On Wednesday, a federal judge will hold a “climate science tutorial” as part of San Francisco’s and Oakland’s nuisance cases against five oil giants for damages related to sea level rise. He has invited plaintiffs and defendants to present the history of climate science and “the best science now available on global warming, glacier melt, sea rise and coastal flooding.” Last week another federal court rejected oil companies’ efforts to get nuisance cases filed against them by Imperial Beach (San Diego County) and Marin and San Mateo counties moved from state courts into the federal system. The decision dealt the companies a huge blow, given favorable California law.

At the heart of both cases are these central questions: What did fossil fuel producers know about climate change and its causes and effects, when did they know it, and how did their public statements square with what they knew? The answers could help determine whether these companies should pay for some of the billions of dollars needed to protect Californians from rising seas and damage from drought, wildfire and other extreme events worsened by climate change.

A decade ago, courts dismissed a series of nuisance suits brought against fossil fuel emitters alleging they should be held responsible for their greenhouse gas emissions. Judges dismissed the cases largely on grounds that plaintiffs lacked the evidence to show that coal-burning power plants and other big emitters caused specific climate harms. Today plaintiffs can show, based on new scientific studies, the clear connection between heat-trapping emissions and worsening impacts.

Scientists have found, for example, that carbon emissions traced to the products of 20 large fossil fuel producers have contributed about 15 percent of global sea level rise — and more than 6 percent result from emissions traced to ExxonMobil, Chevron and BP, the three largest sources, alone. Scientists can also now characterize how climate change has worsened the extent and severity of specific extreme events, such as California’s recent multiyear drought.

These “climate attribution studies” are relevant to the question of company responsibility for climate harms. So, too, is the accumulating evidence of companies’ deception on the issue. Enterprising journalists at the Columbia School of Journalism and the Los Angeles Times published an exposé showing that ExxonMobil claimed for years that climate science was too uncertain to warrant action while privately incorporating the science they were publicly dismissing into business plans to protect their drilling operations in a warming Arctic. Meanwhile, ExxonMobil and other fossil fuel companies financed an enormous multimillion-dollar disinformation campaign to manufacture doubt about climate science. They employed a vast network of trade associations and lobby groups, think tanks and politicians to distort the realities and risks of global warming to block policies that would reduce carbon emissions.

These two changes mean that for the first time, communities affected by climate change stand a real chance of holding fossil fuel companies accountable. The communities have also made some smart strategic choices this time around. Instead of suing power plants, they have chosen to sue the producers and extractors of petroleum products. Evidence tracing rising temperatures and sea levels back to the products of individual fossil energy companies may make it easier for courts to find defendants responsible for a proportion of climate harms. The plaintiff communities have also sued in California courts, where recent nuisance cases make clear that defendants who conceal the dangers of their activities and engage in campaigns against regulation are more likely to be found liable for their actions. The fossil fuel companies are right to be afraid to be in California courts.

The lawsuits may take years to resolve. But at a time when the federal government has retreated from climate leadership, they are an important lever to force big oil to take responsibility for their actions and diminish their ability to thwart sensible climate policies.

The cases also shine a light on the companies’ deceptive behavior and role in creating public confusion about the causes of climate change. And eventually, they can help California communities lead the fight to ensure companies pay for the climate damage their products are already costing to lives and livelihoods.