Toronto records one of its hottest summers on record with six heatwaves, Canada

Toronto, Ontario experienced one of its hottest summers on record in 2025, marked by six heatwaves and prolonged extreme heat events. As of August 24, the city recorded 14 days with maximum temperatures above 32°C (90°F), double the recent five-year average of seven days and more than triple the average of four days recorded in 2000, data from Environment Canada show.

The highest temperature of the year was 36.5°C (98°F) on June 25, followed by 36°C (96.8°F) on June 23. Additional significant heat days included 33.3°C (92°F) on July 28 and 34.7°C (94.5°F) on August 12.

Nighttime temperatures also set records. Toronto has recorded 24 nights so far in 2025 with minimums above 20°C (68°F), compared to a historical average of 12 such nights. Urban heat retention from asphalt, concrete, and high building density contributed to elevated nighttime values, Environment Canada climatologist David Phillips said.

Phillips noted that conservative climate models forecast summers like 2025 becoming the average by 2050, with projections of 15–16 days above 32°C (90°F) and about 23 nights above 20°C (68°F) each year.

The impacts of prolonged heat in Toronto this summer were compounded by poor air quality and widespread wildfire smoke, as Canada recorded its three worst fire seasons in the past three years. Heat also affected infrastructure, with risks of rail track warping and asphalt melting.

Reet Kaur

I’m a science journalist and researcher at The Watchers, contributing to the Epicenter edition, where I cover peer-reviewed scientific research and emerging discoveries across Earth and space sciences. With a background in astronomy and a passion for environmental science, I’ve worked in shark and coral conservation in Fiji, conducting reef and shark-behavior research, contributing to mangrove restoration, and earning PADI Open Water and Coral Reef Certifications. I bring a blend of scientific rigor and storytelling to illuminate the discoveries shaping our planet and beyond.

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