Scientists take opposing sides in youth climate trial

Levi Draheim, a plaintiff in the lawsuit, at a 2017 rally in Washington, D.C. ROBIN LOZNAK/OUR CHILDREN'S TRUST

Next week, barring a last-minute intervention by the Supreme Court, climate change will go to trial for just the second time in U.S. history. In a federal courtroom in Eugene, Oregon, 21 young people are scheduled to face off against the U.S. government, which they accuse of endangering their future by promoting policies that have increased emissions of carbon dioxide (CO2) and other planet warming gases. The plaintiffs aren’t asking for monetary damages. Instead, they want District Judge Ann Aiken to take the unprecedented step of ordering federal agencies to dramatically reduce the amount of CO2 in the atmosphere.

Government attorneys are not expected to challenge the scientific consensus that human activities, including the burning of fossil fuels, cause global warming. But the outcome could hinge, in part, on how Aiken weighs other technical issues. Each side has recruited a roster of high-profile scientists and economists, including Nobel laureates, to bolster their argument. “It’s clearly going to be a battle of the experts,” says Michael Gerrard, director of the Sabin Center for Climate Change Law at Columbia University, who is not involved in the case.

The civil trial will be a milestone in a hard-fought legal battle that began in 2015, when environmental groups joined with youth activists and retired NASA scientist James Hansen to push for climate action. The lawsuit rests on the novel argument that the government has knowingly violated the plaintiffs’ rights to a “safe” climate by taking actions—such as subsidizing fossil fuels—that cause warming. Government lawyers under both President Donald Trump and former President Barack Obama have repeatedly tried and failed to have the case thrown out. Just last week, Aiken, who was appointed by former President Bill Clinton, denied a bid to stop the trial, which was set to open on 29 October. But the Supreme Court then froze the case while it considers the government’s argument that the plaintiffs’ lawsuit has fatal legal flaws.

If the trial proceeds, the youths’ lawyers will have to persuade the judge that the government’s actions have helped cause climate change; that the warming exacerbated storms, droughts, and wildfires; and that individual plaintiffs have suffered injuries as a result. One expert for the plaintiffs, climate scientist Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colorado, filed testimony based on his research that invokes principles of thermodynamics to explain how warming can amplify disasters. Hotter, dryer weather increases the risk of fires, he notes. And warmer air can hold more moisture, boosting rainfall by up to 20%—a factor he says worsened floods that affected plaintiffs living in Louisiana, Florida, and Colorado. “Once thresholds are crossed, things break, burn, or die!” he writes.

Defense expert John Weyant, a management scientist at Stanford University in Palo Alto, California, disagrees that weather extremes can be pinned on climate change. Existing science is not precise enough to attribute individual events and injuries to climate, he writes in his testimony, and Trenberth’s method ignores confounding factors. For example, he argues, poor forest management and human-sparked blazes also cause severe fires.

These confounding factors are “true but irrelevant” to whether warming contributed to a particular weather extreme, says climate scientist Drew Shindell of Duke University in Durham, North Carolina. But Trenberth’s approach is controversial, notes climate scientist Friederike Otto of the University of Oxford in the United Kingdom. (Neither scientist is involved in the case.) Researchers can now at least partly attribute extreme events to warming, Otto says, but Trenberth’s method isn’t able to rule out whether a particular event would have occurred even without climate change.

The two sides may also spar over health impacts. Some plaintiffs claim smoke from worsening wildfires has triggered their asthma attacks. Others say the ecological harm driven by warming has caused emotional distress. But doctors testifying for the defense say the plaintiffs can’t point to medical evidence for these connections. Samantha Ahdoot, a pediatrician at Virginia Commonwealth University’s Inova campus in Richmond who is not involved in the case, notes it’s often impossible to determine the cause of specific ailments. But she says large-scale studies support claims that climate impacts can harm children’s health.

Even if the youth prevail on scientific questions, Gerrard says, they’ll have to persuade the judge that she can provide an effective remedy. In other recent (and so far unsuccessful) climate lawsuits, cities and allied plaintiffs have sought money from energy companies and others to help them address alleged harms. But the youth want Aiken to order the Environmental Protection Agency (EPA) and other agencies to revamp regulations, with the goal of reducing atmospheric concentrations of CO2 to 350 parts per million (ppm), from about 410 ppm today.

The two sides disagree over whether the United States can reduce emissions as fast as the plaintiffs would like. But the government may also argue that any cuts would have a limited impact, because of the global nature of climate change. Other countries now produce roughly 88% of the world’s greenhouse gas emissions, David Victor, a climate policy expert at the University of California, San Diego, notes in his testimony for the defense. Therefore, the solution requires international cooperation, he writes.

Courts have rejected that argument as a rationale for inaction in previous cases, Gerrard says. In the only other climate lawsuit to get to the trial stage—a landmark 2007 case that challenged EPA’s refusal to regulate CO2 from vehicles—the agency claimed doing so wouldn’t matter because U.S. cars contributed just 6% of global emissions. But the Supreme Court disagreed.

Perhaps the biggest question at stake, observers say, is whether judges can—and should—set climate policy. The plaintiffs think so, calling the courts their “last resort,” and Aiken appears open to the idea. “Federal courts too often have been cautious and overly deferential in the arena of environmental law, and the world has suffered for it,” she wrote in a 2016 decision. But that could make the judge “essentially the carbon regulator of the entire United States economy,” says attorney Justin Torres of King & Spalding in Washington, D.C., who handled the case as a government lawyer under Obama. That would be politically and practically unwise, he says, and the government has argued climate policy is best tackled by Congress and the White House.

Such questions will likely resurface during appeals no matter how this case turns out, Gerrard says. But even if the trial is halted, it has already forced the Trump administration to give ground on climate change. The case has required “the administration to make numerous admissions,” he says, “and be much more specific in its scientific claims than it has had to be before.”