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Environment Canada scientists can now rapidly link heat waves to climate change

It helps people understand the effects of climate change, says Nathan Gillett, a research scientist at Environment and Climate Change Canada.
A motorist watches from a pullout on the Trans-Canada Highway as a wildfire burns on the side of a mountain in Lytton on July 1, 2021. Wildfire tore through the area during a heat dome, one day after the mercury hit a record 49.6 C. Climate scientists have said climate change made this heat event 150 times more likely. DARRYL DYCK, THE CANADIAN PRESS

Canadian scientists can now estimate how much human-induced climate change contributed to an extreme heat wave or flood within a week of the disaster.

B.C.-based atmospheric physicist Nathan Gillett, a research scientist at Environment and Climate Change Canada, said they have been working on event attribution — algorithms that allow researchers to calculate how much a heat wave was likely affected by climate change — for some time. But where it used to take months to create a report, now they can do it in days.

The rapid event attribution system analyzes past data and provides a percentage of how much climate change made the event more probable.

“We’re comparing how often, say, a heat wave as strong as the one we observed in B.C. occurs in the present climate with how often it occurred in the pre-industrial climate without human influence, and we use climate model simulations to do that,” Gillett said.

“So while we’re never going to be able to say this one particular event was caused by climate change, we can say the odds of this event were increased by climate change or the likelihood of this event was at least doubled by climate change, that sort of thing.”

Gillett said they’re running a pilot on the new system and will be analyzing the recent heat dome in central Canada that pushed temperatures into the high 30s C, with humidity levels in the 40s.

They’re also analyzing less extreme heat waves to test the system, but when they eventually make rapid analyses public, he said they will come up with criteria, such as how high the temperatures would need to be or the duration of a heat wave is to issue a report.

“I think it helps people understand the effects of climate change on them,” he said. “It’s also useful to policymakers who are planning climate change adaptation.”

A 2021 report found climate change made B.C.’s 2021 heat dome 150 times more likely. That report by the World Weather Attribution group concluded that even if the world meets greenhouse-gas reduction targets, this event could reoccur every five to 10 years.

Why heat waves aren’t just summer weather

Lualawi Mareshet Admasu, a PhD candidate in atmospheric sciences at the University of B.C., said that with climate change, heat waves are more frequent and hotter than they were even just a few decades ago. The temperate summers people knew in the 1960s and ’70s have changed drastically, and he said we need to adapt.

He also said heat waves are no longer happening only in summer but also in the spring, which can mean wilting under hot and dry weather before we’ve unpacked our summer shorts.

“We know heat waves are getting stronger, they’re getting more frequent and they’re actually becoming longer as well,” he said.

“A single heat wave can’t be completely attributed to climate change. But we can say, for instance, that the likelihood has increased because of climate change … and the likelihood of us encountering such events is getting higher and higher as we go into the future, so we should expect and be prepared for more, stronger heat waves.”

Stronger heat waves doesn’t mean balmier beach weather but rather the potential for more deadly events, like B.C.’s heat dome in 2021 that led to the deaths of more than 600 people.

Meteorologists say extreme heat waves can also come with high humidity levels. Humid air retains heat better than dry air, so nighttime temperatures won’t cool off enough to provide relief, according to the Weather Network. This can lead to an increased risk for heat exhaustion and heat stroke.

In June, a report in The Guardian said that more than 500 pilgrims had died on the journey to Mecca from heat-related illness as a brutal heat wave pushed temperatures above 51 C.

Reuters also reported on the heat deaths in Saudi Arabia, and noted that deadly heat waves were scorching cities on four continents as the Northern Hemisphere marked the first day of summer Thursday. The report noted that nearly 100 million Americans were under extreme heat advisories, watches and warnings on Thursday.

— With files from The Canadian Press