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Climate change has found its way into courtrooms around the world more and more often in recent years: Plaintiffs have brought more than 1,500 cases of climate litigation since 1986, and an increasing number of cases are filed each year.

“The power of the courts as a force of climate action really should no longer be in dispute.”

“In the last few years we’ve seen lawsuits in the Netherlands, Germany, Ireland, Belgium, and elsewhere that have shown that successful climate litigation is possible,” said Rupert Stuart-Smith, who researches climate systems and policy at the University of Oxford’s Sustainable Law Program in the United Kingdom. In most of those cases, courts ruled that a country or a company’s climate targets or progress toward meeting those targets needed to be significantly improved. “The power of the courts as a force of climate action really should no longer be in dispute.”

However, climate litigation has failed more often than not to hold greenhouse gas emitters accountable for climate-related impacts like flooding and damage from drought or wildfires. For lawsuits that try to establish a causal link between a defendant’s emission and the impacts on plaintiffs, Stuart-Smith and his team sought to understand why those types of cases tend to fail.

“Why aren’t these cases winning?” he asked. “What is the evidence that is being used in these cases, how does that compare to the state of the art in climate science…and how have the courts interpreted it?”

A Failure to Make the Connection

The researchers examined 73 cases across 14 jurisdictions worldwide that made a claim that a defendant’s emissions negatively impacted the plaintiffs. In those cases, courts did not dispute the general idea that greenhouse gases cause climate change. “What was more of a challenge,” Stuart-Smith said, “was establishing a causal relationship between greenhouse gas emissions of an individual entity…and specific impacts on a specific location.” Making that causal connection is key for the success of climate litigation, he said, and is the goal of climate attribution science, or science that quantifies the extent to which climate change alters an event.

“The evidence submitted and referenced in these cases does lag considerably behind the state of the art in climate science.”

However, 73% of the cases the team examined did not bring forward peer-reviewed climate attribution science as evidence. Of the 54 cases that claimed that an extreme weather event caused the impacts suffered by plaintiffs, 26 claimed that climate change caused the extreme weather event but did not provide evidence of that claim. Six more did provide such evidence, but that evidence did not quantify how much more likely or how much worse climate change made the extreme weather event.

“We found that there is a clear role for attribution science evidence in these lawsuits,” Stuart-Smith said. In the few cases where climate science was submitted as evidence, “the evidence submitted and referenced in these cases does lag considerably behind the state of the art in climate science. And as a result…the evidence provided was not sufficient to overcome causation tests.”

Of the 73 cases they examined, only 8 have been successful so far. (Thirty-seven are pending, and 28 have been dismissed.) The researchers suggest that “growing use of attribution science evidence which is specific to the impacts experienced by plaintiffs…could overcome some of the key hurdles to the success of climate-related lawsuits.” These results were published in Nature Climate Change in June.

Establishing a Dialogue

Not every extreme weather event is caused by or made worse by climate change, but an increasing number of them are: Anthropogenic climate change has been making hurricanes, drought, and wildfires stronger and more frequent; has been tied to worsening health conditions around the world; and has started a climate refugee crisis. As recently as a decade ago, Stuart-Smith pointed out, climate science wasn’t advanced enough to claim that climate change caused any single extreme weather event, but that is no longer the case. For example, the World Weather Attribution initiative, an international collaboration of climate scientists, has already established that the June 2021 extreme heat wave in the North American Pacific Northwest “was virtually impossible without human-caused climate change” and that “this heatwave was about 2°C hotter than it would have been if it had occurred at the beginning of the industrial revolution.”

“We need better paths of communication between the legal and scientific communities.”

This study highlights that “we need better paths of communication between the legal and scientific communities,” Stuart-Smith said. Lawyers need to be able to explain to climate scientists what type of evidence will be helpful and ensure that the claims they’re bringing forward are actually attributable to climate change. Climate scientists, too, need to consider providing evidence to litigators as “an opportunity to make one’s research relevant to important ongoing issues in the courts.…It’s got to come from both sides.”

Although climate attribution cases haven’t been very successful in the past, “it doesn’t seem farfetched anymore to suggest that future cases will force companies to pay compensation to communities impacted by climate change,” either after damage is already done or as communities try to mitigate or adapt to future impacts, Stuart-Smith said. “But that is only going to be the case if…the evidence submitted to courts clearly substantiates the alleged relationship between the defendants’ emissions and the impacts suffered by plaintiffs.”

—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer


Cartier, K. M. S. (2021), Climate litigation has a big evidence gap, Eos, 102, https://doi.org/10.1029/2021EO161031. Published on 23 July 2021.

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