A. Introduction
In a growing number of jurisdictions, courts have held that governments must take action on climate change, including by reducing overall national greenhouse gas emissions.Footnote 1 In many cases, courts have located these obligations in constitutional law, finding that the absence of, or delays in, government action violate individual or collective rights. The success of such claims has produced widespread optimism about constitutional law as an instrumental tool, one that can be engineered into a vehicle of climate ambition.Footnote 2 But this claim, often couched in the language of climate or environmental “constitutionalism,”Footnote 3 can be overstated. Constitutions are not sites of single teleological projects. Instead, they give voice to a range of different, often conflicting, goals, principles, and values. At the level of generality with which climate rights are often declared, such conflicts can be obscured—constitutions—and especially constitutional rights—can be presented as single-mindedly climate-ambitious programs. But as government climate policies become more concrete, conflicts manifest more clearly, in turn bringing governments back into conflict with the courts. The sheer scale of any adequate government response to climate change means that potential conflicts are rife.
Constitutional engagement with climate change involves encounters with uncertainty and conflict. In some cases—as in the German case discussed below—conflicts might take the form of tensions between rights and various structural features of national constitutions: Features often designed to limit government power. In other cases—as in the Canadian case discussed below—conflicts will take the form of line-drawing questions concerning the scope of federal power. In still other cases, conflicts reflect tensions between asserted competing rights, as well as broader political tensions concerning the level of deference owed to governments—as in the Mexican case discussed below. It is not always possible to anticipate the precise form of such conflicts in constitutional design, doctrine, or judicial adjudication. There is a risk that this uncertainty in constitutional climate adjudication will distort policies in ways which are ambivalent, incoherent, or contradictory. In extreme circumstances, this might manifest as a constitutional straitjacket: Pulling toward climate ambition in one direction, while limiting what governments can actually do.
Climate-related adjudication is not the only subject area where courts face challenges of uncertainty and tension. Other issues involving deep disagreement and distributive justice—such as issues related to persistent inequalities, discussed elsewhere in this Special Issue—are also affected by these problems. The argument in this Article is not that climate-related adjudication is uniquely affected by these challenges—though, given the scale of the climate crisis and its relevance to all areas of social and economic life, these challenges are likely to be amplified. Indeed, it may be helpful to draw on other areas of law in understanding how judges should intervene in climate mitigation policy. This aim of this Article is to interrogate how judges might orient their approach to constitutional interpretation in light of uncertainty and tension. It starts from the premise that significant action is needed to address the climate crisis, and that judges might play a useful role—one which will inevitably differ across jurisdictions. But it nevertheless recognizes the pitfalls and limitations of such a role.
In Section B, I set out the hopes of “climate constitutionalism”: The idea that the recognition of climate rights might render constitutional law a powerful tool of climate ambition. In Section C, however, I explain why this hope is far from straightforward. I identify four problems which complicate matters: The challenge of state capacity; the underspecificity of constitutional law; the polyvocality of constitutional values; and the asymmetry between constitutional time, and that of ordinary politics. In Section D, I provide a rough typology of how these challenges can produce adjudicative uncertainty which in turn constrains states’ abilities to respond to the climate crisis. I draw on examples from Germany, Canada, and Mexico. Then in Section E, I offer some suggestions for constitutional climate adjudication. Such adjudication must recognize the embeddedness of courts as repeat players in an inter-constitutional context. Judges should be sensitive to the problem of state capacity and the structural elements of constitutional law, and be conscious of how their decisions might configure subsequent politics. Finally, I suggest that a greater focus on constitutional principles might promote constitutional adjudication more sensitive to the challenges of the climate crisis.
While this Article focuses on climate change, much of its discussion may be relevant to the other two challenges discussed in this Special Issue. Persistent inequalities, like climate change, can be addressed only through effective state capacity. And as with climate change, judges countering democratic backsliding must be conscious of their own limits, and their situation within an inter-institutional context. Furthermore, the three challenges are interlinked. Climate change will significantly deepen existing inequalities and create new ones, and state policies in response may also be deeply unequal. Existing inequalities determine individuals’ and communities’ vulnerabilities to the effects of climate change. Likewise, climate change can contribute to democratic backsliding by creating conditions of dislocation and instability. Conversely, the absence of effective democratic institutions can significantly inhibit state responses to climate change. Even where the three challenges are examined separately, recognising their complex interdependencies is crucial.
Climate change raises a host of constitutional issues. For brevity and focus, this Article is limited to the issue of climate mitigation policy: That is, measures taken to reduce greenhouse gas emissions, and thus limit the long-term impacts of climate change. In constitutional terms, mitigation is often claimed as a rights-based obligation owed by states, arising from rights to life,Footnote 4 privacy or family life,Footnote 5 social and economic rights,Footnote 6 or environmental rights.Footnote 7 This is not to diminish the significance of other climate policy challenges, including government responsibility for adapting to climate change’s inevitable impacts, as well as public and private liability for climate-related loss and damage.
B. The Hopes of “Climate Constitutionalism”
It is tempting to cast significant problems as constitutional ones. Constitutions are popularly imagined as expressions of a nation’s highest shared collective values or identity.Footnote 8 They are often conceived of as “mission statements,” recording a state’s overall policy—and even moral—commitments.Footnote 9 Relatedly, constitutions typically have the status of supreme or higher law, usually enforceable by courts against both executives and legislatures. These two features produce a common argument for the treatment of climate change as a constitutional issue. Climate change is an urgent problem. It cannot be addressed without widespread, sweeping, and transformative government action. Yet existing political action, limited by ineffective institutions and toxic politics, has failed to produce the necessary drastic cuts in greenhouse gas emissions.Footnote 10 In light of pervasive political failures, constitutionalization is imagined as a turn away from politics, transferring authority to judges who can locate climate rights and obligations in new or extant constitutional texts:Footnote 11 “[A] way forward when ordinary legal mechanisms fall short.”Footnote 12
Indeed, there is good reason for faith in such a project. Constitutional climate litigation has in many ways been remarkably successful.Footnote 13 Judges have accepted that wide range of constitutional rights require more ambitious mitigation. Decisions from the Netherlands,Footnote 14 Pakistan,Footnote 15 Brazil,Footnote 16 India,Footnote 17 Mexico,Footnote 18 South Africa,Footnote 19 Belgium,Footnote 20 Colombia,Footnote 21 Nepal,Footnote 22 Germany,Footnote 23 and the European Court of Human RightsFootnote 24—to name only a few—have established such obligations. But they have also perhaps resulted in outsized optimism and a simplistic understanding of ostensibly non-political pathways to decarbonisation. The recognition of climate rights may be a helpful development, but it is necessarily a preliminary step. Climate change joins the ranks of issues deemed “constitutional.” Yet it finds itself jostling in a crowded space, competing with many other values, objectives, and priorities which cannot be resolved through a straightforward objective formula of constitutional interpretation. As discussed in Section E below, the resolution of subsequent conflicts will always be contested and, in at least some respects, political.
C. The Climate Crisis in the Chorus of Constitutionalism
As climate rights are applied to more specific disputes, their indeterminacy is revealed. This is in large part because of the sheer scale of the climate crisis, and of the corresponding government measures necessary to respond. Climate policy cannot be cabined to a specific set of measures addressing just one sector of the economy, or a single type of activity. To be effective, reductions in greenhouse gas emissions must be economy-wide, ranging from transport to energy to agriculture to land use. Such measures are necessarily costly and complex. It is not enough merely to proscribe certain activities. Rather, climate action requires enormous government investment and economic intervention, from the promotion of renewable energy to the development of new infrastructure.Footnote 25 And climate change is as much a distributive challenge as it is a technical one. The economic transition required to meet the climate challenge produces winners and losers, while distributing those wins and losses unevenly.Footnote 26
These dimensions of climate change render it a challenge variously described as “super-wicked”Footnote 27 and “hot”:Footnote 28 It is a problem which requires an enormously wide-ranging and complex set of policy responses, which in turn involve trade-offs between competing objectives. Climate change is not the first such problem that constitutional law has encountered.Footnote 29 But the scale of the problem and corresponding necessary policy challenges perhaps render it a “quantum leap scale of enlargement” in terms of conflict and complexity.Footnote 30
At a high level of generality, these challenges may not be evident. Thus, in an initial round of litigation it might be possible for a court to declare that the government must mitigate climate change as part of its obligations to protect constitutional rights. Such obligations can be roughly quantified in high-level targets and carbon budgets.Footnote 31 But as climate mitigation policies continue to interact with constitutional law, uncertainty and tension in constitutional climate adjudication becomes clearer. This arises from four interrelated factors.
First, the realisation and implementation of climate rights requires enormous legal, institutional, and fiscal state capacity, which in turn may clash with constitutional values of limited or divided government. Second, the very generalized goal of “mitigating climate change” is underspecified. The concrete implementation of mitigation policy manifests in many different ways, encountering conflicts with constitutional law and values that are unpredictable ex ante. Third, constitutions do not speak with one voice: They are typically pluralistic and polyvocal documents and structures which accommodate many conflicting ideas, values, rights, and doctrines. And finally, climate politics can change much more quickly than constitutional rules, producing new coalitions and dynamics which respond differently to preexisting constitutional structures. These can be defined as the phenomena of (a) capacity; (b) underspecificity; (c) polyvocality; and (d) asymmetric time. Together, they produce constitutional climate uncertainty and tension.
I. Capacity
Liberal constitutions can be conceived of through a simple two-part taxonomy. First, constitutions are “power maps,” setting out the structures and powers which establish and discipline government power.Footnote 32 Second, they are rights charters, typically declaring rights held by individuals against the state. While such bifurcation between powers and rights has analytical value, in reality both functions are interdependent. The way in which government power is structured—such as the power of the judiciary or federal separation of powers—determines how rights can be enforced, and by whom. And positive rights claims—such as claims demanding greater government climate action—can only be realized if states have the power and capacity to act.
For governments to effectively respond to rights claims, at least three forms of power are needed. First, governments need legal capacity to pass effective laws and regulations, to implement industrial policy, and to coordinate public institutions and agencies. Without clear constitutional authorisation, legislatures and executives cannot enact and implement such measures. The problem of limited legal capacity is perhaps clearest in the United States, where the federal constitution confers neither a specific environmental power nor a plenary power of regulation on Congress.Footnote 33 This has allowed courts to apply constitutionally-inflected approaches to judicial interpretation which prevent agencies from enacting effective climate regulations.Footnote 34 Second, governments need institutional capacity to develop and implement policies.Footnote 35 Agencies need the requisite expertise to evaluate evidence, develop effective policy, and enforce it. As Mark Tushnet and Madhav Khosla have argued, “[t]here is little point in worrying about the excesses of government power when the government lacks the capacity to get things done in the first place.”Footnote 36 And finally, governments need fiscal capacity. Effective climate policies require not only prescriptive regulations, but also expenditures in infrastructure investment, technology deployment, industrial policy, and consumer subsidies.Footnote 37 Constitutions can establish substantive and procedural parameters for government debt and finance, both through monetary policy—for example, by establishing mandates and objectives for central banks—and, as discussed in the German case study below, by setting limits on government fiscal borrowing.Footnote 38
The focus on constitutional rights which has dominated discussion of climate change and constitutional law is insufficient. While such claims may further climate ambition, it is their interaction with the constitutional powers which structure government capacity that will determine, in large part, whether governments can effectively translate ambition into policy.
II. Underspecificity
The general and apolitical promotion of a high-level right—for example, to a “clean, healthy and sustainable environment”Footnote 39 or a “climate system capable of sustaining human rights”Footnote 40—is underspecified. Even if climate policy were the sole or primary objective of a constitutional order, a broad mandate or commitment to reducing greenhouse gas emissions is not by itself a policy program.
To be sure, climate rights can be further concretized in two remedial forms.Footnote 41 Each has a particular type of underspecificity. First, in “project-based” climate rights claims, which challenge the development and permitting of high greenhouse gas-emitting projects—such as oil exploration or coal power plants—litigants seek a narrow remedy: Setting aside a permitting decision, thus blocking the project. Rights in this context are responsive ad hoc tools for blocking specific projects, rather than the basis of a broader policy program. Second, “systemic” or “strategic” rights claims target economy-wide government policies. Rights in these cases become a vehicle for high-level mandates, often expressed in the language of overall reduction targets or budgets. In Urgenda v The Netherlands, for example, the Dutch Supreme Court affirmed lower court’s order to reduce greenhouse gas emissions 25% below 1990 levels by 2020;Footnote 42 in the Klimaschutzgesetz case discussed below, the German government was ordered to set clearer intermediate greenhouse gas reduction targets which more equitably apportioned its overall carbon budget over time.Footnote 43 While such remedies may be more comprehensive than those awarded in project-based litigation, they say little about the policies necessary to achieve such targets. Instead, the specific features of climate policy are produced through a complex mix of political and economic contingencies, ideologies, available resources, and scientific knowledge. There is no single policy prescription: Policy programs can come from a range of conflicting political standpoints and assumptions, including market-based solutions—such as cap-and-trade schemesFootnote 44—industrial policy—such as Green New Deal proposalsFootnote 45—and degrowth programs—premised on overall reductions in economic activity.Footnote 46
All these approaches at least plausibly fulfil a constitutional mandate to protect climate rights. Yet the scale of the crisis means the full constitutional programs may not be obvious in advance—and each program will raise different types of constitutional issues. Different programs require different exercises of government power, and engage different conflicts with different values. It is only once a program—and the specific measures needed to enact it—is specified that such conflicts become apparent. A simple constitutional directive to reduce greenhouse gas emissions in line with a stated target cannot foresee the full range of needs and conflicts that such a conflict will produce. This is particularly so given the amount of positive government action necessary to respond to the climate crisis. Governments will inevitably run into constitutional constraints on legal, institutional and fiscal capacity discussed above—often in ways not anticipated by the broad policy mandates of ex ante judicial decisions.
III. Polyvocality
Constitutions do not speak with one voice. They are polyvocal:Footnote 47 They promote a wide range of values and goals. Even where constitutions directly specify, or are interpreted to specify, the climate crisis as a central objective, it is only one among others: Dividing and limiting arbitrary government power; setting rules and procedures for government institutions; expressing a national identity; protectingrights, whether civil and political, economic and social, or cultural and collective; regulating exceptions and emergencies; and establishing a range of different institutions. Different versions of climate ambition will give rise to different kinds of conflicts with different kinds of goals and values.
One particularly stark conflict is that between countermajoritarian judicial involvement in climate policy on the one hand, and the maintenance of separation of powers and democratic values on the other hand.Footnote 48 But this is only one of many possible constitutional conflicts—many of which will ultimately be presented to judges for resolution. These include potential clashes between, as well as harmonies with, constitutional values related to democratic backsliding and persistent inequalities. Measures which aggressively reduce greenhouse gas emissions may come up against, or enhance, these other priorities. Climate policy is not neutral as to social inequalities: Policies concerning renewable infrastructure siting, sunsetting industries, and fuel taxes can be highly regressive. At the same time, because climate change disproportionately affects the most vulnerable, an effective climate policy will by definition protect the most vulnerable—and in particular, children and future generations—from further entrenchment of inequality. Climate policy might also conflict with democratic values, best illustrated through the thought experiment of the Ökodiktatur—a state governed by an ecological dictatorship, suspending democracy and individual freedoms in pursuit of environmental policies.Footnote 49 Such a possibility is contrary to any plausible version of liberal constitutionalism, but an authoritarian climate constitution could nevertheless be imagined.
IV. Asymmetric Time
Constitutional time operates differently to that of “ordinary politics.” The pace of change is deliberately slower. Constitutions constrain ordinary politics by taking issues off the table, and by setting the ground rules through which a more bounded ordinary politics can play out.Footnote 50 Part of the raison d’être of constitutions is that they retain a degree of stability as political currents change. As Gabriele Britz argues in this Special Issue, this “future-sensitivity” forms part of the very justification for constitutionalization of long-term issues such as climate change—enshrining environmental and climate protections in constitutional law can constrain the short-term “egocentricities” of ordinary politics.Footnote 51
But this dynamic presents a problem from the standpoint of ideal, timeless constitutional design. What might be an “optimal climate constitution” will depend on the prevailing politics of the day. For example, whether federalism advances or hinders effective climate policy depends on the prevailing political alignment between central and state governments. When a broadly “pro-climate” national government is in power, climate advocates might support strong, centralized government powers, and weak roles for potential spoilers—such as subnational governments and courts. When a broadly “anti-climate” government is in power, climate advocates might call for greater checks on central government power: Enforceable rights, judicial review, and devolved powers for subnational governments.
Furthermore, one’s ideal of “climate constitutionalism” depends at least in part on one’s set of epistemic assumptions about ordinary politics. If one believes that voters will generally elect climate-ambitious governments, one will likely favor centralized government authority; if one believes otherwise, they will likely favor devolved and checked power. The constantly shifting sands of ordinary politics makes it extremely difficult to design stable ex ante “pro-climate” constitutional rules. Rather, as argued in Section E, constitutional design and adjudication must be contextual and responsive.Footnote 52
D. Constitutional Climate Uncertainty in Action
A central hope of climate constitutionalism is that it can provide a stable and predictable baseline, guaranteeing core climate rights and obligations in the face of the oscillations and pathologies of everyday politics. But the four features described above make it hard to construct an ideal blueprint of “climate constitutionalism.” Instead, judges are presented with sets of conflicting values and assumptions. The existence of conflict produces uncertain climate adjudication. In the three examples discussed below, apex courts have at first ruled one way, only to later rule in another direction. They typify three different types of uncertainty.
First, uncertainty might, perhaps paradoxically, follow a particular structure: On the one hand, courts might accept that rights-based guarantees require greater government climate action, but on the other hand, to the extent that such guarantees are implemented at greater levels of specificity, courts will favor other values in limiting the powers that governments have to realize such rights. In this configuration, suggested by the German example, interpretive uncertainty manifests as a “straitjacket,” requiring while also limiting government action. In other cases, uncertainty might manifest in granular and unpredictable line-drawing between lawful and unlawful climate policies, as in the Canadian example. And in other cases, courts might produce almost directly conflicting jurisprudence on precisely the same issue, resulting in years of protracted litigation and confusion as to the limits of government action and market intervention, as illustrated in the Mexican example.
I. Uncertainty as Constitutional Straitjacket: The Case of Germany
In a remarkable 2021 decision, the German Federal Constitutional Court struck down parts of Germany’s federal climate law, the Klimaschutzgesetz (KSG).Footnote 53 In the decision—referred to in Germany as the KSG decision and internationally as the Neubauer case—plaintiffs challenged national legislation which set a 55% reduction target for Germany’s greenhouse gas emissions by 2030—against a 1990 baseline—and a net-zero target 2045. The KSG set out concrete annual sector targets up until 2030, but no interim post-2030 targets, and instead delegated that power to the executive. The relatively small cuts to be made by 2030 implied that very large cuts would be needed over the following fifteen years. Plaintiffs argued that this scheme deferred the bulk of mitigation actions to the future, requiring extreme action on the part of future generations—more specifically, existing children—violating their constitutional rights.
The Court accepted that the Act breached the plaintiffs’ fundamental freedoms, protected by Article 2(1) of the Grundgesetz. The Court also referenced Article 20a of the Grundgesetz, which requires the state to “protect the natural foundations of life and animals by legislation and, in accordance with law and justice, by executive and judicial action, all within the framework of the constitutional order.”Footnote 54 Although the Court found that Article 20a did not give rise to enforceable subjective rights, the Court premised its decision on a general constitutional obligation to cut overall greenhouse gas emissions. The problem was that such cuts were not reconcilable with individual freedoms as distributed across time and generations, contrary to an obligation “to treat the natural foundations of life with such care and leave them in such condition that future generations who wish to carry on preserving those foundations are not forced to engage in radical abstinence.”Footnote 55 The Court directly acknowledged the problem of asymmetric time as a core rationale for its decision: The short-term and oscillating nature of ordinary politics “plac[es] it at a structural risk of being less responsive to tackling the ecological issues that need to be pursued over the long term.”Footnote 56
The Klimaschutzgesetz decision was largely accepted by the then-German government and has likely contributed to changes in Germany’s climate policy.Footnote 57 But a general rights-based obligation to set interim targets and reduce greenhouse gas emissions is not, by itself, enough. The implementation of such a program will be expensive and complex, requiring legal, institutional, and fiscal capacity. And in this respect, the German government is uniquely hamstrung by its constitution.
German constitutional law prescribes limits on government borrowing, requiring that federal budget structural deficits not exceed 0.35% of GDP, outside of stated exceptions.Footnote 58 These constitutional provisions, collectively known as the “debt brake” or Schuldenbremse provisions, do not obviously have anything to do with climate policy. But in reality, reducing greenhouse gas emissions, and adapting to the impacts of climate change, both require enormous infrastructural investments. To cover these costs, the German government sought to transfer sixty billion Euros of unused 2021 COVID-19 pandemic funds to Germany’s Climate and Transformation Fund for 2022. The COVID-19 funds had been legitimately approved as an “emergency” exception to the Schuldenbremse. In a 2023 decision, however, Court found that the reappropriation of funds violated the debt brake.Footnote 59 The Court found that: The legislature had failed to demonstrate a factual connection between the emergency, and the crisis measures taken in response; it was impermissible to reappropriate borrowing from one fiscal year to another, that is, from 2021 to 2022; and that the government’s action had violated a principle that the government budget be set in advance.
The debt brake places significant limits on climate investment. The climate fund is intended for projects such as retrofitting buildings, decarbonizing industry, subsidizing clean energy technologies, and investing in rail.Footnote 60 The German legislature did eventually find a way to finance its budget after the debt brake decision, but with significant reductions in climate investments—forty-five billion Euros worth of cuts between 2024–2027.Footnote 61 While it is legally possible for the German government to invoke annual emergency exceptions to authorize further borrowing, such proposals would require political will which parts of the current government coalition—and German electorate—lack. Any legislative measure to circumvent the Court’s decision through emergency borrowing would be perceived as subversion of a broadly popular constitutional culture. In other words, the Court’s decision did not directly block effective climate policy, but it set up a constitutional politics which made it politically challenging for the government to act, and lent a vocabulary of fiscal constitutionalism to its opponents.Footnote 62 And while the Court’s ruling does not directly challenge the importance of responding to climate change, the Court’s interpretation of the Schuldenbremse is far from the most climate-friendly available.Footnote 63 Rather than enabling ongoing transition, the limits on borrowing are premised on the idea of discrete, short-term emergencies with easily-identifiable policy responses. This is reflected in the Court’s insistence that money must be appropriated and spent in the same year, that emergencies be justified with detailed reasoning about the ongoing nature of the emergency, and “why its planned crisis management measures continue to be suitable.”Footnote 64 This cribbed interpretation of the emergency provisions sits uneasily with the reality of climate change, which requires a wide-ranging suite of responsive measures, and which will remain an ongoing challenge for decades to come. Indeed, climate change challenges the very notion of what an “emergency” is.
The German dynamic suggests the possibility of a constitutional climate straitjacket. While Court identified a rights-based climate mandate it ran up against other values. The underspecificity of climate rights meant that they were vulnerable to competing priorities in the context of Germany’s polyvocal constitution. This led to a lack of state fiscal capacity necessary to follow through on the mandate. While the particular form of the ambivalence on display in this example may be unique to Germany—that is, fiscal conservatism as a constitutionally-entrenched value—adjudicative uncertainty is pervasive. Two further examples, involving very different factual contexts and constitutional regimes, illustrate other manifestations of the climate ambivalence of constitutional law.
II. Uncertainty in Line-Drawing: The Case of Canada
Canada’s constitution contains no explicit environmental rights or obligations. While plaintiffs in several lawsuits have argued that such rights are implied by rights to life and non-discrimination, none of these lawsuits have been successful.Footnote 65 Nevertheless, climate change has featured prominently in recent litigation because of its conflict with another important value: Federalism. Canada’s government is separated between a national government, based in Ottawa, and ten provincial, as well as three territorial, governments. The division of powers between the two is set out in sections 91–95 of the Canadian Constitution. The federal government lacks plenary power, but retains a residual power over “Laws for the Peace, Order and good Government of Canada” which are not otherwise reserved for the provinces. The stability of the distinction, and the scope of these “POGG” powers, has been tested in two climate suits.
The first is the Greenhouse Gas Pricing Act Reference.Footnote 66 The case concerned a challenge to federal legislation—the Greenhouse Gas Pricing Act (GGPA)—which set a pricing mechanism for greenhouse gases. Specifically, the Act created a national backstop pricing mechanism which would apply wherever provinces failed to legislate their own. The GGPA was swiftly challenged by several fossil fuel-rich Canadian provinces, who argued that it exceeded the federal government’s constitutional authority. The Supreme Court rejected the challenge. While the GGPA did not fall under enumerated federal powers, the Act was a lawful exercise of the federal government’s residual POGG powers. The Court applied a two-stage test, first characterising the subject matter of the challenged legislation; and second then determining whether the subject matter fell within a federal or provincial head of legislative power.Footnote 67 To classify the legislation as falling with the federal POGG powers, the legislation must deal with a matter of “national concern”—that is being of “sufficient concern to Canada as a whole,” and a matter with a “singleness, distinctiveness, and indivisibility that clear distinguishes the matter from provincial concern.”Footnote 68 The test presents challenges for climate legislation. On one hand, climate change is indeed a “singular” issue which cuts across provincial boundaries. But on the other hand, it involves a range of different policy responses across different scales and regulatory regimes, making it hard to define as “distinctive[] and indivisibl[e]”; the formulation of this test is in part what explains the difference between the Greenhouse Gas Pricing Act Reference, and the Impact Assessment Act Reference discussed below. Finally, the exercise of POGG powers must be “reconcilable with the fundamental distribution of legislative power under the Constitution,” including “unjustified intrusions on provincial autonomy.”Footnote 69
The majority found the GGPA met the threshold test of “national concern.” The specific subject matter of the Act was “a distinct and limited regulatory mechanism.”Footnote 70 Furthermore, the Court accepted that “the matter is critical to our response to an existential threat to human life in Canada and around the world.”Footnote 71 Because it operated as a backstop to greenhouse gas regulation, it amounted to a less intrusive violation of federalism. Furthermore, the need for uniform national standards to avoid a provincial race-to-the-bottom could justify national regulation. And greenhouse gas regulation was sufficiently “distinct,” because it concerned regulation of a “specific and precisely identifiable type of pollutant.”Footnote 72 The Court’s reasoning nevertheless points to an awkward fit between longstanding constitutional provisions and doctrine, and contemporary climate challenges—particularly in applying the test of “distinctiveness and indivisibility” to a problem as pervasive and transversal as climate change.
As of 2021, it seemed the Supreme Court had resolved the general conflict between climate regulation and federalism: Greenhouse gas regulation was a matter of national concern, falling within federal POGG powers. But a more recent decision highlights the unpredictability inherent in drawing the line at which climate policy shifts from a provincial to a national concern.
In 2023, the Supreme Court of Canada issued a ruling in the Impact Assessment Act Reference.Footnote 73 The energy-rich province of Alberta challenged the lawfulness of the Impact Assessment Act (IAA), which reserved some infrastructure permitting review powers to the federal government rather the provinces. The change would have allowed the federal government to prevent some projects—including those with significant downstream greenhouse gas emissions—from going ahead, even where provincial regulators might have otherwise permitted them.Footnote 74 The Court found the Act contravened the Constitution’s federal structure because it allowed federal decision-makers to consider not only inter-provincial or federal effects of projects, but also the effects of a project on a single province.Footnote 75 It would also extend federal jurisdiction over a range of activities not traditionally falling within federal power.Footnote 76 The Court stressed that its earlier holding in the Greenhouse Gas Pricing Act Reference did not bring the issue of climate change as a whole under federal authority, but only “narrow and specific regulatory mechanism[s],” such as emissions pricing.Footnote 77 The Court cautioned that many policies without the narrow—and essentially backstop function—of the GGPA would fall outside the federal legislature’s POGG powers. Clearly, climate change is not uniformly a matter of “national concern” for the purposes of Canadian federalism.
There are important differences between the GGPA and IAA, which partially explain the different results. The GGPA is a single government policy which applies uniformly across the country; the IAA involves the conferral of power and discretion onto federal decisionmakers across a range of different decisions of varying scale and character. It is perhaps therefore understandable that the Court was more cautious in recognising the GGPA as within the scope of federal power, and the IAA as falling outside it. But it is not clear precisely where the line has been drawn. The categorisation of laws into federal and provincial authority is an awkward fit for a problem as pervasive as climate change. The Canadian example suggests that not just rights, but also powers suffer from the problem of underspecificity in constitutional climate adjudication. This in turn can inhibit central governments’ legal capacity to take effective climate action. The problem is closely linked to the polyvocality of Canada’s constitutional order, balances competing values of provincial autonomy, and federal coordination.
Uncertainty can chill or distort on climate policy. It forces federal legislators to search for new, and more tenuous, heads of power to justify future regulation. The contrasting decisions also call into question planned government measures, such as Canada’s proposed overall cap on greenhouse gas emissions.Footnote 78 The government’s initial response to the ruling has been to significantly amend the legislation—in some cases more than environmental groups claim is necessary to comply with the Court’s ruling.Footnote 79
Yet a uniform rule that climate policy is solely a matter of “national concern” would also not be an ideal principle of constitutional design. While the federal government is currently more climate-ambitious than many provincial governments, such a position could change in the future, with conservatives currently polling strongly in advance of elections scheduled before October 2025.Footnote 80 A blanket rule in favor of federal control could produce oscillating results between contrasting governments. Rather than developing ironclad constitutional rules, it might be better to harness the iterative and inter-institutional dynamics of constitutional adjudication into a productive tension, as argued in Section E.
III. Uncertainty in Constitutional Design: The Case of Mexico
From the earlier two cases, it might be thought that an empowered central government is the right principle of constitutional design and interpretation in securing effective climate policy. But unleashing centralized government power can also be environmentally disastrous. Because climate policy cuts across so many areas of economic policy, it will often be unpredictable just how central government authority can be harmful to climate policy: Government actions can be unintentionally harmful. The unfolding climate jurisprudence of the Supreme Court of Mexico (SCJN) illustrates this problem.
The Mexican Constitution contains an environmental right,Footnote 81 and mandates that government development policies be “sustainable.”Footnote 82 The Supreme Court has developed a constitutional climate jurisprudence grounded in human rights, finding, for example, that national fuel standards cannot weaken limits on greenhouse gas emissions,Footnote 83 and that the environmental right can count in favor of otherwise constitutionally-suspect measures in proportionality balancing tests, such as the issuance of new taxes by state legislatures.Footnote 84
But this jurisprudence has recently come up against another competing value: A particular version of market socialism, premised on strong central powers, expansive market participation by state enterprises, and extensive social and economic rights. It is premised on a development agenda itself reflected in Mexico’s Constitution, which—at Article 25—promotes and regulates government-led economic development. This extends to the energy sector. In 2021, the government repealed earlier laws protecting competition in the energy market.Footnote 85 As with Germany’s debt Schuldenbremse and Canada’s scheme of federalism, the proponents of these measures did not primarily or directly intend to impede effective climate policy. But Mexico’s energy market reforms have enormous climate implications. Renewable energy investment and existing generation is dominated by private companies, while the state energy producer—the Comisión Federal de Electricidad—relies largely on fossil fuels. Promoting state-owned energy, therefore, promotes fossil fuels. Among other matters, the electricity sector reforms downgraded the priority of wind and solar electricity,Footnote 86 and allowed largely state-owned legacy—rather than only new—power plants to sell energy credits, thus reducing the overall price and incentives for renewable energy development.Footnote 87
The government’s electricity sector reforms have unleashed a torrent of litigation brought by an unlikely coalition of environmentalists, and private investors. This litigation has led to a high level of uncertainty. In 2022, one case reached the Supreme Court.Footnote 88 The law was challenged as a constitutional violation of both the right to a healthy environment, Article 4, as well as constitutional guarantees of free markets and competition, Article 28. The SCJN’s decision was fractured. While eight of the eleven judges voted to strike down parts of the law—meeting the usual eight-judge qualified majority threshold—there was insufficient consensus on the grounds for striking down the law. In a controversial procedural ruling by Chief Justice Arturo Zaldívar, the law was upheld.Footnote 89 Those judges who voted to uphold the law cited the importance of countervailing social and economic rights, and the government’s economic development agenda. Justice Ortiz Ahlf justified the reforms based on an unenumerated right to electricity, arguing, controversially, that the measures could improve energy security.Footnote 90 Chief Justice Zaldívar argued that the Court should not be seen to be passing judgment on the government’s choice of economic model, and should accordingly apply significant deference.Footnote 91
Two years later, however, another challenge to the same laws reached the SCJN. This time, the Court struck down most of the reforms.Footnote 92 The Court based its decision both on the Mexican Constitution’s guarantees of free competition,Footnote 93 as well as the constitutional mandate to complement economic development with sustainability.Footnote 94 The Court found that the law impermissibly deprioritized renewable development, disincentivized investment in renewables, and devalued clean energy carbon credits.Footnote 95 While the decision is particular to the plaintiffs before the Court, it will guide the many other pending suits against the reforms.
The difference between the two results can be partially explained on procedural and institutional grounds. First, the first action was an acción de inconstitucionalidad, reserved for facial challenges. By contrast, the second case was brought under the amparo procedure, which concerns the impact of the law on the rights of the plaintiffs. While the acción de inconstitucionalidad requires supermajority support for striking down the law, the amparo requires only a simple majority. Furthermore, Chief Justice Zaldívar, whose procedural decision was instrumental to the survival of the law in the first decision—and who has been criticized for his close ties to the Mexican governmentFootnote 96—had left the SCJN by the time of the second decision.
The Mexican example illustrates an uncertainty of a different type to the German and Canadian cases. While it took several years and many cases, the Court’s jurisprudence was ultimately determinate: The law at issue violated constitutional guarantees. And it is not a cautionary tale about constitutional restrictions on government capacity. But it illustrates three other problems. First, as reflected in the SCJN’s first decision, climate values can conflict with other constitutional goals, including state-led economic development and, arguably, novel economic and social rights, such as a “right to electricity.” Second, courts’ determinations can be hard to predict. Two iterations of the SCJN presented with the same law reached different conclusions as to the validity of major electricity reforms. Even in the second case—where the Court struck down the law—it was split 2-2, with the presiding judge casting the tiebreaker. This can lead to a high degree of uncertainty for regulators and investors, who cannot be sure what measures will ultimately be upheld as constitutionally valid. And finally, it illustrates that there are no easy “pro-climate” answers to conflicts between competing constitutional values. Default deference to central government would have produced a “pro-climate” answer in the German and Canadian cases; but in the Mexican case, it would do the reverse. Underspecificity and polyvocality will produce conflicts between climate rights, and competing values, including countervailing rights. Ex ante, predicting the adjudication of such conflicts, or establishing rules for their resolution, is no easy task.
E. What is to be Done?
Underspecificity, polyvocality, and asymmetric time are features, not bugs, of legal constitutionalism. Underspecificity allows for flexibility; polyvocality reflects the facts of pluralism;Footnote 97 and asymmetric time is produced by intentional constraints on government action. But together, they render climate adjudication uncertain, and threaten to limit states’ capacities to respond to climate-related challenges. Establishing broad constitutional rules—such as a default rule in favor of deference toward government action—would not necessarily produce consistently pro-climate outcomes.
The limits of law’s determinacy necessitate a reflexive turn to politics. But I mean “politics” in a specific sense. This is not a call for judges to be openly “political” by pursuing an overtly partisan program. Rather, a turn to politics is call for courts to recognize their embeddedness in an inter-institutional ecosystem of repeat players, and calibrate judicial interventions be accordingly.
Adjudicative uncertainty should be reconfigured as a productive tension between different values, which can focus and frame subsequent contestation. Constitutional adjudication must be situated in an inter-institutional context, building the capacity and vocabulary that states can draw on to meet the urgent needs of the climate crisis. And judicial climate engagement is necessarily dynamic. Rather than expositors of a single grand decisive solution, courts are iterative players, finessing and experimenting over time with a range of responses to an immensely complex problem. Courts should be sensitive to the inter-institutional dynamics in which they operate, viewing themselves as repeat structure subsequent politics, policy, and bureaucratic practices.
This context demands some modesty in the hopes for “climate constitutionalism.” This call for modesty is distinct from other such calls, grounded in concerns related to judges’ democratic or institutional legitimacy. Even if one accepts that judges have an important role to play in climate adjudication, as I do, interventions may nevertheless prove ineffective in many circumstances.Footnote 98 A constitutional right cannot resolve or depoliticize more foundational conflicts and tensions. Instead, constitutional climate questions will always be deeply contextual, shaped by political contingencies and particular values-conflicts.
In this context, judges cannot avoid questions of politics. Nevertheless, they find themselves operating in a particular political space: That of constitutional politics. Constitutional adjudication may be uncertain, but it is nevertheless bounded by the constraints of constitutional law and norms. Judges should see themselves as participants in extended forms of “experimentation, monitoring, and adjustment in light of ever-present prospects of unpleasant surprise.”Footnote 99 The recognition of rights or setting of targets, for example, will inevitably be the start of a conversation, not the end of it.
I conclude with three modest suggestions. First, courts must be sensitive to problems of state capacity, and conceive of climate change both as an issue which raises questions about states’ obligations, as well as the enormous, but never unchecked, capacity necessary to realize them. Second, courts should be sensitive to the constitutional politics which inevitably follow from any judicial intervention. This includes sensitivity to the way in which their judgments might channel or distort subsequent constitutional debate, and the political vocabularies generated by judicial decisions. Finally, to more productively resolve tensions and even out the unpredictability of constitutional climate adjudication, courts could more frequently rely on the development of flexible yet substantive principles, rather than rigid rules. The development of constitutional climate principles might complement pragmatic adjudication with a degree of predictability and consistency, while framing a valuable vocabulary for future climate action.Footnote 100
I. Sensitivity to Capacity
Adjudicative uncertainty can undermine state capacity. Courts should be sensitive to the potential of their decisions to undermine state capacity to respond to the climate crisis. Such an approach sits somewhat awkwardly with traditional approaches to constitutional law, which have focused on limits on state action.Footnote 101 By contrast, courts should be attentive to the need for constitutional law to enable and support effective climate policy, rather than restrict it: A turn to positive constitutionalism.Footnote 102 This is not to say that courts should grant governments a blank cheque. “Climate policy” must not be a shibboleth for absolute deference. Such an approach would enable governments to use climate policy as a pretext for violations of individual rights, or unaccountable expansion of government power. But more modestly, sensitivity to government capacity could manifest in two ways.
First, courts could develop an interpretive presumption in favor of government policy where there is textual or doctrinal ambiguity. In other words, capacity could act as an interpretive tiebreaker. Such an approach could operate as a substantive canon of constitutional interpretation: A canon justified by a substantive value and set of outcomes, namely to promote governments’ legal capacities in addressing climate change.Footnote 103 Where there are two plausible arguments as to the validity of law, courts could favor an interpretation which upholds it. In the Schuldenbremse case discussed above, for example, the relevant constitutional text was open-ended. The Court opted to interpret the text narrowly, giving effect to the purpose and values of fiscal responsibility. Likewise, as argued above, in the Impact Assessment Act the Court was presented with an open-ended test as to whether the legislation fell within the scope of federal powers—one which proved an ill fit for the more recent challenge of climate change. plausible arguments were available to the Court to either uphold or strike down the law—or at least preserve more of its provisions. An interpretive canon could have tipped the balance.
Second, courts can calibrate their interventions to promote the development of institutional capacity of other branches of government.Footnote 104 Within an inter-institutional framework, courts can engage in an iterative process of dialogue and experimentation,Footnote 105 identifying “institutional inertia,” and targeting remedies and interventions accordingly.Footnote 106 In other words, adjudicative uncertainty makes it difficult for courts to finally address governments’ climate policies in one fell swoop. But by centring the challenges of state capacity and recognising their inter-institutional context, courts can iteratively intervene to build state capacity over time in a process built on “dialogue” and conversation, rather than outright conflict.Footnote 107
This function will be particularly valuable in countries lacking in effective climate laws, or with poorly-resourced bureaucracies. For example, rather than placing obstacles in the way of agencies climate policies, courts might identify and highlight where agencies’ failure to establish effective climate policy is a consequence of inadequate government resourcing, or include such analysis in the development of climate rights. Courts should expressly identify the need to strengthen the capacity of executive agencies—both through effective legislation and regulation, but also through adequate training, funding, and establishment of agencies. Simply highlighting the need for capacity-building—rather than only recognising a right or target—can provide opportunities for future litigation to identify more specific obligations. And as discussed below, it might also focus the attention of the political branches on the need to concretize climate measures not only through targets and goals, but through concrete administrative practices.
II. Forming a Constitutional Political Vocabulary
Judicial decisions shape subsequent political debate. Aside from any formal remedies enforcement measures, the sanctioning of a policy as constitutionally-mandated or “unconstitutional” can confer legitimacy, or otherwise, on future government action.
Subsequent political debate following the three case studies discussed above illustrates this point. The Schuldenbremse case not only foreclosed the proposed borrowing at issue, but also made it more difficult for the government to raise more funds through legislative emergency authorisation. Proposals to do so were wildly unpopular, and perceived as an illegitimate workaround against the Court’s decision: A perception fostered by Germany’s conservative opposition.Footnote 108 In Canada, the Impact Assessment Act Reference was portrayed by fossil fuel-rich provincial leaders as a formal rebuke for a federal government taking a “wrecking ball to the Constitution.”Footnote 109 And ironically, in Mexico the SCJN’s initial greenlighting of the electricity industry reforms may have sapped energy from proposed constitutional amendments supporting the government’s agenda, as legislators were satisfied that electricity sector reforms were constitutional regardless of any proposed amendments.Footnote 110
Judges should recognize that constitutional adjudication can “set in motion ongoing debates about the role of law in contributing to environmental protection.”Footnote 111 The language of judicial decisions matters. Even where courts intervene to curb government powers to address climate change, they must be careful not to provide ammunition to political forces which seek to wholesale undermine climate action. They must also be careful not to set up false choices. In the first SCJN intervention described above, for example, the Mexican Court’s decision risked setting up a choice between climate action on the one hand, and redistributive policies on the other. And in the Impact Assessment Act Reference, the Canadian Court’s decision risked setting up a false choice between effective checks on the power of central government, and climate action. Courts should be careful to frame their decisions in narrow terms.
III. Principles in Constitutional Climate Adjudication
Uncertainty and tension in climate adjudication cannot be avoided. But it might be possible to mitigate. One approach is through the development of climate constitutional principles.
Principles are a widespread feature of constitutional systems.Footnote 112 Principles such as democracy, separation of powers, and individual liberty are integral to liberal constitutions. In contrast to rules or doctrines, they reflect higher-order values which structure subsequent constitutional rules. Constitutional principles occupy an intermediate space between first-order substantive reasons, and the more detailed doctrinal content of constitutional law.Footnote 113 In some respects, principles are weaker than rules, in that they do not generate specific obligations. But a strength of principles is that they are transversal: They influence the interpretation of both rights and powers, as well as the development of remedies. And importantly, they permit clearer recourse to substantive values and outcomes.
The quest for constitutional climate rules is a challenging one. Rules which produce optimal climate outcomes in one case may fail to do so in another. The development of substantive climate principles within the framework of constitutional law may be a more fruitful approach.
Many such principles exist in the field of environmental law: Principles of precaution, prevention, non-regressivity/progressivity, and in dubio pro natura, to name a few. Such principles could be productively integrated into constitutional law, and indeed some courts have already done so. The principle of sustainable development was critical to the SCJN’s ultimate conclusion that Mexico’s electricity sector reforms were unconstitutional. Many of these environmental law principles would be foreign, however, to constitutional judges and scholars. But an interpretive approach resting on such principles might assist judges in recognizing the conflicts before them, and providing them with the flexibility to identify the competing values in play, while also working toward an interpretive approach which substantively pushes toward greater climate ambition, counteracting pervasive uncertainty. The recognition of climate rights—and even the general judicial recognition of climate change as a matter of great importance—has been an invaluable first step. But as we enter an era in which the realization of such rights will be crucial—even existential—judges will be called on to make hard decisions. Being armed with the right framework through which to approach such decisions will be vital.
F. Conclusion
One obvious objection to the argument made here is that it appears a paltry response to the urgent challenge of the climate crisis. Such urgency is not contested. And this Article does not rule out the possibility that in some contexts, radical and far-reaching judicial intervention may be justified. But in considering their responses to such an urgent problem, judges ought to consider the institutional context in which their decisions intervene. Constitutional climate adjudication sits at a critical juncture. On one hand, progress has been made towards an ideal of “climate constitutionalism.” Climate obligations are increasingly recognized as latent within existing constitutional rights. But on the other hand, courts are being presented with more difficult questions about conflicts between climate goals, and sometimes-countervailing constitutional values. These conflicts breed uncertainty, which can in turn sap governments of the state capacity necessary to meet the climate crisis. In this Article, I have tried to at least identify that tension as a key challenge of constitutional law. And I have offered some modest suggestions to work through that tension. Resolution remains a long way off. But as the climate crisis becomes an increasingly unavoidable challenge for all areas of law, its resolution will become an imperative.
Acknowledgements
For helpful comments and suggestions, thank you to Nicole Bassoff, Sagnik Das, Angela Hefti, Liz Hicks, Vicki Jackson, Marcelo Lozada, Mathias Risse, Mark Tushnet, and participants at the Safra Center Graduate Fellows Colloquium.
Competing Interests
The author declares none.
Funding Statement
No specific funding has been associated with this Article.
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