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Why Canada’s wildfires will affect air quality for weeks to come

Canada’s fire season is especially bad, and it could lead to smoke drifting southward for the rest of the summer.

Chicago’s skyline is seen from the 360 Chicago Observation Deck of the John Hancock Building with heavy smoke from the Canadian wildfires blanketing the city, on June 27, 2023, in Chicago, Illinois.
Kamil Krzaczynski/AFP/Getty Images
Li Zhou is a politics reporter at Vox, where she covers Congress and elections. Previously, she was a tech policy reporter at Politico and an editorial fellow at the Atlantic.

US cities are again experiencing air quality issues this week as wildfires continue to burn in Canada and smoke drifts south. That smoke includes contaminants, which can exacerbate respiratory conditions and affect breathing, and it could well spread for weeks to come.

Typically, Canada’s wildfire season runs through the spring and summer, so there’s some expectation of blazes taking place around this time. There is a notable difference in 2023, however: Because Canada has experienced an exceptionally hot and dry spell this year, it’s seeing the most destructive fire season in decades, resulting in record acreage burned and smoke emissions released.

Here are answers to five questions about the impact the wildfires have had, how lawmakers have responded, and what to expect in the coming weeks.

1) How are the Canadian wildfires affecting US air quality?

The wildfires have had a significant impact on the air quality in multiple US states. In the past few months, they’ve affected different parts of the country due to the locations of the fires as well as weather patterns that have carried smoke southward.

In May, western states including Montana and Colorado issued air quality warnings as fires in British Columbia and Alberta contributed to smoke in those areas. In early June, East Coast states and cities including New York and Philadelphia also put forth air quality alerts due to severe smoke and haze in the region. And this weekend, Midwestern and western states bore the brunt of the latest wave of wildfire smoke, with Iowa, Montana, and Minnesota among those issuing air quality alerts.

This summer, more than a dozen US states have issued some form of air quality alert as the wildfires in Canada have continued. All told, almost 90 million Americans live somewhere that has a warning in place.

The smoke from the fires can have a range of health effects: It increases pollutants, like particulate matter, in the air, which can disproportionately affect people who have respiratory conditions and make breathing more difficult generally. According to CNN, the inhalation of particulate matter can contribute to conditions including heart disease and asthma.

The Environmental Protection Agency measures air quality using what’s known as the Air Quality Index, or AQI, which effectively tracks how many pollutants are in the air. The lower a place’s AQI is, the better. Places with an AQI that’s 100 or lower have satisfactory air quality, according to the EPA. Meanwhile, a place with an AQI from 101-150 has air quality that’s harmful to sensitive individuals, and a place with an AQI from 151-200 has air quality that’s harmful to a broader population.

When the East Coast was dealing with heavy wildfire smoke in early June, there were areas with an AQI above 400. In June, Detroit’s AQI came in as high as 306.

US residents can check the air quality of their town or city at this link.

2) How big are the wildfires in Canada?

As of Monday morning, there were 882 active wildfires across different provinces in Canada, with the highest number — 373 — concentrated in the western province of British Columbia and 121 in the western province of Alberta. Of these fires, about 579 were deemed “out of control” by the Canadian Interagency Forest Fire Centre, which means that they haven’t yet responded “to fire suppression efforts and [are] expected to grow.”

The number of fires in the eastern provinces of Quebec, Nova Scotia, and Ontario has been especially high this year compared to past years, displacing tens of thousands of people. Collectively, the Canadian fires have burned roughly 25 million acres this year, which far surpasses the scale of the 2021 and 2022 fire seasons.

3) How long have the wildfires been burning and how long is the wildfire smoke expected to last?

Canada’s annual wildfire season typically goes from May to October, though it’s rarely this destructive this early. Some of this year’s earliest wildfires began at the start of May and have kept burning in the months since.

Historically, the wildfire season peaks in July and August and is over by the end of October. Experts have warned that the rest of the season could prove just as damaging as the first part.

“The images that we have seen so far this season are some of the most severe we have ever witnessed in Canada, and the current forecast for the next few months indicates the potential for continued higher-than-normal fire activity,” Canada’s emergency-preparedness minister Bill Blair told the Associated Press. That means the US is likely to continue to see the effects of these fires for months, including the ongoing presence of smoke and haze.

4) What have the US and Canada done in response?

The Canadian federal government has deployed its military to help with firefighting efforts in multiple provinces. Additionally, the US and several other countries around the globe including Costa Rica, France, and Australia have sent over 1,700 supplemental firefighters.

The wildfires have raised questions about whether Canada needs to establish a more centralized federal agency to address natural disasters, akin to the Federal Emergency Management Agency (FEMA) in the US. Currently, each province is responsible for the front-line response to wildfires in their region, though they’re able to request additional aid and support from the federal government.

Both Canadian and US officials have also faced critiques for the lack of timely information and response to air quality problems these wildfires have posed. New York City Mayor Eric Adams was criticized, for example, for failing to provide clear updates about the state of air quality in the region and making resources like masks and shelter available to vulnerable populations.

States and cities have been working to issue air quality alerts to their residents so that people can better prepare for these developments. Authorities in both countries have also issued guidance encouraging people to run air conditioning (as long as it circulates indoor air) while they’re inside and use an N95 mask outdoors in order to make sure they’re protecting themselves from hazardous chemicals in the air.

5) Is climate change to blame for Canada’s wildfires?

It’s not abnormal for Canada to have a wildfire season, but climate change has played a role in exacerbating the magnitude and frequency of the fires. As the Earth has warmed, it’s gotten hotter and drier. Because of that, there’s been more available kindling in Canadian forests, and there’s also been more lightning, which contributes to many of the country’s wildfires.

“Most fires in the boreal forest of northern Canada are started by lightning. A one-degree Celsius increase in temperature amounts to about 12% more lightning. So the warmer it gets as the climate heats up, the more triggers there are for fires to burn,” Edward Struzik, a fellow at Queen’s Institute for Energy and Environmental Policy, told CBS News.

Additionally, as climate change worsens, so will fires and air quality, according to Morgan Crowley, a fire scientist with Canada’s forest service who spoke with Vox’s Benji Jones:

Climate change is going to impact Canada more than other regions because it’s closer to the poles. In the west, we expect longer fire seasons. And across Canada in general, we expect fire seasons to get more extreme. The annual area of burned regions is expected to increase — some predictions suggest it could as much as double by 2100.

With climate change, it’s hotter. So our forests are drier. That means they’re more stressed out, and there’s more dead fuel. They’re basically a tinderbox when lightning strikes.

Update, July 17, 10:40 am ET: This story was originally published on June 28 and has been updated with new data about wildfires in Canada and areas affected by smoke.

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