Obligations of Conduct and Intergenerational Equity as reflected in principles of International Law: Divergences Between EU and Member State Submissions in the Wake of the ICJ AO on Climate Change
By Nathalie Frisch* and Marike Dieluweit**
Introduction
Legal obligations, as characterised in international climate law and human rights jurisprudence, encompass duties pertaining to intergenerational equity, requiring states not only to prevent foreseeable environmental harm but also to act with foresight and ambition in protecting the rights and interests of future generations. The European Union (EU), as a prominent geo-political actor, has long sought to position itself as a global leader in climate governance. Its legal framework reflects this commitment: particularly in Art. 3 III 4 TEU the EU commits itself to “solidarity between generations” and the preamble to the EU Charter of Fundamental Rights highlights this nature, reiterating that the enjoyment of its rights carries responsibilities and duties toward future generations.
Recognizing that “human-induced climate change, including more frequent and intense extreme events, has caused widespread adverse impacts and related losses and damages to nature and people”, the UN General Assembly requested an advisory opinion from the ICJ in March 2023 regarding “the obligations of states concerning climate change”.
The EU put forward a joint submission. However, the disparity between Member States’ individual submissions, specifically in relation to arguments on due diligence, historical responsibility, and the interpretation of key principles of international law, is evident. Germany’s national submission, in particular, must be criticised for lacking ambition and undermining more progressive voices within the bloc, exposing growing incoherence in the EU’s external climate messaging and raising concerns about the reception and implementation of the Advisory Opinion across the Union.
In the following, the divergence of selected Member State submissions and that of the European Union will be examined, first, within its legal and political context and, secondly, through a comparative analysis of the submissions by France, Germany, Portugal, and Spain. The focus lies on how these countries, each within the EU’s top 20 emitters of greenhouse gases, frame responsibility for climate action and climate justice in contrast to the EU’s collective stance.
Legal and Political Context
In response to the UN General Assembly’s request, the ICJ is expected to clarify legal responsibilities of states to protect the climate system and the potential legal consequences for failing to do so, including implications for the rights of future generations. The ICJ’s forthcoming advisory opinion is situated within a broader trend of climate litigation and legal clarification, including the advisory opinion of the International Tribunal of the Law of the Sea (ITLOS), which addressed states’ responsibilities regarding climate impacts on the marine environment.
Historically, the EU was a latecomer to the development of environmental policies. While France and the United Kingdom had already appointed environmental ministers, and Western Germany introduced a first environmental programme in 1971, the EU only commenced formulating environmental plans after the 1972 Stockholm United Nations Conference. However, today, the EU has established itself as a prominent actor in global environmental negotiations, attempting to promote a unified European position. And within Europe, EU environmental regulations shape policy making processes in its Member States, contributing to the harmonization of environmental governance across Europe. More recently, the so-called European Climate Law (ECL) was introduced alongside the Governance Regulation to form a key EU climate governance framework to legislate climate targets including the goal of climate neutrality by 2050 (Review of the governance regulation and the European Climate law, p. 6). Despite this, it should be noted that, in 2023 the EU remained the world’s fourth largest greenhouse gas emitter, with Germany as the largest emitter among the Member States.
In parallel with its climate legislation, the EU is also bound by fundamental principles of international environmental law, particularly the principles of due diligence, Common but Differentiated Responsibilities and Respective Capabilities (CBDR-RC) International Cooperation, and Intergenerational Equity. It is stated that an estimated 42 international environmental agreements mention the principle of intergenerational equity or reference future generations (CIEL, written statement, memo on the rights of future generations, para. 8). Whilst the focus lies on the EU, it is important to note that the principle can be found in national and regional systems across the world.
These principles collectively uniform the aforementioned international environmental agreements as well as international law more broadly which finds application not at least because of references in jurisprudence of the ICJ (OPIL, General Principles, para. 17 ff.), the effects of which the EU is not exempt from.
Analysis
The principle of due diligence represents a cornerstone of international climate law, first articulated in Principle 21 of the Stockholm Declaration, whereby States must “not cause damage to the environment of other States or of areas beyond the limits of national jurisdiction”. It is best understood as an obligation of conduct, requiring states to take reasonable steps to prevent harm or violations, especially by private actors within their jurisdiction. While it needs to be viewed between primary rules of conduct and secondary rules of state responsibility, it also plays an important role in situations where harm cannot be directly attributed to the state, requiring the state to exercise reasonable care within its jurisdiction and control.
The European Union recognizes the importance of acting according to due diligence, pointing out that the difference between obligations of conduct and obligations of result lies in the unconditional performance of the latter (EU written submission, para. 73), while both types of obligations are equally legally binding.
It then initiates its analysis of due diligence obligations by referencing examples identified in international cases and advisory opinions of the ICJ, ITLOS and the South China Sea Arbitration Tribunal (SCS Arbitration). In particular, the ICJ’s Pulp Mills on the River Uruguay (Argentina v. Uruguay) judgment is referenced, noting that environmental impact assessments can now be regarded as a requirement, and must be conducted with due diligence, which includes, “a certain level of vigilance in their enforcement” (EU written submission, para. 86 f.).
Regarding climate measures, the EU notes that the Paris Agreement comprised multiple due diligence obligations. While the Agreement establishes normative frameworks such, as Nationally Determined Contributions (NDCs), it does not “exhaustively describe what form mitigation efforts should take” (EU written submission, para. 141). Though, importantly, the EU also highlights that this “does not, however, imply, that there are no normative parameters” (EU written submission, para. 141).
However, while Parties have discretion to determine the content of their respective NDCs, Art. 4(4) of the Paris Agreement shall encourage developed country Parties - including the EU - to continue leading by adopting economy-wide absolute emission reduction targets (EU written submission, para. 144).
The EU consistently emphasizes that the Paris Agreement requires NDCs to reflect a “higher level of ambition”, while also noting that the term “highest possible ambition” is not clearly defined (EU written submission, para. 145 ff.). As a result, the EU interprets it to mean the pursuit of “best efforts”(EU written submission, para. 147). The EU highlights that all Parties, both developed and developing, are obligated to work towards the goals of Paris and are required to “pursue domestic measures”. However, it remains open to question whether the EU itself is already demonstrating its “best efforts” in adopting more ambitious emission reduction targets and climate policies, or if this rather is a smooth way of escaping liability.
Spain, for its part, emphasizes that due diligence is rooted in customary international law and applies across all areas of international law (Spain written submission, para. 6 f.). Still, the framing suggests a reluctance towards fully embracing individual state responsibility as well. While Spain recognizes that the Paris Agreement aligns with due diligence obligations by combining procedural commitments with a collective goal of limiting global warming to 1.5 degrees Celsius, it notably emphasizes the collective nature of these obligations (Spain written submission, para. 7). Although NDCs are determined individually, Spain highlights their role as instruments that collectively serve the global temperature goal. This emphasis arguably shifts focus away from individual, national accountability, in favor of a more collective framing. While Spain does reference ARISWA and the Advisory Opinion of ITLOS to support the idea that due diligence includes proactive duties (e.g. notification, information sharing), it situates these obligations largely within the procedural structure of the Paris Agreement. Although Spain does not explicitly reject the notion of individual state responsibility, its emphasis on the collective dimension and procedural compliance may signal an attempt to soften potential claims of state liability.
In its 2024 Advisory Opinion, ITLOS had stated that the “the standard of due diligence States must exercise […] needs to be stringent” while the implementation depends on capabilities and resources. Therefore, a state with greater capabilities and adequate resources is expected to take more extensive action than one with limited means (ITLOS, Advisory Opinion on climate change, para. 241). Arguably, such a responsibility could befall Germany whose emissions and financial resources can be similarly described as substantial, with Germany boasting the largest GDP within the EU.
In light of this, it is unsurprising that within the German submission , the concept of due diligence is only mentioned once – when citing the questions to the ICJ that were agreed upon in the Resolution of the General Assembly. Instead, Germany focuses on the need to distinguish clearly between legally binding obligations and voluntary political commitments (Germany written submission, para. 26 ff.).24 Even though the German Constitutional Court concluded in 2021 that the federal government’s measures are insufficient to effectively combat climate change (Germany Federal Constitutional Court Order, para. 256 - 263) , Germany stresses the procedural flexibility of Paris, insisting that most obligations are predominantly political in nature and not enforceable as legal duties (cf. Germany written submission, para. 28 f.; 32 f.; 36), and thereby attempting to escape any potential claims of accountability.
While the EU and Spain at least acknowledge the importance of due diligence, Germany avoids engaging with the concept altogether, offering instead a narrowly procedural interpretation of its climate obligations and downplaying any suggestion of individualized legal accountability.
Spain stresses that inadequate climate action harms the dignity and rights of vulnerable and future populations, linking due diligence to environmental and human rights and framing a foundation for intergenerational equity. Intergenerational equity describes the right of the present generation “to use the Earth and its natural resources to meet its own needs” while obligating it to “pass the Earth on to future generations in a condition no worse than that in which it was received so that future generations may meet their own needs” (MPEIL, intergenerational equity, para. 6) .
Due diligence, however, often lacks connection to concrete climate outcomes like emissions reductions, risking formal compliance without real protection for future generations. This is especially problematic given the time lag between mitigation and its benefits, raising doubts about the effectiveness of conduct-based obligations in safeguarding intergenerational equity.
The principle of common but differentiated responsibilities and respective capabilities (CBDR-RC) underlines another approach to tackling climate change and reinforces intergenerational equity when interpreted progressively by requiring states with greater resources and emissions to take the lead in preventing harm to future generations. This is reflected in Art. 3(1) UNFCCC, which explicitly links CBDR-RC to the duty to protect the climate for “the benefit of present and future generations”, and reiterated in Paris, where Art. 2(2) and Art. 4(4) require the implementation to reflect equity and CBDR-RC (MPEPIL, CBDR, para. 6). However, the contribution to intergenerational equity is not automatic. While the “differentiated responsibilities” aspect supports fair burden-sharing, some states use “respective capabilities” to downplay their obligations, even when their emissions and resources are significant (MPEPIL, CBDR, para. 8). Thus, CBDR-RC can promote intergenerational equity, but only if applied in a way that holds states accountable, rather than justifying inaction.
Germany continues to downplay its obligations by arguing that CBDR-RC should only apply within the context of the Paris Agreement, and further contends that historical emissions remain exempt from consideration (Germany written submission, para. 80). More than simply a restrictive position, this positioning is relevant when considering that Germany has historically been the EU’s highest contributing Member State to pollution. Yet, without legal recognition of past contributions, meaningful accountability may be avoided.
France’s submission illuminates the divergences in this approach, suggesting the ICJ should clarify the temporal scope of climate obligations, potentially establishing a date from which States incurred an obligation to avert climate harm, asserting however, that attributing responsibility to individual states is beyond the court’s mandate.
Portugal, for its part, emphasizes that “it is extremely difficult” to assess the extent to which a Party’s action or lack of action impacts reaching the goal set in the provision, “even when guided by [the] principle of [...] common but differentiated responsibilities” (Portgual written submission, para. 53). Portugal then links CBDR-RC to international cooperation, viewing it as a legal consequence of climate obligations, deriving a “duty to cooperate” from the Paris Agreement.
International cooperation, as a foundational principle of the modern “law of cooperation”, obliges states to engage in coordinated action under a legal framework to achieve shared goals, in particular where individual efforts appear insufficient (MPEPIL, cooperation, para. 1 ff.). It is specifically prominent in international environmental law, as reflected in Principle 7 of the Rio Declaration and numerous environmental agreements that rely on cooperation for their development, implementation, and effectiveness (MPEPIL, cooperation, para. 28 ff.).
As yet another way of escaping liability, Germany clarifies that neither the Stockholm Declaration nor the Rio Declaration are legally binding in international law (Germany written submission, para. 76), which would imply that states cannot be held legally accountable for failing to comply with principles of those declarations.. Germany later acknowledges obligations stemming from customary international law, especially the “duty to cooperate” (Germany written submission, para. 77) as per ITLOS (Max Plant Case, para. 82) and is accepted as applicable beyond the context of the Law of the Sea before the ICJ. Despite this acknowledgement, it argues that the derived duty to cooperate does not extend to an obligation to contribute to the fund for responding to Loss and Damage (Germany written submission, para. 27).
The definition of the principle of "loss and damage" describes the "impacts of climate change that have not been, or cannot be, avoided through mitigation or adaptation efforts".
Other submissions such as that of France also identify that such contribution does not constitute a legal obligation but describe the guiding principle of loss and damage as “essentially co-operative in nature” (France written submission, para. 230 ff). While Germany made no further statements to the fund or the broader principle, France made a commitment of 6 billion EUR a year between 2021 and 2025 (France written submission, para. 240). Comparatively, Spain’s submission itself makes no mention of the fund; the Spanish government has supposedly expressed support and pledged a contribution of 20 million EUR – although there is no official confirmation of this.
In light of this, it is understandable as to why broad criticism as to the funding gap between the EU and Member State commitment of 400 million EUR made at COP28 and the sum that is needed to adequately address the challenges posed by climate change remains. Referencing collective obligations (EU written submission, para. 90), the EU in its submission argues that “the climate should be regarded as a common good” and it is from this that such obligation is derived (EU written submission, para. 19).
This is also reflected in Portugal’s submission wherein “climate change and its adverse effects” are described “as a common concern of humankind” (Portugal written submission, para. 43). It goes further to cement this as dependent upon “international cooperation” as per the UNFCCC (Portugal written submission, para. 44) whilst firmly positioning itself as a proponent of a CBDR approach in which States with the means to do so should adopt “precautionary” measures into national policies to the benefit of current and future generations (Portugal written submission, para. 47). Nevertheless there is no explicit confirmation of a financial contribution to the fund in the submission or other official documents. This observation is not intended to minimise the very progressive approach that Portugal has taken to its own understanding of obligations of conduct when it comes to a duty to future generations, but underscores that the inconsistencies between the submissions of Member States reflect a broader divergence in national regulation and depth of commitment to these principles.
The principle of due diligence, the concept of CBDR, and the establishment of the Loss and Damage Fund are all essential pillars in advancing intergenerational equity and climate justice. Although the EU and its Member States often position themselves as progressive leaders in climate governance, the divergences within the EU are striking. In particular, the more conservative and cautious statements made by some Member States offer little support in promoting the level of ambition and solidarity required to address the climate crisis effectively, especially in ways that honour obligations to future generations.
Reflection
The divergences between the EU and its Member States in their submissions to the ICJ reveal not only legal and political fragmentation, but also a deeper uncertainty about the meaning and implementation of due diligence and intergenerational equity. In the case of Germany, it demonstrates an interesting departure from contemporary decisions such as Neubauer et al. v. Germany, with the Federal Constitutional Court of Germany emphasizing that climate mitigation burdens cannot be “unilaterally offloaded onto the future,” affirming intergenerational justice as a binding constitutional obligation. Yet, Germany’s cautious language in the ICJ proceedings appears to undercut this principle on the international stage.
These internal discrepancies have broader implications for the EU’s climate governance. Beyond weakening the Union’s ability to present a united front externally, they risk obstructing the adoption of ambitious climate legislation at the EU level. As the most populous Member State, Germany holds significant institutional leverage: under the qualified majority voting system in the Council of the EU, it could help form a blocking minority, which is triggered when four Member States representing at least 35% of the EU population oppose a proposal.
If populous states like Germany and France advocate only moderate climate action in their ICJ submissions, this hesitation could well influence future negotiations on key EU directives. In the past, Germany has repeatedly blocked progressive legislation, such as the Equal Treatment Directive and a directive targeting violence against women, illustrating how internal divergences can directly affect the EU’s legislative output.
In the climate context, similar outcomes could critically undermine the Union’s ability to meet its own legal commitments and broader climate goals.
Conclusion
The legal discourse around climate responsibility, especially the principles of due diligence and intergenerational equity, highlights the urgent need for states to not only act, but to act effectively and ambitiously. As Greta Thunberg reminds us, “we can’t just continue to live as if there was no tomorrow, because there is a tomorrow.”
The accelerating pace at which we exhaust the planet’s resources makes this warning painfully tangible. In 2025, the Earth Overshoot Day falls on July 24th, meaning that from that day forward, humanity is effectively living on ecological credit. For Germany, that arrived even earlier, on May 3rd, and for the European Union as a whole, on April 29th. These dates are not just symbolic; they reflect a legal and moral failure to exercise due diligence in protecting the environment for future generations. If Member States continue to fulfill climate obligations only in form rather than in substance, the principle of intergenerational equity risks becoming hollow. The law alone cannot solve the climate crisis, but it can and must demand that states take meaningful, science-based, and forward-looking action, not just to meet today’s standards, but to safeguard tomorrow’s world.
*Nathalie Frisch is a German national and law student at the University of Hamburg, Germany, having specialized in law and economics. As part of the climate law clinic “CLIC - Climate Law in international Context” she has worked on several international environmental law issues in cooperation with the University of Chile.
**Marike Dieluweit is a German national and law student at the University of Hamburg, Germany, having specialized in European and Public International Law. As part of the climate law clinic “CLIC - Climate Law in international Context” she has worked on several international environmental law issues in cooperation with the University of Chile.
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