What Does the International Court of Justice’s Climate Ruling Mean for SRM?

The Advisory Opinion should increase pressure on major polluters to accelerate mitigation efforts. While it doesn’t mention SRM specifically, the Court’s clarification of how customary international law governs climate harm would apply to the risks posed by SRM: the duty to prevent significant climate harm requires states to act with due diligence. This means using “all the means at [their] disposal” to regulate the conduct of public and private operators, including introducing and enforcing national laws for assessing and minimising risk. Within their respective capability, states should obtain the scientific information necessary to assess the probability and seriousness of risks posed by SRM, through robust, effective environmental impact assessment laws. This requirement arguably supports the case for better understanding of SRM risks and benefits, through responsible research.

More broadly, the Opinion establishes a stronger platform for future international cooperation on SRM governance. A state considering SRM activities involving transboundary impacts must also notify and consult with potentially affected states to determine the measures needed to prevent this risk. This weighs strongly against any kind of unilateral or minilateral¹ SRM deployment.

In my view, the ICJ’s new climate ruling has little if any direct bearing on SRM. Instead, its meaning for SRM lies in demonstrating how disconnected SRM is from international law as it pertains to climate change. Two examples make this clear.

First, in its discussion of the United Nations Framework Convention on Climate Change (UNFCCC) and other climate treaties as the primary source of state obligations under treaty law, the opinion underscores the fundamental way in which this body of law is organized around controlling greenhouse gases (GHGs). SRM, however, would not act on GHGs, rather it would modulate solar radiation by reflecting sunlight. As things currently stand, SRM would seem to have no role to play in meeting the UNFCCC’s “ultimate objective” of achieving “stabilization of [GHG] concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system” (Article 2).

Second, in its consideration of obligations deriving from customary international law (such as the duty to prevent significant harm), the opinion highlights the degree to which international environmental law is rooted in the assumption that environmental protection is achieved by minimizing interference in nature. This assumption is perfectly understandable from a historical perspective, but it is hostile toward the kind of protection SRM may offer, i.e., one interference (aerosols) intended to (partially) offset another, more damaging interference (GHG emissions), when the latter is seemingly out of control.

For SRM to be integrated into international law, a significant evolution in both treaty law and state practice will thus be required.

The ICJ’s Advisory Opinion on the obligations of States in respect of climate change is relevant for the interpretation of international law in the context of SRM governance. Even though the Advisory Opinion does not explicitly mention SRM or geoengineering, it sheds important light on the obligations of States under international law regarding climate change more broadly.

The ICJ considers a wide range of legal frameworks, including customary international law, climate change treaties, and human rights law. Not only has the ICJ reinforced that States must do their utmost to ensure their nationally determined contributions represent the highest level of ambition possible, but it has also clearly recognised the link between human rights law and climate protection. Furthermore, it has clarified that the international customary duty to prevent significant transboundary harm applies to climate change, and that the obligation to protect the environment from anthropogenic GHG emissions applies to the international community, whilst recognising the principle of common but differentiated responsibilities.

What this opinion means for SRM governance and research remains unaddressed here, but the Court did make it very clear that States have a responsibility to prevent harm caused by climate change.