While new records in disaster-related damages continue to make the news and shake lives, scientists are getting better at establishing links between climate change and extreme weather events. This has led to a growing interest in the role of law in dealing with climate related damages. Scientific findings are a requirement for being able to sue. In court, the principle applies that each party must prove the facts that are favorable to it. If climate science can connect the dots between human greenhouse gas emissions and the emergence of extreme weather events or other adverse climate impacts, it will be possible to bring actions before the courts. These lawsuits could aim at establishing responsibility for incurred damages or risks thereof, or at preventing future damages. A general introduction to the topic of climate litigation and the different categories of climate lawsuits can be found in this ISIpedia article.

The following ideas will focus on climate litigation lawsuits against private actors, in which plaintiffs are generally seeking monetary restitution for damages or risks associated with glacier melting, heat waves, extreme precipitation and associated floods, and sea level rise, and that are attributable to the defendant’s contribution to climate change. The number of climate lawsuits for liability and compensation is low compared to mitigation cases against governments but is now slowly beginning to rise. Amongst other things, this seems to be related to major advances in attribution science. In this respect, attribution research is providing more and more evidence on the responsibility of specific actors for specific climate related damages. This evidence starts to play a role when judging who has to compensate for such damages. As attribution science is becoming increasingly precise and robust, courts might soon be willing to issue rulings that require defendants to pay for damages attributable to impacts of climate change (Marjanac and Patton 2018). Let’s take a closer look at a prominent case to understand how these lawsuits have been conceived and what lessons we can learn from them.

Luciano Lliuya v. RWE: a notable example of science’s role in compensatory claims against Carbon Majors

Luciano Lliuya v. RWE (lawsuit filed in 2015, and yet pending) is a very prominent example of a climate litigation lawsuit against a Carbon Major. Until date, this is the first and only climate case in which a court found that a private company could potentially be held liable for climate damages from its emissions (Toussaint 2020), allowing the case to progress to the evidentiary phase in November 2017. As such, the case has attracted international attention and was covered by high-profile news outlets across the globe, including the Guardian, the New York Times Magazine and Nature. This particular lawsuit also illustrates the crucial role attribution science has started to play in lawsuits seeking to establish liability for climate impacts.

With support of the environmental NGO Germanwatch, Peruvian small-scale farmer and mountain guide Saúl Luciano Lliuya wants the energy giant RWE to assume its share of responsibility for adverse climate impacts in his hometown. Due to climate-induced glacial retreat, a glacial lake above the Andean city of Huaraz has grown in size and threatens to overflow or even break its dam. The plaintiff’s property along with large parts of the city are at risk of a devastating flood that would affect around 50,000 people. Saúl Luciano requests the court to determine that RWE is liable, proportionate to its GHG emissions, to cover the expenses for appropriate safety precautions. This could mean, for example, paying part of the cost of a much bigger dam and/or a pumping system.

Lake Palcacocha surrounded by the Pucaranra and Palcaraju glacier. In front of the lake, the broken dam from which a flood wave emerged in 1941 that destroyed a third of Huaraz.

FIG 1 / Image source: Alexander Luna / Germanwatch e.V.

The claimant himself explains his motivation for the lawsuit as follows:

“Every day I see the glaciers melting and the lakes in the mountains growing. For us in the valley, the threat is immense. We cannot simply wait and see what happens. For me, RWE is partly responsible for the risks that threaten us in Huaraz. According to scientific studies, the lake above my hometown is growing because of accelerated glacier melting. RWE is one of the world’s biggest emitters. But so far, these companies have not assumed any responsibility for the consequences of their emissions. You don’t have to be a legal scholar to see that this is wrong. That is why we demand that they now at least install flood protection at our glacier lake. And even better, that they should stop contaminating the climate in the future so that all people can survive. We used to be powerless, but we aren’t anymore. This is about our protection and about justice.”

Saúl Luciano’s claim is based on the general nuisance provision under German civil law (§1004 BGB). Nuisance is a very old and widely used concept under both civil and common law1. It presumes that persons in possession of property are entitled to its quiet enjoyment. If a neighbor interferes with that quiet enjoyment, either by creating smells, sounds, pollution or any other hazard that extends past the boundaries of the property, the affected party may make a claim in nuisance. Saúl Luciano wants to create a “test case” that can be replicated by other claimants. And indeed, the court decided that in the case of climate change, a neighborhood could actually extend to a global scale, which makes RWE Saúl Luciano’s ‘neighbor’ and §1004 applicable.

Even more importantly, §1004 can be used for both, liability for preventing as well as liability for remedying harm. In climate policy terms, this means that a test case created through this lawsuit could be used to sue companies to either pay for adaptation measures, or to compensate for damages (‘loss and damage’) induced by anthropogenic climate change. In the lawsuit against RWE, Saúl Luciano uses the general nuisance provision to ask that RWE pay for protection measures such as dam construction, which falls under the category of adaptation. But he could use the exact same paragraph if there actually was a flood in Huaraz, to have RWE compensate for the incurred damages.

In a historic sentence, the appeals court in Hamm recognized Saúl Luciano’s claim as well-pled and admissible, giving a clear statement that large emitters like RWE are liable for supporting people affected by the adverse impacts of climate change. By this, the case has already set a precedent in legal terms: the court has accepted the claimant’s legal argumentation as valid - as long as it can be factually proven through evidence - and thus allowed the case to progress to the evidentiary stage. Its decision establishes a solid argument for legal causality in cases that were not accepted before. Legal causality means, in cases like this one, that the plaintiff can demonstrate a direct link between the actions of the defendant (e.g. its emissions) and climate-change related damages or risks. While before, courts refused to adjudicate on such cases referring e.g. to the political question doctrine or standing (see Climate Litigation article for detail), this first step is no precarious obstacle any more.

What is left to be done now is to provide proof of the factual argumentation of this particular case. This is being done during the evidentiary phase where attribution science will play a decisive role. Just after the court had announced its decision, the plaintiff’s lawyer Dr. Roda Verheyen commented: ‘The entering into the evidentiary phase in this case in itself is already writing legal history […] Major emitters of greenhouse gases can be held liable for protective measures against climate damages. Now we can prove in a concrete case that RWE contributed and continues to contribute to the risk of a local glacier outburst flood in Huaraz’

Saúl Luciano Lliuya at the Higher Regional Court of Hamm on the climate lawsuit against RWE.

FIG 2 / Image source: Alexander Luna / Germanwatch e.V.

The underlying scientific causal chain of this lawsuit is complex. In its Order for the Hearing of Evidence, the Higher Regional Court of Hamm indicated that independent expert opinions need to be obtained to provide evidence for the following allegations by the claimant:

  1. A flood and/or mudslide resulting from the significant expansion and increase in the volume of water in Lake Palcacocha poses a serious threat to the plaintiff’s property, which is situated below the glacial lake in the city of Huaraz in the Ancash region of Peru.
    1. The CO₂ emissions released by the defendant’s power plants rise into the atmosphere and, in accordance with physical laws, lead to a higher concentration of greenhouse gases throughout the Earth’s atmosphere.
    2. The result of the increased concentration of greenhouse gas molecules is a reduction in the global emission of thermal radiation and an increase in global temperature.
    3. The resulting increase in average local temperatures accelerates the melting of the Palcaraju Glacier; as the glacier loses mass and recedes, the volume of water in Lake Palcacocha rises to a level that can no longer be contained by the natural moraine.
    4. The defendant’s share in the contributory causation, as shown in the causal chain outlined in a) through c), is measurable and calculable, and accounts for 0.47% of the total. If, on further assessment of the defendant’s share in the contributory causation, a different percentage is identified, the expert will quantify the correct proportion.

This court order makes it clear that, in order to win the case, climate science will play a crucial role. This needs both, basic climate science regarding the concentration of greenhouse gases throughout the Earth’s atmosphere leading to higher temperatures (‘climate attribution’), as well as the very specific evidence for the local impact of that warming (‘impact attribution’) and the exact share of RWE’s contribution to the threat at hand (‘source attribution’). Climate attribution is now widely accepted as basic climate science, and continues to improve, but source attribution and impact attribution are relatively new research areas, although quickly developing. These developments are of great importance in compensatory claims against private actors. In order to be able to hold a ‘Carbon Major’ accountable for its contribution to climate impacts, a claimant will have to be able to prove that the particular emissions of this actor have contributed to the threat or harm at hand. This rapid development is not just supporting Saúl Luciano’s claim, but it is also becoming one major driver of the recent increase in lawsuits seeking to hold private actors accountable for their contribution to climate change (Burger, Wentz, and Horton 2020).

What is more, without climate (impact) science, the court would not have been able to conclude that there is legal causality and allow the case to proceed to the evidentiary phase in the first place. Indeed, the claimant’s allegations are based on pioneering work in attribution science by the IPCC. Saúl Luciano’s claim (full text in English available here) refers, in particular, to the contributions of IPCC Working Group I (WG I: Climate Change 2013: The physical science basis) and Working Group II (WG II: Climate Change 2014: Impacts, Adaptation and Vulnerability) in the 5th Assessment Report. According to this work, and as elaborated in the claim (pp. 13-16):

Greenhouse gas emissions cause the global temperature increase, which is also observed locally and is attributed to climate change. ‘More than half of the observed increase in global mean surface temperatures from 1951 to 2010 is due to the observed anthropogenic increase in greenhouse gas (GHG) concentrations’ (high confidence, very likely) (IPCC 5th AR, WG I: p. 932). The effects of heightened concentrations of greenhouse gases in the atmosphere are delayed. Glaciers worldwide are retreating partly due to increases in local temperature levels. For the northern and central part of the Peruvian Andes, over the period from 1961-2009 a temperature increase of between 0.2 and 0.45% per decade has been recorded (IPCC 5th AR, WG II: p. 1507, Table 27.1). The retreat of the tropical glaciers has been accelerating, especially since the late 1970s. ‘Tropical glaciers’ retreat has accelerated in the second half of the 20th century (area loss between 20 and 50%), especially since the late 1970s in association with increasing temperature in the same period (Bradley et al., 2009)’ (IPCC 5th AR, WG II: Chapter 27, p. 1520). This trend was recently also confirmed for Peru, among others, with “high confidence”.

‘A rapid retreat and melting of the tropical Andes glaciers of Venezuela, Colombia, Ecuador, Peru and Bolivia has been further reported following the IPCC AR4, through use of diverse techniques (high confidence based on high agreement and robust evidence)’ (IPCC 5th AR, WG II: Chapter 27, p. 1518-1520). The qualitative confidence level in this assertion by the IPCC team of authors is hence “very high”. Glacial melting in the Andes and particularly in the Cordillera Blanca is well-documented. It is among the phenomena that can be attributed to human influences. ‘The reduction in tropical glaciers and icefields in extratropical and tropical Andes over the second half of the 20th century … can be attributed to an increase in temperature (…).’ (IPCC 5th AR, WG II: Chapter 27, p.1543). There is a very high degree of confidence in the attribution“ of climate change to the glacier retreat in the Andes in South America (IPCC 5th AR, WGII: Chapter 27, p. 1544, Table 27.8). Only recently a report by the Peruvian government documented that climate change, in the last 40 years, has diminished the Peruvian glaciers by 40%, and that the melt water released thereby has resulted in the formation of approximately 1000 new lakes (see also IPCC 5th AR, WG II: Chapter 18, p. 984). The Cordillera Blanca, the section of the Peruvian Andes in question, has lost 27% of its area since 1970 (Ministerio de Agricultura y Riego/Autoridad Nacional del Agua). Therefore global climate change is concretely contributing to the melting of the glaciers whose melt water is released into Lake Palcacocha. Furthermore the risk of growlers breaking off and causing devastating floods would be less high.

In addition, Richard Heede’s ‘Carbon Majors’ study was the basis for the estimate of RWE’s share of responsibility included in Saúl Luciano’s claim (‘share in the contributory causation’ in 2d above - ‘source attribution’). Heede’s work examines the share of global global greenhouse gas emissions attributable to fossil fuel and cement companies since the beginning of industrialization. According to this study, ‘the share of RWE and its legal predecessors in global historic emissions, i.e. its share in global total emissions from 1751 to 2010 is about 0.47%’ (Heede (2014); cited in claim p. 18) - a share as high as that of whole countries such as the Netherlands or Belgium. The plaintiff believes this to be a substantial contribution to global greenhouse gas emissions, which it needs in order to link the relevant impacts to the defendant’s conduct.

The 90 Carbon Majors in 2017 based on the ‘Carbon Majors’ study by Heede (2014).

FIG 4 / Image source: Climate Accountability Institute via Klima der Gerechtigkeit

Several climate scientists also agreed to serve as expert witnesses to support the claimant’s allegations or provide additional information if requested by the Court.

On the basis of this scientific information, the Court decided that there is in fact legal causation, and that it is possible and probable that RWE contributes to climate change and the flood risk in Huaraz in a significant way.

However, while the more general findings within the 5th Assessment Report and the ‘Heede Study’ (Heede 2014) were sufficient to allow the case to progress to the evidentiary phase, more specific local evidence may have to be provided to actually win the lawsuit, potentially requiring dedicated local studies. Some of the questions that might arise during the evidentiary phase include: Is there a ‘human signal’ in the regional temperature trend? How significant is the anthropogenic part? To what extent is the melting of the Palcaraju Glacier accelerated by climate change/local temperature rise? What is RWE‘s share of emissions vs. the global total and can this be calculated as a share of temperature rise globally or even locally? Is this necessary or is the absolute contribution (emission volume) sufficient?

As the very first climate compensatory claim entering the evidentiary stage, it is hard to predict what level of detail the Court will require of the plaintiff. For now, the proceedings are still at the stage where court-appointed experts are examining question 1 of the above court order. No experts have been appointed to look at question 2 a-d yet and it is unclear whether these experts would want to conduct a full impact and/or source attribution study.

Interestingly, recent local impact attribution studies confirm the allegations contained in Saúl Luciano’s claim. According to one of the leading voices in attribution science, Friederike Otto, recent research lead by some of her colleagues (Stuart-Smith et al. 2021) has been able to clearly attribute the melting of the glacier that feeds the Palcacocha Lagoon above Huaraz to climate change. This statement is exemplary of the rapid development of attribution science. According to Otto, ‘if this scientific evidence had been available when the lawsuit was filed, it would have improved the burden of proof from the outset’. As mentioned above, it remains to be seen whether the expert who will be appointed to look at evidentiary questions 2 a-d will use existing studies such as the work of Friederike Otto, Richard Heede and their colleagues, or conduct a new impact and/or source attribution study. There is a possibility that the Court and/or the defendant will insist upon new studies by Court-appointed experts in order to preclude any bias.

The fact that Luciano Lliuya v. RWE has reached the evidentiary phase as the first climate compensatory case worldwide might have an impact on how climate scientists see and define their role in climate litigation. Amongst other initiatives, the Union of Concerned Scientists has just launched a Science Hub for Climate Litigation. While the facts of the case must still be adjudicated, the court’s recognition that a private company could potentially be held liable for the climate change related damages of its greenhouse gas emissions marks a significant development in law.

Climate litigation for corporate liability is still at an early stage, but case numbers are on the rise. While the first climate compensatory claim still needs to be won, it is already possible to draw some preliminary conclusion.

The courts’ engagement with climate science has generally been detailed, comprehensive, and thoughtful. Courts have struggled with scientific uncertainty in relatively few areas, such as long-term projections and localized impacts, which rely on complex modelling and assumptions (Banda 2020). The entering into the evidentiary phase of compensatory climate claims might serve as occasion to produce such modelling. In many cases, this is already possible with the necessary financing and a good reason to run the model.

Given projected increases in the frequency and intensity of adverse climate events, it is likely that liability and compensation will feature more prominently in future climate lawsuits (Toussaint 2020). Such cases will have to rely on scientific evidence, based on robust research and modelling.

Climate claims that seek to establish liability may have the greatest chances for success when based on impacts that can be attributed to anthropogenic climate change with high confidence, such as sea level rise, melting snowpack, increases in average temperatures and extreme heat, and ocean acidification (Burger, Wentz, and Horton 2020). However, climate science is rapidly evolving, and the area of scientific uncertainty is shrinking (Banda 2020) so that other types of liability cases might have chances of success, too.

To date, lawsuits seeking to hold corporations liable for their contribution to climate impacts have not failed due to any limitations in the science, but because of procedural obstacles (see Climate Litigation article). Once plaintiffs overcome these obstacles, and judges apply traditional tort principles, the science may be strong enough to support a finding of liability (Burger, Wentz, and Horton 2020). Improvements in attribution science increase the likelihood that courts will be willing to issue both traditional and novel and far-reaching rulings that require defendants to pay damages to plaintiffs adversely affected by climate impacts (Marjanac and Patton 2018). Luciano Lliuya v. RWE might become the first successful lawsuit in this regard.

Irrespective of the success of climate cases, their global symbolic effect should not be underestimated (Burger and Gundlach 2019). They involve a strong narrative that helps people understand the global impacts of climate change. The plight of an individual facing disaster and taking matters into his own hands, such as Saúl Luciano Lliuya from Peru is doing, is a story that is more accessible for many people than abstract reports on temperature rise and climatic processes.

In the case of company defendants, climate litigation also involves reputational and financial risks. For example, on the day of the oral hearing in Luciano Lliuya v. RWE, the RWE share plummeted without this having been anticipated or intended by the claimant. Finally yet importantly, climate liability claims can be a trigger and driver for the long-term establishment of mechanisms to ensure just compensation for those affected by climate change (Burger and Gundlach 2019).


Banda, Maria L. 2020. “Climate Science in the Courts: A Review of US and International Judicial Pronouncements.” Environmental Law Institute.
Burger, Michael, and Justin Gundlach. 2019. “The Status of Climate Change Litigation: A Global Review.” United Nations Environment Programme.
Burger, Michael, Jessica Wentz, and Radley Horton. 2020. “The Law and Science of Climate Change Attribution.” Columbia Journal of Environmental Law 45 (1).
Heede, Richard. 2014. “Carbon Majors: Accounting for Carbon and Methane Emissions 1854-2010.” Climate Mitigation Services.
Marjanac, Sophie, and Lindene Patton. 2018. “Extreme Weather Event Attribution Science and Climate Change Litigation: An Essential Step in the Causal Chain?” Journal of Energy & Natural Resources Law 36 (3): 265–98.
Stuart-Smith, RF, GH Roe, Sen Li, and MR Allen. 2021. “Increased Outburst Flood Hazard from Lake Palcacocha Due to Human-Induced Glacier Retreat.” Nature Geoscience 14 (2): 85–90.
Toussaint, Patrick. 2020. “Loss and Damage and Climate Litigation: The Case for Greater Interlinkage.” Review of European, Comparative & International Environmental Law n/a (n/a).

  1. Legal systems around the world vary greatly, but they usually follow civil law or common law. In common law, past legal precedents or judicial rulings are used to decide cases at hand. Under civil law, codified statutes and ordinances rule the land. Some countries like South Africa use a combination of civil and common law. Source↩︎

Cover image: Collage of the Lake Palcacocha (Image source: Alexander Luna / Germanwatch e.V.) and the plot of the Global surface temperature observed from NASA vs the 1850–1900 average used by the IPCC as a pre-industrial baseline. (Image source: Wikimedia Commons)


1 Germanwatch e.V., Bonn, Germany