6.3.1 Justiciability

When courts consider whether a climate case is justiciable, separation of powers is the single most decisive underlying principle. Many procedural rules serve the purpose of protecting each branch’s core constitutional powers, that is, separation of powers. One could think of standing, availability of legal instruments to require governmental action, or time limits. This subsection considers the judicial reasoning, first, in cases that were found non-justiciable, and second, in cases in which justiciability was the focus of the judicial reasoning and that were found justiciable.

On a more abstract level, judges may be concerned that rulings in strategic climate litigation aiming at mitigation measures could interfere with the core task of elected politicians to prescribe general public policy choices.Footnote ¹³ According to a strict functional view of what separation of powers requires, judges may consider that they cannot decide that general policy choices are necessary and find the case non-justiciable. At the same time, the far-reaching interferences of the climate crisis with the enjoyment of human rights in a concrete and identifiable manner, not just in the future but also in the present, have become apparent. These interferences highlight the failure of the executive and the legislature to take measures that could be seen as adequate in light of established science.Footnote ¹⁴ Under a more relational conception of separation of powers, it is the task of the judiciary to prompt the other branches to carry out their constitutional mandates when they fail to do so.

Furthermore, even non-justiciable cases may have considerable political influence and contribute to the development of legal doctrine. Often, cases are found inadmissible on procedural grounds that serve the purpose of separation of powers but do not necessarily relate to whether judges could generally review climate policy. An example is standing requirements.Footnote ¹⁵ Our materials reveal that considerations of courts, which ultimately result in dismissals, may also include legal interpretations and doctrinal reasons that may lay the ground for more far-reaching climate policy. In light of the fact that the judiciary has a constitutional duty to ‘deliver justice’,Footnote ¹⁶ the logical minimum of reaction, when a case is brought, is declaring a case non-justiciable on specified grounds.

Juliana v United States is an example of a non-justiciable case from the United States.Footnote ¹⁷ In this case, a group of child plaintiffs alleged that several United States agencies had continued policies allowing for exploitation of fossil fuels, despite knowing of the hazards for more than fifty years. The plaintiffs claimed that the government thereby violated their constitutional rights, including a right to due process under the Fifth Amendment to a ‘climate system capable of sustaining human life’. The Ninth Circuit concluded in a 2-1 decision ‘reluctantly’ that the plaintiffs’ ‘impressive case for redress must be represented to the political branches of government, not the judiciary’.Footnote ¹⁸ In justifying the outcome, the court sided with a more functional conception of separation of powers.

Outside the United States, justiciability has been the focus of climate cases in Australia, Canada, New Zealand, and Pakistan.Footnote ¹⁹ Similarly, in the supporting judicial reasoning one can pinpoint elements of a more functional conception of separation of powers. In Sharma and Others v Minister for the Environment, eight young people, claiming to represent all people under 18, filed a putative class action in Australia’s Federal Court to block a coal project. They asserted that it would exacerbate climate change and harm young people in the future. The Federal Court of Australia established a new duty of care to avoid causing personal harm to children but declined to issue an injunction to force the minister to block the coal mine extension. The judge rejected the minister’s argument as to why alleged ‘policy reasons’ ought to have prevented the recognition of the duty of care. Contrary to the minister’s claims, the judge stated that the recognition of this duty would not interfere with the minister’s statutory task, nor necessarily render tortious any activity generating GHGs. Despite the Federal Court’s decision, the minister granted approval for the proposed mine expansion, and in March 2022 the Full Federal Court of Australia unanimously overturned the primary judge’s decision to impose a duty of care on the minister. The three judges had separate reasonings. Chief Justice Allsop found that the duty would require consideration of questions of policy ‘unsuitable for the judicial branch to resolve’.Footnote ²⁰

By contrast, the Superior Court of Ontario in Canada found in Mathur et al v Her Majesty the Queen in Right of Ontario (preliminary decision) that ‘[t]he fact that the matter is complex, contentious or laden with social values does not mean that the courts can abdicate the responsibility vested in them by our Constitution to review legislation for Charter compliance when citizens challenge it. In such circumstances, it is the court’s obligation to decide the matter’.Footnote ²¹ This case emphasises the functional argument that it is the judiciary’s mandate and duty to apply constitutional law.

Equally grappling with issues of justiciability, Justice Mallon argued for the High Court of New Zealand in the case of Sarah Thomson v The Minister for Climate Change Issues that:

In its reasoning, the Court relied on a relational conception of separation of powers while stressing the importance of functional considerations. It reasoned more specifically that the ‘importance of the matter [climate change] for all and each of us warrants some scrutiny of the public power in addition to accountability through Parliament and the General Elections’, yet noted that there are ‘constitutional limits’ to the role of the judiciary, and that, if a ground of review ‘requires the Court to weigh public policies that are more appropriately weighed by those elected by the community’, it may be necessary for the Court to ‘defer to the elected officials’.Footnote ²³

In the case of Michael John Smith v Fonterra Co-Operative Group Limited and Ors, the respondent companies are some of New Zealand’s largest GHG emitters (including from the dairy and meat industry).Footnote ²⁴ In this case the issue was whether tort law could be used to seek wide-ranging private law remedies with respect to climate change. According to one cause of action, the defendants allegedly had a duty to cease contributing to climate change. The High Court found that there were ‘significant hurdles’ for Smith in persuading the Court that this new duty should be recognised but determined that the relevant issues should be explored at a trial.Footnote ²⁵ Invoking a more functional conception of separation of powers, the High Court ultimately decided against any regulation of policy content. It argued that ‘[t]he Courts are poorly equipped to deal with the issues which Mr. Smith seeks to raise. This country’s response to climate change involves policy formation, value judgments, risk analysis, trade-offs and distributional outcomes. These matters are well outside the normal realms of civil litigation’.Footnote ²⁶ It further explained that ‘[i]f the Courts were to reach different conclusions than Parliament, there could be inconsistent and different net zero emission targets and different ways of dealing with the problems thrown up by climate change. That would be highly undesirable and would put significant emitters in a quandary’.Footnote ²⁷

6.3.2 Recognise a Right or Duty

Separation of powers concerns remain equally present after judges have found a case justiciable and recognise a legal right or duty – positive or negative.Footnote ²⁸ Recognising a legal right or duty is an important step in the judicial process including in those cases that determine a particular obligation, with notable examples being Urgenda, VZW Klimaatzaak v Kingdom of Belgium and Others, Future Generations v Ministry of the Environment and Others, Neubauer and Others v Germany, Notre Affaire à Tous and Others v France, and Shrestha v Office of the Prime Minister and Others.Footnote ²⁹ However, a court may also stop at this level of identifying rights or duties of the parties, for example if it does not establish a breach. These rulings may have a symbolic value in political discourse or obligate the executive or legislative branches to take these rights or duties into consideration.

An example of a case with high constitutional and symbolic value is Neubauer.Footnote ³⁰ In this case, the German Federal Constitutional Court recognised that the German State had a constitutional duty to address the harm posed by climate change in order to protect the constitutional rights to life and health, protected under the German Constitution and the ECHR, ‘by taking steps which […] contribute to stopping human-induced global warming and limiting the ensuing climate change’.Footnote ³¹

Urgenda confirmed in three different instances that climate change fell within the scope of protection of the rights to life and to private and family life, under Articles 2 and 8 ECHR.Footnote ³² It also confirmed that the State is subject to a duty of care in tort, which is interpreted in light of these human rights provisions. While the District Court reasoned that the State’s duty of care in tort, as an open-textured norm, must be interpreted in a manner that is, so far as this is possible, consistent with its obligations under international law.Footnote ³³ The Dutch government appealed the decision, and Urgenda filed a cross-appeal with respect to the ECHR claim. In late 2018, the Court of Appeal upheld the decision of the District Court, while permitting Urgenda to make a claim under the ECHR. The Dutch government appealed to the Dutch Supreme Court, which affirmed in December 2019 the order of the District Court and the Court of Appeal’s admission of Urgenda’s claim under the ECHR. The Supreme Court interpreted the Netherlands’ obligations under Articles 2 and 8 ECHR by drawing on non-binding commitments of the Dutch State under the United Nations Framework Convention on Climate Change (UNFCCC), soft law sources such as Conference of the Parties’ (COP) decisions, and ‘scientific insights and generally accepted standards’.Footnote ³⁴

Building on Urgenda, the case of Milieudefensie et al v Royal Dutch Shell plc extends the duty of care under tort law (Article 6:162 of the Dutch Civil Code informed by Articles 2 and 8 ECHR) to private companies.Footnote ³⁵ The District Court accepted that given the Paris Agreement’s goals and the scientific evidence regarding the dangers of climate change, Shell has a duty of care to take action to reduce its GHG emissions.

6.3.3 Establish a Breach

The next stage at which separation of powers concerns arise is when courts consider whether they recognise a breach, even if that does not necessarily imply that the court orders the defendant to take action. Again, even if such rulings may not prescribe a specific enforceable obligation, they may have high symbolic value in the political discourse and establish important and potentially replicable interpretations of the law.

In VZW Klimaatzaak, the Brussels Court of First Instance found a duty and a breach of that duty, but did not establish an enforceable obligation. The Court found the federal state and the three regions jointly and individually in breach of their duties of care for failing to enact good climate governance. However, the Court declined to issue an injunction ordering the government to set the specific emission reduction targets requested by the plaintiffs. The Court found that the separation of powers doctrine limited the Court’s ability to set such targets and that doing so would contravene legislative or administrative authority. On appeal, this aspect of the decision was overturned – with the Court of Appeal issuing an order requiring the federal state and regions to adhere to a more ambitious 2030 mitigation target.Footnote ³⁶

There are various other examples where separation of powers has not proven to be a barrier in establishing duty and breach. In the Future Generations case, the Supreme Court of Colombia found that the State’s failure to prevent deforestation, which exacerbates climate change, violated the claimants’ constitutional rights of life, health, and minimum subsistence: ‘It is clear that despite several international commitments, legislation, and jurisprudence on the subject, the Colombian State has not efficiently tackled the problem of deforestation in the Amazon’.Footnote ³⁷

An example from Nepal is the Shrestha case.Footnote ³⁸ In this case, the Supreme Court of Nepal determined that the State’s failure to adopt a comprehensive law on climate change and to adequately address the existing impacts of climate change violated the right to life and to live with dignity, as well as the right to a healthy environment under the Nepalese Constitution.Footnote ³⁹

In Neubauer, the German Federal Constitutional Court found that the duty to take ‘measures that help to limit anthropogenic global warming and the associated climate change’ applies despite ‘[t]he fact that the German State is incapable of halting climate change on its own’.Footnote ⁴⁰ The Court found that this requires the legislature to adopt legislation to reduce GHG emissions in a ‘sufficiently prudent manner’, without ‘offload[ing] reduction burdens onto the future’.Footnote ⁴¹ The Court established a breach of the rights protected under the German Constitution.Footnote ⁴²

The Municipal Court of Prague found in the first instance in the Klimatická žaloba case that the ‘far-reaching effects’ of climate change posed a threat to the right to a favourable environment, which is protected under the constitution.Footnote ⁴³ The constitutional duty to protect human rights thus required the government to develop specific and comprehensive mitigation measures ‘without undue delay’.Footnote ⁴⁴ The court found that the government was not doing enough to adequately reduce emissions before 2030, and thus violated its duty to protect human rights. It concluded that ‘[t]he defendants’ failure to act deprived the applicants of their right to a favourable environment’.Footnote ⁴⁵

In Pakistan, the High Court of Lahore held in Leghari v Federation of Pakistan that the State’s failure to address the impacts of climate change within the country violated the plaintiff’s right to life as well as the right to a healthy environment (among other rights).Footnote ⁴⁶ In this case, Ashgar Leghari, a Pakistani farmer, argued that the government had failed to meet its climate change mitigation and adaptation targets, which had resulted in immediate impacts on the water, food, and energy security of Pakistan in a way that interfered with his fundamental right to life. The Court ruled in response that ‘the delay and lethargy of the State in implementing the Framework offends the fundamental rights of the citizens which need to be safeguarded’.Footnote ⁴⁷ When establishing the breach, the Court argued that fundamental rights must be guided by the constitutional values of democracy, equality, and social, economic, and political justice, as well as the international environmental principles of sustainable development, the precautionary principle, intergenerational and intragenerational equity, and the doctrine of public trust.

Equally, in Urgenda, the first successful strategic climate case aimed at general emission reduction, the Dutch Supreme Court concluded that Dutch climate mitigation efforts were not consistent with IPCC science and the government thus violated its obligation to protect under Articles 2 and 8 of the ECHR.Footnote ⁴⁸

6.3.4 Determine an Enforceable Obligation

Finally, a court may impose an enforceable obligation on the parties to the case. These enforceable obligations may be procedural or substantive.Footnote ⁴⁹ From a separation of powers perspective, determining procedural obligations may prima facie be seen as less controversial than determining substantive ones. The principled reasoning of the Supreme Court in Nature and Youth Norway and others v Norway may serve as an illustration. The case concerned the validity of a royal decree of 2016 to grant ten petroleum explorations licences in the southern and south-eastern parts of the Barents Sea. The Court did not rule in favour of the plaintiffs but provided extensive reflections in relation to separation of powers. It held that ‘decisions involving basic environmental issues often require a political balancing of interests and broader priorities’.Footnote ⁵⁰ Therefore, the Court stated, ‘[d]emocracy considerations […] suggest that such decisions should be taken by popularly elected bodies, and not by the courts’.Footnote ⁵¹ Yet, the Court also noted that democratic considerations have less bearing in regard to procedural duties, noting specifically that ‘restraint is less required when it comes to assessing the procedure’ as ‘in reviewing the political balancing of interests’.Footnote ⁵²

We treat procedural and substantive obligations in separate subsections later on. We should add, however, that the dividing line between procedural and substantive obligations is at times difficult to draw. A case in point is Neubauer, which primarily established procedural obligations but also determined that the German Constitution entails a substantive constitutional obligation to establish a law with a zero-emission target for 2050. Similarly, in Friends of the Irish Environment CLG v The Government of Ireland, Ireland and The Attorney General, the Supreme Court of Ireland ordered the Irish government to return to the drawing board and develop a new National Mitigation Plan, which is a procedural obligation aiming for a substantive outcome.Footnote ⁵³

6.4.1 Role of the Judiciary in Applying the Law

The first emerging best practice results from how judges understand their own role vis-à-vis the other branches of government and provide arguments for this understanding. Several courts have emphasised that it is the role of the judiciary to apply the law. In other words, when the legislature has adopted a national law this mandates the judiciary to ensure that the legally binding commitments made under that national law are given effect.Footnote ⁶³ They also generally emphasised the necessity of judicial review of executive conduct with respect to climate change legislation.Footnote ⁶⁴ This exercise of judicial review renders matters which once might have been reserved to ‘politics’ a matter of lawful conduct.

DG Khan Cement Company v Government of Punjab is illustrative of this practice. In that case, the Supreme Court of Pakistan found that the judiciary is not only able but actually required to adjudicate cases that can help address the dangerous consequences of climate change.Footnote ⁶⁵ The Court argued that ‘[t]his Court and the Courts around the globe have a role to play in reducing the effects of climate change for our generation and for the generations to come. Through our pen and jurisprudential fiat, we need to decolonize our future generations from the wrath of climate change, by upholding climate justice at all times’.Footnote ⁶⁶

In Germany, which has a constitutional court that enjoys strong review powers over general laws and exceptionally high public support, including in politics and academia, the judiciary is formally in a position to directly restrain politics (legal constitutionalism). In the Neubauer case, a group of youth filed a legal challenge against the Federal Climate Protection Act arguing that the target of reducing GHGs 55 per cent by 2030 from 1990 levels was insufficient. The German Federal Constitutional Court struck down parts of that Act, which is a general federal law, as incompatible with fundamental rights protected under the German Constitution.

For its reasoning, the Court could rely on constitutional provisions that limit the scope for political decision-making to take measures to protect the environment or not. The Court found that Article 20a of the German Constitution obliges the legislature to protect the climate and aim towards achieving climate neutrality. Further, the Court stated that Article 20a ‘is a justiciable legal norm that is intended to bind the political process in favour of ecological concerns, also with a view to the future generations that are particularly affected’. Accepting arguments that the legislature must follow a carbon budget approach to limit warming to well below 2°C, and, if possible, to 1.5°C, the Court found that the legislature had not proportionally distributed the budget between current and future generations. Because ‘one generation must not be allowed to consume large parts of the CO₂ budget under a comparatively mild reduction burden if this would at the same time leave future generations with a radical reduction burden and expose their lives to serious losses of freedom’, the Court ordered the legislature to set clear provisions for reduction targets from 2031 onward by the end of 2022.Footnote ⁶⁷

An example from Canada is Mathur et al. Although judicial review is relatively weak in Canada, the Superior Court of Ontario explained that the Constitution ‘requires’ the Court to decide a climate case, even if ‘the matter is complex, contentious and laden with social values’.Footnote ⁶⁸

In the Netherlands, by contrast with Germany and more like Canada, the judiciary is in a comparatively weak position vis-à-vis the political branches and may not review general laws in light of national constitutional rules or principles. However, this did not stop the courts in three instances (District Court, Court of Appeals, and Supreme Court) from ruling in favour of Urgenda, determining that, by failing to reduce GHG emissions by at least 25 per cent by end-2020, the Dutch government was acting unlawfully in contravention of its duty of care. In the higher two instances, the courts relied on Articles 2 and 8 of the ECHR, which enjoy constitutional status and direct enforceability in the Dutch system. Directly addressing the matter of separation of powers, the Dutch Supreme Court concluded

In respect of a functional separation of powers, the Dutch Supreme Court insisted that it was a legitimate function of the judiciary, as required by the rule of law, to determine whether the State was complying with its legal obligations, and had ‘remained within the limits of the law by which they are bound’.Footnote ⁷⁰ The Court argued further that ‘this order does not amount to an order to take specific legislative measures, but leaves the State free to choose the measures to be taken in order to achieve a 25% reduction in greenhouse gas emissions by 2020’.Footnote ⁷¹

Notably, this was the first decision by any court ordering a State to limit GHG emissions for reasons other than statutory mandates. The Court pointed to ‘the severity of the consequences of climate change and the great risk of climate change occurring’.Footnote ⁷² The functional separation of powers arguments put forth by the defendant against justiciability, for example, were rejected ‘also because the State violates human rights’.Footnote ⁷³

6.4.2 Giving Effect to International Norms

Judges have regularly relied on international law to substantiate their reasoning, either because no national climate legislation existedFootnote ⁷⁴ or because international law further strengthened the case as it illustrated the objectives for which the national climate legislation had been adopted.Footnote ⁷⁵

France is an illustrative example of a jurisdiction in which several courts have emphasised the relevance of a State’s previous commitments to an international legal framework that acknowledges and aims to fight the climate emergency. In Notre Affaire à Tous, for example, the Administrative Court of Paris explained in 2021 that, by ratifying the UNFCCC and the Paris Agreement, the French government recognised ‘an “emergency” to combat current climate change’ and ‘recognised its capacity to act effectively on this phenomenon in order to limit its causes and mitigate its harmful consequences’.Footnote ⁷⁶ One year earlier, in Commune de Grande-Synthe v France, the Supreme French Administrative Court had established the pre-eminence of the UNFCCC and the Paris Agreement in the context of domestic mitigation action, explaining that the treaties ‘must be taken into account in the interpretation of provisions of national law’ aimed at reducing GHG emissions.Footnote ⁷⁷

The status of international law within the domestic legal order is highly relevant to judges’ considerations of a State’s international commitments. When courts are asked to determine the relevance and meaning of international law in domestic proceedings, they usually enjoy additional discretion. They act as gatekeepers determining which international norms meet the domestic requirements of enjoying direct effect and what the relationship between domestic and international norms is. Hence, reliance on international norms as the basis for a ruling rather than, for example, national constitutional law increases the power of the judiciary vis-à-vis the other branches. At the same time, the legislature does not have the same powers over the creation of international norms as it has over national laws, even if it may be formally involved in the ratification of international agreements. Thus, giving effect to international norms, in particular in relation to national laws, may be prima facie read as disempowering parliament. Separation of powers concerns may increase if decisions rely predominantly on international norms rather than national laws.

Very different constitutional framework conditions establish very different conceptions of separation of powers, for example that the judiciary is given the explicit mandate to review the constitutionality of general laws (Germany) or not (Netherlands). However, this does not exclude replicable best practices from emerging, such as reliance on non-binding norms of international law or (repeated) political commitments to substantiate a particular mitigation obligation.

6.4.3 A Matter of Protecting Human Rights

Where there is a right, there is a remedy.Footnote ⁷⁸ The right to a remedy when one’s rights are violated lies at the heart of the rule of law and separation of powers. Generally, human rights are seen as the prime example of rights for which the judiciary must offer remedies to enforce them against the executive and the legislature. In line with this, the Dutch Supreme Court, followed by several other national courts, emphasised that it is for the courts to ensure that the other branches do not overstep the law when exercising their political discretion, particularly when human rights are at stake.Footnote ⁷⁹ When assessing the scope of judicial scrutiny in the context of human rights protection, the Municipal Court of Prague in its first instance decision in Klimatická žaloba stated that ‘[i]n accordance with the precautionary principle, persons have the right to be concerned about the quality of their environment and do not have to wait until the climatic conditions are so unfavourable that they do not allow the fulfilment of their basic needs of life’.Footnote ⁸⁰ This line of reasoning appears to broaden the protection of human rights by establishing that persons may enforce their rights before a(n irreversible) situation of severe human rights violation has occurred. This is particularly meaningful in the context of the climate emergency, which is a cumulative global common action problem, that is, every ton of CO₂ emitted anywhere in the world creates an irreversible temperature increase that changes life on Earth.

Separation of powers concerns in human rights adjudication play out in different ways. On the one hand, judges may consider that separation of powers weighs in favour of exercising judicial review because (human) rights protection at the end of the legislative cycle lies at the centre of their role within a democratic system.Footnote ⁸¹ On the other hand, human rights adjudication is seen as a field where judges are necessarily empowered vis-à-vis the other branches because judges need to give meaning to open-textured norms and balance interests.Footnote ⁸² This could support an argument in favour of more judicial restraint. At the same time, it appears relevant whether the rights norms that the court relies on were produced with the democratic legitimation of the domestic law – or even constitution-making process – or whether they emerged from international treaty-making.Footnote ⁸³ In the case of the latter, additional considerations relating to the empowerment of the executive in external relations come into play.

Perhaps the most innovative decision so far has been the decision granted by the High Court of Lahore decision in the Leghari case, as it resulted in procedural obligations for a breach of substantive duties.Footnote ⁸⁴ The Court created a Climate Change Commission composed of representatives of key ministries, NGOs, and technical experts to monitor the government’s progress in terms of its own climate change policy and implementation framework. In other words, while refraining from imposing higher substantive targets, the Court established the institutional framework to oversee the execution of the State’s existing policies.

Another highly relevant point on the judicial mandate to protect human rights was made by the Superior Court of Quebec, when it noted in ENvironnement JEUnesse that ‘in the case of an alleged violation of the rights guaranteed by the Canadian Charter, a court should not decline jurisdiction on the basis of the doctrine of justiciability’.Footnote ⁸⁵

The need to exercise judicial review over executive but also legislative action has been particularly recognised as a result of the growing scientific evidence of the ubiquity and intensity of interferences with human rights caused by the climate crisis. This connects to the widely shared understanding that protecting the rights of individuals, including large numbers from foreseeable harm in the future, is the core task of courts under separated powers.

6.4.4 Developing Legally Enforceable Norms from Best Available Science

The Dutch Supreme Court in Urgenda relied heavily on the IPCC reports to argue that ‘objective’ standards exist against which to review the State’s conduct.Footnote ⁸⁶ This highlights the role of courts as independent fora, where impartial judges need to be convinced, not only of what the law is and what legal obligations may flow from it within the particular case but also of the climate science that should underpin any political and judicial decision-making on climate issues.

Generally, many courts have heavily relied on climate science for their reasoning. Examples include the case of Friends of the Irish Environment, in which the Irish Supreme Court found that the scientific understanding of the ‘safe temperature rise target’ in Article 2.1(a) of the Paris Agreement has increasingly gravitated towards ‘a lower figure […] in the region of 1.5°C’, as scientific knowledge has developed since the Paris Agreement.Footnote ⁸⁷ Furthermore, the Administrative Court of Paris recalled in Notre Affaire à Tous the IPCC’s findings in the Special Report on 1.5°C (2018) and concluded that ‘a warming of 2°C rather than 1.5°C would seriously increase these various phenomena and their consequences’.Footnote ⁸⁸ Similarly, in Klimaatzaak, the Court of Appeal pointed out scientific evidence regarding the risks of exceeding the threshold of 1.5°CFootnote ⁸⁹ and, in Milieudefensie, the Hague District Court converged towards the same conclusion, establishing that ‘in the last couple of years, further insight has shown that a safe temperature increase should not exceed 1.5°C’.Footnote ⁹⁰

One may conclude that climate litigation necessarily brings science back into the debate, ideally in a rational, non-interest-driven, and fact-checking fashion. By relying on the IPCC reports as reflecting the best available science established in a transparent and inclusive process that vouches for its scientific impartiality, judges vest climate science in the societal debate with legal authority.Footnote ⁹¹ In all climate litigation cases, judges are required to establish the relevant facts underpinning the claims of the parties on what reduction obligations flow from the law. While this point may prima facie appear only indirectly linked to separation of powers, it reinforces the function of the judiciary to rationalise societal conflict pursuant to pre-established procedural rules and, by doing so, offers a procedural mechanism of systematically debunking scientific myths that lacks in the less formal political debate, for example, in parliament.

Judges have also justified why climate issues are justiciable irrespective of the complex science involved, the alleged uncertainties under the scientific models sketching the probable impacts of rising emissions, or the numerous interests affected by the impacts and mitigation measures. On the first aspect, the German Federal Constitutional Court acknowledged in Neubauer that, while there are several scientific methods for determining a State’s necessary emissions reductions to hold global warming to a particular temperature limit, all of which entail uncertainties, ‘this does not make it permissible under constitutional law for Germany’s required contribution to be chosen arbitrarily. Nor can a specific constitutional obligation to reduce CO₂ emissions be invalidated by simply arguing that Germany’s share of the reduction burden and of the global CO₂ budget are impossible to determine’.Footnote ⁹² Similarly, the Hague District Court established in Milieudefensie that while ‘no one single [reduction] pathway is the measure of all things on a global scale’, there nevertheless exists ‘widely endorsed consensus’ regarding the minimum emissions reductions that are required to avert dangerous climate change.Footnote ⁹³

It should be added that judges must often decide based on incomplete knowledge and rely on science to substantiate their fact finding.Footnote ⁹⁴ This is not different in climate cases; yet, increasingly detailed science on the impacts of climate change are seen by judges as providing them with the necessary knowledge to give rulings.