How many people die from heat-related illnesses? The truth is, we don't actually know

It's the midriff of July, and thither feature been a list of heat up waves across several regions of the country.

On Tuesday, parts of northern and southern Ontario, as well as Quebec and even the Northwest Territories, were under a heat alert. Downtown Toronto reached a scorching temperature of 36 C, making it the hottest place in the country, according to Environment and Climate Change Canada's early data. While temperatures aren't expected to reach that high, the heat is expected to continue until Thursday.

Have there been any deaths? It's hard to say.

That's because in Canada, there is no federal coroner's organization and no standard way to report heat-related deaths across the country.

"So it [means] that every province and territory runs its own system, and a heat-related death that's counted in one place wouldn't necessarily be counted somewhere else," said Jacqueline Wilson, counsel at the Canadian Environmental Law Association (CELA). "So there's this real problem with the data that we're collecting."

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Herein lies the problem: If someone with an existing health condition, say heart disease, dies from a heart attack one night in their bedroom where temperatures exceeded 28 C, did they die from a heart attack or a heat-related illness?

A coroner in one part of the country might report it one way, while a coroner in a different part of the country might report it another way.

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"There are different ways of counting deaths that you'll see in the news," said climate scientist Andrew Dessler, director of the Texas Center for Extreme Weather at Texas A&M University.

"So oftentimes, after a heat wave, they'll give you the death certificate numbers, how many the medical examiner said died, and then academics will come up with excess deaths or they'll come up with these regression methods."

Using the regression method, scientists would correlate how many deaths there are versus temperature and then use that to estimate how many additional deaths there would be per degree of warming.

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"So those numbers don't agree, and I think it can be very confusing for people who are trying to consume the news, trying to understand the impact of extreme temperatures."

Some studies use the metric of excessive heat deaths. That method involves comparing the deaths in a given period with the average number of deaths in the same period.

Heat waves are expected to increase in frequency and duration across Canada due to climate change. As we continue to pump fossil fuels into the atmosphere, the planet continues to warm, and dangerous weather becomes exacerbated.

Eliminating heat deaths is part of the federal government's National Adaptation Strategy, where it has set out to end deaths due to extreme heat waves by 2040.

But how can you eliminate heat deaths if you don't have an accurate number?

A study published in 2025 by Health Canada on heat-related morbidity and mortality in Canada tried to quantify the effects of heat on Canadians. While it did conclude that heat-related deaths have increased across the country over the last decade compared with 30 years before, it noted that there were limitations in collecting data (and Quebec wasn't even included).

Although Canada may be known as the Great White North, this country is no stranger to heat waves.

It's the summer of 2021 that will likely be forever etched into Canadians' memories.

That year, the hottest temperature ever recorded in Canada was 49.6 C in Lytton, B.C., as the province baked under a heat dome. The village was burned to the ground following deadly wildfires.

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At the outset, provincial chief coroner Dr. Jatinder Baidwan didn’t think much about impending heat. But then people started dying. He remembered that he had seen this before while serving in Afghanistan as part of the U.K.'s military, when a Royal Air Force corporal succumbed to the heat and died.

Baidwan promptly reached out to British Columbia's College of Physicians and Surgeons and put a call out to all physicians and nurse practitioners. He told them that if they suspected heat could have played a role in exacerbating existing conditions — such as heart disease, diabetes or other chronic diseases — they should report it to the coroner's office as an accidental death.

Initially, 800 deaths were reported due to the heat, but in the end, the death toll dropped to 600.

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"When this happened, it came as a shock. Should it have been a shock? Absolutely not. We should have been planning for it, but I didn't plan for it. I didn't think about it, and suddenly it was upon us," Baidwan said. "Even now, thinking about it, it makes the hairs on the back of my neck stand up."

Since then, the province has made big changes. It initiated a program to provide air conditioners to those in need; it increased funding to help those in long-term care and assisted living facilities to protect seniors from extreme heat; and it added a standardized heat alert system.

While there hasn't been an extreme heat event in B.C. Quite like 2021, Baidwan said it shows that better reporting can lead to change.

"We actually made a big difference. I think we actually sort of captured the information, reflected it back to policymakers, and they responded in a timely fashion," he said.

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After the B.C. Heat dome, CELA reached out to Ontario's Office of the Chief Coroner to ask it to re-evaluate the method of reporting heat deaths. A study was undertaken, but for some reason, Wilson said, it showed no spikes in heat-related deaths — which both CELA and the coroner's office said didn't make any sense.

However, no further action was taken, she said.

Wilson said that's of particular concern, since it's those who are most vulnerable who are at the highest risk of experiencing heat-related illnesses and potential deaths.

And it illustrates perfectly the troubling issue of getting accurate numbers on heat-related deaths.

In June's deadly European heat wave, there were more than 5,000 excess heat-related deaths in Germany. And German news channel Deutsche Welle reported there were more than 3,700 heat-related deaths in France, Belgium and the Netherlands.

But independent research from climate scientists Christopher Callahan and Andrew Dessler, published by Carbon Brief, concluded that there were 2,700 excess heat deaths in France alone.

Finally, according to official numbers from European Mortality Monitoring, the continent recorded more than 10,000 excess heat deaths during the heat wave.

Those varying numbers are evidence that better standards of measurements need to be put in place across the globe.

"There's nothing like a registry that is counting the heat-related deaths. Something like that doesn't exist," said Oliver Schmoll of the World Health Organization's European Centre for Environment and Health in Bonn, Germany. "So typically, heat-relative mortality is typically estimated and not counted directly. And a common approach is to measure excess mortality during periods of extreme heat."

As climate change continues to heat up the planet, experts warn that we need to better document not only the deaths but heat-related illnesses in general.

"If we're going to help deal with this situation, we want to know exactly who is dying," CELA's Wilson said. "But the other reason it really matters is that we want to be able to assess the changes that are being made and whether they're helping."

Senior Science Reporter

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