A relevant legal framework with implications for environmental health promotion is the International Environmental Law (IEL). IEL is concerned with the attempt to control pollution and the depletion of natural resources within a framework of sustainable development [43]. The resource management and pollution control components which comprise this framework make it inherently linked to public health objectives, despite there being no explicit mention of human health in many IEL statutes [44]. In October 2021, the United Nations, Human Rights Council (HRC), recognized that having a clean, healthy, and sustainable environment is a human right, however this is not a legally binding obligation [45].

Relevant IEL statutes include “The Declaration of the United Nations Conference on the Human Environment” (the 1972 Stockholm Declaration) [46] and “The Rio Declaration on Environment and Development” (the Rio Earth Summit) [47]. Inherent in both statutes is the legal mandate to prevent, wherever possible, the degradation or depletion of environmental resources needed to sustain planetary life. In both declarations, one can observe an anthropocentric focus on human health and the prevention of environmentally destructive actions which would be detrimental to it, namely those which interfere with life sustaining ecosystem services, as defined by the Millennium Ecosystem Assessment [48].

International Human Rights Law (IHRL), like IEL, features an implicit focus on human health and well-being, albeit through the imposition of protective policies against abusive acts which could threaten any one of its many sub-domains. There are notable areas where IHRL and IEL intersect to promote a policy environment conducive to human health. For example, climate-friendly policies are increasingly being linked to our moral duty to uphold Article 3 of the Universal Declaration of Human Rights [49] which states that “Everyone has the right to life, liberty and security of person”—rights which climate destructive actions explicitly threaten. Yet “environmental law continues to struggle with the complaint that it re-articulates some of the patterns of colonial exploitation in environmental terms”, most notably by treating nature’s resources as mere commodities and by failing to provide an enabling framework for indigenous populations to regain rightful stewardship over their lands [50]. Hence, reconciling environmental and human rights law remains an ongoing process, one which will arguably be central to creating a health-friendly legislative environment in the years to come.

On a national level, Environmental Law consists of statutes, regulations, applied common law, and in some countries, constitutional provisions. Currently, 155 countries have binding legal obligations to respect, protect and fulfill the right to a healthy environment [51]. Environmental rights consist of procedural rights (e.g. access to information, access to justice, right to participate in environmental decision making) and substantive rights (i.e. civil and political, economic and social, cultural, and collective rights) which implicate legal requisites to preventing environmental degradation [51].

Mapping the landscape within which environmental health features in international law also requires an understanding of International Health Regulations (IHR) which, in principle, embody a legal commitment of governments to respond to environmental health threats. The IHR are legally-binding for all 194 WHO member states and include requirements to report public health events with potential to cross borders and to maintain core capacities for preparedness, surveillance and response [52]. Consequentially, it can be said that obligations under the IHR imply a commitment to sound governance in response to environmental health emergencies which, by nature, have high potential to transcend international borders.

Climate Change Litigation (CCL) has gained prominence over the past three decades as a “governance mechanism for addressing climate change” [61]. In the late 1980s and early 1990s in the United States, climate legal action began as a means to hold actors accountable for activities knowingly contributing to GHG emissions exceeding national guidelines [61]. Our database searches identified that between 1986 and the end of May 2020, a total of 1,587 cases of CCL worldwide had been brought before courts, with 1,213 (76%) cases in the United States and 374 cases in 36 other countries and eight regional or international jurisdictions. Out of this total we found 65 directly linked public health cases. With the mounting climate crisis unfolding, CCL continues to be a growing field of law that intersects International and National Environmental Law, International Human Rights Law, and a complex range of statutes, regulations, and legal principals spanning national, subnational and, in some countries, constitutional law.

One of the most notable temporal trends we observed was the increasing frequency of climate change being framed as the core issue. Litigation is evidently evolving as a specific tool for climate legal action. Early cases tended to present environmental destruction as the central concern and framed climate change as a peripheral or secondary issue. The 2020 climate litigation snapshot found climate change to be “at the centre of the legal argument” in about 41% of cases, whereas in the remaining 59% climate change was classified as a “peripheral issue” [61]. The increasing discussion of climate change as a core issue suggests the ‘legal mainstreaming’ of climate change, whereby the adaptation, mitigation, and regulation of industry, becomes a matter of business and financial law, discussed in detail below.

Our results confirm reported trends attesting to a substantive rise in the contributions of environmental and human rights law to legal argumentation in litigation.

Regarding human rights, several powerful case studies illustrate a trend towards petitioners increasingly employing rights claims in climate change lawsuits. In the Urgenda case (Table 1, case 1), the courts decided that human rights, which include the “right to health” is linked with decarbonization. In a case brought by Friends of the Irish Environment [89], the courts held that Ireland’s national mitigation plan partially violated statutory law, because it was not set to reduce GHG emissions sufficiently over the near term. In this case, human rights were used as part of the justification.

In the case of Maria Khan et al. v the Federation of Pakistan (Table 1, case 3), rights to life, dignity, and a clean and healthy environment were argued to be under threat by the actions of the defendants. Likewise, the constitutionally guaranteed “Right to Life” is evoked in the legal argumentation of Future Generations v Ministry of the Environment (Table 1, case 2), as is “Article 2(2) of the Basic Law: Right to Life and Physical Integrity” in the lawsuit filed against District of Columbia vs. Exxon Mobil Corp. (Table 1, case 5). In their analysis of other rights-based claims in climate litigation cases, Peel and Osofsky (2017) conclude that receptivity of courts to rights-based framing is on the rise because it provides a “tangible legal framework for analyzing state actions that lead to climate change” [90]. This is encouraging from a public health standpoint, as all UN human rights treaty bodies now recognize individual rights to life, health, food, and water [49, 91], providing a stronger legal avenue for plaintiffs to link claims of health threats to rights-based legal frameworks.

Human rights have also been used by the defense in ‘just transition litigation’ to question the “benefits and burdens of the transition away from fossil fuels and towards net-zero emissions” [92]. Public health science can provide critical evidence to ensure that human rights are protected, defended and upheld. That defensive interests do not succeed in using a human rights narrative, when it is corporate rights that are at stake, and not human well-being.

In relation to rights for nature, we also observed a rise in eco-centric framings of the environmental. This included the attribution of personhood to nature in some of the more recent cases and the recognition of the inherent value of the environment independent of ecosystem services.

In the case of Future Generations v Ministry of the Environment (Table 1, case 2), a group of youth plaintiffs in Colombia sued the government, municipalities and several corporations based on a “right to a healthy environment, life, health, food and water”. The court determined that the “fundamental rights to life and health are linked and determined by the environment and ecosystem”. The court further recognized the Colombian Amazon as subject to rights.

There are similar cases in India, Bangladesh, Colombia, Ecuador, and New Zealand. In Modh Salim v State of Uttarakhand, the court declared two rivers to be ‘juristic/legal persons/living entities having the status of a living person with all corresponding rights, duties and liabilities”. In 2017 the Whanganui river in New Zealand, the Ganges and Yamuan rivers in India, and the Rio Atrato in Colombia were also granted legal rights [93].

Globally, less than 15% of the land, 21% of the freshwater and 8% of the ocean are protected areas [34]. Yet, indigenous communities, which make up 5% of the global population hold 25% of the land, with 80% of planetary biodiversity. Many of the first countries to adopt rights for nature are post-colonial nations with living indigenous cultures.

In the US, which constitutes the majority of litigation cases, 70% of litigation based on federal statute is brought under the National Environmental Policy Act and Clean Air Act, which are more anthropocentric in their objectives [94]. However, it is likely that the codification of eco-laws, in the US at the local level, will bring challenging cases before the courts on the issue of personhood for nature.

The trend in the growing volume of cases brought by, or on behalf of youth, introduces the concept of intergenerational equity. The UN convention on the rights of the child holds that “state parties shall undertake all appropriate legislative, administrative and other measures for the implementation of the rights recognized in the convention” [95]. In addition, the concept of intergenerational equity, is at the core of both the UN Charter and the Stockholm declaration on the environment: “the present generation has a right to use and enjoy the resources of the Earth but is under an obligation to take into account the long-term impact of its activities and to sustain the resource base and the global environment for the benefit of future generations of humankind” [96]. The right to a healthy environment is now recognized in law by more than 80 percent of United Nations Member States (156 out of 193) [97].

In the case of Saachi v Argentina [98], 16 children filed a petition through the UN convention on the rights of the child. The violated rights included “the right to life, right to health, prioritization of the child’s best interest, and cultural rights of petitioners from indigenous countries”. In the case of Future generations v Ministry of the Environment (Table 1, case 2), a group of plaintiffs aged between 7 and 26 years claimed the rights to a healthy environment, life, health, food and water. In the case of Youth for Climate Change v EU [99], a group of youths claimed that the impact of climate change upon them would go as far as harming their mental health.

Considering that the environmental impact will disproportionately affect certain communities, there are cases of climate litigation that have been brought by groups that include: women, climate refugees, elderly women, organic farmers, indigenous people, and civil society.

In most rulings, the courts have declined to give such groups unique standing to bring a case, for example by stating that all people will be impacted by climate change. Therefore, the strategy of framing the issue as one of disproportionate impact has not yet proven to be highly effective. However, the impact of climate litigation in generating media coverage, creating publicity, and changing public perception is evidently growing and can be expected to escalate further.

Despite growing awareness of health impacts of climate change, the public health lens is yet to be widely adopted by plaintiffs. Our study revealed that only 65 (3.96%) of the 1641 cases used a litigation strategy which included climate change at the center, with extensive use of the word “health” mentioned in the case file submitted to the court. We identified a rise in explicitly health-linked cases over recent years. This rise is consistent with the general increase in litigation cases and is not specific to litigation pursued on public health grounds.

In their study on the role of health in climate litigation, McCormick et al. (2018) found that the Clean Air Act (CAA) was used to support 32% of all cases in the US in which litigants relied on health concerns to support their claims [100]. Interviews with plaintiffs revealed that their primary incentive for pursuing cases under the CAA was that, unlike laws such as the California Environmental Quality Act and the National Environmental Policy Act, the CAA has the protection of public health as its principle goal [100]. This shows that where health is the main focus of a given legal doctrine or environmental regulation, there exists a more direct and powerful avenue for individuals to pursue litigation on the basis of health concerns.

Amongst the 65 directly health-linked cases, there were 11 wins, 11 losses and 43 remain undetermined. The low number of directly health-linked climate cases and the number where decisions are pending, precludes accurate assessment of trends in the receptivity of courts to public health-framed argumentation. The early successes, such as Urgenda Foundation v State of the Netherlands (Table 1, case 1) and other cases are testament to the potential power of public health claims in legal argumentation, yet it remains premature to conclude whether or not public health arguments presented to courts will be seen with the credibility and weight that they warrant.

Nonetheless, one may postulate that as climate-health science matures, making clearer the links on which legal claims rest, the receptiveness of courts to public health language may rise. While McCormick et al. found that cases in which health was an issue had a win rate nearly the same as that for non-health cases (31% and 30%, respectively) [100], claims made by litigants attested to the perceived power of health risk attributions in legal argumentation. As stated, many litigants were “motivated to include health allegations in climate cases because they make the consequences of unabated climate change tangible and may increase the chances that courts will grant the relief sought by satisfying the substantive criteria needed to achieve success on the legal merits of the claim” [100]. Additionally, McCormick et al. noted that several cases in the database that centered on claims about contaminated water and used health as a central argument were won by plaintiffs seeking improved protections for local communities [100].

We contend that health ought to have a bearing on court rulings given the inherent political salience it holds. In his review of fishery management law, Craig (2014) argues that when it comes to advocating for laws targeted at ocean-focused climate change adaptation, a public health connection can provide “a political saliency and importance that is often otherwise missing” [101].

Likewise, Nosek (2018) argues that, so long as health threats in litigation cases can be proven as imminent and knowingly created, debate should naturally “shift towards the necessity of intervention by government and industry officials” [102].

Litigation rests fundamentally upon the ability of the plaintiff to link the accused actions to evidence-backed consequences. Climate attribution science offers the ability to prove causation and is now viewed as a central ingredient for success. Contemporary use of extreme event modelling and the accessibility of this data to the court plays a large role in determining the “attributable risk” of scrutinized actions in climate litigation [103].

With climate-health science currently increasing in strength and credibility, data-backed argumentation offers powerful leverage in future health-centred climate litigation. For example, in Neubauer et al. v Germany (Table 1, case 4), plaintiffs cite IPCC data showing the risk of death, injury, and damage to health in low-lying coastal areas vulnerable to storm surges, coastal flooding, and sea level rise. Plaintiffs cited robust evidence of the link between rising allergies and lengthening pollen seasons, between respiratory diseases and both ragweed blooms and flood-induced indoor mould growth, and storm/flood disasters and psychological trauma. This is supported by the conclusion drawn by McCormick et al. (2018) that “the strength of the scientific evidence mustered to support litigants’ challenges is likely to be an important determinant of case outcomes” [100].

Cases reviewed by McCormick et al. [100] revealed that climate science was only occasionally a central part of the court decisions. This indicates the existence of competing factors which weigh into the decision-making on legal outcomes. Thus, to strengthen the relative weight placed on scientific evidence in legal decision-making on climate litigation, an argument can be made that emphasis should be put on the most scientifically sound, and socially, politically, and economically salient points, backed by expert testimony and robustly generated syntheses of the literature. An additional requirement may be for evidence to show that health risks are imminent, since it has been shown that the narrative of climate risks being distant in space and time dilutes the urgency to act now or the credibility of climate risk allegations [102].

With regards to leveraging the insights, research, and testimony of public health experts in climate litigation, it is worth noting the possibility of COVID-19 having opened a policy window for such action. Undoubtedly, COVID-19 has raised the profile of public health expertise and the value of epidemiology. Thus, public health expertise may be accorded rightful recognition in courts of law in a post-COVID-19 era, something which can and should be exploited in upcoming climate litigation.

The case law brings forward economic and financial considerations, presenting as either incentives or barriers to ‘adaptation and mitigation’, accompanied by liability for market actors. This can give rise to climate laws and policies, that are concerned with “mitigating, adapting and regulating” industrial activity which causes climate change.

Whilst the unmitigated consequences from climate change are catastrophic, a hesitance persists in some courts to “overhaul industries”, as indicated by the Juliana case [67]. Despite pledges by many corporations to reach ‘net zero’ emissions by 2050, there is not yet any contractual or legal obligation to enforce this. The agreement at COP26 to establish rules for a global voluntary carbon market also raises complex issues about the ethics of carbon offsetting, and whether access to finance comes with a human rights and health cost for local and indigenous communities in low-income countries [104].

The evolving link between financial systems, climate change, and the public health cost, is an important indicator in climate litigation [105]. It is extensively documented in the publications of UNEP(FI) [106] where “climate change is referred to by leading economists as the greatest market failure in human history”. The 2020 EU taxonomy regulation on sustainable finance, is framed along the same lines as ‘climate law and policy’, namely objectives of Climate change mitigation, Climate change adaptation, Sustainable use and protection of water and marine resources, Transition to a circular economy, Pollution prevention and control, and Protection and restoration of biodiversity and ecosystems [107] (other jurisdictions such as China have a similar, yet distinct objectives).

In the case of Milieudefensie et al. v Royal Dutch Shell (Table 1, case 9), litigants sought to extend the ruling of Urgenda to private companies. Shell is the parent company of many subsidiaries and has a principal place of business in the Hague, Netherlands. According to the summons, “the financial incentive for Shell to continue its fossil business model developed since 1890 is enormous, which is why it hampers the energy transition, and every year continues to invest dozens of billions to secure the future of the fossil industry for much of this century”. Milieudefensie campaigns for “climate-friendly banking” and believes “private banks and public asset managers are the ideal partners in that respect”. In the ruling against Shell the court stated that although “RDS cannot solve this global problem on its own. However, this does not absolve RDS of its individual partial responsibility to do its part regarding the emissions of the Shell group, which it can control and influence”.

The centrality of financial capital in global economies embeds financial institutions within the broader climate law and mitigation landscape. Financial investment is a powerful influencer on industrial and economic activities serving as an enabler, through incentives, or as a barrier. These organizations offer another avenue for communities to ensure their sentiments are reflected. With regards to financial institutions, several cases illustrate this indicator of financial liability in climate change lawsuits, in which the strategy of litigation has been referred to as “investor activism” [108].

In McVeigh v Rest [109], the respondent sought information from his investment fund, about any actions the respondent was taking, regarding the financial risk posed to his investment by climate change. The court decided that funds have a duty to disclose information that allow the investor to make an informed decision about the investment in relation to such climate risk. Considering the shifting values as citizens on all continents witness climate catastrophes, and the emergence of global youth movements, consumer and social preferences are changing in favor of the environment, health, and well-being. Consequentially, banks, insurers and investment funds face increasing risks of litigation if their activities are not compliant with climate frameworks.

In JAM v International Finance Corp [110] (IFC), a group of Indian villagers brought a case against IFC, the investment arm of the World Bank, before the US Supreme Court, because it had financed the construction of a coal fired plant in India, which polluted the surrounding area. Prior to this case, the IFC held immunity from such prosecutions, in the same manner enjoyed by foreign governments. This ruling overturned the IFC’s immunity from liability for its investments. Because the case involved the World Bank, such a ruling exemplifies how financial entities can be liable in law for financing harm to the environment and public health.

Cases of climate litigation reinforce the need for a globally coordinated approach to climate law, public health, and economics. The World Bank has offered categories for Environmental and Social Investing (ESG) including negative screening, best in class, impact investing, ESG integration, and responsible ownership [111]. All of this relies upon data provided by sovereign countries. The challenges of climate adaptation and mitigation have been translated into a new economics. This must be fully embedded in all legal systems, before massive public health devastation ensues [42]. Despite 29 of the largest 30 financial institutions having set 2050 climate goals, all 30 institutions remain committed to short terms actions, which oppose emerging sustainable finance policy, and have cumulatively enabled at least $740 billion in primary financing to the fossil fuel production value chain in 2020 and 2021 [112]. It remains likely that the financial sector will continue to enable real-economy activities misaligned with 1.5°C climate scenarios as long as they remain legally and economically viable in the short term [112].

Litigating against corporations so that they bear the liability for harm to public health is another means to internalize the costs that these companies are currently externalizing.

In 2020, a series of cases [113–116] were brought by US states against oil companies, using arguments similar to those used to curtail the tobacco industry for its devastating impact on public health [117]. In an ongoing case, Washington DC (AC Racine v Exxon/BP/Shell/Chevron) [118], the defendants are accused of “systematically and intentionally misleading the public about the central role their products play in causing climate change, one of the greatest threats facing humanity”, including through coordinating campaigns of disinformation.

In City and County of Honolulu v Sunoco oil [119], the claim is that not only have “Native Hawaiian cultural sites, built structures, natural resources, and infrastructure including roads, sewerage, and beach parks, and other resources been more frequently flooded and, in some cases, inundated”, but oil companies knew the climate science, and impending harm to public health since the 1950’s. The state is thus seeking financial compensation for losses, which illustrates how the courts are asked to price the impacts of climate change.

In this way market forces incentivize adaptation of corporates’ business model and capital away from harmful activity [120, 121]. The courts play a central role in deciding how quickly new legal incentives are integrated into legal systems, and these cases may become important milestones.

Legal epidemiology is the study of law “as a factor in the cause, distribution, and prevention of disease and injury” [122]. The impact of tax and employment law on public health [123] has been studied. In the 65 public health cases included, there is an expectation from plaintiffs that government and economic actors will prioritize human health and planetary survival over economic profit. In the case of Youth Verdict v Waratah Coal, youth argue that the government has a duty of care to protect the health of its citizens. Further, in the 2020 ruling on modification to ethanol [124], the Mexican Supreme court decided an agency was restricted from raising the ethanol content in fuel, as the ‘right to a healthy environment’ must be prioritized over economic profit. Research has shown that “carbon-only” approaches to mitigating climate change that do not explicitly integrate air and water pollution and environmental justice considerations could fail to alleviate the public health harms and disproportionate burdens of fossil fuel production and use or even exacerbate them [56]. Considering that in response to the Covid-19 crisis, many (though not all) governments acted forcefully to prevent a public health emergency, including by deprioritizing the economy, it is likely that the expectation of prioritizing planetary health will only rise. With global fiscal support for the pandemic already amounting to a sheer $9 trillion by April 2020 [125], the Covid-19 crisis also further demonstrated the financial capacity for large-scale investment when imminent threats arise. At a minimum, to prevent a climate-health crisis, there is an expectation for the risk to be fully priced into the financial markets. Yet, eco-centric laws can go further. The concept of ecocide is a way of protecting the environment and health, which goes beyond civil liability, and makes it a crime to harm nature [126]. As highlighted in the 2020 status report on global climate litigation, there is mounting evidence of an increased appetite by the general public to crack down on corporate irresponsibility, requiring greater climate disclosure and an end to “corporate greenwashing” on the subject of climate and the energy transition.