Polluters on trial: How climate science is rocking the courtroom
Attribution science is enabling climate victims to sue the world’s top polluters for damages and the first successful case may not be very far away, writes Chloé Farand.
When Peruvian farmer and mountain guide Saúl Luciano Lliuya took energy giant RWE to court in Germany accusing the company of contributing to the melting of the glaciers in the Peruvian Andes and to a higher flood risk to his home, his chances of success were slim.
But a decade on, advances in climate science paved the way for the case to set a landmark legal precedent, which experts and climate campaigners hailed as a turning point for climate litigation.
Despite rejecting the case, the judges ruled that, in principle, a company like RWE can be held liable for its contribution to specific climate damages under German law – a decision that opens the door to a wave of new lawsuits against the world’s biggest polluting companies.
“This is a really remarkable verdict,” said Dr Noah Walker-Crawford, a research fellow at Imperial’s Grantham Institute – Climate Change and the Environment, who researches how climate science shapes litigation.
“This gives an important tool to communities around the world that are affected by climate change, because it means that companies have a legal duty to take responsibility for their emissions and for climate harms,” he said.
Notably, the case wouldn’t have been possible without the fast-developing field of attribution science – a body of research that identifies the actors contributing to rising global temperatures and aims to understand the influence of climate change on extreme weather events and their impacts.
Attribution is crucial to this case... If attribution science hadn't evolved from where it was when the case started, it wouldn't have been possible.
As the case made its way through the court system, advancements in climate attribution strengthened Mr Lliuya and his legal team’s argument that RWE’s emissions contributed to the risk of flooding to his home despite the fact the company has never operated in Peru.
“Attribution is crucial to this case,” said Dr Walker-Crawford, who helped initiate the lawsuit with NGO GermanWatch in 2015 before joining Imperial’s Grantham Institute and its sister organisation at the London School of Economics and Political Science (LSE). He remained an expert witness for the plaintiff, Mr Lliuya.
“If attribution science hadn't evolved from where it was when the case started, it wouldn't have been possible,” he added.
At the end of May, the German court in Hamm ruled that the risk of flooding to Mr Lliuya’s home was not high enough to investigate whether RWE should be held legally liable to pay towards the costs of a planned flood defences project – ending the lawsuit before the court could examine any specific attribution study.
But the verdict showed that “in principle, it's possible to use climate science to establish legal causation and legal responsibility,” said Dr Walker-Crawford.
In addition, the case relied on a simple law which protects people from unreasonable interference to their property and exists in almost every country – giving “a tailwind to similar claims in other parts of the world,” he said.
Saúl's case has permanently moved the dial on how climate litigation can be seen by courts around the world.
Legal and climate experts agree it’s only a matter of time before a similar case successfully demonstrates the chain of causation that would hold a polluter legally liable for a specific climate risk.
“Saúl's case has permanently moved the dial on how climate litigation can be seen by courts around the world,” said Joe Snape, a senior associate at law firm Leigh Day.
"This groundbreaking case has helped to demonstrate how victims of climate harms can seek justice and accountability from those who are responsible for – and have massively profited from – anthropogenic climate change.”
“As the field of climate attribution develops, lawyers are understanding more and more how climate change can be applied to litigation” to link specific climate harms to polluters, he said.
Saúl Luciano Lliuya at the Higher Regional Court for the hearing of his climate lawsuit against energy giant RWE (c) Rolf V/dpa/Alamy Live News
Saúl Luciano Lliuya at the Higher Regional Court for the hearing of his climate lawsuit against energy giant RWE (c) Rolf V/dpa/Alamy Live News
Saúl Lliuya v. RWE: the role of attribution science
In the case against RWE, Mr Lliuya argued that the glaciers above the city of Huaraz were melting because of rising temperatures, creating a growing risk that a falling bloc of ice or rock landing in Lake Palcacocha would cause it to overflow and flood his home in the valley below.
He argued that the greenhouse gas emissions generated by RWE’s activities – one of Europe’s top polluters, which is responsible for nearly 0.4% of global industrial emissions – contributed to the melting of the glacier and therefore demanded that the company pay a proportional fraction of the costs for building flood defences to protect his and local people’s homes.
When Mr Lliuya filed the case in 2015, scientists had established that glaciers in the region were retreating as a result of climate change. But the legal team didn’t think a more specific study attributing local glacier melt to rising temperatures was possible.
“We were surprised at how quickly the science developed and how it was able to catch up with the case,” said Dr Walker-Crawford.
The previous year, Professor Fredi Otto, now a senior lecturer in climate science at Imperial, had co-founded World Weather Attribution (WWA), an initiative to develop global methodologies to identify the influence of climate change on extreme weather events through rapid attribution studies.
Since then, WWA has published more than 100 studies following peer-reviewed methods – establishing a vast body of evidence demonstrating the link between climate change and extreme events.
In 2021, a study published in Nature Geoscience concluded it was “virtually certain” the retreat of the glacier above Lake Palcacocha was caused by human-caused greenhouse gas emissions and that changes to the lake “significantly increased” the risk of flooding. However, the court never got to discuss the finding.
For Professor Otto, the ruling in Mr Lliuya’s case is still “historic” because it recognises the physical causal chain that links emissions from polluters like RWE to specific climate impacts.
Although the judges decided that this specific causal chain wasn’t strong enough, “they accepted this case without a specific attribution study, but by accepting the whole scientific field that has established that we can make these causal chains between emissions and individual weather events and impacts,” she said.
We will soon see cases that will go all the way, where an oil company will have to pay for climate damages.
In the case, Mr Lliuya was asked to prove that climate change is posing a threat to this house. But “from a scientific point of view, you should reverse the burden of proof”, Professor Otto added.
Reports from the Intergovernmental Panel on Climate Change (IPCC) “very clearly say that climate change is affecting extreme weather events everywhere around the world” and no evidence exists to suggest this isn’t the case in the Peruvian Andes, she explained.
But “in a court case, you don’t start with the state of the art of the science, you start with what courts are prepared to do”.
With each new case building on previous ones, “we will soon see cases that will go all the way, where an oil company will have to pay [for climate damages]” – an outcome that would pose a serious risk to fossil fuel companies’ business model, she added.
In a statement, RWE said the attempt to use the lawsuit to create a precedent for holding individual companies responsible for climate damages had “failed”. It added it is phasing out its coal-powered plants and plans to be carbon neutral by 2040.
Professor Fredi Otto and Dr Noah Walker-Crawford
Professor Fredi Otto and Dr Noah Walker-Crawford
Dr Joana Setzer on the panel at a Responsible Investor event
Dr Joana Setzer on the panel at a Responsible Investor event
The challenges of using climate science in court
With the number of climate cases still on the rise, courts are becoming increasingly receptive to climate science, according to a recent LSE analysis on global climate litigation trends.
Attribution science is necessary in cases seeking damages from a polluter, when the claimant needs to demonstrate the causal chain linking the defendant’s emissions to the climate impacts. But it is also being used more generally in climate cases to demonstrate how unchecked emissions lead to more severe damages.
Yet, using climate science in court brings challenges, with lawyers and scientists not always speaking the same language. As part of his work, Dr Walker-Crawford is striving to act as a translator between the realms of law and science.
Lawyers and scientists think about the world in very different ways and they ask different sorts of questions.
In his research for both Imperial and LSE, Dr Walker-Crawford seeks to bridge the two disciplines by studying how science is being used in legal practice and informs legal decision-making. At Imperial's Grantham Institute, he works with climate scientists to understand how the latest developments in attribution science might shape present and future litigation. He helps scientists understand how their work can inform judges in climate cases. In addition, he advises claimants and NGOs on how to use legal tools to fight for climate justice and helps to explain the latest science to lawyers.
“That’s the challenge with bringing science into climate litigation,” he said. “Lawyers and scientists think about the world in very different ways and they ask different sorts of questions.”
In Mr Lliuya’s case, judges wanted to know the specific flood risk to his home. In contrast, “scientists are thinking about the climate system and are less concerned about the differences in damages to [Lliuya]’s house versus his neighbour’s if the flood is likely to happen,” explained Dr Joana Setzer, an associate professorial research fellow at the LSE and the co-author of the Global Trends in Climate Litigation report.
There is also an “intrinsic mismatch” between the way law and science deal with uncertainty, she added. Legal decisions require a very high level of certainty, whereas scientific uncertainty – which means that something cannot be quantified precisely, not that it doesn’t happen – is an important part of the scientific process.
Judges also err on the side of caution, when a decision to hold a polluting company liable for climate damages will have implications for hundreds of other corporations, said Dr Setzer.
“It’s a really reiterative process” that “will have “better chances of success” as the number of cases grow, she added.
Today’s science is tomorrow’s litigation
Fast-moving developments in attribution science could see new types of litigation cases emerge.
“The science that's being done now is essentially going to be the basis of tomorrow and the day after tomorrow’s cases,” said Dr Walker-Crawford.
At Imperial’s Grantham Institute, researchers are working to develop methods for rapid attribution studies that seek to pinpoint the extent to which climate change is responsible for damages caused by any given extreme event – a field of research which could eventually provide new evidence to demand the world’s biggest polluters pay for the impacts attributable to human activities.
The main purpose is to challenge the social license of these companies [to operate], to show that the model of producing energy in ways that result in emissions is just a bad idea.
In the US, researchers have developed a framework for climate litigation, which they say allows plaintiffs to quantify the economic damages attributable to extreme heat that individual fossil fuel companies are responsible for in a single causal chain.
“Drawing quantitative linkages between individual emitters and particularised harms is now feasible, making science no longer an obstacle to the justiciability of climate liability claims,” researchers wrote in a study published in Nature.
Others cases have started to focus on polluters’ future climate impacts.
In one such case four inhabitants of the Indonesian island of Pari are suing the Swiss cement giant Holcim based on its past, current and expected future emissions. They are demanding compensation for climate-related damages on Pari, a financial contribution for adaptation measures to protect themselves against future impacts, and argue that Holcim should reduce its emissions.
However, cases in which a citizen or a group of people sue a single polluter for a fraction of the costs of specific climate damages remain “insufficient” to deliver the scale of change that is needed, argues Dr Setzer.
“These cases create pressure, they push the boundaries, but they are never going to be close to the kind of solution [that is needed],” she said.
But if a region or a city like Dakar in Senegal brought a case demanding millions of dollars to improve adaptation measures, for example, that could make a bigger difference, she argued.
Ultimately, “the main purpose is to challenge the social license of these companies [to operate], to show that the model of producing energy in ways that result in emissions is just a bad idea”. Those, she said, are the cases that give her hope.
In Peru, Mr Lliuya hopes his legal pursuit will inspire others to take action. “I feel very happy that even after 10 years I have able to do something for climate justice,” he told an event in London ahead of the ruling. “I hope this case can help [others] to put these cases forward.”
Read more about the latest Grantham Institute research on attribution science: The true costs of climate disasters
Chloé Farand is a freelance climate journalist and editor who has covered climate and environment stories for The Guardian, AFP, Climate Home News and Dialogue Earth, among others. Follow her on BlueSky, and read more of her work on Authory.
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