17.1.1 Objective of This Chapter

Given that so far only a limited number of cases explicitly discuss attribution directly, the approach in this chapter is to emphasise the emerging nature of the judicial treatment of attribution with regard to climate change. Courts have made authoritative statements about the reality of climate change,Footnote ² they have used reports of the Intergovernmental Panel on Climate Change (IPCC) as expert evidence,Footnote ³ and they have shaped the wider normative context in which causal explanations in the field of climate change are embedded.Footnote ⁴ Yet to date, attributing a specific climate-related impact to a defined emitting geographical region or an individual major emitter has been a difficult task in the court room.Footnote ⁵ Compensatory claims against individual emitters remain at risk of failing the legal tests for causation and attribution across jurisdictions.Footnote ⁶ Only prospectively have courts found a causal link between planned major infrastructure projects and their anticipated contributions to global emissions and to further adverse climate change impacts – as discussed in the preceding chapter.Footnote ⁷

Meanwhile, a thorough analysis reveals that even a dismissed case can shed light on legal criteria for causation and attribution while pointing to the need for further legal and scientific research. An example is Comer v Murphy Oil USA, Inc, where the Court dismissed the case but alluded to the defendants’ memorandum and stated that the plaintiffs would need to demonstrate the following:

1. (1) what would the strength of Hurricane Katrina have been absent global warming;

2. (2) how much of each plaintiff’s damages would have been attributable to Hurricane Katrina if it had come ashore at a lower strength; and

3. (3) how much of each plaintiff’s damages was attributable to failures by others, such as the Federal Emergency Management Agency (FEMA) and other governmental agencies, to prevent additional injury.Footnote ⁸

This list of criteria merits critical evaluation. The Court’s three points may indeed not set forth a conclusive selection that fully reflects the causally relevant contribution of climate change to Hurricane Katrina. Climate change may not only have contributed to the strength of the hurricane and the resulting damages, it may also have exacerbated the failures by others, thereby amplifying existing vulnerabilities. These interdependencies between existing vulnerabilities, administrative failures, and climate change deserve attention from a scientific and from a legal point of view, to make clearer statements about causation and attribution. Exploring these factual connections should not be limited through a constricted set of criteria.

An increased focus on the intersection of science and law, where scientific research is informed by a better understanding of legal criteria for attribution, is certainly timely. Attribution-based cases represent a key trend in litigation, albeit one that is moving more slowly than originally anticipated.Footnote ⁹ This may be due to the fact that the legal analysis of ‘attribution’ incorporates a normative operation: it is never purely scientific or merely counterfactual but entails the judicial determination of a factual, social, and legal reality.Footnote ¹⁰ This determination will be case-specific and dependent on the relevant law. However, it can be informed by filing cases into categories derived from environmental case law beyond climate change, such as the differentiation between ‘look back’ and ‘in the moment’ cases.Footnote ¹¹ The respective category defines the applicable standard for judicial intervention so that protective measures can be adopted before harm occurs, despite remaining scientific uncertainties. Therefore, and with an emphasis on the status nascendi, emerging best practices in this chapter are derived from judicial pronouncements that prune the normative context and pave the way for a rigorous and comprehensive causal analysis in future cases.

17.1.2 Climate Science and Attribution Studies as a Matter for Courts

Climate science has already become a matter for courts. Courts across a number of jurisdictions have established a causal link between increasing greenhouse gas (GHG) emissionsFootnote ¹² and an increasing risk of climate-related extreme events and slow-onset events.Footnote ¹³ The relevant available scientific evidence is often directly derived from the reports of the IPCC, such as in Milieudefensie v Royal Dutch Shell,Footnote ¹⁴ or indirectly, from national scientific advisory committees that provide independent advice and devise national carbon budget calculations based on IPCC reports.Footnote ¹⁵ The Administrative Court of Berlin in German Farmers v Germany argued that there ‘is much to be said for at least an equal global per capita distribution of the remaining global CO₂ budget’.Footnote ¹⁶

The physical science on climate change, and, in particular, detection and attribution studies, provides important and steadily evolving information for the causal analysis generally and for the specific criteria of legal attribution.Footnote ¹⁷ Relevant studies can deliver expert evidence in court and they also more generally improve our understanding of the human contribution to extreme events,Footnote ¹⁸ such as floods,Footnote ¹⁹ hurricanes,Footnote ²⁰ heatwaves,Footnote ²¹ or slow-onset events and impacts on vulnerable ecosystems.Footnote ²² The conventional approach of probabilistic event attribution uses inductive reasoning to establish a quantifiable fraction of the magnitude or probability of risk or harm that can scientifically be attributed to climate change or even localised regional emissions.Footnote ²³ Studies that claim to evidence the link between a concrete climate-related impact and an individualised amount of emissions carry the potential to change the outcome of litigation.Footnote ²⁴ However, only reliable, unbiased, and carefully reviewed studies can produce the legally relevant evidence through assessing observed changes in weather extremes and climate-related impacts, their attribution to causes, and their future trajectories and return periods.Footnote ²⁵

The IPCC has acknowledged that case-specific studies provide evidence in addition to the ‘established fact that human-induced greenhouse gas emissions have led to an increased frequency and/or intensity of some weather and climate extremes since pre-industrial time, in particular for temperature extremes’.Footnote ²⁶ The IPCC stated in its Sixth Assessment Report (AR6), Working Group I, that since the 2018 IPCC Special Report on Global Warming of 1.5°C was published, new evidence has emerged that:

The legal evaluation of these scientific insights requires judicial engagement with general and case-specific scientific evidence on climate changeFootnote ²⁸ and climate literacy.Footnote ²⁹ The relevant scientific knowledge and the law evolve often at different time scales, and this poses challenges to the science/law intersection. A continuous, mutually informing interdisciplinary discourse is necessary. An illustrative example is Native Village of Kivalina v ExxonMobil Corp, where the link between the defendant’s emissions and the erosion of the coastal line as a result of climate change at the time of the decision was too indirect to fulfil the criteria of ‘fair traceability’ (a requirement to establish standing).Footnote ³⁰ Scientists nowadays claim that it would be possible to establish a causal link between the losses claimed and the defendant’s GHG emissions.Footnote ³¹

Challenges and constraints in accessing the most relevant, recent, and unbiased scientific evidence in the court of law persist.Footnote ³² Any limited availability of scientific evidence in court, or the actual lack of data, cannot simply be interpreted as implying that no relevant trends exist, or that anthropogenic climate change has not contributed to the intensity and frequency of a studied event.Footnote ³³ Data limitations may only indicate that either the quality or the temporal length of the case-specific data collection, or both, are not suited to provide a full and specific account for attribution.Footnote ³⁴ Even then, it remains possible and necessary to analyse the factual circumstances of a case in light of the already available and steadily growing body of climate science.

Given the significant and increasing importance of climate science for legal developments, both in legislation and in litigation, Section 17.2 defines the analytical steps of climate causality and explains how attribution studies can be used for legal attribution. It then explains the potential role of normative correctivesFootnote ³⁵ to soften the outcome of a strict causal analysis, and points to the critical function of three, instead of just two, logical fundamentals for a coherent legal analysis. Section 17.3 identifies emerging best practices of judicial engagement with climate change that could inform legal attribution. Section 17.4 discusses the potential for replicability of these arguments and Section 17.5 concludes.

17.2.1 Attribution as a Scientific and Legal Field of Study

Event attribution as a field of scientific study is defined as ‘the process of evaluating the relative contributions of multiple causal factors to a change or event with an assignment of statistical confidence’.Footnote ³⁹ A number of different analytical tools are employed, spanning climate observations, modelling, and statistical (re-)analyses.Footnote ⁴⁰ These attribution studies provide the ‘human contribution assessment’ for observed changes in ecosystems,Footnote ⁴¹ such as ocean heat content increase or arctic sea ice loss – cases where since 1970 anthropogenic emissions have become the main drivers for those changes.Footnote ⁴² Scientists identify changes in characteristics of the climate system, such as trends and variations in single extreme events, including their frequency, intensity, and duration.Footnote ⁴³

As a scientific field of study, attribution science is relatively young. One of the first attribution studies concerned the human contribution to the European heatwave of 2003.Footnote ⁴⁴ The study found that it was very likely (confidence level >90%) that human influence had at least doubled the risk of a heatwave exceeding a threshold for mean summer temperatures in Europe.Footnote ⁴⁵ The IPCC recognised for the first time in its Fourth Assessment Report (AR4) of 2007 the relevance of the data of formal detection and attribution studies as a further source for the understanding of the physical science basis of climate change, in addition to climate records and observational data.Footnote ⁴⁶ Since then, evidence of observed changes in weather extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, ‘and in particular their attribution to human influence’, has been significantly strengthened; most recently in AR6.Footnote ⁴⁷

As introduced in Chapter 3 on Attribution Science, two main methodological approaches can be differentiated: probabilistic event attribution studies and the so-called storyline approach. Probabilistic attribution studies employ inductive reasoning and ask two main questions.Footnote ⁴⁸ First, whether the likelihood or strength of an event has changed in the observational record, and second, whether this change is consistent with the anthropogenic influence as found in one or more climate models.Footnote ⁴⁹ These climate models compare the world with climate change with the counterfactual world where no climate change exists, thereby assessing the fraction of the attributable risk that can be assigned (quantitatively and qualitatively) to anthropogenic climate change.Footnote ⁵⁰

The so-called storyline approach is mainly deductive. Studies using this approach do not assess the change of likelihood in a specific event’s occurrence (they take that change as a given), but ask whether the impact of the particular event was affected by known changes (induced by climate change) in the climate system’s thermodynamic conditions.Footnote ⁵¹ Thus, the focus rests primarily on specific qualitative changes in the studied event that can be attributed to climate change.Footnote ⁵² From a legal perspective, both approaches can provide complementary evidence for causation and attribution.Footnote ⁵³

A further layer is added by differentiating between event attribution and source attribution. Source attribution concerns the nexus between a certain activity, a project, or another defined source of emissions, and the additional and quantifiable amounts of emissions.Footnote ⁵⁴ An example are wetland emissions and atmospheric sink changes that explain the growth of methane.Footnote ⁵⁵

For the purpose of this chapter, and with a view to capture the relevant scientific findings of event attribution studies, the meaning of legal attribution is defined within the broader concept of climate causality that involves general causation and specific causation as a sequence of analytical steps. General causation means that a factor has altered the probability of the occurrence of a certain class of events in a statistically significant way.Footnote ⁵⁶ This could encompass the general link between human-caused climate change that is affecting many weather and climate extremes in every region across the globe,Footnote ⁵⁷ or between increasing human-caused climate change and heavy precipitation associated with tropical cyclones.Footnote ⁵⁸ Specific causation describes the factual finding that a factor (e.g. increasing GHG emissions, increasing mean temperatures) has altered the specific characteristics of a concrete event (e.g. the duration, frequency, and/or intensity of a heatwave in a certain region and year) in a statistically significant way.Footnote ⁵⁹ In the legal assessment, general and specific causation rely on counterfactual inquiries that seek to identify if, and to what extent, the factor was either necessary or sufficient for the studied event(s).Footnote ⁶⁰ Neither general nor specific causation stipulates that the factor, i.e. the amount of emissions over a certain period of time, must be the only cause. There can be a set of factors that act as concurrent causes.Footnote ⁶¹ It is a related but different question to measure and objectively quantify the contribution of each cause.

On that basis, attribution in law is understood as the final step that describes the adequate and quantifiable contribution of an individualised factor or activity to the studied event (impact or damage), in a specific normative context.Footnote ⁶² It asks, for example, if the changed characteristics of a concrete event (increased outburst flood hazard of a glacial lake) have not only been caused by human-induced glacier retreat (i.e. specific causation between glacier retreat and increased risk)Footnote ⁶³ but can be adequately assigned to a concrete human contribution. Attribution spans the nexus between the human activity and the concrete adverse impact. The term ‘adequate’ has its roots in the ‘theory of adequate causation’Footnote ⁶⁴ and indicates that there can be causal chains that – for various reasons – cannot or no longer be linked to a particular source.Footnote ⁶⁵

The normative considerations that are relevant to establish legal attribution will depend on the circumstances of each case and relevant scientific and legal determinations such as the role of natural variabilities, the distribution of risk spheres, and provisions concerning the onus of proof.Footnote ⁶⁶ Absolute certainty is not required to prove either causation or attribution in law.Footnote ⁶⁷

Within the normative evaluation of ‘adequacy’, the law – and courts in interpreting and applying legal criteria – can attribute climate-related impacts to human-controlled emissions and thereby (re-)allocate responsibilities, potentially beyond the strict ‘but for’ analysis albeit within the rule of law. However, these legal determinations can work in both ways: they can either interrupt or expand the causal chain, that is, exclude or include certain factors as causes.

An example of the former is the exclusion of so-called ‘cruise emissions’ from the consideration of an airport expansion in Vienna-Schwechat Airport Expansion.Footnote ⁶⁸ The Austrian Constitutional Court interpreted the requirement for airline operators to comply with EU emissions monitoring and reporting schemesFootnote ⁶⁹ so as to conclusively assign the responsibility to manage so-called ‘cruise emissions’ to airlines and not to airports or airport operators.Footnote ⁷⁰ On that basis, the Court overturned an earlier decision of the Austrian Administrative Court.Footnote ⁷¹ The Administrative Court had refused to grant permission for a third runway extension with the argument that the public interest of ‘no further significant increase in GHG emissions in Austria due to the construction and operation of the third runway’ prevailed over the interest to expand the airport’s capacity.Footnote ⁷² The Constitutional Court did not deny that additional emissions would occur; however, it found that these had wrongly been included in the consideration of relevant public interests by the Administrative Court, given that the majority of predicted emissions would occur as cruise emissions – thus falling within the responsibility of airline operators.Footnote ⁷³

The Constitutional Court’s reasoning in this case demonstrates the normative operation that furnishes attribution, and it illustrates how important it is to clearly distinguish between a factual consideration of a proposed project’s future emissions and assigning legal responsibility for those emissions. Specific causation captures the quantifiable emissions resulting from the expansion of the airport; these would not exist ‘but for’ this individual project. The next analytical step relates to the attribution of these additional emissions. It is indeed a legal determination to attribute cruise emissions to the airline operators. This legal attribution and the assigned responsibility that comes with it in terms of accounting and reporting, and possibly ‘off-setting’, are to be distinguished from specific causation, as the factual assessment of the amount of predicted emissions. According to the relevant Austrian law, the evaluation and balancing of the various ‘public interests’ affected by the project depend precisely on the factual consideration of the project’s emissions,Footnote ⁷⁴ not on the legal attribution of these emissions.

Interestingly, the Philippines Commission on Human Rights included in its National Inquiry on Climate Change Report a section on ‘Recommendations for the Judiciary’.Footnote ⁷⁵ Therein, it noted that ‘in many jurisdictions, courts evaluate evidence linking actors to climate-related losses using the stringent standards of legal causation’.Footnote ⁷⁶ According to the Commission, ‘this disregards the work of climate and attribution science, and causes more climate injustices’.Footnote ⁷⁷ The Commission proceeded to define event attribution as to establish ‘(i) whether the likelihood or strength of a natural event has changed in the observational record, and (ii) whether this change is consistent with the anthropogenic influence as found in one or more climate models’.Footnote ⁷⁸ This statement confirms that measurable changes in the likelihood of an event’s occurrence or strength are legally relevant.Footnote ⁷⁹

It should be mentioned that in exceptional circumstances, beyond the context of climate litigation, courts have acknowledged that normative considerations can also function in the opposite direction and draw factors in as factual causes. These are cases where a mechanistic causal analysis was found to be ‘in contradiction to law’s function to achieve justice and fairness’.Footnote ⁸⁰ For example, in asbestos litigation, courts have attributed harm to the actions or omissions of the defendant, even when the traditional causal tests of ‘but for’ and ‘conditio sine qua non’ have failed.Footnote ⁸¹

This interpretative approach stresses the fundamental role of the judiciary in the evolution and affirmation of so-called ‘normative correctives’ that form part of the legal concept of attribution.Footnote ⁸² However, specific normative correctives in the context of climate change are not yet widely articulated or accepted. Therefore, the attribution of a specific climate risk, damage, or loss involves not only a variety of forensic, evidentiary, and legal questions, it fundamentally still proceeds in the shadow of a yet unresolved ethical debate of global climate equity and fairness.Footnote ⁸³

17.2.2 Normative Correctives v Extended Logical Fundamentals?

As the Philippines Human Rights Commission remarked, an overly stringent application of causal tests will not easily be reconciled with the evidence produced by attribution studies.Footnote ⁸⁴ Research has demonstrated that two main approaches are available to soften the outcome of a strict causal analysis in specific cases of alternative or hypothetical causation in multi-stage scenarios.Footnote ⁸⁵ One option would be to apply in the context of climate change normative correctives, given that factual circumstances can make it just as difficult as in medical exposure cases to establish causation across a set of multiple factors. So far, these normative correctives in some jurisdictions have included considerations of fairness, distributive justice,Footnote ⁸⁶ and the allocation of risk spheres between the claimant and the defendant.Footnote ⁸⁷ Similarly, courts have used the ‘material contribution to risk’ test in situations where the plaintiff was unable to establish the exact contribution of a particular tortfeasor.Footnote ⁸⁸ Applying these correctives has changed the outcome of the analysis in situations of alternative, hypothetical, or concurrent causation.Footnote ⁸⁹

This type of an outcome-correcting approach is, therefore, neither foreign to the law nor has it been widely rejected as conflicting with a positivist approach to the law. For some specific case categories, legal provisions across a number of jurisdictions even set aside the strict rule of the ‘but for’ test.Footnote ⁹⁰ For example, if a tort has been committed jointly, each tortfeasor will be liable for the full damage if it cannot be established who exactly caused the injury or damage.Footnote ⁹¹ Meanwhile, normative correctives have had a lesser bearing on climate jurisprudence and the causal analysis in relation to complex climate-related extreme events that are often characterised through combined contributions of natural and human-induced factors.Footnote ⁹²

An alternative option to reflect the scientific evidence of attribution studies through attribution in law is therefore to extend the logical fundamentals upon which the legal analysis of the ‘but for’ test rests.Footnote ⁹³ This can be achieved by using three instead of the usual two logical fundamentals to reflect the contributory nature of concurrent causes in a set of conditions.Footnote ⁹⁴ A coherent causal analysis in these multi-factor causation scenarios over a range of factors can be based on necessity, sufficiency, and, in addition, sustenance.Footnote ⁹⁵ Sustenance accounts for the capacity of a factor to produce and maintain the event, even if the factor is only one among others in a set of conditions, provided its relative contribution can be objectively measured.Footnote ⁹⁶ The case-specific causal analysis on sustenance will be influenced by our general understanding of the physical science basis of climate change and the evidence for the human contribution to certain types of extreme events. This general causal knowledge is captured by the novel concept of the distinctive causal field that encompasses certain types of events with common characteristics (i.e. heatwaves in a specific geographical region).Footnote ⁹⁷ The distinctive causal field forms the backdrop for the assessment of the case-specific evidence, for example, concerning the occurrence of a concrete heatwave in the specific geographical region.

Recent scientific research buttresses the validity if not the necessity of the distinctive causal field for assessing scientific evidence, in arguing that attribution studies often contain far more information, ‘about other hazards of the same type, than is currently utilised’.Footnote ⁹⁸

The case against the German energy provider, Lliuya v RWE, currently pending in the Higher Court of Appeal in Hamm, Germany, could be one of the first cases to illustrate how emissions could qualify as a cause for an increased flood risk on the basis of sustenance and within the context of scientific evidence on glacier melting. Two scientific studies (one using probabilistic event attribution (inductive) and one using the storyline (deductive) approach) assessed the increased outburst flood hazard from Lake Palcacocha in the context of human-induced glacier retreat.Footnote ⁹⁹ At the time of writing, the legal attribution of this flood risk to a so-called ‘carbon major’, the largest German energy provider RWE, is being considered at the evidentiary stage.Footnote ¹⁰⁰ This means that the Court was convinced that the case is conclusively argued from a legal point of view.Footnote ¹⁰¹

17.3.1 The Determination of the Scope of Relevant Emissions

A critical starting point is to establish which emissions, and over which periods of time, should be included in the judicial consideration. In Urgenda, the Supreme Court of the Netherlands confirmed that all emissions are causal for further climate change, thereby opposing the ‘drop in the ocean’ argument of the government.Footnote ¹⁰⁷ The logic of a limited global carbon budget that demands full consideration of all GHG emissions has also been confirmed by the New South Wales Land and Environment Court in Gray v The Minister for PlanningFootnote ¹⁰⁸ and in Gloucester.Footnote ¹⁰⁹

In a similar vein, the Supreme Court of Norway stated in Nature and Youth Norway and Greenpeace Nordic v The State that GHG emissions from combustion of oil and gas (so-called downstream or scope 3 emissions) from exploration of the Barents Sea could interfere with the right to a healthy environment under Article 112 of the Norwegian Constitution.Footnote ¹¹⁰ However, the final conclusion of the Supreme Court was based on the premise that the State could nevertheless formulate its climate policy in the light of the ‘division of responsibilities’ enshrined in international agreements.Footnote ¹¹¹ This reference to international agreements led the Supreme Court to conclude that emissions from combustion would fall within the remit of the respective State using the oil and gas,Footnote ¹¹² a position that risks conflating factual causation with the allocation of responsibilities for emissions accounting. The normative and/or legal attribution of these emissions, including the allocation of accounting obligations and potential off-setting responsibilities of the ‘end-user’, should be reserved for the final step in the analysis as explained in Section 17.2.

The Court of Session (Scotland) equally confirmed that excluding emissions from fossil fuel consumption from consideration as ‘direct or indirect significant effects of the relevant project’ would not render the environmental impact assessment (EIA) unlawful.Footnote ¹¹³ According to the Court, these emissions stemmed from the ‘use of a finished product’.Footnote ¹¹⁴

Conversely, a specific case in point that illustrates a comprehensive analysis of climate causality – including attribution – is the judgment of the Rechtbank Den Haag (District Court) in Milieudefensie v Royal Dutch Shell, where the Court explicitly included scope 1, 2, and 3 emissions in its causal analysis and ordered Royal Dutch Shell (both directly and via its legal entities which form the Shell group) ‘to limit or cause to be limited, the aggregate annual volume of all CO₂ emissions into the atmosphere (scope 1, 2 and 3 emissions) due to the business operations and sold energy-carrying products of the Shell group to such an extent that this volume will have reduced by at least net 45% at end 2030, relative to 2019 levels’.Footnote ¹¹⁵ In reaching this decision, the District Court not only stated that there was a causal link between GHG emissions and dangerous climate changeFootnote ¹¹⁶ but also established a further causal link between the limitation of fossil fuel production and global emissions reductions. The Court found that there is a ‘direct, linear link between man-made greenhouse gas emissions, in part caused by the burning of fossil fuels, and global warming’.Footnote ¹¹⁷ Thus, limiting the production of fossil fuels would result in reduction of emissions, as ‘research shows that there is a causal relationship between production limitation and emission reduction’ and ‘studies using elasticities from the economics literature have shown that for oil, each barrel left undeveloped in one region will lead to 0.2 to 0.6 barrels not consumed globally over the longer term’.Footnote ¹¹⁸

The Court’s reasoning rejects the conventional ‘carbon leakage’ argument that the demand for fossil fuel will remain constant regardless of any changes in the supply chain. The decision stands in sharp contrast to the view held by the Court of Session in Greenpeace Ltd v the Advocate General, where the material effect on climate change of discontinued oil exploitation in the North Sea was seen as ‘difficult to argue’.Footnote ¹¹⁹ In addition, Milieudefensie demonstrates that private actors’ duties are no longer fully separate from States’ duties: rather, the company’s emissions reductions duties are legally intertwined with the State’s commitment to the Paris Agreement and its temperature thresholds that define the global and each State’s carbon budget (see Chapter 9).

Accordingly, three important insights resonate from the judgment in Milieudefensie and define the Court’s position on attribution. The first concerns the Court’s emphasis on a scientifically supported and internationally endorsed consensus that each company must work towards achieving net zero emissions by 2050.Footnote ¹²⁰ The second insight relates to the recognition of a direct and linear link between Royal Dutch Shell’s GHG emissions, dangerous levels of global warming, and the imminent environmental damage in the Netherlands.Footnote ¹²¹ Finally, the Court confirmed the plaintiffs’ argument that all CO₂ emissions attributable to the Shell group had to be reduced.Footnote ¹²² This means that the localised, imminent environmental damage is attributable to the individualised emissions of the Shell group.

17.3.2 Reviewing National Climate Targets and Measures

Cases against governments often concern insufficient national climate targets for mitigation, but lawsuits challenging States’ adaptation measures are also rising.Footnote ¹²³ Furthermore, and as deadlines for sectoral climate targets approach, new administrative case law begins to emerge that is concerned with adequate response measures if targets are not met.Footnote ¹²⁴ So far, cases against governments have often relied on a general causal link between the challenged national climate targets, further climate change in the absence of enhanced targets, and an interference with fundamental rights.Footnote ¹²⁵ The focus rests on whether or not the impugned action or inaction is capable of depriving individual rights,Footnote ¹²⁶ with the aim of compelling governments to increase ambition levels.Footnote ¹²⁷ These decisions are covered in more detail in Chapters 7, 9, and 16. The following only draws on some of the relevant case law where climate targets were challenged to point out where the reasoning could also inform the analysis on attribution.

The premise for the review of national climate measures is that the Paris Agreement’s long-term temperature goal can be translated into corresponding global and national carbon budgets and modelled pathways, as in Milieudefensie.Footnote ¹²⁸ Climate targets and corresponding measures can then be reviewed in light of domestic administrative and constitutional frameworks.Footnote ¹²⁹ The scrutiny of national targets is most effective in cases where national climate targets are enshrined in law, as seen in UrgendaFootnote ¹³⁰ and Thomson,Footnote ¹³¹ and where domestic law includes interim and sectoral targets as in NeubauerFootnote ¹³² and Deutsche Umwelthilfe.Footnote ¹³³ Acknowledging the causal link between targets, corresponding national emissions, and their effect on the global carbon budget has indeed been critical for the intervention of courts that in turn increased the level of ambition of the defendant State. These decisions indirectly acknowledge that governments’ targets and corresponding implementing policies constitute factors to which further climate change and related impacts can be attributed. This nexus is reflected in Friends of the Earth Ltd and others v Secretary of State for Business Energy and Industrial Strategy, where the High Court of England and Wales overturned a decision of the Secretary of State as it failed to address how the shortfall towards the national target would be addressed under statutory requirements, and for failure to provide a quantitative explanation to Parliament as required by law.Footnote ¹³⁴

Courts have an important function when adjudicating on matters such as the role of the Paris Agreement and its implications for national decision-making processes.Footnote ¹³⁵ For example, the Court of Appeal of England and Wales concluded in R. (on the application of Plan B Earth Ltd.) v Secretary of State for Transport that the Secretary of State had wrongly omitted climate change considerations and due regard for the Paris Agreement in his decision-making on the expansion of Heathrow Airport.Footnote ¹³⁶ The decision was overturned on appeal, with the UK Supreme Court remarking that ‘the Paris Agreement itself is not Government Policy’.Footnote ¹³⁷

A similar pattern emerges in other jurisdictions, where the lower courts afford the Paris Agreement and nationally determined contributions (NDCs) a legal valence that is not confirmed in next instance. For example, the Municipal Court in Klimatická žaloba v Government of the Czech Republic decided that the government was legally bound under Article 4(2) of the Paris Agreement, and also under the State’s NDC, to adopt mitigation measures aimed at achieving the objective of its NDCs.Footnote ¹³⁸ The Court acknowledged a direct link between the State’s climate target, the adequacy of measures, and the impact on the global climate.Footnote ¹³⁹ Moreover, the Court applied the rules on treaty interpretation enshrined in Article 31, paragraphs 1 and 2(a), of the Vienna Convention on the Law of Treaties,Footnote ¹⁴⁰ which are recognised as customary international law.Footnote ¹⁴¹ However, on 20 February 2023, the Supreme Administrative Court overturned the decision in Klimatická žaloba v the Government of the Czech Republic, based on the collective nature of the EU Member States obligations to reduce GHG emissions by 55 per cent by 2030, and referred the case back to the Municipal Court.Footnote ¹⁴²

Arguments concerning ineffective mitigation measures and non-compliance with governments’ own targets were also tested based on private law in two cases brought against the French government in the Paris Administrative Court and the Conseil d’Etat. These cases illustrate that ecological damage can be attributed to emissions that exceed the State’s target.

The Paris Administrative Court applied a specific tort law provision of the French Civil CodeFootnote ¹⁴³ that prescribes that every person is responsible to provide reparation for ecological damage.Footnote ¹⁴⁴ The Court thereby affirmed that exceeding the national emissions limits will lead to ecological damage; in other words, the damage is attributable to the State’s excess emissions. In a second decision, the Court then decided that the ‘Prime Minister and the competent Ministers are ordered to take all useful measures to repair the ecological damage and prevent it worsening for the share of greenhouse gas emissions not made good compared to the first carbon budget’.Footnote ¹⁴⁵ In a similar vein, the Conseil d’Etat in Grande-SyntheFootnote ¹⁴⁶ found that the French government was under an obligation to take additional measures by 31 March 2022 to meet the target of reducing GHG emissions by 40 per cent compared to 1990, by 2030.Footnote ¹⁴⁷

It should be noted that the argument that an event is attributable to climate change may serve as a defence for the Respondent. In Burgess v Ontario Minister of Natural Resources and Forestry, both parties to the dispute argued that the damage was attributable to climate change.Footnote ¹⁴⁸ After the flooding in Houston, Texas, caused by Hurricane Harvey,Footnote ¹⁴⁹ owners of properties upstream of the Addicks and Barker Dams brought suits against the United States. They alleged an uncompensated taking under the Fifth Amendment.Footnote ¹⁵⁰ The government argued that it was not responsible for the harm that resulted from the flooding because the damage was attributable to Hurricane Harvey as an ‘Act of God’.Footnote ¹⁵¹ The Court of Federal Claims joined all cases and then split them into two sub-dockets, one for the Upstream cases and one for the Downstream cases.Footnote ¹⁵² For the Upstream cases, the Court determined that the United States was liable to thirteen property owners under the Fifth Amendment of the United States Constitution for the taking of a non-categorical, permanent flowage easement on their properties.Footnote ¹⁵³ These easements were the result of government-induced flooding during Hurricane Harvey and produced by the government’s construction, maintenance, and operation of the Addicks and Barker Dams.Footnote ¹⁵⁴ For the Downstream cases, the Court granted the government’s motion to dismiss and denied appellant motion for summary judgment.Footnote ¹⁵⁵ On appeal, the United States Court of Appeals for the Federal Circuit remanded the case back to the Court of Federal Claims to consider, inter alia, whether Appellants have established causation when considering the impact of the government actions that address the relevant risk.Footnote ¹⁵⁶

17.3.3 Permissibility of Emissions-Intensive Projects or Activities

Cases concerning the permissibility of emission-intensive projects and activities regularly involve private actors. Litigation against corporations, especially against so-called ‘carbon majors’,Footnote ¹⁵⁷ is on the rise and contiguous strategies are constantly refined.Footnote ¹⁵⁸ Cases are often initiated by non-governmental organisations to halt emissions-intensive infrastructure projects or activities. In some instances, lawsuits have also been initiated by local or State governments: for example, several States have filed suits in the United States, seeking to hold oil and gas companies liable for climate change-related harms.Footnote ¹⁵⁹ A couple of States have also tried to challenge federal measures such as quantifying estimates for the social costs of GHG emissions.Footnote ¹⁶⁰

A key case for causation and attribution that is still pending in second instance before the Higher Regional Court in Hamm (Court of Appeal, ‘Oberlandesgericht’) at the time of writing is Lliuya v RWE, as mentioned earlier.Footnote ¹⁶¹ The case is based on German nuisance law (section 1004 Civil Code) and concerns climate adaptation measures in response to flood risks. The claimant, a Peruvian farmer from the Andes region, requests a pro-rata contribution of the energy company for protection measures against flood outburst of the glacial Lake Palcacocha, thus a contribution to adaptation costs. The claimant’s calculation, which is open for the Court’s own determination, is rooted in the global percentage of historic emissions contributed by RWE, amounting to 0.47 per cent according to a study of carbon-major corporations.Footnote ¹⁶² In the first instance, the Regional Court in Essen (‘Landgericht’) rejected a causal link between the contributions of RWE to global climate change, due to the many contributions and contributors to climate change.Footnote ¹⁶³ A mechanistic application of the ‘conditio sine qua non’ (equivalent to ‘but for’) formula prevented the Court from engaging more closely with scientific evidence that seeks to attribute quantifiable amounts of emissions to specific major emitters. By contrast, the Higher Regional Court stated that the case was conclusively argued (meaning the legal argument per se is valid and the case will depend on providing pertinent evidence) and allowed it to proceed to trial. Now at the evidentiary stage, claimants must prove that there is a serious threat of an avalanche that could lead to flooding, and they must demonstrate how this would affect the property of the claimant.Footnote ¹⁶⁴

Cases to compel further regulatory action or to review authorities’ approval for emissions-intensive infrastructure projects have been brought across jurisdictions. These include situations where authorities below the level of national government unlawfully refused to take regulatory action,Footnote ¹⁶⁵ limited public participation, and/or insufficiently considered climate change impacts when granting permissions.Footnote ¹⁶⁶ The latter category impliedly connects emissions attribution (e.g. the anticipated future emissions) and event attribution (the contribution of the project to further climate-related impacts). For example, in Earthlife Johannesburg v Minister of Environmental Affairs, the High Court of South Africa held that an assessment of climate change impacts in the environmental authorisation process will ‘best be accomplished by means of a professionally researched climate change impact report’.Footnote ¹⁶⁷ This approach was confirmed in Sustaining the Wild Coast NPC v Minister of Mineral Resources.Footnote ¹⁶⁸ In Save Lamu v National Environmental Management Authority, the National Environment Tribunal of Kenya set aside the EIA licence, because the climate impacts of what would have been the first coal fired power plant in Kenya had not been fully evaluated given that comprehensive access to information had not been possible.Footnote ¹⁶⁹

The decision in Gloucester Resources Limited v Minister for Planning provides a causal analysis that includes an explicit statement on attribution.Footnote ¹⁷⁰ The Court stressed the causal link between the proposed coal mine, climate change, and further impacts, stating that: ‘[A]ll of the direct and indirect GHG emissions of the Rocky Hill Coal Project will impact on the environment’.Footnote ¹⁷¹ The additional emissions would be directly attributable to the project. Consequently, a measurable impact of the project on the environment would be attributable to the project and the emissions generated by it.Footnote ¹⁷²

In Citizens for a Healthy Community v U.S. Bureau of Land Management, the Court held that the agency had failed to comply with the National Environmental Policy Act by not taking a hard look at the reasonably foreseeable indirect impacts of authorising oil and gas developments.Footnote ¹⁷³ In Sierra Club v Federal Energy Regulatory Commission, the US Court of Appeal for the District of Columbia Circuit found that the Federal Energy Regulatory Commission should have considered the impacts of the project’s downstream carbon emissions and climate effects, or explained why such considerations were not relevant for the project.Footnote ¹⁷⁴ All of these decisions strengthen the proposition that, from a legal point of view, measurable climate impacts could be attributed to a concrete project and its respective emissions.

A more direct attempt to attribute quantified emissions amounts to a certain activity was made in the Indonesian case Ministry of Environment and Forestry v PT Asia Palem Lestari, in which the Ministry challenged a private company for the illegal burning of peatland.Footnote ¹⁷⁵ The government argued that the clearing of peatland for a palm oil plantation released 2,700 tonnes of carbon into the atmosphere and that the activities led to a loss of carbon sinks equal to 945 tonnes of carbon.Footnote ¹⁷⁶ The District Court of North Jakarta dismissed the case because the Ministry had failed to include other landowners as concerned parties.Footnote ¹⁷⁷ Meanwhile, the Supreme Court of Indonesia decided in a tort-based lawsuit in Minister of Environment v PT Selatnasik Indokwarsa and PT Simpang Pesak Indokwarsa that a quantifiable amount of emissions was attributable to illegal mining activities and awarded the Indonesian Ministry of Environment restoration costs and compensation for GHG emissions.Footnote ¹⁷⁸

17.3.4 Expanding the Normative Lens

Instantiations of emerging best practices that could change the analysis of causality often result from re-assessing legal concepts. For example, the Constitutional Court in Neubauer re-conceptualised the meaning of ‘interference’ with a fundamental right and developed the ‘advanced interference like effect’.Footnote ¹⁷⁹ Other courts draw from precedent outside the climate context to adjust the threshold for review. An example is Hauraki Coromandel Climate Action Inc v Thames-Coromandel District Council.Footnote ¹⁸⁰ The Court opined that judicial review in the context of climate change deserves ‘heightened scrutiny’, as ‘decisions about climate change by public decision-makers is similar to that for fundamental human rights’.Footnote ¹⁸¹ A key example in that respect is Mathur v Ontario, where seven young claimants made an application in ‘solidarity with millions of youth in Ontario and around to world’, to the Superior Court of Justice of Ontario (Canada), seeking, inter alia, a declaration that Ontario’s climate target to reduce GHG emissions by 30 per cent below 2005 levels by 2030 violated their rights and that of future generations.Footnote ¹⁸² They asserted that Ontario had to establish a science-based target consistent with Ontario’s share of the minimum level of GHG reductions to limit global warming to below 1.5°C above pre-industrial temperatures, or, in the alternative, well below 2°C.Footnote ¹⁸³

The Canadian Court first rejected the government’s motion to dismiss the application,Footnote ¹⁸⁴ stating that many of the claims were capable of scientific proof,Footnote ¹⁸⁵ and that the applicants should be afforded the opportunity to present their full evidence.Footnote ¹⁸⁶ In its decision on admissibility, the Court also elaborated on the standard of proof for causation, based on the jurisprudence of the Supreme Court of Canada on the more flexible ‘sufficient causal connection’ standard.Footnote ¹⁸⁷

In its decision on the merits, the Superior Court of Ontario made several important statements about causality.Footnote ¹⁸⁸ First, it held that the government’s target as the impugned action did not need to be the dominant or the only cause for the prejudice suffered by the claimants.Footnote ¹⁸⁹ The Court explained that ‘while Ontario’s contribution to global warming may be numerically small, it is real, measurable and not speculative’.Footnote ¹⁹⁰ Second, the Court relied on evidence stemming from event attribution science: it acknowledged that the applications had established on a balance of probabilities that the State action ‘contributes to an increase in the risk of death or in the risks faced by the Applicants with respect to the security of the person’.Footnote ¹⁹¹ Third, the Court found that by setting a climate target below the ‘scientific consensus’ of what would be required to align with 1.5°C, Ontario was ‘contributing to an increase in the risk of death and in the risks faced by the Applicants and others with respect to the security of the person’.Footnote ¹⁹² Fourth, the Court acknowledged that the ‘causal connection standard’ was sensitive to the context of the particular case, explaining that a very high causal standard would serve to hinder solving global problems.Footnote ¹⁹³

The Court thus rejected the government’s argument that to meet the causal connection standard, the applicants had to prove ‘beyond a reasonable doubt’ or ‘even on the balance of probabilities’ that the harm will occur. Nevertheless, the Court dismissed the case given that the rights under section 7 of the Charter had to be interpreted as a restriction on the State’s ability to deprive of the rights and did not (yet) include positive obligations.Footnote ¹⁹⁴ A further argument concerning intergenerational equity was equally rejected, based on the inability of the Court to determine a generational cohort as an analogous ground under section 15(1) of the Charter.Footnote ¹⁹⁵ This decision is on appeal at the time of writing.

Courts have of course expressed different views on the possibility to adjust thresholds for judicial review. The Supreme Court of Norway in Greenpeace Nordic found that wherever the Storting (Norwegian Parliament) had considered a matter, the threshold for review must be very high.Footnote ¹⁹⁶ In a similar vein, the concepts of heightened judicial scrutiny, or variable intensity review, were rejected in Students for Climate Solutions Inc v Minister of Energy and Resources where the Court explained that ‘what varies is the nature and extent of the legal controls over discretions, not the intensity with which the Court undertakes its tasks’.Footnote ¹⁹⁷

In some cases, courts have turned to legal developments that are external to the growing body of climate law. Scholars have pointed out that in China, cases concerning air pollution begin to serve as a gateway for climate change litigation.Footnote ¹⁹⁸ Courts have applied the ‘burden shifting’ doctrine under the Chinese Tort Liability Law (TLL) 2009, which operates on a legal presumption of causation and shifts the burden to prove the absence of a causal relation in environmental tort disputes to the defendant.Footnote ¹⁹⁹

Another approach for assessing causation and attribution stems from the introduction of case categories, as in R (on the application of Richards) v Environment Agency, a case concerning unsafe levels of hydrogen sulphide from a landfill site.Footnote ²⁰⁰ The case was overturned on appeal.Footnote ²⁰¹ However, it is interesting to note that the High Court for England and Wales had reasoned that, in some situations, courts should acknowledge a presumed causal chain in line with scientific knowledge, at the point where intervention was still possible and harm could be avoided. Although this case is concerned with air pollution and not climate change directly, it is nevertheless instructive as the Court made several impactful statements about causation and attribution, derived from European Court of Human Rights’ jurisprudence that had also been previously endorsed by the UK Supreme Court.Footnote ²⁰²

The Court distinguished two main categories, the so-called ‘look back’ and the ‘in the moment’ cases. The Court held that the inexorable logic of these human rights cases, especially the ‘in the moment cases’, is that ‘public authorities – and courts – must “step up” at the time when it is still possible to prevent that the foreseeable damage will materialise’.Footnote ²⁰³ In other words, in situations where the causal chain has not yet fully materialised, the duty of ‘stepping up’ entails that authorities must act before a damage occurs and despite remaining uncertainties. This approach aligns with the precautionary principle.Footnote ²⁰⁴