By Sachi Kitajima Mulkey and Harry Stevens
If the planet continues to warm at its current rate, exposure to wildfire smoke will kill an estimated 70,000 Americans each year by 2050, according to new research.
The results are some of the strongest evidence yet that climate change endangers people in the United States, said Marshall Burke, an environmental economist at Stanford University who contributed to the study. For Americans, “the impacts are much larger than anything else that has been measured,” Dr. Burke said.
Wildfire smoke, intensified by rising temperatures, is on track to become one of America’s deadliest climate disasters, causing as many as two million deaths over the next three decades, the analysis found. Published Thursday in the journal Nature, it is the most robust estimate yet of how deadly wildfire smoke could become as the planet warms.
The researchers used roughly two decades of death records and satellite and ground data on wildfire smoke pollution to measure how exposure affects mortality.
“This paper is a wake-up call for people,” said Kai Chen, an associate professor at the Yale School of Public Health, who was not involved in the study. “It shows this is a nationwide problem, and it’s tied to climate change.”
At the end of July, the Trump administration proposed repealing the endangerment finding. That measure, an Obama-era scientific determination that greenhouse gases pose a threat to public health, has been used as the legal basis for strict limits on industrial sources of greenhouse gas emissions.
Greenhouse gases, like carbon dioxide and methane, are produced when fossil fuels are burned and trap heat in Earth’s atmosphere. Since the industrial revolution, the planet has warmed about 1.3 degrees Celsius.
Other researchers have found that the most extreme wildfires have doubled in frequency and intensity over the past two decades. The trend has persisted this year, with record-breaking blazes sweeping across parts of Canada, California and Hawaii.
Even under a more moderate climate scenario, in which humans curb greenhouse gas emissions to lessen future warming, the study found the death toll from wildfire smoke would remain similarly high, reaching some 67,000 annual deaths by 2050. Even the mildest scenario, in which emissions are nearly eliminated, results in about 66,000 deaths each year.
Scientists track air quality by measuring tiny airborne particles that measure 2.5 microns across, or less than half the size of a red blood cell. This pollution is known as PM 2.5 and is regulated by the Clean Air Act and monitored by the Environmental Protection Agency. The Trump administration has proposed loosening national air quality standards, which would result in more of this kind of pollution.
These tiny particles are small enough to lodge deep in the lungs and enter the bloodstream, where they can cause inflammation and a cascade of health problems. The PM 2.5 found in wildfire smoke can be more hazardous than other kinds of air pollution, like dust.
It’s “basically a toxic soup of chemicals,” said Francesca Dominici, a professor of biostatistics at the Harvard School of Public Health. Long term heath effects from exposure can include heart problems and respiratory issues.
And when wildfires reach urban areas, “things get much worse,” Dr. Dominici said, as burning plastic, concrete and car parts make the smoke even more harmful.
In January, large wildfires in Los Angeles County razed entire neighborhoods in Altadena and the Palisades. Some firefighters who fought the blazes without masks have since developed serious cancers, a New York Times investigation has found.
But linking health problems or deaths to any environmental event is notoriously difficult, as scientists often struggle to isolate the effects of a single cause among all possible factors. Analyzing effects from smoke, which travels vast distances and may cause health problems years after the exposure, is especially challenging. It may not have been possible to do this study 10 years ago, Dr. Burke said, because there was not yet enough data on extreme wildfires to credibly estimate the future impacts of their smoke.
“Our worst-case scenarios of the past are what guide our understanding of what could happen in the future,” he said.
In their analysis, the researchers had to overcome a particularly challenging hurdle: How do you predict where a fire might start.
“Where fire happens is kind of a random process,” said Minghao Qiu, an assistant professor of atmospheric science and public health at Stony Brook University who led the study. But he added that “super clear patterns” emerge at the regional level.
The specific spark that starts a large wildfire, whether from a careless campfire to a lightning strike, is not possible to predict with a scientific algorithm, he said. Instead, the researchers modeled the average likelihood of a fire happening in any given location, based on historical occurrences and climate conditions.
“There’s no question that they’ve done the best possible study they could have with the available data,” Dr. Dominici said. The complexity in navigating these uncertainties is one of the reasons this study is a first of its kind.
The researcher’s model estimates that the West Coast will experience the most significant increase in wildfire smoke pollution, with California facing the highest rise in annual smoke-related deaths among all states. In a moderate warming scenario, this amounts to around 4,500 additional fatalities each year compared with the 2010s.
The effects will also be felt nationwide.
The researchers estimate that New York could see as many as 1,800 additional deaths, and nearly as many in Washington State and Texas. In Pennsylvania, as many as 1,600 additional people could die. The study found over half the nationwide smoke mortalities would occur in Eastern states, where population density tends to be higher.
Many of the smoke events that blanket the U.S. cities originate outside the country, particularly in Canada. In June 2023, for example, New Yorkers experienced a significant spike in air pollution as record-breaking fires burned in Quebec.
Dozens of similar haze events have overtaken the East Coast and Midwest since, with nearly 4,000 fires recorded in Canada this year alone. To capture those cross-border impacts, the researchers included wildfire data from both Canada and Mexico in the study.
Future deaths from wildfire smoke also depend on how humans decide to respond to climate change. The models don’t account for future changes to policies that could make air pollution worse, such as recent proposals to roll back air pollution regulations, or rescind the endangerment finding. On the other hand, they also do not anticipate ones that might mitigate wildfires or reduce exposure to smoke.
Strategies such as forest thinning, for example, might lessen the intensity of future blazes. Encouraging people to use air filters and wear masks during smoke events could help lessen resulting health problems, too. Because the data used in the study is based on current policies, Dr. Burke said, that means there’s room for improvement.
“These are projections. They are not what’s going to happen, necessarily,” he said. “But what happens is a choice, and so these don’t have to be an inevitability.”
Sachi Kitajima Mulkey covers climate and the environment for The Times.
Harry Stevens is a Times reporter and graphics editor covering climate change, energy and the natural world.
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