As an unusual heat dome sent temperatures in the Pacific Northwest soaring to 108 degrees Fahrenheit on June 28, 2021, Juliana Leon pulled her car over and rolled down the windows, overwhelmed by the heat.
Hours later, when emergency medical workers reached Ms. Leon, she had died of hyperthermia, or overheating. Her internal body temperature was 110 degrees Fahrenheit, according to court documents.
On Wednesday, Ms. Leon’s daughter, Misti, sued seven oil and gas companies, claiming wrongful death. The suit alleges that they failed to warn the public of the dangers of the planet-warming emissions produced by their products and that they funded decades-long campaigns to obscure the scientific consensus on global warming.
The case represents a major escalation in the growing efforts to hold fossil fuel companies accountable for climate change.
Cities and states have been bringing climate lawsuits against big oil and gas producers for years now, claiming they engaged in deceptive marketing, fraud and even racketeering.
But experts said Ms. Leon’s case, filed in state court in Washington, was the first time that fossil fuel companies have been sued over the death of an individual as a result of conditions caused by man-made climate change.
The companies named in the complaint are Exxon Mobil, Chevron, Shell, BP, ConocoPhillips, Phillips 66 and Olympic Pipeline Company, a subsidiary managed by BP.
Phillips 66 said it did not comment on pending litigation. None of the other companies named in the suit responded to requests for comment. In previous cases, oil and gas companies have asserted that they cannot be held liable for the monetary damages caused by global warming.
In the complaint, Ms. Leon’s attorneys lay out a well-established set of facts: that the oil and gas companies knew for decades that their products would dangerously alter the planet’s atmosphere, that they continued to produce those products despite knowing the risks, and that they worked to suppress public awareness of theses dangers.
Numerous independent investigations, including recent inquiries by Congress, have revealed that many major oil companies and their trade groups spread disinformation about climate change and worked to hold back the clean energy industry.
And scientists around the world overwhelmingly agree that fossil fuel emissions have caused significant planetary warming in recent decades.
Average global temperatures in 2024 were more than 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, higher than those the planet experienced at the start of the industrial age, leading to extreme heat, violent weather, rising seas and melting glaciers.
The broad outlines of that story are often cited in legal complaints against fossil fuel companies. But until now, no case has tried to hold corporations liable for a specific death tied to a weather event.
Legal scholars have been anticipating the filing of a case like this for years. In 2023, a paper published in the Harvard Environmental Law Review made the case that prosecutors could charge oil companies with criminal homicide and “every type of homicide short of first-degree murder.”
While Ms. Leon’s complaint is civil, rather than criminal, it follows a similar logic.
“There’s a reasonable framework for a complaint,” said Cindy Cho, a former federal prosecutor who now teaches law at Indiana University Bloomington and is not involved in the case. “You have a chain of causation, and yes, you have to back it up with that evidence. But the allegations, taken at face value, are reasonable.”
The heat dome that scorched the Pacific Northwest in 2021 would have been “virtually impossible” were it not for man-made climate change, according to researchers with World Weather Attribution, an international group of scientists and meteorologists.
As a result of the heat dome, a phenomenon that occurs when high pressure traps hot air over a large area for an extended period, about 600 more people died in Oregon and Washington than would have been typical for a week in late June, a New York Times analysis found.
Around the world, extreme heat has emerged as one of the deadliest manifestations of a warming planet. Heat deaths have doubled in the United States in recent decades, a recent study found. And while tallying such deaths can be difficult, heat waves are creating mass casualty events from India to Australia. A 2022 heat wave in Europe killed more than 60,000 people.
Juliana Leon, who was 65 at the time of her death, was retired and spent her time writing poetry and visiting with her family, according to the lawsuit and her daughter.
On the morning of her death, she had driven 100 miles from her home in Ferndale, Wa., to a doctor’s appointment in Seattle. It was the third day in a row when temperatures exceeded 100 degrees Fahrenheit, or about 38 Celsius. Shortly after she left her appointment, Juliana pulled over and rolled down the windows.
Ms. Leon said she had spoken to her mother that morning, but grew worried when she was unable to reach her later in the day. After calling the local police, she learned that her mother had perished in the heat.
“I never would have in a million years guessed that a heat dome and climate change would be what killed my mother and what took her from me,” Ms. Leon said in an interview. “There’s no way to comprehend that and to kind of even rationalize it.”
The campaign to hold fossil fuel companies accountable for the destruction caused by climate change has gained significant momentum in recent years.
But none of the cases brought by cities or states have yet gone to trial.
Vermont last year enacted the nation’s first climate superfund law, an effort to allow the state to recover money from fossil fuel companies to help pay for damage from extreme weather events. New York also passed a similar law last year.
In recent months, some of the climate suits have faced substantial setbacks in court, with cases in New York, New Jersey and Maryland getting dismissed by judges. President Trump recently called the lawsuits “ideologically motivated” and said they were holding back American energy production.
But some of the climate cases are moving forward, giving climate activists hope that the fossil fuel companies may be made to pay.
“Why shouldn’t we hold someone legally accountable for this kind of behavior?” said David Arkush, director of the climate program at Public Citizen, an advocacy group that has called for brining criminal charges against fossil fuel companies, and a co-author of the Harvard Environmental Law Review paper.
“There would be no question that we would hold them accountable if they caused other types of deaths,” he added. “This is no different. They foresaw this, they did it anyway, and they hurt people.”
Ms. Leon was first approached in late 2023 by a nonprofit group, the Center for Climate Integrity, which helps assemble and promote cases against big oil and gas companies.
She then began working on building a case with Tim Bechtold, a lawyer in Montana with an interest in climate and environmental law. The suit also includes claims of creating a public nuisance, and a failure to warn under Washington’s product liability act.
Ms. Leon is seeking monetary damages, but her complaint does not request a specific amount of money.
She said that while she had been aware of climate change before her mother’s death, it was only when she began working on the lawsuit that she learned about the oil and gas industry’s efforts to downplay the dangers posed by a hotter planet.
“My reaction was shock and disbelief,” she said. “It actually felt more personal. Like a punch to the gut.”
David Gelles reports on climate change and leads The Times’s Climate Forward newsletter and events series.
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