In November 2015, a Peruvian farmer and mountain guide, Saúl Luciano Lliuya, launched a pioneering offer for climate justice in a German court more than 10,000 km from his home in the Andean city of Huaraz.
Lliuya claimed that climate change caused the Palcaraju Glacier to retreat 2 km up a mountain, enlarging a large lake as a result of its retreat. This lake threatens to burst on Huaraz with catastrophic consequences.
The case argues that RWE, a German energy company and one of the largest emitters of greenhouse gases in the world, is responsible for part of the costs of protecting the city due to its contribution to climate change. His case is one of growing number of climate-related lawsuits filed in courts around the world.
Just weeks after Lliuya filed for her lawsuit, governments around the world accepted the terms of the Paris Agreement. However, he left it up to individual countries to determine what actions they would take to contribute to his long-term goal of limiting warming to 1.5 ° C or “well below” 2 ° C.
Taken together, current national commitments to reduce emissions fall short of the Paris targets. And because the deal does not directly confer binding targets on individual states, lawyers began to wonder: can courts compel countries, and even businesses, to set and meet climate-aligned targets? ‘Paris Agreement?
More and more, the answer to this question is yes. However, cases seeking damages for the impacts of climate change – like Lliuya’s – have been far less successful.
In our new study, published in Nature Climate Change, we find that the evidence used in these cases often does not reflect the most recent advances in climate science.
We show how attribution of climate change – the area of research that quantifies how man-made climate change modifies the likelihood and intensity of extreme weather events – could be used to fill the evidence ‘gap’ in climatic disputes.
The climate in court
This year has already seen major legal successes on climate change in courts around the world.
At the end of April, the judges of the highest German court condemned the country’s climate protection law as inadequate for failing to protect future generations from the impacts of climate change and demanded that the government strengthen the law. A week later, the German government announced major changes to its climate targets, including reducing emissions by 65% by 2030 and eliminating net emissions by 2045.
In recent weeks, courts have ruled that the Australian government must take reasonable precautions to ensure that new coal mines do not harm children and that Belgium’s climate policy is inadequate and violates human rights.
In Dutch courts, Shell was ordered to align its activity with the Paris Agreement and reduce its CO2 emissions 45% by 2030, compared to 2019 emissions. This includes emissions associated with all the oil and gas it produces, even if it is burned by other companies or consumers.
The power of the courts as a force for climate action can no longer be challenged. However, these successful cases are still limited in number, and most climate-related lawsuits that rely on evidence linking greenhouse gas emissions to the impacts of climate change have failed.
So if cases seeking compensation for losses suffered due to climate change are also to be successful, what needs to be changed?
The role of scientific evidence in climate litigation
In our study, we examined the evidence provided by litigants to support their arguments in more than 70 lawsuits, filed in 14 jurisdictions, and the interpretation of that evidence by the courts.
In many of the cases we have investigated, plaintiffs have sought financial reparations from high-emission companies for losses suffered due to climate change. Courts rely on scientific evidence to assess the causal link between the defendant’s behavior and the plaintiff’s losses. In all jurisdictions, courts assess this evidence by applying legal tests that set evidence-based thresholds for establishing causation, but the stringency of these tests varies.
When more stringent tests are applied, plaintiffs may have to show that the defendant’s actions constituted “material contributions to the damage”, while softer standards simply ask whether the damage is “sufficiently attributable” to the defendant’s actions.
Lawyers have long championed the crucial role of attribution science as evidence for causal claims in climate trials. However, we have found that the evidence submitted and referenced in these cases still lags significantly behind cutting-edge climate science, hampering causal claims.
Our analysis found that in many cases the evidence provided by complainants was not sufficient to overcome even the most flexible causation tests. While accepting that greenhouse gas emissions cause climate change, courts have generally found that plaintiffs failed to demonstrate that defendants’ emissions caused the alleged impacts.
In jurisdictions as diverse as the United States, Germany and New Zealand, courts have held that plaintiffs were unable to establish that their injuries would not have occurred in the absence of the defendants’ broadcasts. In some cases, for example, courts have highlighted the low contribution of defendants to climate change, the high number of responsible issuers, or the lack of a method to discern the entities responsible for the impacts.
Our assessment is that it was not due to scientific limitations that the evidence provided failed to convince the judges. Instead, we found that at least some of these hurdles could be overcome if complainants make better use of climate science – especially in the area of attribution science.
The field of attribution science has been applied to an increasing number of extreme events and provides, in many cases, the tools and understanding needed to assess the full causal chain of countries’ greenhouse gas emissions. and from businesses to losses suffered by individual communities.
Attribution can bridge the gap identified by judges between a general understanding that human-induced climate change has many negative impacts and provide concrete evidence of the role of climate change at a specific location for a specific extreme event that has already caused or will result in damage. The attribution of causal relationships in science can therefore be translated into legal causality.
As a result, it can provide concrete causal evidence for specific lawsuits. Another implication of the growing body of attribution research is a broader scientific understanding of the damage caused by natural hazards today that are made worse by climate change and those that are not.
Attribution research identifies the types of hazards for which human-made climate change is, or is not, a key factor. It also highlights scientific gaps. For example, in some places and for certain types of weather events, it is not yet possible to assess the role of climate change. For example, the limitations of climate models limit our ability to provide attribution assessments for certain winter storms. Nonetheless, this body of literature helps contextualize specific causal claims and has the potential to improve their effectiveness in meeting evidentiary standards of courts.
Based on our analysis, we have identified three areas where scientific research on attribution could fill the gaps in the evidence provided to lawsuits on climate change impacts.
First, evidence link the emissions of individual entities – such as countries or companies – to the specific impacts of climate change shows how the defendants’ emissions contribute to the damage.
Second, researchers can provide a more comprehensive assessment of how climate-related risks interact with the vulnerability and exposure of complainants to help identify legally relevant causes of losses.
Finally, attribution studies show how an event of a given magnitude was made more likely to occur and / or how an event of a given probability was made more intense. In some contexts, the numbers of these two approaches to effect attribution may be sensitive to the exact definition of the hazard. The science of attribution can help identify these sensitivities and lead to a stronger causal argument overall.
The path to follow
So if attribution science can provide the proof, what will it take to make this research more widely used?
Greater scientific awareness of the legal community, and vice versa, could ensure that the cases filed focus on the impacts that are in fact attributable to climate change – and that the evidence before the courts clearly corroborates the alleged relationship between the emissions of the defendants and plaintiffs losses. In many past trials, this has not been the case.
Improved dialogue between the legal and scientific communities on the basis of causal claims would ensure that lawyers know – and are able to ask – evidence that can be used to robustly assess causal claims. Lawyers can identify key evidentiary questions that plaintiffs need to answer in order for cases to be successful. Scientists can then assess whether these causal links exist.
Previously seen as a speculative attempt to get the courts to enforce climate action or simply to draw attention to the problem, the lawsuits are forcing governments and businesses to step up their climate ambition. It no longer seems far-fetched to suggest that, backed by good scientific evidence, future cases will force companies to pay compensation to communities affected by climate change.
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