On September 4, 2017, smoke from Western wildfires entered the gulfstream and spread across the country. Image: NASA Earth Observatory / Suomi NPP

2017 was a smoky year for the United States. In September, the haze was visible from space, appearing as a smear obscuring almost half of the country.

What's new: Climate change is increasing the length and severity of our fire seasons, and scientists are starting to quantify the health impacts of all that smoke. In a poster presented Wednesday at the fall meeting of the American Geophysical Union (AGU), Colorado State University atmospheric scientist Jeffrey Pierce estimated about 15% of the roughly 200,000 air quality related deaths in 2000 were caused by wildfire smoke. By 2100, he estimates it could reach 40%. That's just one model (some predict even more extreme fire seasons, some less) but it's clear that smoke poses a real and serious health risk.

Some good news: Although deaths from smoke increase in Pierce's model, he also shows deaths from other types of air particulates decreasing. If clean energy progresses as he has it doing in the model, the total number of air quality related deaths ultimately holds steady at 4%.

Yes, but: that 4% number is the average across the entire country. In areas with increased fire activity, says Pierce, exposure could increase — while areas that are traditionally polluted by fossil fuels, like the Ohio valley, may clean up.

The immediate impacts: It's well documented that on days with lots of air pollution, deaths increase, explains Pierce. Katelyn O'Dell, a research assistant at Colorado State University, looked at rates of hospitalization for respiratory illness and inhaler refills during the 2013 Oregon wildfire season. In results presented in a poster Monday at the AGU fall meeting, she reported that on a mildly smoky day (10 micrograms of the particle PM 2.5 per each cubed meter of air), there was a 7% increase in medication refills. But on a day with a PM 2.5 measurement of 100, there's over a 100% increase. O'Dell tells Axios that increase can last a week after the smoke exposure ends.

An underestimation: “The impact of smoke exposure is probably a lot greater than what we're saying," says O'Dell. The model doesn't catch people who get sick, but don't need to go to the hospital, for example. Her team is also starting to look at the impacts on heart health. “This is only the tip of the iceberg," she says.

Off the charts: In the 2017 fire season, regions of the US had PM2.5 levels of 500 or higher — some people were inhaling an entire years' worth of particulate matter in a single day.

The long-term impacts of breathing smoke are hard to parse, because it's hard to measure just how much smoke someone has been exposed to. But “there's a mechanism, and a pathology, so it makes sense it would have an impact," says Manvendra Dubey, a researcher at Los Alamos National Laboratory.

What's in the smoke: Plants uptake different types of salts and heavy metals (think: spinach is rich in iron) so they give off different types of particles when they burn. Dubey can even identify the region smoke came from by its chemical composition. He's creating models of what burns in different areas to help study the health impacts, since many of those particles are known to cause cancer. Dubey is particularly concerned about exposure to smoke from wildfires that destroy entire neighborhoods because there are many different types of fuel burning in a house.

The bottom line: “If people in California are being exposed to these smoke events more regularly and in higher concentrations, we would expect this to have an impact on the average lifespan of people in California," says Pierce. The same is true everywhere else fires increase.

Correction: This story initially stated that an estimated 25% of the roughly 200,000 air quality deaths in 2000 were due to smoke inhalation, and that number would increase to 75% in 2100. The correct number is roughly 15% (25,000 deaths) increasing to roughly 40% (75,000.)

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