The Burning Question: Just How Bad Will It Get?

We can see (and feel) that heat waves are getting worse. Now we have clearer data about how they're becoming more frequent, and more deadly.


After the last few years, it seems almost quaint to highlight the concerning trend of more frequent and severe heat waves around the world. Everyone can feel it coming. Europe’s recent 2023 heat wave broke numerous records, while North America saw its worst heat wave in recorded history only two years prior.

Researchers have begun focusing more attention on this deadly phenomenon, with some studies examining the most vulnerable populations and others examining the factors making these heat waves deadlier. A new study from a team of researchers, including from the University of Ottawa and Health Canada, grants us further insight by examining how much the frequency and severity of heat waves will increase in the future.

The Study

The research team behind the study began by collecting data on temperatures and mortality rates from 748 locations in 47 countries. They then combined this data with five large-scale climate models called single-​model initial-​condition large ensembles (SMILEs). To account for possible variations of climate patterns in the future, they ran the climate models 234 times in total — producing over 1 terabyte of climate data!

The researchers were able to identify a “minimum mortality temperature” (MMT) for each location, or the optimum temperature associated with the lowest risk of mortality. They were then able to calculate the percentage of deaths in each location that could be attributed to heat. Using the aforementioned climate models, they projected these heat-mortality risk rates into the future.

More Frequent, More Deadly

For example, the authors highlight that in 2003, the city of Paris experienced a high heat-related mortality rate of 5.9%, due largely to the historic heat wave that killed tens of thousands of Europeans during that summer. In the climate of the year 2000, this level of heat mortality was expected to happen approximately only once every 100 years.

In the climate of 2020, this same magnitude of heat mortality would be expected once every 18 years. Concerningly, should the planet experience an average warming of 2.0°C — well below the current 2.8°C of warming estimated by the UN by 2100 — this level of heat mortality would become quite common, occurring once every few years.

Even the most rare heat seasons, such as those expected once every 500 years in 2000, will become more frequent. These ultra-rare heat waves will become more frequent by a factor of almost 70, and should be expected almost 14 times in 100 years should the Earth reach 2°C of warming.

Not only will heat waves become more frequent, they will also become more deadly. The study’s climate models reveal that severe heat waves (i.e., heat mortality rates of over 10%) will see a potential doubling or tripling of mortality, with this impact being particularly high for Southeast Asia, Europe, and the Pacific coast of Latin America.

The authors do acknowledge some limitations in their study, such as a lack of accounting for demographic changes including age and population growth, but they maintain the urgency of their results. As one author stated in a press release, “we should now prepare and manage the unavoidable, while avoiding the unmanageable at all costs.”

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Borna Atrchian is an MA student in the Department of Political Science at the University of Toronto. Having previously completed a Behavioural Neuroscience degree, he is passionate about issues where politics and power intersect with psychology and human behaviour. He is interested in understanding the conditions that create distrust of the scientific community, as well as finding the most effective ways to rebuild this trust.