Fire-induced air pollution is claiming more lives each year as climate change worsens wildfire conditions globally, doubling mortality rates over the past 60 years and intensifying health risks.
Study: Attributing human mortality from fire PM2.5 to climate change. Image Credit: josh.tagi / Shutterstock
In a recent study published in the journal Nature Climate Change, researchers estimated global mortality attributable to pollutant emissions from fires caused by climate change. Their findings indicate that annual fire-related deaths more than doubled from the 1960s to the 2010s and that climate change has been responsible for nearly 13% of fire-related deaths in recent years.
Background
Forest fires are significant health risks, with events like the 2023 Canadian fires and Australian mega-fires causing significant health costs and emergency visits. Fire smoke contains fine particulate matter with diameters less than 2.5 micrometers (PM2.5), a significant environmental hazard contributing to millions of global deaths annually. Fire-related PM2.5 is responsible for 339,000 to 677,745 deaths annually, including 130,000 infant deaths.
Human actions, such as fire suppression activities and landscape fragmentation, have led to lower fire activity across regions like tropical savannas. However, the study emphasizes that climate change has increased burned areas, particularly in tropical and boreal forests, and intensified fire weather conditions.
Climate change increases drought and air temperatures, drying fuels and making it more difficult to suppress fires. It has contributed to large fires during extreme weather events, significantly increasing short-term mortality from PM2.5.
Recent extreme events, like the 2005 fires in southern Europe and the 2015 fires in equatorial Asia, showed higher short-term mortality due to fire smoke under extreme weather. However, the study highlights significant year-to-year variability in fire activity, with some years showing considerably higher mortality than others. For instance, mortality peaked in 2015 but was much lower in 2013. Despite this variability, there is limited research on the historical impact of climate change on long-term fire-related health burdens globally.
About the study
This study estimated PM2.5 mortality from fires caused by climate change over the past six decades by comparing simulations of actual climate conditions with detrended (unchanged) climate conditions. Researchers used advanced fire-vegetation and chemical transport models, following international frameworks for attributing climate impacts.
The study used a three-step modeling process to assess fire PM2.5 mortality. First, emissions from three fire-vegetation models were simulated. Based on biomass and soil moisture data, fire emissions were calculated by converting burned areas into dry matter emissions. Each model accounted for socio-economic factors affecting fire activity, such as population density and land use. The models—CLASSIC, SSiB4, and JULES—varied in their estimates of fire mortality, with CLASSIC showing lower fire mortality in certain regions compared to the others.
These emissions were then fed into an atmospheric transport model to understand their atmospheric effects. These effects were then linked to health impacts using a dataset on the global burden of disease.
Researchers used two kinds of climate data: factual data, which included historical climate and socio-economic influences, and counterfactual data, which removed long-term climate change trends to isolate the impact of climate change on fire health risks.
Findings
Fire PM2.5 concentrations were implicated in 46,401 deaths annually during the 1960s, rising to 98,748 in the 2010s. Fire-related PM2.5 and mortality initially showed declines until 1990 before increasing. The models showed that climate change increased fire risks and mortality over the decades. In the 2010s, climate change caused an excess of 12,566 fire-related deaths globally, compared to 669 in the 1960s.
Climate change significantly affects fire mortality in certain regions, including temperate grasslands, the Amazon Basin, southern Australia, and southern Europe. However, in some areas, such as Southeast Asia and Central Asia, fire mortality remained stable or even decreased. Fire mortality varied based on the model used, with one showing lower mortality in certain regions like Africa and South America.
Researchers also found that fire-related emissions were higher in tropical and temperate forests, increasing fire risk as conditions become drier. Fire-related mortality was higher in boreal forests, particularly in Europe and Australia, due to climate change-driven alterations in humidity and temperature.
The study also emphasizes the importance of interannual variability in fire activity. Some years, such as 2015, saw significant increases in fire activity and related mortality, while other years showed much lower fire-related deaths. This variability highlights the challenges of predicting fire mortality trends. Socio-economic factors, such as baseline mortality rates, also impacted the results, showing a need for better health data.
Conclusions
Assessing the uniform effect of climate change on fires globally is difficult due to various regional differences in factors like fire weather or fuel moisture. The study estimates historical PM2.5 levels from fires and associated mortality linked to climate change over the past 60 years.
The model had some limitations, with some regions, including China and India, showing poor agreement with satellite data and highlighting challenges in capturing spatial patterns. In particular, the CLASSIC model consistently simulated lower fire activity in certain regions, such as northern Africa and South America. Researchers also noted overestimations in fire activity in certain areas, pointing to the need for increased model accuracy. The analysis also focused on annual rather than daily exposure and assumed that all PM2.5 sources have similar toxicity.
Researchers highlighted that climate change has led to increased fire-related PM2.5 and mortality. As temperatures are expected to rise by 1.5°C by 2040, countries must enhance emergency preparedness, wildfire suppression, and fire monitoring to reduce health impacts. Additionally, adaptation strategies must account for significant year-to-year variations in fire activity and mortality, which the study suggests may be influenced by both climate change and socio-economic factors. Resilient land-use planning and fire-resilient structures can aid these efforts, with adaptation strategies crucial in high-risk regions identified in this study.
Journal reference:
- Park, C. Y., Takahashi, K., Fujimori, S., Jansakoo, T., Burton, C., Huang, H., Reyer, C. P., Mengel, M., Burke, E., Li, F., Hantson, S., Takakura, J., Lee, D. K., & Hasegawa, T. (2024). Attributing human mortality from fire PM2.5 to climate change. Nature Climate Change, 1-8. DOI: 10.1038/s41558-024-02149-1, https://www.nature.com/articles/s41558-024-02149-1