Expert Commentary

Wildfires, health and climate change: Research and resources

Climate change is causing wildfires to consume ever-larger swaths of forest, scientists say, breaking records and blanketing many states in dangerous smoke.

(Kari Greer/National Interagency Fire Center)

Fires have always burned in the planet’s temperate forests. They hasten regeneration by thinning undergrowth and fertilizing the soil. Before there were humans to flick cigarette butts into the brush, there were lightning storms and cyclical droughts.

In recent years, wildfires have consumed ever-larger swaths of forest, breaking records and blanketing many states in noxious smoke. The U.S. government and many climate scientists blame the same thing: the unpredictable fluctuations in temperature and precipitation known as climate change. 

Since 1984, climate change has been responsible for roughly doubling the area that has burned in the American West, according to a 2016 study in the Proceedings of the National Academy of Sciences. (That means two areas the size of Switzerland, rather than one, burned over three-plus decades.)

The fires are not only releasing carbon into the atmosphere, thereby exacerbating climate change. The smoke is deadly: “Wildfires emit fine particles and ozone precursors that in turn increase the risk of premature death and adverse chronic and acute cardiovascular and respiratory health outcomes,” said a 2016 report by the U.S. Global Change Research Program, the coalition of government scientists leading federal climate change inquiry. On smoky days in the American West, wildfires are responsible for the majority of fine particles known as PM2.5, according to a 2016 study in Climactic Change that estimated the number of people in western states affected by the smoke is expected to rise almost 44 percent by 2051.

Around the world, wildfires cause more than 300,000 premature deaths each year, estimated a 2012 paper in Environmental Health Perspectives. Increasing scientists’ concern is how climate change is causing extreme weather events, which in turn can cause a staggering loss of life. A 2014 paper in Epidemiology attributed 10,000 deaths in the Russian capital, in 2010, to a heatwave and subsequent wildfires (largely burning peat bogs), which blanketed the city with smoke for weeks that summer.

Back in the U.S., the number of acres burned annually has grown steadily, according to statistics from the National Interagency Fire Center in Boise, Idaho, which coordinates federal and state efforts to fight wildfires. The Center also publishes the costs to the federal government of suppressing wildfires back to 1985.

(Graph and trend line by Journalist’s Resource. Data from the National Interagency Fire Center.)


With little doubt that the number and size of fires will continue to grow, researchers have turned to studying adaptation strategies. A 2017 paper in the Proceedings of the National Academy of Sciences recommends recognizing that humans can do little to stop “climate-driven fires” and that authorities plan “residential development to withstand inevitable wildfire.” Other papers have looked at how different types of vegetation burns and which types of fires are most damaging to private property.


“Impact of Anthropogenic Climate Change on Wildfire Across Western US Forests”
Abatzoglou, John; Williams, A. Park. Proceedings of the National Academy of Sciences, 2016. DOI: 10.1073/pnas.1607171113.
Abstract: “Increased forest fire activity across the western United States in recent decades has contributed to widespread forest mortality, carbon emissions, periods of degraded air quality, and substantial fire suppression expenditures. Although numerous factors aided the recent rise in fire activity, observed warming and drying have significantly increased fire-season fuel aridity, fostering a more favorable fire environment across forested systems. We demonstrate that human-caused climate change caused over half of the documented increases in fuel aridity since the 1970s and doubled the cumulative forest fire area since 1984. This analysis suggests that anthropogenic climate change will continue to chronically enhance the potential for western US forest fire activity while fuels are not limiting.”

“Human-Caused Climate Change Is Now a Key Driver of Forest Fire Activity in the Western United States”
Harvey, Brian, Proceedings of the National Academy of Sciences, 2016. DOI: 10.1073/pnas.1612926113.
Abstract: “Effects of climate warming on natural and human systems are becoming increasingly visible across the globe. For example, the shattering of past yearly records for global high temperatures seems to be a near-annual event, with the five hottest years since 1880 all occurring since 2005. Not coincidentally, the single hottest year on record, 2015, also broke records for area burned by wildfire in the United States, eclipsing the previous high mark set just one decade prior. Scientists have known for some time that climate is a key driver of forest fires; records from the past and present provide strong evidence that warmer temperatures are associated with spikes in fire activity. Therefore, recent increases in wildfire activity as the planet warms are not a surprise. However, just how much of the recent increases in forest fire activity can be attributed to human-caused climate change vs. natural variability in climate? This question has profound scientific, management, and policy implications, yet answers have thus far remained elusive. In PNAS, Abatzoglou and Williams present strong evidence that human-caused climate change is increasing wildfire activity across wide swaths of forested land in the western United States. They demonstrate that human-caused climate change has lengthened the annual fire season (i.e., the window of time each year with weather that is conducive to forest fires) and, since 1984, has doubled the cumulative area in the western United States that would have otherwise burned due to natural climate forcing alone.”

“Critical Review of Health Impacts of Wildfire Smoke Exposure”
Reid, Colleen E.; et al. Environmental Health Perspectives, 2016. DOI: 10.1289/ehp.1409277.
Conclusions: “Consistent evidence from a large number of studies indicates that wildfire smoke exposure is associated with respiratory morbidity with growing evidence supporting an association with all-cause mortality. More research is needed to clarify which causes of mortality may be associated with wildfire smoke, whether cardiovascular outcomes are associated with wildfire smoke, and if certain populations are more susceptible.”

“Mortality Related to Air Pollution with the Moscow Heat Wave and Wildfire of 2010”
Shaposhnikov, Dmitry; et al. Epidemiology, 2014. DOI: 10.1097/EDE.0000000000000090.
Results: “The major heat wave lasted for 44 days, with 24-hour average temperatures ranging from 24°C to 31°C and PM10 levels exceeding 300 μg/m3 on several days. There were close to 11,000 excess deaths from non-accidental causes during this period, mainly among those older than 65 years. Increased risks also occurred in younger age groups. The most pronounced effects were for deaths from cardiovascular, respiratory, genitourinary, and nervous system diseases. Continuously increasing risks following prolonged high temperatures were apparent during the first two weeks of the heat wave. Interactions between high temperatures and air pollution from wildfires in excess of an additive effect contributed to more than 2,000 deaths.”

“Estimated Global Mortality Attributable to Smoke from Landscape Fires”
Johnston F.H.; et al. Environmental Health Perspectives, 2012. DOI: 10.1289/ehp.1104422.
Conclusions: “Fire emissions are an important contributor to global mortality. Adverse health outcomes associated with LFS [landscape fire smoke] could be substantially reduced by curtailing burning of tropical rainforests, which rarely burn naturally. The large estimated influence of El Niño suggests a relationship between climate and the burden of mortality attributable to LFS.”

“Particulate Air Pollution from Wildfires in the Western U.S. Under Climate Change”
Liu, Jia Coco; et al. Climatic Change, 2016. DOI: 10.1007/s10584-016-1762-6.
Abstract: “Wildfire can impose a direct impact on human health under climate change. While the potential impacts of climate change on wildfires and resulting air pollution have been studied, it is not known who will be most affected by the growing threat of wildfires. Identifying communities that will be most affected will inform development of fire management strategies and disaster preparedness programs. We estimate levels of fine particulate matter (PM2.5) directly attributable to wildfires in 561 western US counties during fire seasons for the present-day (2004–2009) and future (2046–2051), using a fire prediction model and GEOS-Chem, a 3-D global chemical transport model. Future estimates are obtained under a scenario of moderately increasing greenhouse gases by mid-century. We create a new term “Smoke Wave,” defined as ≥2 consecutive days with high wildfire-specific PM2.5, to describe episodes of high air pollution from wildfires. We develop an interactive map to demonstrate the counties likely to suffer from future high wildfire pollution events. For 2004–2009, on days exceeding regulatory PM2.5 standards, wildfires contributed an average of 71.3 percent of total PM2.5. Under future climate change, we estimate that more than 82 million individuals will experience a 57 percent and 31 percent increase in the frequency and intensity, respectively, of Smoke Waves. Northern California, Western Oregon and the Great Plains are likely to suffer the highest exposure to wildfire smoke in the future. Results point to the potential health impacts of increasing wildfire activity on large numbers of people in a warming climate and the need to establish or modify U.S. wildfire management and evacuation programs in high-risk regions. The study also adds to the growing literature arguing that extreme events in a changing climate could have significant consequences for human health.”

“Future U.S. Wildfire Potential Trends Projected Using a Dynamically Downscaled Climate Change Scenario”
Liu, Yongqiang; Goodrich, Scott; Stanturf, John. Forest Ecology and Management, 2013. DOI: 10.1016/j.foreco.2012.06.049.
Abstract: This study investigates trends in wildfire potential in the continental United States under a changing climate. […] It is shown that fire potential is expected to increase in the Southwest, Rocky Mountains, northern Great Plains, Southeast, and Pacific coast, mainly caused by future warming trends. Most pronounced increases occur in summer and autumn. Fire seasons will become longer in many regions. The future fire potential increase will be less pronounced in the northern Rocky Mountains due to the changes in humidity and wind. […] The projected increases in wildfire potential for many regions of the U.S. suggest that increased resources and management efforts for disaster prevention and recovery would be needed in the future.

“Climate Change Impacts on Wildfires in a Mediterranean Environment”
Turco, Marco; et al. Climactic Change, 2014. DOI: 10.1007/s10584-014-1183-3.
Abstract: “We analyze the observed climate-driven changes in summer wildfires and their future evolution in a typical Mediterranean environment (NE Spain). By analyzing observed climate and fire data from 1970 to 2007, we estimate the response of fire number (NF) and burned area (BA) to climate trends, disentangling the drivers responsible for long-term and inter-annual changes by means of a parsimonious Multi Linear Regression model (MLR). In the last 40 years, the observed NF trend was negative. Here we show that, if improvements in fire management were not taken into account, the warming climate forcing alone would have led to a positive trend in NF. On the other hand, for BA, higher fuel flammability is counterbalanced by the indirect climate effects on fuel structure (i.e. less favorable conditions for fine-fuel availability and fuel connectivity), leading to a slightly negative trend.”

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