The lawsuit, brought against Chevron, Exxon, ConocoPhillips, Shell, the American Petroleum Institute and several other companies and industry groups, stems from the 2021 heat dome that killed 69 people in Multnomah County as temperatures exceeded 100 degrees for five consecutive days. The county argues that the companies knowingly deceived the public for decades about the safety of their products, burying and undermining scientific evidence that burning fossil fuels would drive catastrophic greenhouse gas emissions and destabilize the climate.

The county is seeking billions in damages on claims of negligence, fraud and deceit, alleging that the companies spent vast sums marketing their products as safe while privately understanding the climate risks. The defendants had argued that the county was effectively attempting to regulate interstate and global pollution, a power reserved for the federal government under the Clean Air Act. But Ridenour ruled that the county is not seeking damages for pollution itself, but for the companies' deceptive conduct toward Oregonians.

"It's deception. That's — again to use the court's language — that's the gravamen of this case," said Roger Worthington, a Bend-based lawyer assisting the county. "Did the defendants engage in deceptive practices designed to sell more oil, and in so doing, try to convince the public that climate change was a hoax? That they had no involvement? And then, did they engage in greenwashing efforts to convince the public that they're actually working on the problem when they're really not?"

The companies also contended that the case could not be heard in state court because it involves business conducted outside Multnomah County and Oregon. Ridenour rejected that argument, finding that the state has the authority to hear the case and the county has standing to bring it because the allegations center on lies told to Oregonians. She did dismiss one defendant, Valero, after finding the county had not established that the company conducted enough business or messaging in the state.

The ruling is a significant moment for climate accountability efforts nationwide. Multnomah County is one of 40 local and state governments that have sued fossil fuel companies over their role in causing climate change. A pending U.S. Supreme Court case brought by Boulder County, Colorado, against Exxon and Suncor could influence the Multnomah County proceedings. Boulder has argued for eight years that the companies are responsible for climate deception that has led to costly disasters, but the case has yet to reach trial as the industry has repeatedly sought dismissal or removal to federal court.

Worthington said he hopes the Multnomah County case reaches trial in his lifetime, but the companies have another avenue to potentially stall it. They are challenging the county under Oregon's anti-SLAPP law, which prohibits lawsuits brought solely to silence critics. A judge heard arguments on that motion last week, and it is unclear when a decision will be issued.

"It was disturbing to hear some of the most powerful companies in the world argue that the county was trying to punish them for engaging in political speech," Worthington said. "There's political speech, and then there's commercial speech. There's speech by companies designed to market their product and, in our theory, deceive the consumers about the dangers of burning their product in terms of climate change. And moreover, fraud is not protected speech."

The defendants' attorneys did not respond to requests for comment.