Pacific Heat Wave Alters Jet Stream, Delivering Unseasonable Warmth to Canada

On October 7th, 2025, a marine heat wave in the northern Pacific Ocean was found to be the primary driver behind the unusually warm weather experienced across much of Canada the previous weekend. Temperatures in many regions soared into the mid to high 20s Celsius, well above the typical seasonal averages for early October.

In the nation's capital of Ottawa, the mercury reached 29.9°C on Sunday, breaking a longstanding heat record. Similar record-breaking temperatures were also observed in Toronto and Montreal. Geoff Coulson, a meteorologist with Environment and Climate Change Canada, noted that it is highly unusual for temperature records to be shattered by such a large margin, typically only seeing fractional or 1-2 degree differences.

Atmospheric scientist Lualawi Mareshet Admasu explained that the abnormal warmth is being driven by a massive marine heat wave in the northern Pacific, which is pushing the jet stream—a key atmospheric system—further north. This is allowing warmer air from southern regions to flow into Canada, disrupting the typical fall weather patterns.

Experts warn that such marine heat waves are becoming more frequent and intense due to the ongoing effects of climate change. William Cheung, director of the Institute for the Oceans and Fisheries at the University of British Columbia, stated that there have been heat waves in the Pacific every year since 2019, with devastating impacts on local fisheries and marine ecosystems. He cautioned that without effective climate change mitigation, Canadians should expect to see more of these extreme weather events in the future.