Last week, a federal judge at the US District Court for the Northern District of California held a five-hour tutorial to lay the scientific foundation for two lawsuits against the five biggest oil companies in the world.
The plaintiffs, the cities of San Francisco and Oakland, brought three world-renowned climate scientists to the tutorial. The defendants — BP, Chevron, ExxonMobil, Shell, and ConocoPhillips — sent one lawyer, from Chevron. And when it was his turn to present, the Chevron attorney agreed that human activity is changing the climate and that it warrants action.
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This is a seismic shift from years past, when "uncertainties" about climate change were the party line for oil companies. Humanity's role in rising temperatures has now been established in court, and future legal wrangling will have to build on this foundation.
But both sides agreeing to the fundamental mechanisms behind climate change now will give way to the thornier legal debate of establishing blame.
The suits are part of a suite of litigation filed by nine American cities against big oil to pay for current and future damages to some of the most expensive real estate in the country caused by rising seas and hotter weather.
The cities are arguing that oil companies promoted the use of fossil fuels while denying or downplaying their harmful effects, and so should help cities pay for infrastructure like coastal barriers to protect them.
But the judge presiding over the suits, William Alsup, wanted to get the science straight first, and he invited the cities and the oil companies to present the history of climate change research and the best available findings in a kind of unusual hearing that he's become known for. Alsup prepared a list of wonky questions and rewatched An Inconvenient Truth to ready himself for the in-depth lesson.
Ann Carlson, an environmental law professor at the University of California Los Angeles, said that similar lawsuits faltered a decade ago because the evidence linking heat waves and flooding back to burning fossil fuels wasn't as robust as it is today.
"This attribution science is much stronger," she said.
So the next question is whether there's an argument for holding big oil in particular liable. And what we learned from the tutorial is that these companies are likely to use the agreed-upon science to make the case that they shouldn't have to pay for the impacts of climate change.
If the cities' lawsuit survives a barrage of motions to dismiss, they will still have to show that oil majors deliberately sowed confusion on climate change in bad faith. Let's walk through what we know about the various arguments so far.