In front of a standing room only courtroom audience, the case of The People of California vs. B.P. P.L.C. et al. took an important step forward yesterday. In this case, the cities of San Francisco and Oakland, Calif., are aiming to hold five major fossil fuel companies responsible for climate damages, particularly with respect to sea level rise. In a federal court in San Francisco, the presiding Judge William Alsup had specifically asked both sides to present a “tutorial on climate science” and to address eight questions he had posed. So how did the big oil company defendants present their version of climate science? And how did it compare to the scientific consensus? Together with my UCS colleague Deborah Moore, Western States Senior Campaign Manager, I was lucky enough to get a seat in the courtroom. Here are four of our takeaways from the day:

1. Judge Alsup was highly engaged with the presenters from each side

The plaintiffs had three renowned scientists present their tutorial: Dr. Myles Allen of Oxford University, Dr. Gary Griggs of the University of California at Santa Cruz, and Dr. Don Wuebbles of the University of Illinois. The defendants had one representative–Chevron lawyer Theodore Boutrous–presenting. Alsup interrupted each presenter many, many times to get clarification, to dissect a chart or graph, or to ask additional questions. I came away with the sense that Alsup truly wanted to understand the causes and consequences of climate change, and it is great to see such engagement.

2. The Fifth Assessment Report done by the IPCC no longer fully reflects the most current scientific consensus on climate change

For the defendants’ presentation, Mr. Boutrous relied almost entirely on results from the 2013 Intergovernmental Panel on Climate Change (IPCC) report. He opened his portion by stating that Chevron accepts the scientific consensus on climate change represented in the IPCC report, including that humans are the primary cause of observed warming in recent decades. This, he said, has been the company’s position for about ten years. He then walked Judge Alsup through a series of slides highlighting conclusions, as well as uncertainties, from the IPCC report. By relying so exclusively on the IPCC report, he bolstered his claim that Chevron’s views are in line with mainstream science, but also exposed just how much climate science has progressed since the report was released in 2013. Among the many major scientific developments of the last five years are:

A greater understanding of the potential contribution of the Antarctic Ice Sheet to sea level rise this century; and

The ability to rigorously attribute virtually all observed warming since the mid-1900’s to human activity, and a portion of the observed warming and sea level rise to the products of specific fossil fuel producers. As Mr. Boutrous went through his presentation, I was struck by how much the consensus view has sharpened in the last five years. A few minutes later, Dr. Wuebbles began his presentation, the final one for the plaintiffs, by explaining, from the perspective of a lead author for both the 2013 IPCC Fifth Assessment and the US Fourth National Climate Assessment issued in 2017, that “science didn’t stop in 2012.” He then proceeded to highlight results from the 2017 report, which is the latest and most comprehensive assessment of the state of climate science for the U.S.

In UCS’s 2016 Climate Accountability Scorecard, Chevron scored “poor” on acknowledging climate science. So it was a big step for Chevron to state, on the record, that it accepts the scientific consensus on climate change. But since the IPCC Fifth Assessment Report, the trends have become clearer and our ability to attribute climate change to human activity has progressed. So accepting the consensus view as of five years ago is simply not sufficient.

3. Chevron continues to highlight uncertainties and cherry-pick information

While Mr. Boutrous did rely almost entirely on information and graphics from the 2013 IPCC report, many of those graphics were chosen carefully to highlight uncertainty or sow seeds of doubt about the reliability of the underlying scientific studies and the severity of the predicted impacts.

For instance, Mr. Boutrous showed projections for future warming from a suite of climate models and highlighted that some models are overly sensitive to changes in carbon dioxide concentrations and likely overestimate future warming. Later, when showing sea level rise trends globally, Mr. Boutrous highlighted a roughly decade-long period when sea level in the San Francisco area was relatively unchanging, which deliberately ignores the consistent long-term rise here and around the globe.

In addition to this questionable presentation of the data, Chevron repeatedly tried to downplay the role the fossil fuel industry plays in exacerbating climate change—by pointing to language in the IPCC report that states that population and economic growth are the drivers of increasing carbon emissions. Yes, as the world’s population grows, emissions rise because fossil fuel use increases.

But multiple investigations have uncovered evidence showing that the fossil fuel industry funded a decades-long climate science disinformation campaign to block policies that would reduce carbon emissions, and actively promoted its products to ensure fossil fuels would remain central to global energy production. Chevron continues to dismiss and deny climate risks and fund trade associations and other industry groups that still spread climate disinformation or block sensible climate policies.

When questioned by Judge Alsup on the finer points of the graphics he was showing, Mr. Boutrous was often forced to admit that his scientific understanding of the issue was limited and that he could not answer. It was striking that the oil companies chose a lawyer to present their scientific narrative, and the choice contrasted sharply with the deep scientific knowledge that the plaintiffs brought to the table.

4. Science has a key role to play in public nuisance cases, and scientists are stepping up to the plate

As graduate students, many of us climate scientists were told to be wary of wading too close to the politics of climate change, that we’d best stick to the science. Yesterday, three very prominent scientists stuck to the science, but used scientific information to establish that fossil fuel burning has already and will increasingly harm public well-being. Rather than putting “climate science on trial,” Judge Alsup’s climate science tutorial provided the case with a strong scientific underpinning that can help support making a determination, based on a set of legal standards and precedents, about the liability and responsibility of big oil companies.

Deborah Moore, Western States Senior Campaign Manager at the Union of Concerned Scientists, contributed significantly to this post.