Wildfire Smoke: A Growing National Health Crisis

Wildfire smoke is an emerging nationwide crisis for the United States, supercharged by climate change. New evidence reveals these conflagrations are killing far more people than previously known as smoke travels hundreds of miles, aggravating conditions like asthma and heart disease. One study estimated that January's infernos in Los Angeles killed 440 people, not the official 30, once smoke is factored in. Another recent study estimated that wildfire haze already kills 40,000 Americans a year, which could increase to 71,000 by 2050. Two additional studies published in December paint an even grimmer picture of the crisis. The first finds that emissions of greenhouse gases and airborne particles from wildfires globally may be 70 percent higher than once believed. The second finds that Canada's wildfires in 2023 significantly worsened childhood asthma across the border in Vermont. Taken together, they illustrate the desperate need to protect public health from the growing threat of wildfire smoke.

Recent research indicates that greenhouse gas and particulate emissions from fires globally may be 70 percent higher than once believed. This emissions study is not an indictment of previous estimates, but a revision based on new data. Satellites have spied on wildfires for decades, though in a somewhat limited way. They break up the landscape into squares measuring 500 by 500 meters. If a wildfire doesn't fully fill that space, it's not counted. This new study increases that resolution to 20 by 20 meters in several key fire regions, meaning it can capture multitudes of smaller fires.

Individually, tinier blazes are not producing as much smoke as the massive conflagrations leveling cities in the American West. However, they add up significantly. With the 500-meter satellite data, the previous estimate was around 400 million hectares charred each year. Adding the small fires bumps that up to 800 million hectares, roughly the size of Australia. In some parts of the world, like Europe and Southeast Asia, burned area triples or even quadruples with this improved resolution. While scientists used to think annual wildfire emissions were around 2 gigatons of carbon, that's now more like 3.4 gigatons.

The type of fire makes a huge difference in the emissions. A forest fire has a large amount of biomass to burn, but a grass fire on a prairie has much less. Blazes also burn at dramatically different rates. Flames can race quickly through woodland, but carbon-rich ground known as peat can smolder for days or weeks. Peat fires are so persistent that when they ignite in the Arctic, they can remain hidden as snow falls, then pop up again as temperatures rise. Scientists call them zombie fires. It really matters where you're burning and also how intense the fire can become.

Why would a fire stay small, when recent years have shown how massive and destructive these blazes can get? It's partly due to fragmentation of the landscape. Roads can prevent them from spreading, and firefighters stop them from reaching cities. In general, a long history of fire suppression means they're often quickly extinguished. Ironically, this has also helped create some monsters, because vegetation builds up across the landscape, ready to burn. This shakes up the natural order of things, in which low-intensity fires from lightning strikes have cleared dead brush, resetting an ecosystem for new growth. This is why Indigenous tribes have long done prescribed burns.

Farmers, too, burn their waste biomass and obviously prevent the flames from getting out of hand. Whereas in remote areas, like boreal forests in the far north, lightning strikes typically ignite fires, the study finds that populated regions produce a lot of smaller fires. In general, the more people dotting the landscape, the more sources of ignition:

• Cigarette butts
• Electrical equipment producing sparks
• Chains dragging from trucks

Yes, these smaller fires are less destructive than the behemoths, but they can still be catastrophic in a more indirect way, by pouring smoke into populated areas. As noted by wildfire researcher Guido van der Werf from Wageningen University & Research, "Those small fires are not the ones that cause the most problems. But of course they're more frequent, close to places where people live, and that also has a health impact."

The health implications of this smoke are severe. One study estimated that January's infernos in Los Angeles didn't kill 30 people, as the official tally reckons, but 440 or more once you factor in the smoke. Another recent study estimated that wildfire haze already kills 40,000 Americans a year, which could increase to 71,000 by 2050. The second study on asthma is particularly alarming. Researchers compared the extremely smoky year of 2023 in Vermont to 2022 and 2024, when skies were clearer. They were interested in PM 2.5, or particulate matter smaller than 2.5 millionths of a meter, from wildfire smoke pouring in from Quebec, Canada.

That can be especially challenging to dispel from lungs, and especially irritating to those airways. There is research that shows that exposure to wildfire smoke can have much longer-term impacts, including development of asthma, especially for early exposure as a child. This study looked at the exacerbation of asthma symptoms in children already living with the condition. While pediatric asthma patients typically have fewer attacks in the summer because they're not in school and constantly exposed to res, the smoke from Canada's wildfires significantly worsened the situation in Vermont.

Taken together, these studies illustrate the desperate need to protect public health from the growing threat of wildfire smoke. Better monitoring air quality with networks of sensors is one potential solution. As the climate continues to change, the frequency and intensity of these fires are expected to rise, bringing more smoke to populated areas across the United States.