In 2019, the UN High Commissioner for Human Rights, Michelle Bachelet, described climate change and its threat to human rights in the following terms:

The physical reality of climate change is assessed by the Intergovernmental Panel on Climate Change (IPCC), whose consecutive reports over the past three decades have each described the nature and causes of the climate change our planet is experiencing with increasing scientific confidence.

At the launch of the IPCC’s latest assessment in 2021, IPCC Working Group I co-chair Valérie Masson-Delmotte stated: ‘It has been clear for decades that the Earth’s climate is changing, and the role of human influence on the climate system is undisputed’ (‘Climate change widespread, rapid, and intensifying – IPCC‘, IPCC news release, 9 August 2021).

Global trends in climate change litigation demonstrate the importance of human rights law as a tool for improving the response of public authorities and corporations to climate change.1Jacqueline Peel and Hari M Osofsky, ‘A rights turn in climate change litigation?’, Transnational Environmental Law, vol 7, issue 1, March 2018, page 37, and Annalisa Savaresi and Juan Auz, ‘Climate change litigation and human rights: pushing the boundaries’, Climate Law, vol 9, issue 3, June 2019, page 244. No region has seen more rights-based climate cases than Europe, both at the domestic and regional level.2Ibid. At the domestic level, there have been setbacks but also notable successes, and following the groundbreaking decision in State of the Netherlands (Ministry of Economic Affairs and Climate Policy) v Urgenda Foundation, Supreme Court of the Netherlands, 20 December 2019, an increasing number of pioneering claims have drawn attention to the disproportionate detrimental effect climate change will have on the rights of the most vulnerable members of our society: the elderly; the disabled; children; and future generations.

Recent developments in scientific evidence underpin both the KlimaSeniorinnen and Duarte Agostinho cases and are summarised below.3The science is set out further in Joeri Rogelj and Marc Willers KC, ‘Youth activists are forcing governments to take account of the intergenerational impact of climate change’, Energy and Climate Change Law Institute Review, issue 3, Queen Mary University of London, 29 October 2021, page 7.

In October 2018, the IPCC reported that human activities had caused the Earth’s surface to warm by more than 1oC since the industrial period of 1851–1900.4‘Summary for policymakers’, in Global warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty, Cambridge University Press, 2018, para A.1, page 4. It reported two further significant findings: (i) the climate impacts of 2°C of warming would be very much more serious than those of 1.5°C of warming;5Ibid, paras B.1–B.5.7, pages 7–10. and (ii) there were then only 12 years in which to take action to prevent global temperature rise above 1.5°C.6Ibid, para C.1, page 12.

Human-induced climate change has adverse consequences for natural and human systems, in particular food and water security, and human health.7Ibid, para A.3.1, page 5, and Making peace with nature, UN Environment Programme, 18 February 2021, page 27. These adverse consequences will become even more significant in the coming decades as the climate continues to warm. Every fraction of a degree of warming increases the adverse effects of climate change.

In August 2021, the IPCC published the contribution of Working Group I to the IPCC’s Sixth Assessment Report, regarding the physical science basis of climate change. Its key findings of fact can be summarised as follows:

In February 2022, the IPCC published the contribution of Working Group II to the IPCC’s Sixth Assessment Report. Its key findings of fact are:

The overarching international treaty addressing climate change is the UN Framework Convention on Climate Change (UNFCCC). Article 2 articulates that the ‘ultimate objective’ of the convention ‘and any related legal instruments that the Conference of the Parties may adopt’ (which includes the Paris Agreement) is to achieve ‘stabilisation of greenhouse gas concentrations in the atmosphere’ at a level that would prevent ‘dangerous’ human interference with the climate system.

In December 2015, the state parties to the UNFCCC adopted the Paris Agreement in relation to climate change. Article 2 commits parties to three key goals, the first of which is known as the long-term temperature goal, to hold:

In order to achieve the long-term temperature goal, article 4(1) requires parties to ‘aim to reach global peaking of greenhouse gas emissions as soon as possible’. This aim includes parties undertaking ‘rapid reductions’ after global peaking, ‘in accordance with best available science, so as to achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century, on the basis of equity, and in the context of sustainable development and efforts to eradicate poverty’. In other words, the Paris Agreement embodies not just a consideration concerning 2050 and beyond (‘second half of this century’), but a significant focus on emissions reductions in the years up to that point.

The applicants were: the Verein KlimaSeniorinnen Schweiz (the Association of Swiss Senior Women for Climate Protection, made up of more than 2,000 members) and four individuals.

In essence, the applicants complained that the Swiss government’s failure to tackle climate change, by failing to adopt the necessary short- and long-term GHG emission reduction targets, breached their rights protected by articles 2 and 8 of the European Convention on Human Rights (ECHR), and that the Swiss courts’ failure to determine their complaint and provide them with a remedy breached their rights protected by articles 6 and 13.19See Verein KlimaSeniorinnen and others v Switzerland – revised applicants’ draft speech for the oral hearing of 29 March 2023 (for the court’s interpreters). The applicants’ detailed arguments were well documented in written submissions and are all on the KlimaSeniorinnen website.

In response, the Swiss state argued that the applicants were trying to ‘circumvent’ the Paris Agreement by seeking to construct an international judicial review of its climate measures and that the court should not admit and determine the complaint because that would involve it taking on the role of a ‘supreme environmental court’. It also argued that the unprecedented and complex issues and challenges of climate change, as well as Switzerland’s democratic system, warranted it being granted an ‘ample margin of appreciation’ when determining how to tackle climate change and what targets for carbon emission reductions it should adopt.

There were a large number of interventions by member states, UN special rapporteurs, non-governmental organisations, universities and legal experts on international environmental law, as well as scientific experts.20Some of these are available here. In the event, the court directed that two of those interveners would be given permission to make oral submissions: the Republic of Ireland and the European Network of National Human Rights Institutions.

A few weeks before the hearing date, the court sent to the parties and the interveners a number of additional questions that it requested be addressed orally during the hearing, including two key questions:

At the hearing before the Grand Chamber,21This is a dubbed version, though the hearing in the original languages may be viewed from the same page. See also the draft speech per note 19 above. the applicants opened their case by making the point that the world is faced with an existential threat to which we must respond with action:

They then made the following submissions.

First, they argued that the failure of the Swiss courts to determine the applicants’ case at all – on the grounds that there was still time before the Paris Agreement temperature thresholds were reached and that accordingly the applicants could not yet claim that their rights were affected – breached their rights protected by ECHR articles 6 and 13.

Second, they addressed victim status, explaining the direct effect on the applicants of the Swiss government’s ongoing failures to tackle climate change. They relied on scientific papers and data to show that the applicants were already suffering from the effects of climate change. As elderly women, the excessive and sustained high temperatures of increasingly frequent and severe heatwaves posed an extremely serious threat, not just to their health and well-being, but to their lives, and they referred the court to evidence which showed that:

The Swiss government accepted that elderly women are disproportionately affected by excessive heat but argued that the association’s claim should be rejected as an actio popularis. In response, the applicants pointed to the fact that the association is no more than a ‘group of individuals’, each one of whom is directly affected. Thus, it was argued that all of the applicants are detrimentally affected.

Third, the applicants addressed the positive obligations owed to them by the Swiss government. They pointed to the groundbreaking decision of the Dutch Supreme Court in Urgenda that a state’s positive obligations under articles 2 and 8 apply to activities, whether public or private, that contribute to climate change on the basis that climate change is known to involve a ‘real and immediate’ threat to human life and well-being, ie, a risk that is both genuine and imminent (Urgenda at paras 5.2.2–5.2.3). They argued that the court should follow the Dutch Supreme Court’s lead and hold that Switzerland is ‘under a positive obligation to take the necessary steps to guarantee effective protection for the applicants’ lives, health and well-being’.

Fourth, the applicants addressed Switzerland’s failure to take adequate steps to mitigate climate change. They made the point that the court was not being asked to determine whether Switzerland was in breach of any of its commitments under the Paris Agreement but rather to decide whether Switzerland had violated the applicants’ rights under the ECHR.

They argued that to protect the rights of the applicants, the Swiss government must ‘do everything in its power to do its share to prevent a global temperature increase of more than 1.5 degrees above pre-industrial levels’. This necessarily meant the adoption of a legislative and administrative framework to achieve that objective.

They demonstrated, by reference to evidence from experts in climate change science and the Climate Action Tracker (CAT) – an independent scientific project that tracks government climate action and measures it against the globally agreed Paris Agreement – that Switzerland’s short- and long-term GHG emission reduction targets were woefully inadequate (and not embedded in legislation), and that Switzerland had not carried out any studies or due diligence in relation to the 1.5°C limit identified by the IPCC in its Global warming of 1.5°C Special Report.

Switzerland had no real answer to these points. It responded by referring to the fact that it had taken adaptation measures and argued that it should in any event be given a wide ‘margin of appreciation’. On the latter point, the applicants accepted that it was for Switzerland to decide ‘what measures to take to give effect to targets; to that extent it has a margin of appreciation. But no such margin exists in relation to the fixing of the targets themselves, nor the need for legislation to give them practical effect.’

Fifth, the applicants explained that if the remaining global carbon budget is distributed fairly on the basis of the principles of international environmental law, such as ‘common but differentiated responsibilities and respective capabilities’, then Switzerland is already using other countries’ shares of the small remaining global carbon budget. They described this as ‘carbon theft’.

In answer to the court’s key question (b), the applicants relied on the CAT and an article by Lavanya Rajamani et al, ‘National “fair shares” in reducing greenhouse gas emissions within the principled framework of international environmental law‘ (Climate Policy, vol 21, issue 8, 2021, page 983), and argued that Switzerland’s fair share requires it to do the following:

Sixth, the applicants addressed the Swiss government’s general defences. Switzerland had argued that its actions alone would not prevent or avoid the risks that climate change posed to the applicants and that its failures could not therefore be considered causative of the relevant harm and risk.

The applicants noted that this argument has been roundly rejected by apex courts, including the Dutch Supreme Court in Urgenda, for very obvious reasons. It is common sense that the temperature goal in the Paris Agreement cannot be achieved without mutual trust between contracting states, and if a state as rich and technically advanced as Switzerland does not take the lead and do its fair share by pursuing its highest possible ambition, then it is likely that other states will also fail to do so.

Moreover, they argued, it should not be forgotten that every degree – indeed every fraction of a degree – of temperature increase matters.22See Climate change 2021, ibid, para B.1 and Urgenda at paras 4.4 and 5.7.8, referring to the judgment of the US Supreme Court in the case of Massachusetts v Environmental Protection Agency 549 US 497 (2007) at pages 22–23, which made precisely this point. See also Neubauer and others v Germany, Federal Constitutional Court, 24 March 2021 at paras 32, 119 and 122. Even today’s global temperature increase of 1.13°C is causing enormous damage, and a 1.5°C global temperature increase will exacerbate that harm.

Switzerland had also argued that it could not be held responsible for its failures because proposed legislation that it had intended would tackle climate change was rejected in a referendum. The applicants countered that point by reminding the court that Switzerland is responsible for its ECHR violations irrespective of how they came about. Contracting states are not subject to different ECHR obligations depending on the technical operation of their democratic system.

Finally, the applicants stressed the urgent need for Switzerland to make the necessary emission reductions, and noted that its actions to date had been woefully inadequate and that there were no signs that it would change course, before arguing that it was essential that the court order Switzerland to take the necessary measures. The applicants concluded their oral argument with the following powerful submission:

On 3 September 2020, six Portuguese children and young adults filed an application with the ECtHR against 33 European states, in which they argued that these states were breaching their obligations under the ECHR by failing to adopt adequate climate change mitigation measures.

The lynchpin to the application was that, because each of the respondents contribute to global emissions, they must be presumed responsible for the harm/risk that climate change at its current trajectory poses to the applicants and therefore for breaching the above-mentioned ECHR rights. In making their legal case as to shared responsibility, the applicants drew on the authoritative ‘Guiding Principles on Shared Responsibility in International Law‘ (André Nollkaemper et al, European Journal of International Law, vol 31, issue 1, February 2020, page 15). In line with the Guiding Principles, they argued that states share responsibility for multiple internationally wrongful acts when each of them engages in separate conduct that:

The argument on presumptive responsibility is further supported by the general principle of law that where one or more of a number of potential wrongdoers must have caused a particular harm, but there is uncertainty as to which of them in fact caused that harm, then each of those potential wrongdoers is presumptively responsible in law for the harm in question, such that the onus is on those potential wrongdoers to show that they did not cause it.23See separate opinion of Judge Simma in Oil Platforms (Islamic Republic of Iran v United States of America) (2003) ICJ Rep 161 at paras 66–71.

Accordingly, the starting point of the application was that the respondents share presumptive responsibility under the ECHR for the ‘indivisible injury’ that climate change causes the applicants, and therefore bear the onus of extricating themselves from this default position. It further followed from this position that the ambiguity surrounding what constitutes a state’s ‘fair share’ (having regard to, for example, its historic emissions, its economic wherewithal, or its current per capita emissions) of the necessary global climate change mitigation effort must be resolved in favour of the applicants. In effect, this means that states’ mitigation efforts must be assessed according to the relatively more demanding measures of their respective ‘fair shares’ (consistent with the methodology adopted by the CAT), with greater emphasis being placed on the extent to which they are consistent with their ‘highest possible ambition’ as per article 4(3) of the Paris Agreement.

Nor should the margin of appreciation doctrine be read as allowing states broad discretion in the area of climate change mitigation. There is a critical difference between the issues in cases such as Hatton and others v UK App No 36022/97, 8 July 2003 (at para 97), concerning the regulation of noise pollution, and that of climate change. In Hatton, the margin of appreciation was relied on to determine the extent of the interference to the rights protected by article 8 that was permissible in that case, having regard to the competing economic interests at stake. If, however, in the case of climate change, it is accepted that the ECHR must be read in light of the temperature target prescribed by the Paris Agreement, then the interference with article 8 rights that will result from global warming exceeding that target cannot ever be deemed ‘necessary in a democratic society’. Accordingly, the question that the margin of appreciation was relied on to address in Hatton is, when it comes to climate change, already answered.

The ‘best available science’ is entirely clear as to the extent of the emissions reductions that are required, at a global level, to meet the goal of the Paris Agreement. Nonetheless, to the extent that there is any uncertainty in this regard, the precautionary principle comes into play as regards the precise amount by which the atmosphere will warm on the basis of current emissions. The most likely projected temperature rise will still cause devastating impacts to the applicants and others.

The uncertainty with which the application was principally concerned relates to the ‘fair share’ question. On this issue, and, ultimately, on the determination of the amount by which emissions must be reduced, states ought not to enjoy a wide margin of appreciation. This follows from the very nature of the margin of appreciation as a feature of the principle of subsidiarity: as the ECtHR first noted in Handyside v UK App No 5493/72, 7 December 1976 (at para 48), the margin stems from the observation that ‘[b]y reason of their direct and continuous contact with the vital forces of their countries, state authorities are in principle in a better position than the international judge to give an opinion on’ certain matters relating to the interpretation and implementation of the ECHR.

In various domestic climate change cases decided to date, courts (in the UK, Ireland, Germany and Norway, for example) have referred to ‘separation of powers’-type considerations when determining the scope of the margin of appreciation that states enjoy when determining their emissions reduction efforts. Even in the vitally important decision in the Urgenda case, the Dutch Supreme Court emphasised the need for judicial restraint when applying the ECHR to the Netherlands’ climate mitigation policies. This led the court to endorse the lowest end of the equity range of emissions reduction (25–40 per cent on 1990 levels by 2020 for developed countries) that was presented to it – an approach that, if replicated, is inherently incapable of keeping global warming to the goal of the Paris Agreement. Moreover, the conflation of domestic constitutional law-based principles with the margin of appreciation conflicts with the ECtHR’s understanding of that principle. As it held in A and others v UK App No 3455/05, 19 February 2009:

This leads to the question of why the Agostinho case was filed directly with the ECtHR, before the applicants had exhausted domestic remedies. The applicants first made the entirely reasonable argument that it would not be practically feasible for them to pursue proceedings through the domestic courts of each of the 33 respondents. They also contended, however, that thus far domestic courts in Europe have not provided adequate remedies in respect of inadequate climate mitigation policies – largely because of how they have misapplied the margin of appreciation in this context. This, together with the exceptionally urgent need for the provision of adequate remedies in this context throughout Europe, further justified their filing of an application directly with the ECtHR.

As held in Budayeva and others v Russia App Nos 15339/02, 21166/02, 20058/02, 11673/02 and 15343/02, 20 March 2008, ECHR article 2 imposes a ‘duty to do everything within the authorities’ power’ (para 175) to protect human life in the environmental context. It is hardly consistent with this view that a state could, for example, export vast quantities of fossil fuels without any consequence for its responsibility under the ECHR.

In Ilaşcu and others v Moldova and Russia App No 48787/99, 8 July 2004, the ECtHR held:

The applicants’ case was firmly grounded on evidence of the direct effects that climate change – to which, of course, each of the respondents contribute – is having, and will have, on their lives. The fact that countless others stand to endure similar effects, and therefore to benefit from the decision they seek, does nothing to undermine their status as ‘victims’ for the purpose of ECHR article 34 (see, for example, Zakharov v Russia App No 47143/06, 4 December 2015 at paras 173–179). Indeed, it is a fact to which the ECtHR must have regard when addressing the responsibility of the respondents for breaching the applicants’ rights (see, for example, Broniowski v Poland App No 31443/96, 22 June 2004 at paras 162 and 198).

Similarly, the fact that enforcement of the respondents’ obligations to the applicants may ultimately depend, in practice, on other individuals bringing cases before the domestic courts throughout Europe does nothing to undermine their status as victims. Indeed, it is a reality that is consistent with their argument that it would not be feasible for them to exhaust remedies before each of the respondents’ domestic courts.

This article demonstrates that the development of greater certainty in the scientific evidence underpinning climate change has created a proper foundation to bring legal challenges to state inaction to meet obligations to limit temperature increase. It is clear that climate change is a threat to life on Earth, and that it engages states’ obligations under human rights law. Such litigation is still in its early stages in Europe and elsewhere, but the oft-cited ‘rights turn’ in climate litigation24See, for example, César Rodríguez-Garavito, ed, Litigating the climate emergency: how human rights, courts, and legal mobilization can bolster climate action, Cambridge University Press, November 2022. clearly shows that it is central to the battle against the climate emergency. Harnessing scientific evidence that informs enforcement of human rights law in tackling climate change is beginning to yield results, and the legal strategies involved in doing so continue to develop and evolve. The authors consider that there is still considerable work to do to ensure that obligations under international treaties are enforced, and human rights litigation will become an ever more important tool in this endeavour.