In an unprecedented courtroom tutorial on climate science, the oil company Chevron went on record agreeing with the scientific consensus that people are causing global warming.

But the company also deflected any responsibility for it under federal law and played up uncertainties in projections for both the volume and future consequences of greenhouse gas emissions. The tack signals a potential legal defense against financial liability for climate change impacts such as rising sea levels.

The odd hearing in federal court came as part of a lawsuit brought by two coastal cities, San Francisco and Oakland, who claim that oil companies are liable for the cost of adapting to sea level rise. The cities claim that the companies ignored the risks to the environment posed by the fossil fuels they were producing.

Federal district judge William Alsup asked the cities and their Big Oil defendants to present an hour each on two subjects: the evolution of climate science to date, and the best available science now.

No ‘Monkey Trial’

“I read in the paper this was going to be like the Scopes Monkey trial. I couldn’t help but laugh,” Alsup said. “Please don’t call this a trial.” The reference was to the 1925 case when the theory of evolution was effectively put on trial in Tennessee.

As the four-plus-hour tutorial began, Alsup warned that it was meant to be wonky. “You will find this probably boring,” he said. “If you get bored, you can just leave.”

At times the presentations lived up to Alsup’s promise, especially as scientists allied with the coastal city plaintiffs addressed the intricacies of sea level rise. The judge interrupted Myles Allen, a climate scientist at Oxford University, to ask for clarification on the movement of carbon dioxide in the atmosphere, and to quibble with graphs.

Deep Dive

Allen summarized early developments in climate science, including the work of Svante Arrhenius, a 19th century Swedish physicist who predicted that temperatures would rise when more carbon dioxide became trapped in the atmosphere; Roger Revelle, who warned that the ocean would not absorb all of the rising carbon emissions and that, as a result, a greenhouse effect would warm the planet; and Charles Keeling, who collected carbon dioxide samples at Mauna Loa to establish what has been a rapid and constant rise in greenhouse gas in the industrial era.

Representing Chevron, Theodore Boutrous, a lawyer with Gibson, Dunn and Crutcher, began his presentation quoting approvingly from the Intergovermental Panel on Climate Change’s fifth and most recent assessment. “It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century,” IPCC authors wrote in 2014.

Boutrous, too, quoted Arrhenius approvingly, leading to a strange exchange with Alsup in which the judge said it was “amazing” that the Swede could have, in 1896, made “a projection that even today sounds pretty reasonable.”

“These scientists were brilliant,” Boutrous responded, trying to pivot back to a separate point about scientific uncertainty.

“Yeah, but this was one guy, you have to admire that,” Alsup noted.

Presentations from scientists and from Boutrous were shaped by Alsup’s interruptions, inquisitiveness, and research, as well as questions for which the judge had asked parties to prepare answers.

Seeding Doubt

For Chevron, Boutrous sought to establish that climate change has a global history, in order to bolster the argument, submitted to the court on Tuesday, that plaintiffs’ claims should be dismissed from federal court. And he sought to characterize climate science as a discordant and tumultuous process filled with uncertainty and trial and error, even as he acknowledged the importance of the IPCC’s most recent assessment.

Scientists, for their part, said that the IPCC represented good work, but not the final word in climate research. University of Illinois climatologist Don Wuebbles pointed out that seventeen of the last eighteen years have been the warmest on record. And while he led a chapter of the 2014 IPCC report, Wuebbles said, “science did not stop” when that work was published.

The plaintiffs’ experts also presented evidence that impacts for coastal cities are worsening. UCSC researcher Gary Griggs said that severe weather events are becoming more important to local communities. “Waiting for absolute scientific certainty is not an option because of what’s at stake,” he said.

Where to from Here?

The significance of the tutorial to the underlying legal claim or to climate liability remains unclear. Legal jurisdiction for tort claims like this one remains murky; another federal judge has sent similar claims brought by San Mateo and Marin Counties, and Imperial Beach against oil companies to state court, and observers say the conflict among state and federal authorities could take time to unwind. Chevron filed a motion to dismiss this case for jurisdictional and other reasons on Tuesday.

But the unprecedented nature of the tutorial heaped attention on what the oil companies say now, what they knew about climate science over the last century, and how they responded to the risks changing climate has posed.

Late in the day, Judge Alsup seemed surprised to learn that Boutrous, as Chevron’s attorney, was speaking only for his client and not the other oil company defendants. He ordered ExxonMobil, ConocoPhillips, Royal Dutch Shell, and BP to go on the record within two weeks, either agreeing with what Boutrous presented or specifying their own positions on the science.

“You can’t get away with sitting here in silence and then later saying he wasn’t speaking for us,” he told them.