Wildfire smoke could kill 2 million more Americans by mid-century

There's a new study in Nature, Wildfire smoke exposure and mortality burden in the US under climate change. One of the co-authors, Marshall Burke kindly sent me a preprint copy of the paper, since it's behind a paywall.

In short, they find that wildfire smoke could cause over 70,000 additional premature deaths per year in the USA in 2050 under a relatively high-emissions scenario, with a total of nearly 2 million excess deaths over the next 30 years.

It's a difficult thing to model and estimate, because the link between climate change and wildfire smoke-related deaths is complicated. You have to estimate how much the increased heat and dryness from climate change will worsen wildfires, when other factors like forest management are also playing a role.

And then how much those more extreme wildfires will also worsen particulate matter (PM2.5), when other factors also contribute to those air pollution levels. And also estimate the impact of breathing PM2.5 on adverse health outcomes. You can see the complex associations and data incorporated in the study here:

To put the wildfire projections in context, 2020 was the worst wildfire season on record in the western USA (it was a horrible year in California especially). The study projects that in 2050, if we're effectively on track with the Paris agreement (scenario SSP1-2.6), annual wildfire emissions will be on par with 2020.

On our current path (roughly scenario SSP2-4.5), annual wildfire emissions will be 36% higher than 2020, and if we backtrack on emissions reductions (scenario SSP3-7.0), they'll be 65% worse than 2020. You can see from these figures, the western US has the biggest threats from wildfire air pollution:

They estimate that in 2050, wildfires will account for 14–18% of PM2.5 in the USA, which is about triple the wildfire contribution today (5.4%). In Oregon and Washington, wildfires will account for ~63% of PM2.5 emissions, and 24% in California.

They estimate that today, wildfire PM2.5 emissions cause 41,380 annual deaths in the USA. In 2050, that number will increase by another 26,500–30,040 (64–73%). The number will also increase as the US population ages, as older people are more vulnerable to air pollution health effects.

To put these numbers in context, the authors note,

by mid-century in the US, increasing mortality from more frequent extreme heat is likely to be more than offset by declining mortality due to cold weather, with a projected net decrease in annual excess deaths of 15,640 … Our projected increase in smoke mortality in the same period and scenario is nearly twice the estimated reduction in direct temperature-related deaths

This is a relatively frequent argument from contrarians, that climate change won't be so bad because while we get more heat-related deaths, we get fewer cold-related deaths. But this study finds that wildfire smoke-related deaths more than offset any benefit from fewer cold-related deaths. And of course there will be more deaths from other types of worsened extreme weather like hurricanes and floods.

They also reference this 2017 study that estimated the US costs of climate damages from temperature-related mortality, agriculture, crime, coastal storms, energy, and labor channels at about $166-332 billion, whereas using the value of a statistical life, this study would estimate the costs of wildfire smoke-related mortality at potentially over $600 billion. Though I've always been wary of putting a dollar value on lost life. The important conclusion is that we're on track for nearly 2 million American premature deaths over the next 30 years because of climate-worsened wildfire smoke.

The study also notes the importance of adaptation measures, including better forest and wildfire management. Like the Fix Our Forests Act, I would add! 🤓

Marshall also pointed me to this cool website they created to track wildfire, heat, and cold-related deaths across the country: