Unseasonably Warm Weather Hits Canada: Pacific Ocean Heatwave to Blame
Many Canadians experienced unusually warm weather last weekend, with temperatures reaching the mid to high 20s Celsius across much of the country. This is well above seasonal averages and has prompted experts to investigate the cause, pointing to a significant heatwave in the northern Pacific Ocean.
Record-Breaking Temperatures and Beach Visits
Unusual for early October, many people flocked to beaches in Toronto and Ottawa. The nation's capital broke a heat record on Sunday, reaching 29.9°C, while Montreal also matched that temperature, also breaking a record. These temperatures are far from typical fall weather.
The Culprit: A Northern Pacific Ocean Heatwave
Experts attribute the warm weather to a large heatwave in the northern Pacific Ocean. Lualawi Mareshet Admasu, an atmospheric scientist at the University of British Columbia, explains that the unusually warm ocean temperatures are pushing the jet stream north.
The Jet Stream's Role
The jet stream, a fast-flowing band of air moving west to east over the Northern Hemisphere, typically separates colder northern air from warmer southern air. Scientists are actively researching the link between ocean heatwaves and the jet stream's behavior. As the jet stream shifts, Canada has been experiencing "very warm air from southern or Equatorial regions."
Geoff Coulson, a warning preparedness meteorologist at Environment and Climate Change Canada, noted that some temperature records were broken by over five degrees, a particularly rare occurrence. He explained that records typically only break by fractions of a degree, or at most, a degree or two.
Marine Heatwaves and Global Warming
The current marine heatwave is similar to the "blob," a multi-year warm water band that significantly impacted marine life and fisheries off the U.S. and Canadian west coasts starting in 2013. William Cheung, director of the Institute for the Oceans and Fisheries at the University of British Columbia, notes that studies show marine heatwaves are becoming more frequent and intense due to global warming.
Cheung stated that "we would be seeing more frequent and more intense heatwaves happening as we move forward if we don't do a good job of mitigating climate change." He also highlighted the ocean's role in absorbing around 90% of the atmosphere's excess heat, which continues to warm due to greenhouse gas emissions from fossil fuels. Berkeley Earth analysis suggests that northern Pacific temperatures are nearly 2.5 degrees warmer than the pre-industrial average, indicating that this is likely not a short-term fluctuation.
Impacts on Fisheries and Communities
Previous marine heatwaves have had devastating consequences for local fisheries. The Pacific cod fishery off the coast of Alaska was closed in 2020 due to low numbers. The Bering snow crab fishery, valued at over $200 million US per year, collapsed abruptly in 2018-19 after a 90% population decline.
Cheung emphasized the dependence of many communities on the ocean for food, culture, and livelihood. He also noted that the changes in weather systems caused by marine heat affect people more indirectly as well.
Looking Ahead: A Warmer Fall?
While temperatures on land are expected to return closer to seasonal normals this week as a cold front moves through Ontario and Quebec, Admasu says researchers will continue to monitor the Pacific heatwave, which shows no sign of abating. He adds that the ocean changes at slower timescales than the atmosphere, so the impacts "tend to stay or persist for some time," suggesting a warmer than usual fall in North America overall.
