Massive wildfires in Canada helped keep the world cooler in 2023

2023 smashed the record for the hottest year, but it might have been even hotter. The entire northern hemisphere would have been nearly 1°C warmer on average during its summer without the cooling effect of smoke from massive wildfires in Canada, a climate model suggests. The smoke may also have led to the driest August in India on record.

“I think it’s really hard to comprehend how gigantic the fires were. It was insane,” says Iulian-Alin Rosu at the Technical University of Crete in Greece, who presented his team’s findings at a meeting of the European Geosciences Union in Vienna, Austria.

The emissions were around five or six times higher than those during any previously recorded wildfire season in Canada, estimates Rosu. The carbon dioxide from these fires is having an ongoing warming effect, but in 2023 this warming was outweighed by the cooling effect of smoke blocking sunlight.

To estimate how much cooling the smoke caused, Rosu and his colleagues ran a series of climate model simulations with and without the Canadian wildfire emissions. The results suggest that between May and September, the smoke caused local cooling of as much as 5.4°C (9.7°F) in small parts of Canada, and that the northern hemisphere as a whole was 0.9°C (1.6°F) cooler.

This may seem surprising given that parts of Canada saw record temperatures during that summer. But the heat records were mostly in western regions, says Rosu, whereas the smoke blew east and had the biggest cooling effect on that side of the country.

The impacts weren’t limited to Canada. In the model, the wildfire emissions led to changes in winds over Asia that weakened the monsoon and led to less rainfall in India – and that is what happened in reality.

“The precipitation anomaly that is seen in the data is really, really close to what we see in our model,” says Rosu. That is an indication that the model did a very good job, he says.

However, the cooling effect didn’t last long. “When I looked at the data for November and December, there really wasn’t much of any effect left,” says Rosu.

The record set in 2023 for hottest year didn’t last long either – 2024 turned out to be even hotter.