Due Regard for Future Generations? The No Harm Rule and Sovereignty in the Advisory Opinions on Climate Change

Abstract

States have long been understood to have an obligation to protect the international legal rights and interests of others, consistent with the maxim sic utere tuo ut alienum non laedas (use what is yours in such a manner as not to injure that of another). As the world's population becomes more interdependent, this no harm obligation becomes more significant. Further, as knowledge increases about the consequences of human activity for the climate and the environment, the no harm obligation takes on greater relevance vis-à-vis the interests of the Earth's future populations. Future generations’ legal interests have been recognized in the context of sustainable development and through the principle of intergenerational equity. The no harm rule requires that these interests be properly considered and addressed appropriately, commensurate with what is at stake. At a minimum, this may require avoidance of ‘manifestly excessive adverse impacts’.

1. Introduction

The obligation of every state not knowingly to allow its territory to be used for acts contrary to the rights and interests of others is well established.¹ In the Corfu Channel case, the International Court of Justice (ICJ) held that ‘a state must not permit the use of its territory for purposes injurious to the interests of other states in a manner contrary to international law’.² In Island of Palmas it was likewise held to follow from the concept of territorial sovereignty that states must protect other states’ rights within their territories.³

The Corfu Channel no harm rule and the sic utere tuo ut alienum non laedas principle (use what is yours in such a manner as not to injure that of another) address how sovereigns must act in relation to the legal rights and interests of other states and their populations. When it comes to state conduct in relation to environmental harm, including anthropogenic climate change, do the Corfu Channel no harm rule and the sic utere tuo ut alienum non laedas principle mean that states may have to consider and respect the interests also of future populations? The Institut de Droit International has suggested that:

[e]very state, when intervening on the basis of decisions taken in the exercise of its sovereignty in fields of activity where the effects of such decisions on the environment are clear, has the responsibility to ensure that activities within its jurisdiction or under its control do not cause damage which may affect the lives of the present and future generations.⁴

When we say that the sic utere tuo principle and the no harm rule require respect for the international legal interests of others, it seems reasonable that this requires conduct respecting the interests of others not only in the immediate present but also in terms of how our actions today will affect these interests in the future. Moreover, it could be argued that international law requires the interests of future generations to be given distinct respect considering in particular the unique threats posed by climate change.⁵ The unique character of climate change, the severity of global disruption and suffering that it has begun to cause, the sudden and unpredictable aspects of its impact, together with the valuable opportunity available to states now to prevent long-lasting damage at scale are all relevant.

Although it is generally the rights and interests of other states that have been held to be protected by the no harm rule, there are several further reasons why the rule can also be regarded as requiring distinct consideration for the interests of future generations in the climate context. Firstly, at the level of principle, the core idea of the sic utere tuo maxim is to respect the rights and interests ‘of others’. Future generations can be argued to be such an ‘other’ or ‘others’ in the context of anthropogenic climate change. Future populations stand to experience the most severe harmful effects of cumulative greenhouse gas (GHG) emissions today and in the future. The physical harm that is being caused to the climate system increases relative to the period of time over which emissions continue without the necessary abatement, as does the unpredictability of the effects of climate change within the natural world. At the same time, the emissions reduction burden on future generations continues to grow, because the concentration of GHGs in the atmosphere is reversible only with prolonged effort over time. The evolving law on cooperation and the respect for others that duties of cooperation may entail may not be of direct assistance in relation to the interests of future populations who have not yet come into being and with whom cooperation is not possible.⁶

Secondly, future generations have specific international legal interests, which have been accepted within international law for some time. The theory of intergenerational equity is part of conventional international environmental law wisdom.⁷ Commonly, it is regarded as inherent in the concept of sustainable development.⁸ Brown Weiss, the intellectual progenitor of the theory, expressly observed that this opens the possibility that decisions ‘deserve to be scrutinized from the point of view of their impact on future generations’.⁹ Such interests may only be soft law interests, but arguably it is not necessary that they be hard law interests in order to ground an application of the sic utere tuo principle: they are nonetheless legally relevant interests.

Further, the no harm rule is a corollary of sovereignty and constrains the conduct of a responsible sovereign. Given this, might the ICJ remarks on the reasonable exercise of sovereignty, and how this may require states to avoid manifestly excessive adverse effects on the interests of others,¹⁰ offer an indicium for establishing whether state conduct shows due regard for future generations’ interests? If a state pursues a course of conduct that will not avoid manifestly excessive adverse impacts, this would seem to indicate a lack of due regard.

Section 1 of this article has introduced the article's enquiry. Section 2 assesses the applicability of the sic utere tuo principle and the no harm obligation in respect of future populations by looking into the concepts of sustainable development and intergenerational equity. Section 3 addresses the concept of due regard as an emerging global regulatory standard, how it may apply as an aspect of the sic utere tuo principle and the no harm obligation, and what due regard may require. This includes an examination of the cases decided by international courts and tribunals indicating that the good faith exercise of sovereignty avoids manifestly excessive adverse effects on the legal rights and interests of others. It also includes a discussion of how due regard sits with states’ customary international environmental law obligations of notification, consultation, and environmental impact assessment. Section 4 turns to the requests for an advisory opinion on climate change put to the ICJ,¹¹ the International Tribunal for the Law of the Sea (ITLOS),¹² and the Inter-American Court of Human Rights (IACtHR).¹³ There is scope for all three advisory opinions, and that of the ICJ in particular, to help in setting the stage for important developments in law and policy on the problem of future populations’ interests in international law, including through the sic utere tuo principle and the no harm obligation.

2. Intergenerational Equity

International law recognizes the legal interests of future generations, inter alia and in a general way, through the principle of sustainable development and the theory of intergenerational equity. These legal interests arguably belong to ‘others’ in the sense embraced by the sic utere tuo principle and for the purposes of applying the no harm obligation.

The 1972 Stockholm Declaration formally recognized a responsibility to future generations in Principle 1.¹⁴ As expressed in 1987 in the Brundtland Report, ‘Our Common Future’, sustainable development is development that ‘meets the needs of the present, without compromising the ability of future generations to meet their own needs’.¹⁵ The core elements of sustainable development are commonly understood to include integration of environmental protection and economic development, the right to development, sustainable utilization and conservation of natural resources, intergenerational equity, intra-generational equity, and procedural elements including environmental impact assessment, public participation in environmental decision making, and access to information.¹⁶ The 1992 Rio Declaration held that ‘[t]he right to development must be fulfilled so as to equitably meet developmental and environmental needs of present and future generations’.¹⁷ Importantly, too, Principle 27 of the Rio Declaration and Chapter 39 of Agenda 21 called for further development of the law in the field of sustainable development.¹⁸ The ICJ endorsed the principle of sustainable development in the 1997 Gabčikovo-Nagymaros Project (Hungary v. Slovakia) case:

Throughout the ages, mankind has, for economic and other reasons, constantly interfered with nature. In the past, this was often done without consideration of the effects upon the environment. Owing to new scientific insights and to a growing awareness of the risks for mankind – for present and future generations – of pursuit of such interventions at an unconsidered and unabated pace, new norms and standards have been developed, set forth in a great number of instruments during the last two decades. Such new norms have to be taken into consideration, and such new standards given proper weight, not only when states contemplate new activities but also when continuing with activities begun in the past. This need to reconcile economic development with protection of the environment is aptly expressed in the concept of sustainable development.¹⁹

With the adoption of the United Nations (UN) Sustainable Development Goals (SDGs) in 2015, following on the heels of the Millenium Development Goals (MDGs), sustainable development has blossomed into a highly faceted kaleidoscopic concept.

Boyle and Redgwell identify the core point: ‘While recognising that the right to pursue economic development is an attribute of a state's sovereignty over its own natural resources and territory, it cannot lawfully be exercised without regard for the detrimental impact on human rights or the environment’.²⁰ Similarly, remarks of leading authorities show that the principle of sustainable development strongly suggests that states must have due regard for the interests of future generations. Judge Weeramantry used the language of ‘due regard’ for environmental considerations in envisaging the implementation of the principle of sustainable development, observing that the components of the principle come from ‘well-established areas of international law – human rights, state responsibility, environmental law, economic and industrial law, equity, territorial sovereignty, abuse of rights, good neighbourliness’.²¹ Sands and his co-authors state that sustainable development reflects a range of procedural and substantive commitments and obligations – including ‘the need to take into consideration the needs of present and future generations’.²² Even Lowe, sceptical of the normative force of sustainable development, indicates that ‘to the extent that international law obliges States to take decisions having regard to the interests of future generations, decisions made in avowed disregard of these interests might be held to be invalid’.²³ Lowe also appears to allow for the practical normative effect of sustainable development when he observes that the concept of sustainable development plainly precludes the possibility of a tribunal deciding a case by upholding a property owner's unfettered right to utilize property in a particular way ‘without any regard for the serious and irreversible harm caused by that particular use’.²⁴

Sands and co-authors have suggested that sustainable development ‘has entered the corpus of customary international law’,²⁵ but this has yet to be formally established. The force of the commitments that sustainable development entails in respect of future generations’ legal interests would be increased if sustainable development were to receive such recognition. However, this article takes the position that, regardless of whether the principle of sustainable development and the theory of intergenerational equity are soft law or hard law, they embody international law's consistent recognition of the interests of future generations. This recognition provides an anchor for the broader application of the sic utere tuo principle.

3. Due Regard

In the light of their recognized legal interests, this article considers the application of the sic utere tuo principle and the no harm obligation vis-à-vis future generations, investigating whether and how the concept of due regard may serve as a vehicle for their respect. Section 3.1 reviews the use of the concept of due regard in international law to date and examines its status as an emerging global regulatory standard.²⁶ Section 3.2 discusses how, if due regard were accepted as an aspect of the no harm obligation and the sic utere tuo principle, it might operate alongside states’ customary international environmental law obligations of due diligence, as well as those of notification, consultation, and environmental impact assessment. Section 3.3 then considers what due regard may require both procedurally and substantively where future generations’ legal interests are implicated in the context of the no harm obligation and the sic utere tuo principle. This part examines the international cases indicating that the good faith exercise of sovereignty will avoid manifestly excessive adverse effects on the legal rights and interests of others.

3.1. Due Regard as an Emerging Global Regulatory Standard

The concept of due regard appears to be an emerging global regulatory standard.²⁷ International courts and tribunals have found international legal rules to call for due regard in a range of cases across many different fields of international law, including world trade law and international investment law. The Appellate Body of the World Trade Organization (WTO) made it clear early in its jurisprudence that measures falling within the exceptions found in Article XX of the 1994 General Agreement on Tariffs and Trade (GATT)²⁸ must be applied reasonably, with due regard both to the legal duties of the party claiming the exception and the legal rights of the other parties concerned.²⁹ The chapeau to Article XX GATT has been clearly identified both as an expression of the principle of good faith³⁰ and as a tool to prevent abuse of the exceptions specified in the subparagraphs to Article XX.³¹ Failure to have regard for a measure's cost to others,³² or to provide them with an opportunity to be heard,³³ may undermine a respondent's Article XX defences.³⁴ Certain recent regional trade negotiations have since made explicit a requirement to consider the costs, benefits, and distributional impacts of proposed new regulations.³⁵ Due regard is further referenced in international investment treaty law. Perhaps understandably, investment arbitral tribunals referencing due regard have tended to couch the need for host states to give due consideration to the burdens that their intended measures will impose in terms of their effects on ‘investments’.³⁶

Due regard has a long history in the law of watercourses and the law of the sea. Classically, the Tribunal in the Lac Lanoux arbitration held that:

[a]ccording to the rules of good faith, the upstream State is under the obligation to take into consideration the various interests involved, to seek to give them every satisfaction compatible with the pursuit of its own interests, and to show that in this regard it is genuinely concerned to reconcile the interests of the other riparian State with its own.³⁷

In the context of the UN Convention on the Law of the Sea (UNCLOS),³⁸ the language of due regard was settled during the negotiations on the legal regime for the high seas rather than referencing due consideration as a tool for balancing states’ competing interests.³⁹ The ITLOS ruling in Chagos Marine Protected Area Arbitration (Republic of Mauritius v. United Kingdom) provides a recent articulation of what both good faith (as a rule of international law applying under Article 2(3) UNCLOS, covering the territorial sea) and due regard (as applicable under UNCLOS in the exclusive economic zone (EEZ)) may equally require in practice.⁴⁰ The ITLOS considered that the ordinary meaning of ‘due regard’ in UNCLOS called for the United Kingdom (UK) to have such regard for the rights of Mauritius as is called for ‘by the circumstances and by the nature of those rights’.⁴¹ The Tribunal identified factors influencing the level of regard required, which included ‘the nature of the rights held by Mauritius, their importance, the extent of the anticipated impairment, the nature and importance of the activities contemplated by the [UK], and the availability of alternative approaches’.⁴² However, the Tribunal declined to find any ‘universal rule of conduct’ or uniform obligation in this formulation.⁴³ Due regard has been carried through in the text of the new Implementing Agreement under UNCLOS on the Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction (BBNJ Agreement).⁴⁴

Due regard is found also in a range of further international legal contexts, including space law, where due regard for the interests of future generations is expressly referenced in the text of the Agreement Governing the Activities of States on the Moon and Other Celestial Bodies (Moon Treaty),⁴⁵ according to which ‘[d]ue regard shall be paid to the interests of present and future generations’.⁴⁶ Due regard also featured in the ICJ's reasoning in Whaling in the Antarctic (Australia v. Japan: New Zealand intervening).⁴⁷ Like the Moon Treaty, the International Convention for the Regulation of Whaling (ICRW)⁴⁸ explicitly identifies future generations’ interests. As referenced in the Court's judgment, the first preambular paragraph to the ICRW refers to ‘[r]ecognizing the interest of the nations of the world in safeguarding for future generations the great natural resources represented by the whale stocks’.⁴⁹ The Whaling in the Antarctic judgment turned on the Court's identification of the requirement for a reasonable relationship between the design and implementation of a scientific whaling programme and its objectives.⁵⁰ In determining whether such a relationship existed, the Court held, inter alia, that a permitting state had a duty to cooperate with the International Whaling Commission (IWC) and its Scientific Committee and to give due regard to its recommendations calling for assessment of the feasibility of non-lethal scientific research methods.⁵¹ Although the interests of future generations were not central to the case, in this respect it is as though the IWC acted as a conduit for the interests both of the parties to the Convention and of future generations.

The notion of due regard serves a variety of functions in the cases canvassed above. As a legal standard, it frequently provides international courts and tribunals with a steady but flexible reference point in situations where the applicable international legal rules are relatively broad and unspecific, helping to enable the law's consistent application across diverse situations.⁵² Due regard facilitates the concurrent existence of legal rights and interests that are in tension with one another. The cases appear to be informed both by the principle of good faith, as mentioned above, and the abuse of rights doctrine that traditionally applies in certain situations where concurrently existing legal rights and interests are to be reconciled. The abuse of rights doctrine has long been considered as a means by which adjudicators may convert absolute rights into less absolute or ‘relative’ rights in the light of others’ interests.⁵³ However, the terminology of ‘abuse of rights’ may be unpalatable because of the connotations of the term ‘abuse’.⁵⁴ The due regard rubric is a potentially more positive and constructive avenue, perhaps employed together with the notion of the good faith exercise of sovereignty.

3.2. Relationship of Due Regard with the Rules of Customary International Environmental Law

As an emerging global regulatory standard appearing across diverse fields of international law, including those considered in Section 3.1, due regard is a concept of broad application. In terms of the role it is playing in the evolution of international law, the concept may be helping to operationalize good faith and avoidance of the abuse of rights as general principles of law. By pointing to practical means by which states can conduct themselves consistently with these principles, the concept of due regard may help in fitting international law for a new era of global physical and intertemporal interdependence. As seen in Section 3.1, the concept has a good pedigree, and accordingly offers a doctrinal legal tool of potentially considerable significance for the development of international law. Further, the concept of due regard has a deep theoretical appeal, resonating with contemporary ‘other-regarding’ theories of sovereignty.⁵⁵

The applicability of the concept of due regard is not limited to situations calling for action to prevent harm, and it may apply in many contexts where a sovereign must act with respect for the interests of others in terms of reconciling these with its own. This can be seen in how the concept has featured in the various settings of water law, oceans law, and international trade policy decision making, as well as legal and policy decisions affecting international investment. One wonders about other types of situation too, for instance, whether due regard could be required if a state unexpectedly were to have to make a decision affecting populations other than its own in a remote location or under severe time pressure, making consultation impossible. Examples could include situations potentially arising at the human-artificial intelligence interface, in space or in various places cut off from communication. Further, the concept of due regard may apply not only in relation to the conduct of sovereigns, but also other entities exercising public authority, including intergovernmental organizations. It may be that international regulatory bodies are expected to give due consideration to the proposals and interests of member states. For example, the Review Panel established under Article 17 and Annex II of the Convention on the Conservation and Management of High Seas Fishery Resources in the South Pacific Ocean (SPRFMO) in 2018⁵⁶ recommended deliberative and specific discussion of the interests of certain states, in this instance developing states.⁵⁷

Accordingly, due regard contrasts with the concept of due diligence, itself also an emerging global regulatory standard.⁵⁸ Due regard requires states actively to consider the effects of their decisions and conduct on others, and to act in ways that take these into account. Due diligence is a standard that requires states to make their best possible efforts under obligations to prevent harm from activities within their jurisdiction or control. For instance, the due diligence standard attaches to the customary international environmental law obligation to prevent harm to the environment of other states and areas beyond national jurisdiction recognized by the ICJ in the 1996 Nuclear Weapons advisory opinion.⁵⁹ The standard of due diligence has a link of its own back to the no harm rule. The customary international law obligation to prevent harm to the environment evolved out of the broader sic utere tuo principle and the no harm rule.⁶⁰ The ICJ has observed that the customary international law obligation for states to prevent environmental harm from activities under their jurisdiction or control ‘has its origins’ in the due diligence that is owed by every state in respect of the rights and interests of others.⁶¹ The due diligence standard is also commonly applied in respect of other preventive obligations in international environmental law, the law of the sea, and beyond.⁶²

Due regard and due diligence may come to bear on a situation simultaneously, and also in combination with other global regulatory standards. Although they may overlap, requirements for due regard will not replace due diligence. However, the due regard and due diligence standards may be mutually informing. Analytical procedures required by either may be useful for determining compliance with the other. Equally, compliance with the freestanding customary international environmental law obligations of notification, consultation, and environmental impact assessment, as well as obligations of cooperation where they may apply, could go a considerable way in helping a state to fulfil requirements to have due regard for the interests of others.

Taking into account all these points, due regard can be understood as more than the ‘temporal’ dimension of due diligence.⁶³ In addition, it bears considering that, while due diligence obligations are often understood as obligations of conduct, the due regard standard may involve an obligation of result. That is to say, more than best efforts to afford due regard might be required. A state or other entity subject to a due regard obligation will potentially have to be able to show that it has engaged in appropriate analytical processes and that it has reached decisional outcomes consistent with practical respect for the interests of others, not only that it has exerted itself to these ends.

3.3. What Due Regard May Require under the Sic Utere Tuo Principle and the No Harm Obligation

There has been little adjudicatory elaboration of what due regard may require procedurally or substantively, apart from in the Chagos Marine Protected Area arbitration in the law of the sea setting.⁶⁴ Procedurally, due regard calls for respect for the interests of others in the form of appropriate analysis and evaluation of a situation, with suitable representation for those interests in decision making depending on the context. Substantively, the term ‘regard’ implies also a respect for the interests at stake that takes practical form, that is grounded in their meaningful consideration, weights these interests accordingly, and adopts policies and pathways forward to reflect this.⁶⁵ Regard that is ‘due’ will correlate with these factors. In the context of the sic utere tuo principle and the no harm obligation, and perhaps beyond, it may also be possible that there is a minimum substantive dimension to due regard. The no harm obligation is understood in international law as a corollary of sovereignty, and there are indications that sovereignty in an interdependent world may require the avoidance of manifestly excessive adverse impacts for others.

The view that sovereignty may be less absolute than in previous periods has been on the horizon since at least the mid-20^th century.⁶⁶ This perspective resonates through a number of ICJ decisions, with supporting authority from international arbitral decisions.⁶⁷ The notion that the proper exercise of sovereignty will avoid manifestly excessive adverse effects can be glimpsed, in particular, in decisions of the ICJ. This avoidance of the ‘manifestly excessive adverse effects’ test might be of assistance in helping to identify situations in which a state has failed to have due regard for the interests of future generations and acted inconsistently with the no harm rule and the sic utere tuo principle. While neither this ICJ practice nor international arbitral practice specifically relates to the no harm rule, the practice does provide insight into the current evolution of sovereignty in international law, including where the exercise of sovereignty will affect the interests of others.

International Court of Justice

The ICJ judgment in the dispute over navigational and related rights between Costa Rica and Nicaragua in 2009 concerned the exercise of Nicaragua's sovereignty, which was subject to bilateral treaty commitments in respect of Costa Rica's navigational rights. The Court required that Nicaraguan regulation (i) should not render impossible or substantially impede the exercise of Costa Rica's right of free navigation; (ii) should have a legitimate purpose (such as safety of navigation, crime prevention, public safety, and border control, or environmental protection); (iii) should not be discriminatory; and (iv) should not be unreasonable, which the Court said would mean that its negative impact on the exercise of the right in question must not be manifestly excessive.⁶⁸ It appears that the Court may have considered these characteristics to represent the essence of the territorial sovereign's regulation-making power, as the Court stated explicitly in relation to Nicaragua's obligation to notify the adoption of regulations.⁶⁹

Relatedly, we could mention here the 2015 decision of the UNCLOS Annex VII Tribunal in the Arctic Sunrise Case (Kingdom of the Netherlands v. Russian Federation),⁷⁰ which referred to criteria that it envisaged would govern the appropriateness of the exercise of a coastal state's regulatory powers to protect its sovereign rights. Specifically, the Tribunal referred to reasonableness, necessity, and proportionality, as referenced in the pleadings of the Netherlands, though there was no call to apply these criteria in the circumstances of the case.⁷¹ There remains scope for reservation about the application of the idea of proportionality testing referred to by the Netherlands. As an international legal tool, proportionality intrudes into sovereignty more directly and overtly than due regard.⁷² Proportionality may rather be a concept to be reserved for application, with the consent of the parties and informed agreement of their citizenry, in the context of regional integration, as in the European Union, or in human rights law, as appropriate.⁷³

Moving away from the question of proportionality, one question arising is whether the requirement cast in these cases as the avoidance of unreasonableness applies only when a state is exercising a discretionary power under a treaty. In the 2020 case of Immunities and Criminal Proceedings (Equatorial Guinea v. France),⁷⁴ the ICJ emphasized that it has ‘repeatedly stated that, where a state possesses a discretionary power under a treaty, such a power must be exercised reasonably and in good faith’.⁷⁵ This is consistent with Bin Cheng's work on general principles of law: ‘Where the right confers upon its owner a discretionary power, this must be exercised honestly, sincerely, reasonably, in conformity with the spirit of the law and with due regard to the interests of others’.⁷⁶ Bin Cheng's text is ambiguous as to whether the same principles apply also where a state is exercising its rights under general international law.⁷⁷ There are indications that they may apply. Indeed, we can question whether many of the cases reviewed above really concern discretionary powers under a treaty or rather, more broadly, simply the exercise of the sovereignty naturally enjoyed by states, and in some cases reserved from the scope of a treaty.

If the cases reviewed actually concern the exercise of sovereignty rather than of discretionary powers under treaties, then the Court's dicta on the ways in which the states in question were required to act may apply generally in respect of sovereign conduct, and not only where states exercise discretionary powers under treaties. This seems to be the case in Navigational Rights, as considered above. The same appears to be the position in respect of the Whaling in the Antarctic case. Annex VIII of the IRCW⁷⁸ is worded in such a way as to preserve the sovereign freedom of a state party to engage in permitted scientific whaling. Specifically, Article VIII(1) ICRW is worded as a savings clause:

Notwithstanding anything contained in this Convention any Contracting Government may grant to any of its nationals a special permit authorizing that national to kill, take and treat whales for purposes of scientific research subject to such restrictions as to number and subject to such other conditions as the Contracting Government thinks fit, and the killing, taking, and treating of whales in accordance with the provisions of this Article shall be exempt from the operation of this Convention. Each Contracting Government shall report at once to the Commission all such authorizations which it has granted. Each Contracting Government may at any time revoke any such special permit which it has granted.⁷⁹

The relevant powers in Immunities and Criminal Proceedings similarly appear not so much as discretionary powers under a treaty but powers or freedoms that exist independently of the treaties concerned, flowing from territorial sovereignty and a state's governmental capacity as sovereign. The specific point at issue in the Immunities case was the power of a receiving state to object to a sending state's designation of the premises of its diplomatic mission.⁸⁰ Article 2 of the Vienna Convention on the Law of Treaties (VCLT)⁸¹ provides that the establishment of diplomatic relations between states and of permanent diplomatic missions is to take place by mutual consent. Yet, so far as the receiving state is concerned, it could be argued that this provision merely safeguards the sovereign power that a territorial state has, in any event, over its own territory. Consistent with this, the Court concluded that, provided any objection to the designation of a mission was communicated in a timely manner, and was not arbitrary or discriminatory, a property would not acquire the status of a mission. Thus, Navigational Rights, Whaling, and Immunities are all cases where it would appear that it is sovereign freedom that has been exercised rather than a discretionary power of a state under a treaty. It is true that in the Navigational Rights and Immunities cases, sovereign freedom is being exercised in relation to legal interests protected by a legal right accepted as belonging to another.

In the 2023 case Certain Iranian Assets (Islamic Republic of Iran v. United States of America) ⁸² Iran successfully challenged United States (US) sanctions. This case differs a little from the cases above. Here there was a treaty provision expressly committing the two governments to ‘refrain from applying unreasonable or discriminatory measures that would impair the acquired rights and interests’ of the other party's nationals and companies.⁸³ However, the Certain Iranian Assets case is important for another reason. The parties’ Treaty of Amity involved an express commitment to refrain from unreasonable conduct,⁸⁴ and the ICJ found that ‘a measure is unreasonable if its adverse impact is manifestly excessive in relation to the purpose pursued’,⁸⁵ also requiring this to be a legitimate public purpose.⁸⁶ The relevant US legislation and its application failed this test.⁸⁷ The case is significant in the context of this article's enquiry because it employs the term ‘not manifestly excessive’, which was the phrase used by the ICJ in Navigational Rights to describe limits on a sovereign's regulation-making power. There may be a pattern emerging here in how the Court articulates the unreasonable exercise of sovereignty in matters that may affect the rights and interests of others.

International arbitral decisions

Three arbitral awards also support the idea that the good faith exercise of sovereignty will respect certain limitations in the light of the interests of others. The North Atlantic Coast Fisheries arbitration of 1910 addressed a dispute over the extent of British regulatory authority over fisheries off the coast of Canada and Newfoundland,⁸⁸ in which the parties’ bilateral treaty of 1818 had provided that ‘the inhabitants of the United States shall have forever, in common with the subjects of His Britannic Majesty, the liberty to take fish of every kind’.⁸⁹ The Tribunal was clear that the right to make regulations for these fisheries, without the consent of the US, was inherent in the sovereignty of Great Britain, even though the exercise of this regulatory power was limited by the parties’ bilateral treaty.⁹⁰ The treaty grant of fishing rights by the UK to US fishermen was understood to subject them to the fisheries regulation of Great Britain, Canada, or Newfoundland. This holding was subject to the British good faith obligation to ensure these regulations were reasonable.

The Tribunal considered that regulations would be reasonable if they were appropriate or necessary for the protection and preservation of the fisheries, or desirable or necessary on grounds of public order and morals without unnecessarily interfering with the fishery itself, and in either case equitable and fair as between local and American fishermen.⁹¹ The Tribunal took into account specific concessions in these terms made by Great Britain in the parties’ special agreement and in the presentation of its case.⁹² It is interesting to see, some decades later, echoes of similar thinking in the decision of the UNCLOS Annex VII Tribunal in the South China Sea Arbitration (Republic of the Philippines v. People's Republic of China), holding that respect for the vested traditional or artisanal fishing rights of foreign nationals would not restrict coastal states from reasonable regulation,⁹³ and that regulation might be ‘necessary for conservation and to restrict environmentally harmful practices’.⁹⁴

Further, in the marine context, the arbitral tribunal in the 1986 Dispute concerning Filleting within the Gulf of St Lawrence (‘La Bretagne’) (Canada v. France) held that states with shared interests in resources may find themselves in relations of voisinage, calling for reasonable or due regard for the interests of others.⁹⁵ In this case, the Tribunal was applying a 1972 agreement between France and Canada providing access to the Canadian fishing zone for vessels registered in St Pierre and Miquelon.⁹⁶ Addressing whether Canada could, in the future, adopt and apply regulations to implement a filleting prohibition on these vessels, the Tribunal found that Canadian regulatory powers were subject to a requirement of reasonableness. The Tribunal stated: ‘Like the exercise of any authority, the exercise of a regulatory authority is always subject to the rule of reasonableness invoked by the [ICJ] in the Barcelona Traction case’,⁹⁷ citing the ICJ Barcelona Traction dictum: ‘The Court considers that, in the field of diplomatic protection as in all of the fields of international law, it is necessary that the law be applied reasonably’.⁹⁸ The Tribunal also observed that a principle of reasonableness had been laid down in the 1910 North Atlantic Coast Fisheries case, viewing the formula articulated in that case as a guide to the reasonableness of regulation.⁹⁹

Finally, the 2005 Iron Rhine arbitration is another case where a treaty between the parties was applicable, yet the Tribunal recognized that its pronouncements related to the underlying territorial sovereignty of the Netherlands rather than a discretion conferred by the treaty.¹⁰⁰ The case is significant also because it represented a high watermark of adjudicatory engagement with the substantive reconciliation of rights in a sustainable development context.¹⁰¹ The case concerned Belgium's right of transit across the Netherlands derived from the 1839 Treaty between Belgium and the Netherlands relative to the Separation of their Respective Territories.¹⁰² The Tribunal considered that Belgium's rights were ‘without prejudice to the exclusive rights of sovereignty over the territory which would be crossed by the road or canal in question’, observing also that the Netherlands had ‘forfeited no more sovereignty than that which was necessary for the track to be built and to operate to allow a commercial connection from Belgium to Germany’ across Dutch territory, and retained the power to establish health and safety standards and environmental standards in the case.¹⁰³ It was open to the Netherlands to apply its national law in a non-discriminatory fashion, unless this would amount to a denial of Belgium's transit right or render its exercise unreasonably difficult.¹⁰⁴ The Netherlands was not obliged to consult Belgium when designating a national park or nature reserve, although it might have been desirable on the basis of good neighbourliness to consult with Belgium at the time of designation, had the Netherlands had reason to assume Belgium would propose a reactivation.¹⁰⁵

Taken as a whole, the cases reviewed above appear to demonstrate that sovereignty as an international legal concept in the contemporary world is indeed less absolute than once supposed. The idea that sovereignty must not be exercised unreasonably is becoming more prevalent, and the ICJ is indicating that, in assessing reasonableness, a requirement is that the adverse effects be ‘not manifestly excessive’. The articulation in these cases of in-built constraints on sovereignty aligns with the restriction on the exercise of sovereignty that is expressed in the no harm rule, and also in the doctrine of abuse of rights. ICJ dicta to the effect that states are to avoid manifestly excessive adverse impacts may be relevant in considering whether a state's conduct is consistent with due regard for the interests of both present and future generations. Pursuing a course of conduct that will have manifestly excessive adverse impacts could indicate a failure in due regard.

In summary, Section 3 of this article has identified a basis on which the concept of due regard may help to operationalize the application of the sic utere tuo principle and the obligation of no harm in respect of future generations’ interests. A widely appearing international legal standard, due regard has been employed previously in many settings, including in conjunction with the general principle of good faith. Due regard has an important emerging role within the systemic development of international law in a world of increasing interdependence among states’ populations. It also lends itself well to settings where future populations are dependent in crucial ways on today's decision making, including where sovereign acts and omissions may be injurious to future generations’ interests.

Due regard has a broader and more fundamental role in international law than the due diligence standard attaching to various preventive obligations, and may apply simultaneously with these and other requirements of customary international environmental law. It has both procedural and substantive components, requiring the analysis and evaluation of a situation in the light of others’ interests. It requires outcomes reflecting a meaningful consideration of these interests. There may also be a substantive floor, requiring the exercise of sovereign power to avoid manifestly adverse impacts on the interests of others. With time, it can be expected that the substantive dimensions of due regard will be elucidated in specific concrete contexts, in processes initiated by various actors.

This reasoning potentially has direct relevance for the requests for advisory opinions on climate change presently before the ICJ, ITLOS, and IACtHR. The customary international law no harm obligation is relevant to each of these requests, and it is clear that future generations’ interests demand attention.

4. Requests to the ICJ, ITLOS, and IACtHR for Advisory Opinions on Climate Change

The March 2023 UN General Assembly (UNGA) Request to the ICJ for an Advisory Opinion on Climate Change asks the Court to address the interests of both present and future generations in respect of protection of the climate system and the environment:

Having particular regard to the Charter of the United Nations, the International Covenants on Civil and Political Rights and on Economic, Social and Cultural Rights, the United Nations Framework Convention on Climate Change, the Paris Agreement, the United Nations Convention on the Law of the Sea, the duty of due diligence, the rights recognized in the Universal Declaration of Human Rights, the principle of prevention of significant harm to the environment, and the duty to protect and preserve the marine environment,

1. (1) What are the obligations of States under international law to ensure the protection of the climate system and other parts of the environment from anthropogenic emissions of greenhouse gases for States and for present and future generations;

2. (2) What are the legal consequences under these obligations for States where they, by their acts and omissions, have caused significant harm to the climate system and other parts of the environment, with respect to:

   1. (a) States, including, in particular, small island developing States, which due to their geographical circumstances and level of development, are injured or specially affected by or are particularly vulnerable to the adverse effects of climate change?

   2. (b) Peoples and individuals of the present and future generations affected by the adverse effects of climate change?¹⁰⁶

These references to ‘present and future generations’ are underpinned by the first sentence of Article 3(1) of the UN Framework Convention on Climate Change (UNFCCC):¹⁰⁷

The Parties should protect the climate system for the benefit of present and future generations of humankind, on the basis of equity and in accordance with their common but differentiated responsibilities and respective capabilities.¹⁰⁸

The Paris Agreement¹⁰⁹ also includes a preambular reference to intergenerational equity,¹¹⁰ as well as many references to sustainable development, including framing its core objectives with reference to sustainable development in Article 2(1).¹¹¹ The right to a healthy and sustainable environment is referenced in the Preamble to the UNGA Request for an ICJ Advisory Opinion, as is the 2030 Agenda for Sustainable Development.¹¹² Further, the International Law Commission's 2021 Draft Guidelines on the Protection of the Atmosphere¹¹³ envisage that ‘[t]he atmosphere should be utilized in an equitable and reasonable manner, taking fully into account the interests of present and future generations’.¹¹⁴

There is considerable scope for the ICJ to pronounce on the legal interests of future generations, whether as an aspect of the sic utere tuo principle and the no harm obligation or indeed otherwise, including through the specific customary international law on prevention of harm to the environment and international human rights law.

The terms of the UNGA request to the ICJ reflect the ambit of the Court's jurisdiction.¹¹⁵ The request made to the ITLOS by the Commission of Small Island States on Climate Change is narrower in ambit and origin.¹¹⁶ The questions are confined to the obligations of parties to UNCLOS, with a specific focus on obligations under Part XII UNCLOS in respect of pollution and the marine environment. However, as part of general international law, the no harm obligation and the sic utere tuo principle are relevant here too, as is the specific customary international law on prevention of harm to the environment of other states and areas beyond national jurisdiction. This means that a requirement to have due regard for the interests of future generations is implicitly embraced, and is within the scope of the request to the ITLOS.

The request to the IACtHR by Chile and Colombia¹¹⁷ focuses on human rights, as protected through the Inter-American human rights system in the context of the climate emergency.¹¹⁸ There are six clusters of questions addressing respectively duties of prevention; the right to life; the rights of children, young people and future generations;¹¹⁹ access to justice and consultation; the rights of women, Indigenous peoples and Afro-descendent communities; and common but differentiated obligations and responsibilities. The specific reference in the request to future generations also effectively invites the IACtHR to consider the relevance of the no harm rule and the sic utere tuo principle, as well as the specific customary international law on prevention of environmental harm, as already addressed previously by the IACtHR in the human rights context in its 2017 advisory opinion on environment and human rights.¹²⁰ Due regard for future generations, therefore, also arises within the scope of this request. Also to be borne in mind is the UN Committee on the Rights of the Child (CRC) General Comment No. 26 of 2023: ‘States bear the responsibility for foreseeable environment-related threats arising as a result of their acts or omissions now, the full implications of which may not manifest for years or even decades’.¹²¹

Thus, in each of the advisory opinion requests, there is scope for the relevant court or tribunal to consider expressly how the sic utere tuo principle, the no harm obligation, and the customary international law obligation to prevent harm to the environment of other states and areas beyond national jurisdiction may call for states to have due regard for the interests of future generations in the climate context.

5. Conclusion

Scholars and practitioners recognize that humankind ‘has a responsibility for the future’.¹²² However, more can be done to determine what international law says about putting this responsibility into practice. Requests presently before international courts and tribunals for advisory opinions on climate change provide a valuable opportunity to consider the matter. The legal interests of future generations are clearly recognized in the principle of sustainable development and the theory of intergenerational equity, as well as in the UNFCCC, but this only takes us so far. Seeking to further the debate, this article considers the operationalization of the sic utere tuo ut alienum non laedas principle and the Corfu Channel no harm rule as they may apply in respect of future generations through the emerging global regulatory standard of due regard.

Due regard is already part of international law's conceptual lexicon and there is considerable doctrinal support for reference to this concept. The concept is employed in various contexts where international law must reconcile competing interests, as seen in the law on watercourses, the law of the sea, trade and investment law, and diverse fields including space law.¹²³ The no harm rule and the sic utere tuo principle also imply due regard for the interests of others. Due regard has both procedural and substantive dimensions. These potentially include a floor: the due regard standard may not be met when a state does not refrain from conduct that would have manifestly excessive adverse effects.

Strands of contemporary moral philosophy on climate change emphasize the idea that actively considering the interests of future generations alongside those of our own will help us to give them their due. Mulgan makes the idea of attempting a justification to future persons of our present-day decisions more real. He writes a hypothetical dialogue between contemporary persons and inhabitants of a possible broken future world in which human-induced climate change has rendered life precarious and resources are insufficient to meet everyone's basic needs.¹²⁴ This reveals challenges in justifying ourselves to these future persons. There is, of course, no guarantee that international law can provide yardsticks that would gauge precisely when we might come near to achieving a justification. However, the international legal concept of due regard may hold promise as an international legal standard of conduct prompting engagement with the problems before us in increasingly appropriate ways.