4. Climate Change and Other Areas of International Law

International law has expanded substantially in the range of topics it addresses. Obviously, it is the climate regime that is of primary significance to the climate crisis, however other aspects of international law are also relevant, particularly those dealing with related environmental issues. All areas of international law are implicated in some way and can assist in small or larger ways in addressing the problem.^[1]

There is also the potential for some areas of international law to operate as handbrakes on action. For instance, international trade law, which seeks to liberalise global trade, may prevent states from adopting progressive climate policies if it involves unjustifiable trade restrictions. Furthermore, international investment law, which is designed to protect foreign investments in host countries, can come into tension with the rights of states to address climate change in the public interest.^[2] Investor–state dispute settlement under investment treaties can, for instance, enable foreign fossil fuel companies to challenge climate policies.

4.1. Other International Environmental Regimes

4.1.1. Ozone Depletion Regime

An important precursor to the climate regime were several treaties dealing with another atmospheric pollution problem — the depletion of the ozone layer. As ozone-depleting substances are greenhouse gases the ozone regime has also played an important role in mitigating climate change.

Following the discovery in the 1980s of a substantial hole in ozone layer, a region of the stratosphere that protects the Earth from harmful ultraviolet radiation, the international community responded promptly through the adoption of the 1985 Vienna Convention for the Protection of the Ozone Layer and the 1987 Montreal Protocol to phase out the production, trade and use of ozone depleting substances such as chlorofluorocarbons. This response, which has become more stringent over time through amendments to the Montreal Protocol, has had significant success, with global emissions of ozone-depleting substances falling by more than 99 per cent.^[3] The ozone hole is now closing.

The ozone regime has also had very substantial co-benefits for mitigating climate change given that ozone-depleting substances are powerful greenhouse gases. The Kigali Amendments to the Montreal Protocol to limit the use of hydrofluorocarbons are expected to prevent the emissions of up to 105 billion tonnes of carbon dioxide equivalent of greenhouse gases.^[4]

4.1.2. Convention on Biological Diversity

Another example of a regime with clear relevance to the climate crisis is the 1992 CBD. The CBD seeks to conserve biological diversity, and promote the sustainable use of its components, and recognises the close connection between safeguarding nature and addressing climate change. This is seen in the recent Kunming–Montreal Global Biodiversity Framework, adopted at COP15, to the CBD in 2022.^[5] The framework succeeds and replaces the Aichi Targets. It includes four overarching goals and 23 accompanying targets to be achieved by 2030. These include Target 8, which is to ‘[m]inimize the impact of climate change and ocean acidification on biodiversity and increase its resilience through mitigation, adaptation, and disaster risk reduction actions’.

4.2. The Law of the Sea

An area of international law that has had increasing engagement with climate issues is the law of the sea, the main content of which is found in the 1982 United Nations Convention on the Law of the Sea (‘UNCLOS’).^[6]

A key climate issue confronting UNCLOS is what happens to the coastlines of states as sea levels rise. Do the baselines at the low-water mark have to be redrawn? If territory is lost, does it mean that states lose valuable maritime zones? The view expressed by some scholars is that the baselines on the coast from which maritime zones are projected are ‘ambulatory’ — that is, they move inland with rising seas.^[7] However, there has been a substantial body of recent state practice taking a different view.

Several groups of states are seeking to make their position clear on these questions. In 2021 the 18 members of the Pacific Islands Forum (‘PIF’) adopted the Declaration on Preserving Maritime Zones in the face of Climate Change-Related Sea-Level Rise (‘PIF Declaration’).^[8] The PIF Declaration states that UNCLOS does not create an ‘affirmative obligation’ to keep baselines and the limits of maritime zones under review, that maintenance of existing maritime zones notwithstanding climate change and sea level rise accords with the UNCLOS, and that once maritime zones have been established and notified to the UN Secretary-General those zones will be maintained without any review or update of baselines notwithstanding ‘physical changes connected to climate change-related sea-level rise’.^[9] That the PIF includes a diverse group of states ranging from G20 member states to archipelagic states to small-island developing states is significant. The PIF Declaration may come to represent a milestone in how states have clarified their position with respect to baselines, maritime boundaries and sea level rise.

UNCLOS also includes detailed provisions relating to the protection of the marine environment from all sources of pollution, including the atmosphere. In a recent Advisory Opinion, the International Tribunal for the Law of the Sea (‘ITLOS’) found that parties to UNCLOS have the specific obligation under Article 194 of UNCLOS to take all necessary measures to prevent, reduce and control marine pollution from anthropogenic GHG emissions.^[10] Importantly, ITLOS found that this obligation will not be satisfied simply by complying with the obligations and commitments under the Paris Agreement.^[11] This is an important conclusion because, as has been seen, the Paris Agreement is relatively undemanding, setting up a process for making emissions pledges but not prescribing what those emissions reduction commitments should be.

The importance of the ITLOS Advisory Opinion should not be underestimated, for several reasons. This is first and foremost because ITLOS has elaborated in detail what parties to UNCLOS, which include most states, must do to protect the ocean, as the most important component of the climate system. The ocean has absorbed around 30 per cent of the carbon dioxide emitted by human activities, and 90 per cent of the extra warmth added to the climate system by heat-trapping gases.^[12] ITLOS found that governments have a due diligence obligation to take all necessary measures to prevent, reduce and control marine pollution from GHG emissions. These measures are to be determined objectively, taking into account the best available science and the relevant international rules set out in the UNFCCC and the Paris Agreement, including the 1.5 °C temperature goal. ITLOS also observed that this standard of due diligence is stringent, given the high risks of serious and irreversible harm posed to the marine environment from GHG emissions, and that states must adopt and implement national laws to give effect to the due diligence obligation.

4.3. General Principles of International Law

Climate change raises a number of questions for general principles of international law. These include whether states can be held responsible under customary rules of transboundary harm for climate change induced damage to other states, and whether states can continue to exist if their territories are submerged or become uninhabitable.

The state responsibility question has always been challenging for several reasons, including the difficulty in clearly establishing causation given that climate change is a global problem and different from the ‘classic’ case of transboundary harm (such as the celebrated Trail Smelter Case^[13] involving air pollution from a metals smelter in Canada damaging farmland across the border in the United States).

In relation to statehood, under international law there are four key criteria. These are territory, a permanent population, effective government and the capacity to enter into international relations. The first two of these, territory and population, are considered the most vital requirements. The loss of these attributes, certainly if permanent, would appear to deprive an existing state of its status as such.^[14] The International Law Commission, a UN body of international legal experts tasked with codifying and progressively developing the law, is currently examining this issue through a Study Group on Sea Level Rise in International Law.^[15] The co-chairs of the study group have noted that there is a strong presumption of the continuity of statehood, and that this position has been expressed by a range of states including the United States (which in 2023 declared that human-induced sea level rise should not cause any country to lose its statehood or membership of the UN).^[16]

Pacific Island states have also been at the forefront of state practice on this issue. In November 2023, the PIF adopted a Declaration on the Continuity of Statehood and the Protection of Persons in the Face of Climate Change-Related Sea-Level Rise.^[17] In that declaration, PIF members recognised that under international law there is a general presumption that a state, once established, will continue to exist and endure, and maintain its status and effectiveness, and that international law does not contemplate the demise of statehood in the context of climate change related sea level rise.

To address the consequences of climate change for a vulnerable state, two members of the PIF, Australia and Tuvalu, adopted the Falepili Union Treaty, which entered into force in 2024.^[18] Under the treaty, Australia recognises Tuvalu’s continuing statehood and sovereignty, notwithstanding the impact of sea-level rise, has committed to assist Tuvalu in response to a major natural disaster, health pandemic or military aggression, and will create a special visa pathway to support mobility with dignity, which will enable citizens of Tuvalu to come to Australia to live, work and study.

This is clearly a rapidly developing area of international law, and further guidance may be provided by the ICJ in its Advisory Opinion on climate change, which is set to be delivered in 2025. The questions put to ICJ by the UN General Assembly in its 2023 Request for an Advisory Opinion are set out below.^[19] Vanuatu led this process, bringing together a coalition of over 130 states that drafted the request for the ICJ, which was adopted by consensus at the UN General Assembly. This was a major diplomatic achievement by Vanuatu and the other sponsoring states and the culmination of a lengthy process.^[20]

Having particular regard to the Charter of the United Nations, the International Covenant on Civil and Political Rights, the International Covenant 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. 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. 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. 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. Peoples and individuals of the present and future generations affected by the adverse effects of climate change?

The ICJ has been presented with an opportunity to provide definitive guidance on the international law of climate change in its broadest sense. This means addressing not only the obligations contained in the UNFCCC and Paris Agreement but also complementary and potentially more demanding standards contained in other regimes, including international human rights law as enshrined in the 1966 International Covenant on Civil and Political Rights^[21] and related treaties.

The intersection between climate change and human rights was brought to the forefront of global concern with the 2022 Resolution of the UN General Assembly recognising ‘the right to a clean, healthy and sustainable environment as a human right’.^[22] The human rights dimension is also being considered in other forums, such as the United Human Rights Committee, which found in 2022 that Australia’s failure to protect Torres Strait Islanders against the adverse effects of climate change was a violation of their rights to enjoy their culture and to be free from arbitrary interference with their private life, family and home.^[23]

It is also significant that the ICJ has been asked to address the consequences of climate change for particularly vulnerable states. Whereas wealthy states have strongly resisted addressing issues of responsibility and compensation under the UNFCCC and Paris Agreement, these fundamental questions of justice are impossible to ignore. Whether the ICJ will accept the invitation to answer these remains to be seen. However, it is fair to say that the ICJ and other international courts and tribunals are far more comfortable addressing environmental issues than they have previously been, and they have the benefit of an increasingly well-developed body of law to apply in order to do so.^[24]