In California Wildfires, Climate and Health Collide

As California authorities search for the causes of the Los Angeles County wildfires, many scientists agree that successive extreme weather events associated with climate change set up the dangerously dry conditions that led to the catastrophe.

After decades of drought, California experienced two years of extremely heavy rainfall in 2022 and 2023 that allowed vegetation to flourish. This was followed by record-breaking heat and dry conditions in late 2024 that resulted in an abundance of tinder-dry grass and shrubs by the time the first LA fires sparked on Jan. 7.

In a new report, scientists at the Yale School of Public Health warn that these compound extreme weather events—droughts, floods, hurricanes, and wildfires —pose an increasing threat to population health and highlight an urgent need for more robust public health preparedness and response. Individuals with pre-existing cardiovascular and other health conditions are particularly at risk, the report says.

“Climate change can’t be perceived as a distant threat; it is here; it is happening; and it’s affecting millions of lives,” said Kai Chen, PhD, a co-director of the Yale Center on Climate Change and Health and the report’s lead author. "These extreme weather events, which are worsening and becoming more frequent due to climate change, are not merely environmental crises— they are pressing public health emergencies.”

Climate-related disasters in the United States have risen alarmingly in recent years. In 2024, according to the National Oceanic and Atmospheric Administration, the U.S. experienced 27 catastrophic weather and climate events, such as wildfires, floods, and droughts, in which property damage and other costs reached or exceeded $1 billion.

The impact of these cataclysmic events often extends far beyond the immediate loss of life and extensive property damage. They also have less visible impacts on population health. Wildfire smoke is particularly dangerous due to the fact that it can contain toxic organic compounds as well as high levels of microscopic particulate matter known as PM2.5. These minute particles are able to penetrate deep into the lungs, triggering inflammation, oxidative stress, and other conditions that make it difficult to breathe and elevate the risk of cardiovascular events, such as heart attacks and arrhythmias.

“Wildfire smoke's composition, filled with harmful organic compounds, and its ability to travel vast distances, makes it exceptionally dangerous,” said Harlan Krumholz, MD, the report’s senior author and a leading cardiologist at Yale School of Medicine. “We are seeing cardiovascular events in people who don’t even live close to the wildfires but are still exposed to the dangerous particulates carried by the smoke.”

The health impacts of wildfire smoke are exacerbated when wildfires overlap with other extreme weather events such as heat waves and when individuals have preexisting cardiovascular or respiratory conditions, Krumholz said. To mitigate these risks, he said, clinicians should encourage people to wear protective masks when wildfire smoke is in the air, and they should consider the potential impact of existing extreme weather conditions when assessing patients’ health risks and treatment guidelines.

"Wildfire smoke is more than a respiratory hazard; it’s a threat to cardiovascular health,” Krumholz said. “When seeing their patients, clinicians must consider the risk multiplier effects of concurrent exposures, such as heat waves or preexisting respiratory conditions, which exacerbate cardiovascular harm.”

The report notes that current public health frameworks don’t fully capture the heightened health risks associated with compound climate events. These events can be categorized into co-occurring or successive events, each having dire consequences for cardiovascular health.

Co-occurring events, such as heat waves combined with wildfire smoke, have been linked to increased mortality rates due to their synergistic health impacts. Successive events, on the other hand, can cascade into further crises. The Southern California fires are a prime example. They were preceded by a severe drought that increased vegetation flammability, setting the stage for more destructive wildfires.

The ripple effects of these compound events extend beyond immediate physical health risks, causing secondary crises like power outages, shortages of essential supplies, and transportation breakdowns. These disruptions can lead to delays in medical care, worsening conditions for vulnerable populations, and further increasing cardiovascular risks.

The report offers a three-pronged approach in which public health officials, policymakers, and the medical community—particularly cardiologists—can help mitigate and prepare for the extreme climate events that most certainly lie ahead.

1. Anticipation: Health systems should identify high-risk regions and populations using predictive models to anticipate cardiovascular health impacts. Clinicians should be trained to recognize and address overlapping risks, such as dehydration during drought combined with respiratory strain from wildfire smoke.
2. Mitigation: Investments in climate-resilient infrastructure, such as emergency power supplies, portable air filtration units, and mobile health units, are crucial. Proactive measures, including stockpiling emergency medications and conducting post-disaster screenings, are essential to minimizing secondary health impacts.
3. Adaptation: Public health strategies must evolve to address the complexities of compound events. Enhanced surveillance of cardiovascular events, improved coordination between health systems and environmental agencies, and targeted interventions in disaster-prone areas are critical steps.

“Our understanding and response to these compound events must evolve,” said Chen. “We need to build resilient health care systems that are prepared for and can properly respond to the multifaceted pressures of a rapidly changing climate."

The report appears in the Journal of the American College of Cardiology. Yuan Lu, ScD, an assistant professor of medicine (cardiology) and of biomedical informatics and data science and of epidemiology (chronic diseases) at Yale University, is also a co-author.