This article belongs to the debate » Longtermism and the Law
11 August 2022

An Intertemporal Perspective on Intergenerational Equity

How to Assess the Legal Relationship Between Present and Future Generations

Imagine it is the year 2100 on planet Earth. Human life has dramatically changed, particularly with regard to the irreversible effects of climate change. Due to progress in attribution science, it is possible to determine which specific human activities are responsible for the catastrophic situation of the environment in the year 2100. Most detrimental effects originated in the first decades of the 21st century (generation A).

The international community in the year 2100 (generation B) decides to establish a High Commissioner for Intergenerational Relations who is tasked with the analysis of the intergenerational responsibility of generation A for climate change. In order to better understand the legal motivations of generation A, the High Commissioner uses the new technology of time travel to visit the year 2022. Upon safe arrival, she is invited to speak at the Stockholm+50 Conference. After illustrating the upcoming irreversible effects on the ecosystems and describing generation A’s contribution to these developments, she ends with one simple question to the State representatives:

Why do you act in explicit violation of your responsibilities under the concept of intergenerational equity?

The Intertemporal Relation Between Present and Future Generations

Leaving aside the unlikelihood of time travel, how would the addressed State representatives answer this question? Are they even violating their intergenerational responsibilities? Before getting to the substance of the answer, the concept of intergenerational equity evidently raises an intertemporal situation, as the content of the relevant legal norms could have changed over time between the year 2022 and the year 2100.

So, the preliminary question of intertemporal law should be which legal regime would be temporally applicable for giving the correct legal answer. Since the 1928 Island of Palmas award (p. 845), international law traditionally has two answers to this question: contemporaneity and evolutionary approaches.

A Contemporaneous Perspective on Intergenerational Equity

First, a legal situation must be assessed in light of the legal regime that is contemporaneous with its creation – the principle of contemporaneity. This first intertemporal perspective requires assessing the current legal regime of intergenerational equity in the year 2022. Although much has been written about intergenerational equity, the exact legal contents of the concept are often confused in international scholarship. The 1987 Brundtland Report first explicitly articulated that sustainable development “meets the needs of the present without compromising the ability of future generations to meet their own needs” (Chapter 2 para. 1).

While some international documents have incorporated this notion of intergenerational equity in their preambles and operative texts (e.g. Principle 3 Rio Declaration; Art. 3(1) UNFCCC; Art. 1 Aarhus Convention), the main contribution to today’s understanding of intergenerational equity has been made by Edith Brown Weiss in several works since 1989.1) She elaborated a doctrine based on a trust for the planetary resources which consists of intergenerational duties and rights.

Despite many inconsistencies in legal documents and scholarship, a proper analysis illustrates that two manifestations of intergenerational equity exist today: On the one hand, a general conception, component of sustainable development, requires the members of the present generation to take into account the interests of future generations (see also Fitzmaurice 2008, 211). It constitutes a legally binding norm of both treaty and customary international law (see Nuclear Weapons Dissenting Opinion, p. 455‑456). On the other hand, a more specific doctrine was elaborated by Brown Weiss, which is not part of binding customary international law as of today (see however 1997 UNESCO Declaration). This doctrine would potentially include intergenerational rights of future generations themselves along with a coherent institutional framework for the effective implementation of intergenerational obligations.

From a contemporaneous point of view, the answer to the hypothetical time traveller would thus be that the present generation is only bound by a rather general concept of intergenerational equity – without specific conservation duties or effective means of implementation.

An Evolutionary Perspective on Intergenerational Equity

However, this is not the only possible perspective. The second element of intertemporal law states that, under specific circumstances, a legal assessment must turn to the evolutionary developments between the norm’s creation and the later decision on a specific dispute (Island of Palmas, p. 845). This requires addressing the evolutionary character of intergenerational equity. If intergenerational equity fulfilled certain conditions – particularly if it has a dynamic object and purpose – its assessment must follow the evolution of law.

Although much could be said about this second element in international environmental law, the analysis for intergenerational equity seems clear: In a nutshell, its purpose, to shape a fair relationship between present and future generations (Brown Weiss, p. 21), is inherently intertemporal as it relates two parties with one another that exist at different moments in time. The evolutionary element of intertemporal law requires an evolutionary approach to the legal assessment of an intergenerational dispute – rather than a static understanding of contemporaneity. Consequently, the answer to the High Commissioner for Intergenerational Relations would be more promising since the intergenerational obligations of generation A would have to be assessed based on subsequent developments of law. These could include the aforementioned rights-based understanding as well as institutional frameworks of implementation.

There is one main difficulty in applying this element to intergenerational equity. So far, intertemporal law has only been utilised by courts and tribunals in a retrospective manner, relating the present to the past. In the current context, this means: the representative of generation B would have to wait until the dispute on the intergenerational responsibility of generation A arises due to environmental damages in the future. Then, a court could resolve the dispute based on the evolutionary developments of law between 2022 and 2100. At this stage, generation A will have become a past generation, while generation B will be the present generation invoking the former’s responsibility. The problem at that point is the irreversible character of most environmental damages, particularly with regard to climate change. While waiting for an evolutionary resolution of the dispute in favour of the affected future generation, the damages will have become irreversible so that they could not be remedied anymore by the perpetrator of intergenerational obligations.

A Modified Intertemporal Perspective on Intergenerational Relations

This traditional understanding of intertemporal law is thus not persuasive – a modified intertemporal approach to intergenerational equity is necessary. This approach would have to shift the perspective of intertemporal law from a retrospective present-past relationship to a future-oriented perspective.2) Instead of observing the evolutionary developments of law over time and retrospectively applying them at a certain point in the future, the new approach departs from the contemporary legal regime and attempts to anticipate its prospective evolutionary developments – with regard to intergenerational equity only. In this sense, Brown Weiss noted in 1989 already that “the proposed principles of equity between generations […] extend the basic concern we already have with intertemporal problems, albeit for a longer time horizon” (p. 34).

It seems preposterous to demand that we should predict the future developments of law, but some general predictions on the future development of intergenerational equity can be possible for two reasons. First, the aforementioned manifestations of intergenerational equity offer certain guidelines how the concept could evolve in the near future: from a general conception of taking into account future generations’ needs to a more elaborated set of planetary rights and obligations which considers future generations to be right-holders and establishes an institutional framework for the concept’s implementation.

Second, it is not necessary to predict the exact legal changes in the future. It is sufficient to approach a probable future scenario of legal development with a high enough certainty and based on methodological reasoning. Charlotte Ku and Paul Diehl elaborated an accordingly sophisticated concept of legal change based on certain observations on the interrelation between normative and operating system changes in international law.3) This reasoning tool can be used to make certain assumptions on the future development of intergenerational equity. If this enables us to anticipate with sufficient probability whether and how the general conception will evolve into its more specific manifestation in the future, then the modified doctrine of intertemporal law will require the present generation to consider these upcoming developments as of today already – instead of awaiting them until it is too late.

While this modified doctrine might seem unrealistic, even utopian, Pierre-Marie Dupuy correctly stipulated: “Utopia is only reprehensible when it is a substitute for action, not when it inspires it. At the very least, this correct intertemporal perspective should raise the present generation’s awareness for the relevance of future interests and legal developments.

In the end, the answer to the High Commissioner for Intergenerational Relations cannot simply rely on the current and insufficient legal regime of intergenerational equity. Instead, the State representatives of the Stockholm+50 Conference must take the correct intertemporal perspective while assessing their intergenerational obligations. From this perspective, they would realise that the representative of the future generation is correct in reproaching them for violating their responsibilities. Hopefully, this finding can still lead to the sufficient change of action – today.


1 See particularly her seminal work: Edith Brown Weiss, In Fairness to Future Generations: International Law, Common Patrimony, and Intergenerational Equity (Tokyo: Transnational Publishers, 1989).
2 On the necessity of focusing more on the future in international environmental law, cf.  Louis J. Kotzé, ‘Earth system law for the Anthropocene’ (2020) 11 Transnational Legal Theory 75, 94.
3 Paul F. Diehl and Charlotte Ku, The Dynamics of International Law (Cambridge: Cambridge University Press, 2010).