Climate change is making Canada’s marathons hotter—and harder
Runners chasing personal bests at Canada’s biggest marathons may soon be racing against the climate itself. A new analysis from nonprofit Climate Central finds that rising temperatures are cutting into the number of days with ideal conditions for performance. Races from Vancouver to Ottawa are expected to see hotter, less predictable weather in the years ahead, creating conditions that make running harder, slower and riskier.
The report analyzed 221 marathons worldwide, including eight in Canada, and found that 86 per cent will have fewer ideal race-day conditions by 2045. The “sweet spot” for marathon running—the moderate temperature range that helps the human body perform at its best—is shrinking as climate change accelerates.
Hotter races, slower times
Researchers paired their findings with an interactive tool showing which events are most likely to maintain that temperature sweet spot, and which are slipping out of it. Nearly all the world’s major marathons, including Boston, London, Berlin and New York, are projected to see a steady decline in performance-friendly weather over the next two decades.
The Tokyo Marathon, currently the most favorable of the Abbott World Marathon Majors with a 69 per cent chance of ideal temperatures for elite men, is also expected to experience the steepest drop by 2045. Climate-fueled heat waves are already changing the sport: the 2025 Berlin and Tokyo Marathons were both run in unseasonably hot conditions that scientists say were made two to three times more likely by global warming.
Canada’s marathons are feeling the heat
At home, the outlook isn’t much better. The Vancouver Marathon is projected to have the sharpest decline in ideal conditions by 2045—down 10 per cent for elite men and 14 per cent for recreational women. The Ottawa, Saskatchewan and Manitoba Marathons are also expected to see their already-low chances of hitting the temperature “sweet spot” fall even further.
In the east, the Newfoundland and Labrador Provincial Marathon faces a 13 per cent decline for elite women, and Toronto’s marathon season continues to trend warmer. This year’s race saw temperatures well above seasonal norms, a sign of what runners may increasingly face in the years ahead.
Heat, smoke and shifting start lines
It’s not only the heat that’s raising concerns. Canada’s lengthening wildfire season, and the smoke that often accompanies it, adds another layer of risk, threatening both performance and participant health. As temperatures and air quality fluctuate, race directors may experiment with earlier start times, closer to sunrise, when air temperatures are cooler.
However, Climate Central researchers caution that such adjustments provide only temporary relief. The most effective solution, they say, is cutting fossil fuel pollution to slow global warming itself.