Thick wildfire smoke has blanketed large parts of the US Midwest and Northeast, as well as parts of Canada, turning skies orange and prompting widespread air quality alerts. The smoke stems mainly from Canadian wildfires, along with fires in Minnesota, and highlights how global warming is making such smoke events an increasingly common summer occurrence.

Canada was battling 119 out-of-control blazes as of Friday afternoon, with smoke carried eastward on the jet stream. This left Chicago and Detroit with the worst air quality of any cities in the world on Friday, while New York and Washington, DC, also ranked among the ten worst. Authorities have urged residents to stay indoors, and although cleaner air is expected in some areas this weekend, the fires remain active, raising the risk of further smoke episodes later in the summer. Researchers have warned that, without a reduction in fossil fuel use, wildfire smoke could cause an estimated 71,420 excess deaths annually in the US by mid-century, a 73% rise on the 2010s.