Acute exposure to emissions from fires presents a significant and immediate threat to human health. Inhalation of wildfire smoke and other pollutants can lead to various health issues, including respiratory and cardiovascular problems. Our study uses the SILAM chemical transport model, integrated with the IS4FIRES fire information system, to assess population exposure to fire-related PM2.5, along with the health burden from all-cause, respiratory, and cardiovascular deaths. Our results show that while population-weighted all-source PM2.5 exposure has declined in Europe and high-income North America, fire-PM2.5 exposure has increased significantly in Eastern and Central Europe, high-income North America, Tropical Latin America, and sub-Saharan Africa. Extreme fire-PM2.5 events have tripled globally since the 1990s, with more than half of the global population experiencing minimum perpetual fire occurrence (at least 1% of fire-PM2.5 in PM2.5 for 50 instances of 3 consecutive days in a calendar year) in 2010-2018. Acute exposure to fire-PM2.5 contributed to 99,000 (95% CI: 55,000-149,000) all-cause deaths annually in 2010-18, with significant cardiovascular and respiratory disease burdens, particularly in Eastern Europe and sub-Saharan Africa. Our findings highlight the escalating health risks of fire emissions, emphasizing the urgent need for mitigation strategies as fire-PM2.5 becomes a growing contributor to global air pollution-related mortality.
Landscape fires (mentioned as 'fires' hereafter), including both controlled or prescribed burns and wildfires, occur in natural vegetated areas like forests, grasslands, and agricultural lands. Although some wildfires are of natural origin, most are ignited by human beings, and they are becoming more frequent due to climate change driven by higher temperatures and drier conditions in all regions globally. Fueled by conducive weather conditions, larger wildfires are burning for longer periods across all the global regions. On the other hand, prescribed fires help reduce wildfire risk and biomass load in specific areas. In some regions, fires are deliberately ignited for land clearance strategies, aiding agriculture or removing crop residues after harvest. However, like wildfires, other forms of fires release air pollutants, including toxic gases, fine particulate matter (PM), and volatile organic compounds, which can travel long distances and impact human health. The severe effects of long-range transport of fire emissions are best exemplified by the periodic regional 'haze' episodes in North India, caused by emissions from burning crop residues upwind. There are also evidences of large transport of emissions from African fires into South America outside of the Amazonian fire season.
Global area burnt was 384Mha in 2023, which is higher than any of the preceding three years but is 12% lower than the 2000-2010 average. While these trends in areas burnt have implications for global carbon emissions, ecosystems and society, the spatial extent of burning is not often closely linked to the impacts of fire on ecosystems and human health. The rapid growth of populations living at the human-nature interface has led to increased exposure to wildfire emissions and a rise in human-induced ignitions. A recent study found that nearly half of all buildings and people worldwide are potentially impacted by the human-environmental hazards concentrated in the wildland-urban interface, and this is expected to increase in the future.
Acute exposure to emissions from fires poses a significant and immediate threat to human health. The effect of inhaling wildfire smoke and other pollutants can lead to a range of health issues, from respiratory and cardiovascular problems to mental health challenges. A recent study has found emissions from fires to be significantly more toxic compared to emissions from other sources of air pollution. Numerous recent studies have linked exposure to landscape fire smoke with all-cause and cardiovascular mortality, though the association with respiratory mortality varies among studies. A recent study, which analyzed data from 749 cities in 43 countries between 2000 and 2016, found a positive association of wildfire smoke with all-cause, cardiovascular and respiratory mortality. Many more studies have associated fire emissions with respiratory morbidity, asthma, chronic obstructive pulmonary disease, mental outcomes and birth outcomes; however, the evidence for cardiovascular morbidity remains mixed.
Studies have employed various methods to estimate the contribution of fires to ambient PM, such as chemical transport models, atmospheric chemistry models, machine learning algorithms, in situ monitoring data, satellite data, or a combination of these tools. Multiple regional studies, especially in North America and Australia, have estimated the health and economic impact of chronic and acute exposure to emissions from fires. However, studies assessing the long-term global trends in health impacts of acute exposure to fire PM are missing. Johnston and colleagues used a combination of chemical transport models and satellite observations to estimate 339,000 all-cause deaths annually from acute exposure to fires globally between 1997 and 2006, with sub-Saharan Africa and Southeast Asia being the most affected. Another recent study combined published dose-response functions with landscape fire PM data, estimating that exposure to landscape fire smoke results in approximately 677,745 premature all-cause deaths annually between 2016 and 2019. Xu and colleagues found that 2.18 billion people were exposed to at least one day of substantial air pollution from fires annually from 2000 to 2019, without assessing the health impacts. In a previous study, we estimated the health effects of chronic exposure to fire-related PM over thirty years in Europe. Our findings indicated that although overall PM exposure has decreased across Europe, fire-related PM has increased during this period, particularly in Eastern Europe. However, we note that acute exposure to emissions from wildfires holds immediate significance. These episodic events can cause significant short-term increases in air pollutant concentrations, which can have acute impacts on human health.
We note that the aforementioned studies are limited in terms of geographical scope or temporal duration of assessment. Additionally, prior research often employs a uniform global exposure-response function linking fire exposure to health outcomes, and most studies use exposure response functions for all-source PM. In our study, we tackle these limitations by using a global chemical transport model called SILAM (System for Integrated modelLling of Atmospheric composition, https://silam.fmi.fi/) integrated with the IS4FIRES fire information system that is capable of forecasting fires to assess population exposure from 1990 to 2018. We also utilize data from a recent study to generate globally variable risk estimates from fire-PM exposure to estimate health impacts of acute exposure to fire PM. While previous studies, including Xu and colleagues have assessed the combined short and long-term health impacts of fire-sourced PM, our study advances prior work by providing more realistic and nuanced estimates of exposure and health impacts of short-term exposure to fire PM. The results are anticipated to inform policy decisions and help prioritize fire management efforts worldwide.