The far-reaching impacts of wildfire smoke – and how to protect yourself

As wildfires blaze through Canada, air quality alerts are in place there and in parts of the US. Here are the profound ways wildfire smoke influences your physical and mental health.

All but 1% of the world's population is exposed to unhealthy air that exceeds World Health Organization (WHO) limits for pollutants. In parts of the world, air quality has rapidly improved through policies that aim to limit pollution. But elsewhere, gains in air quality are at risk of being lost.

More than 25% of the US population is exposed to air considered "unhealthy" by the Environmental Protection Agency (EPA), according to a report by the climate non-profit First Street Foundation. By 2050, the number of people exposed to "unhealthy" days is set to increase by more than half. The worst days of air pollution ("hazardous" or maroon, under the EPA's system) are expected to rise by 27%.

Wildfire smoke is one of the factors driving this trend. One study of PM2.5 (see fact box: What is PM2.5?) from wildfire smoke found that levels had increased by up to five micrograms per cubic metre in the western US in the past decade – enough to reverse "decades of policy-driven improvements in overall air quality", the authors concluded.

More than 800 wildfires are currently burning across Canada, with air quality alerts extending south into multiple US states. The vast majority of the wildfires are burning out of control and air quality in Detroit is currently the worst in the world, followed by Toronto and Minneapolis, according to the air quality tracker IQAir.

To put this in context – one study found that a quarter of the US's PM2.5 pollution was caused by wildfire smoke. In western regions, as much as half was caused by smoke. In 2023, large portions of the US saw significant dips in air quality and visibility as smoke from wildfires north of the Canadian border billowed across the continent. Canada experienced a record number of wildfires in 2023, with the area of land burned far outstripping any previous season. In May 2024, Canada saw an early start to its wildfires season as more than 130 blazes burned around the country. At least one town was evacuated in British Colombia as flames – exacerbated by years of drought and less than average snow pack over the past winter – swept perilously close. Plumes of smoke have blanketed large areas of Canada and blown south to the Upper Midwest of the US, triggering health warnings.

With climate change expected to increase the risk of wildfires around the world, it is likely that air quality will also continue to suffer.

People who have existing respiratory conditions and newborns with developing lungs are the most affected by wildfire smoke. (See factbox: "How to protect yourself from wildfire smoke".)

As climate change makes wildfires more intense, here are some of the profound and unexpected ways air pollution affects our bodies, and what we can do to minimise exposure.

The far-reaching effects of wildfire smoke

Wildfires are not just a local problem to people who live near forests, peatlands and grasslands. Fires can send plumes of smoke up to 14 miles (23km) into the stratosphere, from where they spread all over the globe. In 2023, Siberian wildfires fuelled by unusually warm temperatures released smoke that travelled across the Pacific Ocean to reach Alaska and Seattle.

The health risks that come with wildfire air pollution depend in part on what's on fire – in Siberia, 2020, it was resinous boreal forest and peat, releasing record-breaking quantities of pollution, including high quantities of mercury. Another typical pollutant released in wildfires is PM2.5, particulate matter that measures 2.5 micrometres across or less, linked to respiratory conditions. (Read about the risks of PM2.5 and nanoparticle pollution here, and the link between air pollution and respiratory disease here.)

Wildfire smoke has been found to be harmful to certain........

© BBC