Journal Article Annotations
2025, 3rd Quarter

Climate Change and the Environment

Annotations by Mary Burke, MD
September, 2025

Wildfire smoke exposure and mortality burden in the US under climate change.
Global warming amplifies wildfire health burden and reshapes inequality.

PUBLICATION #1 — Climate Change and the Environment

Wildfire smoke exposure and mortality burden in the US under climate change.

Minghao Qiu, Jessica Li, Carlos F Gould, Renzhi, Makoto Kelp, Marissa L Childs, Jeff Wen, Yuanyu Xie, Meiyun Lin, Mathew V Kiang, Sam Heft-Neal, Noah S Diffenbaugh, Marshall Burke.

Abstract: Nature. 2025 Sep 18. doi: 10.1038/s41586-025-09611-w. Online ahead of print.

Wildfire activity has increased in the US and is projected to accelerate under future climate change ^1–3. However, our understanding of the impacts of climate change on wildfire activity, smoke, and health outcomes remains highly uncertain, due to the difficulty of modeling the causal chain from climate to wildfire to air pollution and health. Here we quantify the mortality burden in the US due to wildfire smoke fine particulate matter (PM_2.5) under climate change. We construct an ensemble of statistical and machine learning models that link climate to wildfire smoke PM_2.5, and empirically estimate smoke PM_2.5-mortality relationships using data on all recorded deaths in the US. We project that smoke PM_2.5 could result in 71,420 excess deaths (95% CI: 34,930 – 98,430) per year by 2050 under a high warming scenario (SSP3-7.0) – a 73% increase relative to estimated 2011-2020 average annual excess deaths from smoke. Cumulative excess deaths from smoke PM_2.5 could reach 1.9 million between 2026-2055. We find evidence for mortality impacts of smoke PM_2.5 that last up to three years after exposure. When monetized, climate-driven smoke deaths result in economic damages that exceed existing estimates of climate-driven damages from all other causes combined in the US ^4,5. Our research suggests that the health impacts of climate-driven wildfire smoke could be among the most important and costly consequences of a warming climate in the US.

Annotation

The finding:
This article, which reached newspapers when it was published in September 2025, uses commonly accepted statistical models (Shared Socioeconomic Pathways of climate change, developed by the Intergovernmental Panel on Climate Change in 2021), to model changes in wildfire smoke and the associated creation of particulate matter 2.5. (PM2.5) in North America. Under the three worse scenarios, in which governments do not take united global action, the authors predicted that wildfire smoke and associated PM 2.5 would increase between 262%-482% between 2046-2055 vs the 9 years of 2011-2020. In the worst-case scenario, concentrations of PM 2.5 could be as high as 10mcg/ml3 ambient air. Increased short and long-term mortality has already linked increases of .75-1.0mcg/ml3. Other morbidities associated with increased PM2.5 include hastening cognitive decline and adverse pregnancy outcomes. The Western US, Canada and Mexico will be most impacted, while the Eastern US will see increases related to smoke from Canadian fires.

Strength and weaknesses:
While the numbers may sound dramatic, this multi-institutional collaboration includes authors who have been tracking the negative mental health and health effects of climate change for years.

Relevance:
Wildfire smoke has become an increasingly common risk in western North America. This study helps us prepare for the coming years, so that we can provide necessary psychoeducation to our vulnerable patients. The health effects of environmental/ climate change will be one of the most pervasive risks to human health in the coming decade. Heat and smoke have been shown to be linked to long-term risks for dementia, to adverse outcomes in pregnancy, and to developmental risks to children. All health care providers can provide anticipatory guidance regarding using N-95’s during periods of high pollution, and how to stay cool during heat waves.

PUBLICATION #2 — Climate Change and the Environment

Global warming amplifies wildfire health burden and reshapes inequality.

Junri Zhao, Bo Zheng, Philippe Ciais, Yang Chen, Thomas Gasser, Josep G Canadell, Longyi Zhang, Qiang Zhang.

Abstract: Nature. 2025 Sep 18. doi: 10.1038/s41586-025-09612-9. Online ahead of print.

Global warming intensifies wildfires and exacerbates greenhouse gas and pollutant emissions¹. However, global projections remain incomplete, hindering effective policy interventions amid uncertain warming futures². Here, we developed an interpretable machine learning framework to project global burned areas and wildfire emissions. This framework accounts for the impacts of future climate change on fire activity and quantifies associated premature deaths and radiative forcing from fire-induced particulate matter (PM_2.5). Here we show that from 2010–2014 to 2095–2099, fire carbon emissions are projected to increase by 23% under the Shared Socioeconomic Pathway (SSP) 2-4.5. Increased fire-related aerosols reduce the 0.06 W m⁻² cooling effect north of 60°N. Projections show a surge in premature deaths from wildfire smoke, reaching 1.40 (95% Confidence Interval: 0.66–2.25) million annually during 2095–2099, roughly 6 times higher than current levels. Africa is projected to experience the greatest rise in fire-related deaths (11-fold), driven by emission changes and an aging population. Europe and the U.S. would experience a 1–2-fold increase under SSP2-4.5, linked to rising fire occurrences in the mid-latitude Northern Hemisphere. Overall, the health burden would become more evenly distributed across nations of differing development levels than present patterns, underscoring the need for coordinated efforts.

Annotation

The finding:
This study builds on an extensive literature demonstrating the strong links between wildfire smoke, and especially PM2.5, and human morbidity and mortality. This study is in line with other studies predicting an increasing risk of fires due to global warming, increasing human exposure to smoke. This study reviews models that highlight that the harms of climate change are not felt equally, with African countries predicted to have higher exposure, although producing far less toxic pollution than Western countries.

Strength and weaknesses:
The lead author has a strong body of research on this topic, with no weaknesses.

Relevance:
The health effects of environmental/ climate change will be one of the most pervasive risks to human health in the coming decade. This article points to fundamental inequities of the burdens of climate/ environmental deterioration.