Smoke from climate-fueled wildfires contributed to thousands of US deaths over 15 years, study says

 By: Dominic Prichard

News Article: https://apnews.com/article/wildfires-pollution-climate-change-deaths-9b8c7459e1f27b7688a137a9f4ef0929 

Research Article: https://www.nature.com/articles/s43247-025-02314-0#Sec10

Background: Climate change and increased global temperatures have led to earlier snowmelt, escalating heat waves (1), and an increased vapor pressure deficit (2). These factors contribute to forests becoming dry earlier in the year and for longer periods of time. This has been shown to cause an increase in the amount of wildfires (3), the severity of those fires (3), and caused these fires to flare up quicker (4). These fires produce lots of small particles (PM2.5) that can travel wide distances and have contributed to a significant amount of deaths due to respiratory complications, although the health impact of wildfire PM2.5 from anthropogenic means has not been broadly classified in studies yet. For this reason the scientific paper has had to assume its health effects are the same as normal PM2.5 air pollution when in actuality this undersells the danger of wildfire PM2.5 as it can vary in concentrations produced/spread and travel much further distances.

Research Article: This peer-reviewed paper “Anthropogenic climate change contributes to wildfire particulate matter and related mortality in the United States” by Law et. al discusses how anthropogenic climate change has directly contributed to the significant increase of wildfires happening in the last two decades, the increased severity of these fires, and how the PM2.5 produced has affected human mortality/economic burden associated. Firstly, they used MODIS database of burned area (BA) and the Fire Weather Index (FWI) to determine fire intensity/spreadability from weather data of previous years that indicated the amount of biomass built up in forests. This biomass is what fuels the flames and thus can proportionally tell you how intense a fire should be. They then used complicated models, equations, and machine learning to calculate how this translates to data for both BA and PM2.5 production from wildfires. They designed it to make datasets for measuring real-world fire data and the counterfactual, a what if scenario for if anthropogenic climate change didn’t affect wildfires, to compare for mortality/economic data.

This study was done on the county/state level, the first study to do so, and used data from 2002-2024. They found 2020 had the highest BA and BA in forested areas increased by a staggering 62% during these two decades. These fires were predominantly in the West especially in states like California, Oregon, and Washington, where anthropogenic climate change accounted for up to 60% of the BA in these areas or more than doubling the BA for those fires. Overall climate change was estimated to account for 39% of the total BA in forested areas and 13.3% more in non-forested areas. The Western BA correlated with a high amount of average annual wildfire PM2.5 coming from this region with 25-60% of this amount attributed to climate change.

The average PM2.5 wildfire related deaths per year was between 3,500 and 28,000 with 2020 making up the largest amount by about double every other year between 2006 and 2020. This combines to a total of 164,000 deaths, 15,000 of which were caused from anthropogenic means or roughly 10%. This comes to about 5.14 deaths per year for every 100,000 Americans, which is about double the deaths per year of the average hurricane. The economic burden associated with annual mortalities was between 31 billion and 325 billion USD a year with 1.2 to 58 billion being associated with climate change. Once again the Western states had the largest rates of mortality and "climate change contributions to total annual wildfire PM2.5 mortality exceeded 50% in 12 western US counties in 2020". Finally, about 13,000 climate change responsible PM2.5 deaths occurred between 2006-2020 estimated at 144 billion USD and an additional 17,000 are expected to occur based on long-term mortality studies (5).

The paper goes onto to compare the deaths and data to several different relevant models such as comparable numbers between vaccine-saved lives from influenza and the amount taken by anthropogenic climate change over the studied time. The ten western counties with the highest annual climate change related mortality rates had numbers ranging from about half of cancer's rates to about even. They highlight that the American government should take into consideration their findings and try to introduce policies in order to help those with incredibly high rates like the Western counties. Lastly, they address what their findings, which they consider conservative, and how several other studies imply that climate change will cause increased mortality rates, BA, and economic burdens on the US in the years to come. This problem will likely only become worse as seen in their data with later years in general having more deaths and more intense fires.

News Article: The news article "Smoke from climate-fueled wildfires contributed to thousands of US deaths over 15 years, study says" by Dorany Pineda begins with the end conclusion and statistics of climate change driven mortality and the cost of burden accurately, if even underplaying it in the title. They then make the critical connection to Western states having higher amounts of deaths from increased amounts of BA and PM2.5 creation. Then a quote from a doctor about increased PM2.5 events and a professor celebrating the paper's isolation of climate change on mortality, which she claims is one of the first to do so. She goes on to highlight the effects of PM2.5 in relation to wildfires for both short and long term health concerns and even states the people most at risk based on several other papers. Drawing from this it goes on to explain how wildfire PM2.5 is likely more dangerous than normal air pollution PM2.5 because of its mixing with burning cars and debris in these fires. Lastly for this section, she describes the effect global warming is having on the forests and extreme weather conditions that make them perfect environments for bigger fires such as the increased amount of dry biomass. 

In the next section, she fairly accurately describes where the three sets of data came from; BA, PM2.5 levels, and mortality, and how each leads to the next. She highlights of total deaths, about 10% were climate change driven and once again mentions the increased mortality rates in the West with another statistic. It ends the article with a Stanford environmental policy professor's concerns with the study, although he does call it overall reasonable. He particularly has a problem with their conclusion being only to reduce carbon emissions and not short-term solutions like prescribed burns and fuel breaks. It ends with the acknowledgement of raising awareness being a critical function of the paper.

Analysis/Criticisms: Immediately some shortcomings I found with the scientific paper was the sheer amount of data they try to draw reference to at the same time and how it is confusingly worded or displayed. I had to reread many of the statistics five or more times as they are worded very similarly but can mean different things entirely. Particularly figure 3 is very confusing as the paper states 5ug/m³ is the acceptable level of PM2.5 by the WHO, but that is below even the highest part of the scale on the graph. This is because if you include city-made PM2.5, it reaches over this possibly in some of the brown regions.

For the news article it immediately links the scientific paper and it even links four other sources later in the article to build up claims that weren't mentioned or proven in the paper. One of the claims of these four sources is that PM2.5 from wildfires are more dangerous than city PM2.5 and although the paper doesn't directly prove this it does make multiple references to it likely being true and their numbers are on the low end because of it. Within the paper they mention their numbers are skewed by Canadian fires not accounted for, assuming PM2.5 to be the same as city PM2.5, and how they explicitly mention how their numbers are "conservative" for these reasons. I would have liked to see the news mention this along with more data in general.

Although the data they used is accurately portrayed, other than downplaying the results in the title, they don't use very much of it. They really just use the final bits of statistics about the total number of deaths, and the money it's associated with. Although I agree the focus is mainly on the mortality statistics and the BA aren't as important, I think at the very least they should have used the 2020 as the largest number for many statistics and gone more into depth on the difference between the west and averages as that was pretty central to the paper. They also use no images from the paper which is a detriment as quite a lot of them show this western phenomenon quite well. The author did a fantastic job of describing where the data came from in a digestible way outlining all the steps quite accurately while leaving out the unimportant aspects of those steps. It also ended with some ways the paper could have improved as stated earlier from a reputable source and it served as a really substantive discourse about short-term improvements to end out their article. Overall I would give it a 7/10 for its understanding of the underlying mechanics to get the data, substantive disagreement, actually linking the paper, and having accurate data throughout. It just needs a bit more data to show parts of the paper like the western front or fiscal detriment contribution better; a graphic would help immensely particularly 2 or 5; and maybe a better explanation of what the data implies for the future or why the results are significant.

References:

1 Kolden, C. A., Abatzoglou, J. T., Jones, M. W. & Jain, P. Wildfires in 2023. Nat. Rev. Earth Environ. 5, 238–240 (2024).

2 Grossiord, C. et al. Plant responses to rising vapor pressure deficit. N. Phytol. 226, 1550–1566 (2020).

3 Abatzoglou, J. T. & Williams, A. P. Impact of anthropogenic climate change on wildfire across western US forests. Proc. Natl. Acad. Sci. USA 113, 11770–11775 (2016).

4 Brown, P. T. et al. Climate warming increases extreme daily wildfire growth risk in California. Nature 621, 760–766 (2023).

5 Lepeule, J., Laden, F., Dockery, D. & Schwartz, J. Chronic exposure to fine particles and mortality: an extended follow-up of the Harvard Six Cities study from 1974 to 2009. Environ. Health Perspect. 120, 965–970 (2012).