Appeal against Strike-out in New Zealand’s Climate Change and Human Rights Case Smith v Attorney-General: Part Two

This analysis from the Supreme Court hearing of the appeal against strike-out in Smith v Attorney-General is in two parts. Part One addresses the matter at the heart of the case: Mike Smith’s assertion of the inadequacy of the state’s response to climate change, with the main focus on mitigating climate change through greenhouse gas emissions reduction. Part Two explores how international law can be expected to play into the interpretation of the rights to life and culture that Mike Smith has invoked under the New Zealand Bill of Rights Act 1990, adding breadth to the pleadings. 

International law dimensions of Mike Smith’s human rights claims that were not all fully probed in the oral proceedings reinforce the appropriateness of allowing the case to proceed through the New Zealand court system and are traversed below.

As the Supreme Court judges evidenced in the hearing, they are well aware that public international law may colour the rights to life and culture protected under s8 and s20 of the New Zealand Bill of Rights Act. However, the full extent of international law’s operation here was not completely revealed in the courtroom exchanges. In international law it is increasingly clear that human rights under the threat of climate change are to be read together with international law relating to the protection of the climate system. This means that there is a significant package of public international law relevant to interpreting s8 and s20, including not only the International Covenant on Civil and Political Rights and wider international human rights law but also customary international law on the protection of the climate system and the international climate treaties, as well as other relevant treaties that were not addressed.

In turning its mind to these matters the Supreme Court is in good company. In 2025 the International Court of Justice (ICJ) responded to the United Nations General Assembly’s 2023 request for an Advisory Opinion on the Responsibilities of States in relation to Climate Change with a highly authoritative, concise and readable advisory opinion. The advisory opinion thoroughly and carefully clarifies States’ international climate obligations as well as their legal relevance to human rights. 

The ICJ made clear that human rights including the right to life, the right to health, the right to an adequate standard of living and the right to privacy, family and home are imperilled by a failure to mitigate climate change. The ICJ also observed that the rights of women and children and the rights of indigenous peoples may be impaired, including in the context of severe weather events. These human rights are to be understood in the light of customary international law and the treaties on climate change. The ICJ was explicit that “international human rights law, the climate change treaties and other relevant environmental treaties, as well as the relevant obligations under customary international law, inform each other” and that “States must therefore take their obligations … under the climate change treaties and other relevant environmental treaties and under customary international law into account when implementing their human rights obligations”. The ICJ read international law harmoniously, as counsel for Smith observed.

Turning first to customary international law, the ICJ articulated two customary international law duties binding on States: first, States’ duty to prevent significant harm to the climate system; and, second, States’ duty to cooperate with one another for this purpose. New Zealand may be only one State on the world stage but the ICJ was clear that activity that is insignificant in isolation can give rise to the duty to prevent, even though it is the sum of all activities that contribute to anthropogenic greenhouse gas emissions over time which produces the risk to the climate system. States are obliged to avert and mitigate this risk through coordinated and cooperative action. Customary international law obligations apply to all States, including non-parties to climate treaties. 

As to the three climate treaties (i) the United Nations Framework Convention on Climate Change; (ii) the Kyoto Protocol and (iii) the Paris Agreement, the ICJ read these treaties consistently with customary international law. The Paris Agreement scheme for the mitigation of climate change relies on States’ Nationally Determined Contributions (NDCs). In the Paris Agreement scheme, a State’s successive NDCs will be informed by global stocktakes, will represent a “progression” beyond a party’s current NDC and will reflect its “highest possible ambition”. As used in the Paris Agreement these terms are prescriptive. An NDC must also be capable of making an adequate contribution to the achievement of the Paris Agreement’s 1.5°C primary temperature goal. Further, States’ NDCs, when taken together, must be capable of achieving the temperature goal. There is no explicit obligation in the Paris Agreement for States to achieve their NDCs, although there is a good faith obligation that parties will aim and intend to do so. However, as well as setting NDCs, States have a clear obligation to pursue domestic measures with the aim of achieving their objectives. This requires States to be proactive and pursue measures that are reasonably capable of achieving their NDCs, as a matter of regulatory coherence.

All of the human rights obligations, climate change treaties and relevant customary international law are then also mutually informed by States’ relevant obligations under the international environmental treaties that the ICJ additionally discussed in the advisory opinion. These treaties include the Convention on Biological Diversity 1992, the United Nations Convention to Combat Desertification 1994, the Vienna Convention for the Protection of the Ozone Layer 1985, the Montreal Protocol on Substances that Deplete the Ozone Layer 1997, and the United Nations Convention on the Law of the Sea 1982. The ICJ’s advisory opinion was issued subsequent to the International Tribunal for the Law of the Sea (ITLOS) advisory opinion of 2024 in response to the Request submitted by the Commission of Small Island States on Climate Change and International Law, and the ICJ endorsed ITLOS’ findings.  

Ultimately, all this means that the interpretation of s8 and s20 of the Bill of Rights is powerfully informed by a large body of international law. Among the chief features of customary international law and the Paris Agreement obligations to mitigate climate change is “due diligence”. Due diligence is employed as a standard of behaviour inherent in certain international legal obligations obliging States to prevent harm to other States. International law’s embrace of due diligence appears to have come about in recent decades mainly for the logical reason that States may not be able literally to ensure certain outcomes. Setting out the contours of due diligence in some detail, the ICJ confirmed that due diligence requires States to “employ all means reasonably available to them, so as to prevent [harm] so far as possible”. In respect of climate change the ICJ and the ITLOS agree that the standard is “stringent” due diligence, because of the seriousness of the situation. The Inter American Court of Human Rights has equally referred in its recent Advisory Opinion on the Climate Emergency and Human Rights to “enhanced” due diligence.

It is clear that New Zealand, together with all States, is under a duty of stringent due diligence to mitigate climate change. It is also clear that New Zealand’s international obligations flow through into how the rights at issue in this case under the New Zealand Bill of Rights Act are to be understood. This is simply the consequence of applying the established principle of statutory interpretation consistent with relevant international legal obligations. For instance, it may be that the requirements of stringent due diligence taken as a whole inform an appreciation of the action required for the protection of human rights and strengthen a case seeking more active rights protection. Obligations for the protection of the oceans and biodiversity under relevant environmental treaties and under customary international law will also inform human rights obligations, including cultural rights.

Before closing, it may be added that the ICJ also recognised the need to exercise due regard for the interests of future generations as incumbent on all States as a matter of intergenerational equity. Yet conduct that is infringing and will continue increasingly to infringe on the enjoyment of relevant rights is taking place in real time now around the world. Even if greater harm than is presently being experienced lies in the future, relevant inadequacies in States’ regulation of greenhouse gas emissions are having their effects at this very moment. Through this inadequacy, States are failing on a daily basis to prevent the accumulation of atmospheric greenhouse gas emissions that will retain their destructive force for the long term.

The Supreme Court’s decision on Mike Smith’s appeal against strike-out has been reserved. In light of these matters, and with domestic courts around the world addressing the climate imperative, it would be unexpected if the New Zealand court system were not able to do likewise. Taking all the possibilities into account, there appears to be a basis on which the Supreme Court could potentially overturn the Court of Appeal’s decision to strike out the proceedings. 

Whatever the decision, the reasoning in the Supreme Court's decision on strike out in Mike Smith’s case will be a valuable contribution to inform New Zealanders’ exercise of their democratic rights and political participation. A well-crafted decision could be particularly important for shaping the terms of debate if legislative amendments were proposed to override judicial consideration of climate-related rights issues going forward, although this is hard to imagine.