Why is eastern Canada on fire — and when will the smoke clear?

A view of the Williamsburg Bridge from Domino Park in Brooklyn, New York, on June 7. | Courtesy of Natalie Kelapire

4 basic questions about Canada’s wildfires, answered.

East Coasters finally understand what it’s like to live in California.

Earlier this week, a giant cloud of wildfire smoke from Canada wafted into New York City, Boston, and other eastern metropolises, engulfing skylines and putting millions of people at risk from air pollution. Tuesday evening, NYC had the worst air quality of any major city in the world.

New York State Mesonet/University at Albany

It’s not only large northeastern cities that are smothered in smoke. States as far west as Minnesota and as far south as South Carolina have watched their air quality plummet, in some cases reaching record levels of pollution. It’s likely one of the worst wildfire smoke events in the last two decades in North America.

Across the eastern seaboard, most of the smoke comes from forest fires in Quebec, a Canadian province in the far east that borders Maine. More than 140 fires were burning in the region as of Wednesday afternoon, most of which were not contained.

This situation is both frightening and usual. While Canada is, on the whole, prone to wildfires, the fires usually aren’t this severe in the east — and especially not so early in the year. Plus, weather patterns have to be just right to bring the smoke hundreds of miles south into the US.

One big question now is whether these wildfires and the conditions they’re currently causing could become more common in the years ahead as the planet warms.

1) Why is eastern Canada burning?

The summer often brings severe wildfires to western Canada, especially as climate change continues to dry out vegetation and heat up the land. 2021 was a particularly devastating year, with blazes destroying entire towns.

Provinces in the east — including Quebec and Nova Scotia — are somewhat more safeguarded from fires, or at least big ones. Air coming off the North Atlantic Ocean typically keeps the region humid and cooler, making it less likely to burn, per Reuters.

The forests out east also tend to be less flammable, Reuters notes. Unlike western forests, which are dominated by fire-prone evergreens, eastern forests also have broadleaf trees, which are less flammable (their branches start higher off the ground and their leaves contain more moisture).

CIRA/NOAA via AP
A satellite image shows smoke drifting south from wildfires burning in Quebec (on the right) and Ontario (on the left) on June 7.

Still, under the right conditions, eastern forests can burn, too.

This spring brought the right conditions across parts of the east — namely, low humidity and rainfall, and lots of heat. Between March and May, for example, Nova Scotia’s capital, Halifax, received only about a third of its average rainfall. And when forests are dry, they ignite more easily.

“What’s unique about this year is that the forests are so dry that the fires are many times larger than they normally are,” Matthew Hurteau, a biology professor at the University of New Mexico, told Vox’s Rachel DuRose.

Still, there needs to be a source of ignition. For the fires out east, that was likely a combination of lightning strikes and people, such as campers who didn’t put out their campfires (they’re both pretty typical sources of wildfires).

2) When will the smoke disappear and the fires stop?

The reason there’s so much smoke leaking south into the US is, in a word, weather. Wind is pushing smoke south from Quebec and parts of Ontario and into a region of low pressure that is then flinging it toward the East Coast.

Accordingly, it will take a change in weather to bring relief to smoke-smothered cities — though don’t expect that in the immediate term. Meteorologists suggest that in places like New York City, the air quality will continue to be poor — or even worsen — Wednesday night and into Thursday. Changes in wind patterns and potential rain could, however, bring relief to much of the East Coast this weekend and early next week.

Longer term, things look a bit more dire, especially for regions closer to the blazes. Forecasters predict Canada will face dry and, in some places, warmer-than-average conditions this summer, so the recipe for wildfires could persist for months. As long as there’s a risk of fire, there’s a risk of far-ranging smoke.

3) Is wildfire smoke really that dangerous?

Yes, very much so, especially for people who already have lung or heart conditions, people who are pregnant, and children. Here’s how Vox’s resident physician and health reporter, Keren Landman, put it:

Breathing polluted air affects the body in a few different ways. Larger pieces of particulate matter — tiny particles of soot and dust — can irritate the linings of people’s airways in their noses, mouths, throats, and lungs. And smaller bits, along with toxic gases and molecules called volatile organic compounds, can sneak from the lungs into the bloodstream, where they can travel to other organs and cause a wide range of short- and long-term problems.

You can find her full story on the health risks of inhaling smoke here.

People who live in large cities like New York and Boston are already exposed to sources of air pollution including car exhaust. Research suggests that wildfire smoke can be worse — up to 10 times more harmful than exhaust, for example.

Thankfully, there are pretty easy ways to avoid dangerous exposure, as my colleague Rebecca Leber writes: Stay indoors when you can, wear an N95 mask when you can’t, and pay attention to outdoor air quality forecasts the same way you do the weather.

4) Are smoky skies the new normal for East Coasters and the upper Midwest?

The world is heating up due to climate change, and warm air can suck moisture out of trees and other plants, making them more flammable. As a result, warming is making fire seasons in Canada, the US, and elsewhere, longer and more severe. Wildfires are now burning larger areas, compared to past decades.

“As the atmosphere warms, the ability to suck moisture out of the fuel [trees and other vegetation] increases almost exponentially,” said Mike Flannigan, a wildland fire professor at the University of Alberta. “So unless we get more rain to compensate for that drying effect, our fields are going to be drier. Most of the models of future fire seasons for Canada look like no change in precipitation or even drier.”

Communications Nova Scotia /The Canadian Press via AP
Firefighters spray water on a forest fire in Shelburne County, Nova Scotia, on June 1, 2023.

That doesn’t mean that the eastern US will be engulfed in smoke every summer — again, the wind patterns have to be just so — but it does make such a frightening event more likely. What cities on the East Coast are seeing is very much a warning sign of what climate change can bring.

Rachel DuRose contributed reporting to this story.

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