Climate change litigation is proliferating in national and international courts, with varying degrees of success. At first, efforts to push states toward taking meaningful measures to mitigate global warming through litigation tended to fail. Domestic, European, and international courts have disposed of many such cases, often for lack of standing.Footnote ¹ But since the Urgenda decisions of the Dutch courts, the tide seems to be turning.Footnote ² Recently, more lawsuits brought against governments and legislatures have proven to be successful. In the spring of 2021, for example, the District Court of the Hague ordered Royal Dutch Shell to drastically cut its emissions,Footnote ³ and a Court in Melbourne held that the Australian minister of the environment has obligations to future generations when making planning decisions.Footnote ⁴ Around the same time, the German Federal Constitutional Court (FCC or Karlsruhe Court) rendered its order of March 24, 2021 (published on April 29, 2021) deciding a string of constitutional complaint proceedings challenging the German Climate Protection Act. The cases were brought by diverse groups of claimants, from young people (claiming special interest in the future of the planet), to farmers (claiming to be specially affected in their fundamental rights to a profession and to the protection of their property), to individuals from Nepal and Bangladesh (emphasizing the especially dire consequences of climate change in their respective countries).

The Karlsruhe Court held the German Climate Protection Act to be partially unconstitutional. On first glance, it seemed to do so on only narrow technical grounds. The Court quashed the Act on procedural grounds, rejecting only its provision allowing the adoption of further CO2 emission reduction targets beyond the year 2020 by executive lawmaking. The Court held that the German Constitution required that parliament take such decisions, in line with its general case law on the requirement of parliamentary decision making for matters of crucial importance for the realization of fundamental rights (the so-called Wesentlichkeitslehre).

However, the significance of Karlsruhe's order goes far beyond its technical holding.Footnote ⁵ The decision is highly innovative with respect to the temporal dimension of fundamental rights protection (as a matter of German constitutional law). The Court also breaks ground in enshrining the need for international cooperation with respect to climate change, finding that the German state and its organs are under a constitutional duty to cooperate. In this sense, the decision is an important contribution not only with respect to climate change litigation, but also to the broader field of comparative foreign relations law.

The Climate Protection Act was enacted in 2019, with aspirations to satisfy various national and international commitments. The Act was designed to ensure compliance with previously announced domestic political goals of emissions reduction. But it was also enacted to comply with EU law and as domestic implementing legislation for the Paris Agreement.Footnote ⁶ Section 3 envisaged a gradual reduction of emissions. Most importantly, it required reductions of 55 percent from the baseline year of 1990 by 2030—proceeding according to concrete yearly steps. But beyond 2030, the Act did not contain a clear pathway to further emissions reductions. It rather authorized the federal government to enact further reduction targets via executive lawmaking.

The petitioners challenged the Act under numerous constitutional provisions. Individuals can bring constitutional complaints to the FCC for violations of the fundamental rights enshrined in the Basic Law. Petitioners relied on several provisions of the Basic Law, most importantly the right to life and bodily integrity (Article 2, paragraph 2), but also other fundamental rights such as the provision on occupational freedom (Article 12) as well as the right to property (Article 14). Though the degree of its justiciability was subject to debate for quite some time, Article 20a of the Basic Law also played a crucial role in the proceedings. Integrated in relevant part into the Basic Law in 1994, this provision provides: “[m]indful also of its responsibility toward future generations, the state shall 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.” This provision was traditionally understood to be a mere goal (Staatszielbestimmung)—binding on the state, but not enforceable by individuals. In particular, it was clear that the provision does not set forth subjective rights that can be relied upon directly when bringing a case to Karlsruhe. This has not changed technically with the decision analyzed here. Still, the Court has built a robust connection between this merely aspirational provision and the fundamental rights of the Basic Law. Even though the FCC still does not allow individuals to bring cases based directly on Article 20a, the provision is of utmost relevance now as part of the objective law against which restrictions of fundamental rights need to be measured.

Under the general standards of admissibility before the FCC, complainants need to show at least a possibility that there has been a violation of their fundamental rights. The Court tends to be flexible about admissibility, leaving controversial issues to be determined at the merits stage. Most of the complaints passed this threshold, including those seemingly more remote claims of the petitioners from Bangladesh and Nepal (para. 101). This in itself was a remarkable finding, in line with the Court's recent widening of the territorial scope of fundamental rights protection to individuals outside of the German territory.Footnote ⁷ The Court found only the complaints by NGOs to be inadmissible as they could not rely on their own rights but merely claimed to act on behalf of the interests of their members and the general public at large—a form of public interest litigation which German constitutional law does not allow (paras. 136–37).

With respect to the merits, the Court proceeded along two different lines of inquiry. It first dealt with the question whether the Climate Protection Act live up to obligations deriving from the positive dimension of fundamental rights under the German Basic Law. Generally, fundamental rights under the German Basic Law are understood to be protections against the state, thus ensuring individual freedom. But it is long-established that they also have a protective aspect—meaning an obligation on the government to affirmatively protect particular constitutional values. Under Karlsruhe case law, a violation of a protective obligation can only be found under three circumstances: if the state did not act at all; if its measures are on their face unable to meet the objective of protection; or if they manifestly lag behind what is needed in order to reach that goal (para. 152). Under these standards, the Court did not find any violations of the Basic Law in the enactment of the Climate Protection Act 2019 (paras. 153–72). It also turned down the complaints of the plaintiffs from Bangladesh and Nepal at this stage, stressing, inter alia, the German authorities’ limited possibilities for effective action in this extraterritorial setting (para. 178). However, the Court was careful to note that these limits would not stand in the way of taking over “political or international law-based responsibility” for protective measures in states which are less well-off and face even harsher consequences of climate change (para. 179).

Even though the Court did not find any current or past violations of positive constitutional obligations, it found that the Act violated fundamental rights of the Basic Law in their “intertemporal dimension.” Intertemporality, here, is a doctrinal innovation. Three issues stand out in this case and help to explain the content and contours of this concept. First, the Court has developed a new standard of “eingriffsähnliche Vorwirkung,” a concept which can roughly (but somewhat clumsily) be translated as “advance interference-like effect” (para. 184). This construction allows the Court to take into consideration the future effects of today's inaction regarding climate change. In its view, delayed action in the present will inevitably make future reactions to climate change even harsher—demanding ever greater restrictions on fundamental rights. This is not necessarily an argument in the interest of future generations not yet born; rather, the Court articulated it with regard to the rights of younger generations living now. In essence, the less stringent climate change mitigation measures are in the present, the more freedom will need to be curtailed in the future (para. 246).

Second, the Court was not particularly specific about which concrete fundamental right had been violated. It seemed to rescue itself from this predicament by adopting an exceptionally broad view of Article 2, paragraph 1 of the Basic Law, in an apparently indirect reliance on the so-called “Elfes doctrine,” going back to a case from the 1950s about the freedom to leave one's country in the Cold War context (para. 184).Footnote ⁸ That decision formulated an understanding of the right to develop one's personality in Article 2, paragraph 1 of the Basic Law as a right protecting all forms of human conduct, subject to proportionate limitations.Footnote ⁹ Within this already wide net of Article 2, paragraph 1, all of the potential wide-ranging limitations of individual freedom considered above would be within the scope of the FCC's analysis. The Court's willingness to consider future interference effects widens the net further still.

Third, this intertemporal construction allowed the Court to bring the future-oriented Article 20a into the analysis. This is a particularly groundbreaking move, greatly enhancing the importance of this constitutional provision. Prior to the decision analyzed here, some commentators regarded Article 20a as mere “goal provision” without any bite (“Verfassungslyrik”).Footnote ¹⁰ Even though Karlsruhe has not here turned it into a directly enforceable right, it has for the first time stressed that it is justiciable (para. 205). It enters the picture as a constraint on the constitutionality of limiting other fundamental rights (a so-called “Schranken-Schranke” in German doctrinal parlance) (para. 214).

In particular, the Karlsruhe Court derives from Article 20a an obligation to protect the Earth's climate. From this finding, the Court extrapolates that this provision ultimately requires climate neutrality, meaning a true balance between emissions and mitigation (para. 198). Moreover, the Court acknowledges the international dimension of the problem and emphasizes that the global nature of climate challenge does not absolve the German state from taking protective measures (para. 199). Rather, the constitutional obligation to tackle this global phenomenon has an a priori international dimension that requires international cooperation by the legislature (para. 200). Understood in this manner, Article 20a requires the state, but in particular the federal government, to work toward climate protection at the global level, through “international coordination, e.g. through negotiations, in agreements and in organizations” (para. 201).

The FCC adds two important caveats, deepening Germany's obligations in this regard. It stresses, first, that if no international solutions are attainable, this would not absolve the German state from its obligation to adopt climate protection measures (para. 202). And, most importantly, inaction by other states does not affect this obligation. No state would be entitled to undercut this required form of international cooperation through inaction, thereby weakening the trust among states in the conduct of their peers. In the Court's view, a practical solution to the global challenge of climate change would depend on mutual trust between states (para. 203), with the Paris Agreement as the current and primary expression of this expectation (para. 204).

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The significance of the Karlsruhe Court's decision extends well beyond the German legal system. In general, it bolsters the wave of domestic and transnational climate change litigation through its innovative intertemporal understanding of fundamental rights protection. Even though its arguments are specific to the German constitutional context and might not lend themselves to being easily transplanted,Footnote ¹¹ the Court has offered an inspiring roadmap for constructively engaging with established limits on individual rights litigation through its innovative intertemporal redefinition of fundamental rights. The decision can also be read as a contribution to separation of powers debates in the field of climate change litigation: it can be viewed as an attempt to demand strict mitigation measures from the other two branches of government, while leaving considerable leeway on how to implement this demand.Footnote ¹² Beyond these general considerations, three issues merit particular attention from an international law perspective. All three point to the Court's complex engagement with the international dimension of the case, enabling it to formulate positions on a global challenge from the perspective of a particular national constitutional system.

First, although the Court found the complaints of plaintiffs from Bangladesh and Nepal admissible, it did not find any violation of their rights with respect to climate change. This is primarily a consequence of the specific doctrinal construction of the intertemporal dimension of fundamental rights protection. By focusing on the future limitations of individual freedoms in Germany, the Court refused to open this pathway of argumentation (and thus this mode of constitutional protection) to petitioners outside of Germany. The Court explained its reasoning by reference to international law. As an initial matter, the FCC leaned on classical understandings of sovereignty and jurisdiction as setting limits on what the German state can demand of third states with respect to mitigation and adaptation measures (para. 178). However, the Court did not stop there. It indicated that these limitations do not stand in the way of taking measures in support of states in the Global South and under particularly severe climate change-related conditions. The Court explicitly pointed to Article 9 of the Paris Agreement and recalled that developed states are expected to contribute financial assistance to less-developed countries in order to adapt to climate change (para. 179). In a nutshell, the Court's reasoning here combines elements of the ideal type images of an international law of co-existence with one of cooperation.Footnote ¹³ On the one hand, it respects the jurisdictional limits of international law, while acknowledging, on the other, the expectation to support less well-off states in their struggle with the climate crisis on the other.

A second central point concerns the obligation to cooperate internationally in the field of climate change governance. The reasoning of the decision comes close to setting forth a philosophical ideal of how a rational and well-governed state should behave in the face of global challenges. The Court emphasizes that states cannot go it alone, and that cooperation is key. It also stresses that the failure of others is no excuse to stand back and wait for concerted action. This can be translated as a call on the German authorities to take every conceivable step on their own—while making use of all realistically available avenues for international coordination—rather than allowing failures on one level to excuse inaction on the other. The Court finds that such forms of cooperation are, at present, most appropriately initiated in the Paris Agreement.Footnote ¹⁴ By connecting the Paris Agreement to the provision of Article 20a of the Basic Law, the Court thus operationalizes the obligation here in a very specific way.

On this point, one might wonder whether the Court's findings are generalizable to other truly global challenges as a matter of domestic constitutional law.Footnote ¹⁵ Following this logic, one could plausibly contend that the German Constitution harbors a similar expectation of cooperation in fields like nuclear security, migration governance or pandemics—all examples of challenges for which purely national solutions will always be second best. Such an extrapolation would connect well with the principles of open statehood (the so-called “Völkerrechtsfreundlichkeit” of the German Basic Law), i.e., its aspiration to open up the German legal system as far as possible to the influence of international law.Footnote ¹⁶ Yet, these principles only offer rhetorical support to such a construction and the specific connection between climate change and Article 20a of the Basic Law caution against drawing overly sweeping conclusions.

At the same time, one might question how far the Karlsruhe Court's approach might be adapted by other national and supranational courts. The decision might prove a source of inspiration in terms of its boldness and legal imagination, even if its concrete doctrinal construction will be difficult to transpose. However, other doctrinal hooks are available. For instance, in the pending climate change cases before the European Court of Human Rights,Footnote ¹⁷ the Strasbourg Court might analogously bring the Paris Agreement into the European Convention by virtue of a “systemic integration”Footnote ¹⁸ approach mandated by Article 31(3)(c) of the Vienna Convention on the Law of Treaties.Footnote ¹⁹

Third, and finally, the decision has given rise to a debate about how to characterize the Court's approach: is this a groundbreaking decision, even reflecting a “post-colonial turn” of the Karlsruhe judges?Footnote ²⁰ Or is it rather a “business as usual” decision in which the Court is not particularly friendly or open to international law, but rather using the Paris Agreement in an instrumental manner—ultimately subordinating it to questions of German constitutional law?Footnote ²¹ The truth may lie somewhere in between.Footnote ²²

The alleged post-colonial turn was identified in light of the Court's consideration of a shared global responsibility and its references to the principle of common but differentiated responsibilities. However, critical voices reproached the judges for unduly limiting extraterritorial rights protections, thereby implicitly differentiating between the worthiness of protecting individuals against climate change depending upon whether they reside in Germany or abroad.Footnote ²³ Commentators have also noted critically that the citation of court decisions from other jurisdictions does not extend to case law from the Global South, where, in particular, the jurisprudence of the Colombian Constitutional Court might have been a source of inspiration.Footnote ²⁴ Taken together, these points seem to call into question an assessment of the decision as being outrightly post-colonial in nature, though I suspect that this was not the Court's ambition.

Yet the FCC did much more than just conduct “business as usual,” and I find it hard to interpret the decision in a way which diminishes the importance of international law in general and the Paris Agreement in particular. In particular, the decision is commendable for operationalizing the Paris Agreement in a very effective manner. That treaty is legally binding, but it contains a highly flexible structure of obligation characterized by a bottom-up approach which leaves it to states parties to define the ambition of their nationally determined contributions.Footnote ²⁵ The Paris Agreement thus counts on a sense of responsibility, understood as a political commitment. The decision of the FCC can be viewed as a contribution to the realization of this ambition, pushing the government and legislature to speed up its efforts on the path toward climate neutrality. In sum, the Court has rendered a landmark decision that adds to recent successful climate change litigation efforts. The decision is replete with innovative and noteworthy contributions to current debates in both comparative constitutional and public international law.