several years, which stands at +1.3°C.
This burst stems in part from the last episode of El Niño (June 2023 to May 2024), which reduces the absorption of heat by the Pacific Ocean.
According to climatologists, it also comes from a reduction in the quantity of aerosols in the air, in particular thanks to China’s anti-pollution efforts and a new rule from the International Maritime Organization which lowers sulfur emissions from ships. . Aerosols are harmful to respiratory health, but stimulate the creation of clouds that reflect the Sun’s rays.
MM. Lucas-Picher and Matthews are not certain, however, that these two effects — El Niño and aerosols — have a significant impact on the temperature in Montreal.
An extremely mild winter
Let’s return to Montreal. Data collected by UQAM researchers show that the winter months of 2024 were particularly mild.
In February 2024, the mercury was 6.9°C warmer than the turn-of-the-last-century average for February. In January and March, the anomaly was around +5°C. Even when compared to recent times (1991-2020), winter 2024 is well above average (around +3°C).
That said, the year 2024 — the hottest ever recorded in Montreal — was not distinguished by heat extremes that left an impression, notes Mr. Lucas-Picher. “Except maybe Halloween night, which definitely stood out. »
The record warming in the metropolis results rather from an “accumulation of anomalies”, occurring from one end of the year to the other, which impose a new, warmer climatic reality.
“It’s difficult now to count on a frozen outdoor rink in winter… The same goes for skiing: when it’s cold, you have to rush there. This is our reality today, and it will continue to get warmer,” says the scientist wistfully.
