Private enforcement of climate law
In law, private enforcement refers to any action brought to court by a private party [1]. This is the process by which private citizens can hold emitters accountable. Individuals and civil society organisations can take governments or corporations to court in an attempt to force these defendants to either cut their emissions or compensate for damages [2]. “Horizontal” climate action targets major emitters individually and retroactively, whereas “vertical” climate action addresses systemic gaps in state policy to drive national legislative change [3].
In common law jurisdictions, judges must follow the binding precedents of higher courts when presented with a similar case. Given that judges rely on legal precedent, a single successful lawsuit holding an emitter liable can pave the way for future plaintiffs to win similar environmental cases.
Private attorney general
When a private party brings a lawsuit against an emitter, it can claim to do so in the public interest, serving as a “private attorney general” [4]. The private attorney general has been key to furthering environmental justice across many national jurisdictions; individuals and civil society actors have successfully filed litigation to protect civil and consumer rights [5].
In some jurisdictions such as the United States, claimants who win public interest cases can have their legal fees recovered, removing a major deterrent to pursuing these cases [6]. A similar provision exists in international law, under the Aarhus Convention, which requires that access to environmental justice not be prohibitively expensive. This allows individuals to take legal action against governments or large corporations without significant financial risk [7].
Case study: Comer v. Murphy Oil USA
Comer v. Murphy Oil USA, a landmark U.S. case in 2005 is often cited as the first attempt at using common law tort legislation to hold emitters accountable [8]. A group of citizens sued several fossil fuel companies, arguing that their emissions had amplified the severity of Hurricane Katrina, thereby contributing to the destruction of their property [9]. After its initial dismissal, a 2007 Supreme Court precedent recognizing the causal link between fossil fuel emissions and global warming led to the case being successfully appealed in 2009. The appeal established two important principles: first, that private citizens could bring state common law tort claims, and second, that plaintiffs must only prove that a company’s emissions contributed to the harm, rather than being the sole cause [10].
Case study: Milieudefensie v. Royal Dutch Shell
After Comer, several similar suits were brought globally, alleging harm to health or property [11]. On 26 May 2021, Dutch NGO Milieudefensie successfully brought a landmark class action suit against Shell, on behalf of the public [12]. Considering both Shell’s corporate policy and the human rights principles affirmed by the UN Charter, the Dutch court found that Shell had an obligation to reduce its Scope 3 emissions [13]. This case set a valuable precedent that corporations have a duty of care that is violated by causing environmental harms [14]. Furthermore, while this case was heard in a national court, the plaintiff’s demands included an international emissions reduction [15].
Case study: Luciano Lliuya v. RWE
Another example is the long‑running lawsuit brought by Peruvian farmer Luciano Lliuya against German energy company RWE. His appeal was dismissed by the German High Court in 2025 due to insufficient evidence of property damage [16]. However, the court did not reject the broader idea that German companies could be held liable for climate‑related harms occurring outside Germany [17, 18]. The ruling left open the possibility that emitters may have a duty to take preventive measures or compensate affected communities in other jurisdictions [19].
Conclusion
Private enforcement has emerged as an effective strategy for holding polluters to account when governments cannot — both nationally and internationally. Recent advisory opinions issued by the International Court of Justice and Inter-American Court of Human Rights suggest that private enforcement as a legal phenomenon will continue to gain momentum in years to come [20, 21, 22, 23, 24].
