Darcel Moro

How much is Canada responsible for the wildfire smoke reaching the U.S.? Right now, nearly 900 wildfires are burning across Canada. Last week, Toronto's air quality was the worst of any major city in the world. But as the smoke spread south to the U.S., many politicians began blaming Canada for poor forest management. It's true that local and regional forestry practices matter. Leafy deciduous trees hold moisture and can act as natural fire breaks; so clearing them for conifer monocultures can leave forests at higher risk to burn. But fire suppression, a big issue in the dry forests of the western U.S. where putting out frequent fires let fuel pile up, isn't a major factor here. Canada's remote boreal forests already burn naturally, in less frequent but higher-intensity fires. The single biggest reason for the record-breaking *increases* in the area burned by wildfires that are causing all this smoke isn't land management. It's human-caused climate change. As the world warms, winters are no longer cold enough to kill off tree-eating beetles. Their populations explode, leaving millions of acres of dead trees ready to burn. Warmer winters also mean less snowpack, so soil dries out earlier and the fire season runs longer. And climate change has more than doubled the frequency of hotter, drier fire weather across Canada and increased the frequency of the lightning strikes that spark most fires in northern Alberta and BC. Every one of those four dials is being turned in the same direction by the same thing: the heat-trapping gas emissions from burning fossil fuels. And that's where the numbers start to tell a different picture. The United States has emitted more carbon than any country in history: around 435 billion tonnes since the 1800s. That's close to a quarter of all the carbon humans have ever put into the air, 12 times Canada's total and still 50% more than China's 285 billion tonnes. Look at it by company instead of by country, and 88 of the world's largest fossil fuel producers are responsible for the emissions that led to more than a third of the forest area burned across western North America since 1986. At the top of that list is Saudi Aramco, followed by US companies Chevron and ExxonMobil. The first Canadian company, Suncor, doesn't appear until number 76 ... but that could change, as Canada is building more pipelines! Bottom line? If politicians want to clear the smoke from our skies, tell them the most effective place to start is by cutting the emissions that are driving these fires - no matter which side of the border we're on. Sources, I'm a scientist so you know I have them: Doubled fire weather risk (World Weather Attribution, 2023). Fire suppression near communities (Parisien et al. 2020, Nature Communications). Climate-beetle-fire connections (e.g. Woo et al. 2024, Ecosphere). Climate-driven lightning increases in northwestern Canada (Burrows et al. 2024, Atmosphere-Ocean). Cumulative CO₂ by country (Our World in Data). 88 producers behind 1/3+ of western N. American area burned (Dahl et al. 2023, Environmental Research Letters). Company ranking (Carbon Majors). And for an exhaustive review of how we know human emissions are driving climate change, see the next post in this thread. cbc.ca/news/science/wildfire…