How scientists are helping sue over climate change
Authors: Isabella Kaminski
Journal: The Lancet Planetary Health (2022)

When a Peruvian farmer launched a lawsuit trying to get compensation from a fossil fuel firm for climate impacts, he stood little chance of success. But over the past 7 years science has caught up with the case. Huaraz is a city high up in the Peruvian Andes under serious threat of flooding. It sits next to Lake Palcacocha which, fed by the melting Palcaraju glacier, is at risk of bursting its banks. Deeply concerned about the risks to his home, local farmer and mountain guide Saúl Luciano Lliuya decided to sue energy giant RWE in Germany for compensation to pay for the cost of flood defenses. Lliuya's argument is that the glacier is melting much faster as a result of climate change, a problem RWE has significantly contributed to over the past century by extracting and burning fossil fuels, which have led to a growth in carbon emissions. He chose to target RWE because the company has its headquarters in the eastern city of Essen and he had the support of NGO GermanWatch. When the case was first filed in 2015, it rested largely on broad analysis of climatic processes in the Intergovernmental Panel on Climate Change's (IPCC) AR5 report on impacts, adaptation and vulnerability which had been published the previous year. This stated with “high confidence” that glaciers are retreating in Peru and that the trend could be attributed to anthropogenic global warming. The lawsuit was initially dismissed by Essen district court on the grounds that, while there was “scientific causality”, lawyers had not managed to prove “legal causality” linking RWE's actions with the specific damages caused. Lliuya and his legal team successfully appealed. In 2017, the Higher Regional Court in Hamm ruled that the case had solid grounds and could proceed to the evidence gathering phase. Legally, this was a hugely significant move. The court asked two key questions: does the glacier melting really threaten Huaraz? And, if so, is climate change responsible? Evidence gathering stalled as the COVID-19 pandemic took hold, but this summer court-appointed scientists will be making a field trip to the Andes, accompanied by judges, to determine whether the plaintiff's house faces a serious threat. Such site visits are common in German civil law cases but it is unusual for a court to travel to a place as far away as Peru. While it was fairly novel when first filed, Lliuya's lawsuit is one of many in the now-burgeoning legal field of climate litigation. Nearly 2000 climate-related lawsuits have been filed around the world to date, according to an LSE database, and proponents of climate action are increasingly succeeding. Since 2019, courts have ordered the governments of the Netherlands, Germany, France, and Ireland to cut their national greenhouse gas emissions, and last year Anglo-Dutch oil giant Shell was ordered to slash its carbon footprint by 45% by 2030. But attempts to hold polluters to account for climate-related damages in court, as Lliuya's lawsuit attempts to do, have so far failed. That may be about to change. The latest scientific report from the IPCC, published in April as part of its sixth assessment report (AR6) and focusing on climate mitigation, identifies litigation as one of several important new avenues through which climate policy is being shaped and says that such cases rely on advancements in climate science, particularly in attribution. Attribution science examines the extent to which a specific extreme weather event was made more likely or worse by climate change. The first such study was published in Nature in 2004, a year after record-breaking temperatures across much of Europe caused more than 70 000 deaths. It concluded that climate change had “at least doubled” the risk of such an extreme heatwave. Over the years, the field has benefitted from advancements in climate modelling and computing power, scientific cooperation between different countries and institutions, and refinements in the kinds of questions being asked. Taken together, this research has helped demonstrate that climate change is already having a tangible impact on the ground. Last year, experts on the IPCC's physical science panel analysed hundreds of attribution studies to conclude that anthropogenic greenhouse gas emissions have “led to an increased frequency and/or intensity of some weather and climate extremes”. But studies of extreme events, such as storms, droughts, heatwaves, or floods, as well as slower changes in average temperature and rainfall, can also be used to show more specific impacts. In Lliuya's case, lawyers now have the support of a paper published last year in Nature Geoscience which concludes that the overall retreat of the Palcaraju glacier is “entirely attributable” to rising temperatures and that the resulting change in the geometry of the lake and valley has “substantially increased the outburst flood hazard”. “The availability of a dedicated attribution study in the peer-reviewed literature, one would think, would provide us with as robust an evidence base for the case as any,” says lead author Rupert Stuart-Smith, research associate in climate science and the law at the University of Oxford's Sustainable Law Programme. As well as the attribution study on the glacier retreat, there are also a number of flood modelling studies that describe in detail the risk affecting the area around Huaraz. “It's up to the court to determine what the scientific evidence means for financial liability. But from a scientific point of view, the evidence here is about as clear as it would be anywhere in the world that climate change is causing this situation”, says Stuart-Smith. Dr Delta Merner, who leads the Science Hub for Climate Litigation at the Union of Concerned Scientists in the US, says key societal decisions are starting to be made in the courtroom, so they should be informed by “the best available, the most meaningful science”. The hub helps write expert scientific documents submitted as part of climate lawsuits in the US and beyond, and reviews legal communications for scientific accuracy. It also undertakes its own source attribution studies which examine the relative contribution of different sectors, activities, and organisations to global carbon emissions. In the Huaraz case, Lliuya is suing RWE for 0·47% of the costs of local flood defences, which amounts to approximately €17 000. That figure, equivalent to the share of man-made greenhouse gas emissions they say RWE has been responsible for since the start of industrialisation, came from a ground-breaking source attribution study by Richard Heede of the Climate Accountability Institute. But Dr Merner says there is much further scope for science to support climate litigation. A study by Oxford University researchers, published in Nature Climate Change last year, found that lawsuits against companies and governments would stand a greater chance of success if they made better use of existing science—especially on attribution. Stuart-Smith, who co-authored the paper, notes that scientists have a long history of providing evidence for lawsuits, for example about exposure to toxic substances in public health cases. But in “something as fresh as climate litigation” there is still work to be done to establish what kind of evidence is needed and how it can be framed. “It's not just a case of lawyers picking science off the shelf,” he says. It is important to make “really robust litigation-relevant science” widely available and accessible, says Dr Merner. “So much of this scientific work has stayed within the scientific community. [It] has gotten a little bit better about talking with policy audiences, but… we want the work to be accessible to legal scholars and practitioners, to local officials, to affected communities and others.” The Science Hub aims to address this by connecting legal teams with technical experts and training scientists in law and communication. It has also identified key gaps in the available evidence. Dr Merner says there is a “huge disparity” in where attribution science is distributed. “A lot is happening in the Global North, so it supports litigation that can happen in the US and Europe but not elsewhere.” Furthermore, she says, methodologies for Western-focused attribution science might not look the same as those needed in, for example, central Africa, because the baseline data is different. “The methods that we have now rely on certain systematic historic data and we don’t have that everywhere, globally.” Dr Merner says this can be addressed by using different statistical methods or by looking at other places that have similar climates. And as well as the physical sciences, she says climate lawsuits based on claims of misinformation and fraud are increasingly reliant on evidence from social science and historical analyses. With people looking to recoup their financial losses, and climate litigation cases increasingly using human rights arguments, Stuart-Smith also sees a significant gap in studies that detail the real-world impacts of an extreme event. “The amount of attribution evidence on the health impacts of climate change, especially in the Global South, is, unfortunately, an obstacle,” he says. “If you don’t have evidence on what the human health impacts of climate change are, then you’re not going to be a very good place to claim that human rights are being violated.” With a date recently set for the first climate trial in US history, Stuart-Smith sees a role for improving scientific literacy among the judiciary. “I think as more and more of these lawsuits get to evidentiary stages, where scientific facts are being contested, the need for judges to adjudicate between potentially conflicting evidence, supported by appropriate scientists, will be increasingly important.” Although 7 years have passed since Lliuya filed his lawsuit, the delay has probably helped rather than hindered the case, says Noah Walker-Crawford, a climate litigation consultant for GermanWatch and research fellow at UCL. “It's an irony to say that the legal process can drag on for ages and the problem is ever more urgent, but the science has been advancing too and that gives a stronger basis to these kinds of cases.” If the case is successful, says Stuart-Smith, it would have ramifications for the fossil fuel industry worldwide. “It sends a powerful message that the impacts of climate change are a matter that courts are willing to adjudicate over and that the fossil fuel industry may be held responsible for harms done as a result of their emissions.”