Introduction
Climate change represents one of the most significant and complex challenges confronting the international community. Its effects, including rising sea levels, extreme weather events, and biodiversity loss, transcend national borders, demanding a global response. International law, while often criticised for its lack of enforcement, provides a framework of principles to guide state action in addressing such transboundary issues. This essay will examine how two of these foundational principles – good neighbourliness and international cooperation – can be used to address present-day climate change. It will argue that while these principles provide an essential legal and moral basis for action, their general nature and the traditional focus on state sovereignty present significant limitations. Consequently, while they are the necessary starting point, their effective application to the climate crisis depends on their codification and implementation through specific, multilateral treaty regimes.
The Principle of Good Neighbourliness and the 'No-Harm' Rule
The principle of good neighbourliness is a long-standing concept in international relations, which has evolved into a binding legal norm in the environmental context, often referred to as the 'no-harm' rule. This principle dictates that states have a sovereign right to exploit their own resources, but also a responsibility to ensure that activities within their jurisdiction or control do not cause significant damage to the environment of other states or of areas beyond the limits of national jurisdiction. This rule is widely recognised as a principle of customary international law (Sands and Peel, 2012).
The classic articulation of this principle is found in the Trail Smelter Arbitration (United States v Canada). In this case, an arbitral tribunal held Canada responsible for damage caused in the US state of Washington by air pollution from a smelter in British Columbia. The tribunal famously concluded that "no State has the right to use or permit the use of its territory in such a manner as to cause injury by fumes in or to the territory of another" (Trail Smelter Arbitration, 1941, p. 1965). This case established a clear precedent for state responsibility for transboundary environmental harm. The principle was affirmed by the International Court of Justice (ICJ) in the Corfu Channel Case, which held that every state has an "obligation not to allow knowingly its territory to be used for acts contrary to the rights of other States" (Corfu Channel Case, 1949, p. 22).
This customary rule has been codified in key international environmental instruments. Principle 21 of the 1972 Stockholm Declaration on the Human Environment and, more recently, Principle 2 of the 1992 Rio Declaration on Environment and Development, both explicitly state the dual concepts of a state's right to exploit its resources and its corresponding responsibility to prevent transboundary harm.
In the context of climate change, the no-harm rule offers a direct legal basis for holding states accountable. Greenhouse gas (GHG) emissions originating in one state contribute to a global atmospheric concentration that causes harm worldwide. For instance, small island developing states (SIDS) face existential threats from sea-level rise caused by historical and current emissions from industrialised nations. From this perspective, large-emitting states are arguably in breach of their customary international law obligation not to cause significant harm to other states.
However, applying the traditional no-harm rule to climate change presents considerable difficulties. Firstly, the issue of causation is complex. Unlike the direct link between the smelter and the damaged crops in Trail Smelter, climate change is a cumulative problem. The harm is caused by the aggregate of global emissions over many decades, making it almost impossible to attribute a specific harm, like a single flood, to the emissions of a single state (Voigt, 2008). Secondly, the threshold of "significant" harm is difficult to define in a slowly developing, global crisis. Finally, the obligation is one of 'due diligence,' meaning states are obliged to take reasonable and appropriate measures to prevent harm, not to guarantee its absolute prevention. What constitutes 'due diligence' for a developing country reliant on fossil fuels for economic growth compared to a wealthy, post-industrial nation is a source of major political and legal contention.
The Principle of International Cooperation
Recognising the limitations of principles designed for bilateral disputes, international law also contains a duty for states to cooperate in addressing shared problems. The UN Charter itself identifies "solving international problems of an economic, social, cultural, or humanitarian character" as a core purpose of the United Nations (Article 1(3)). This general duty has been specified for environmental matters. Principle 24 of the Stockholm Declaration calls for cooperation on international environmental issues, and Principle 7 of the Rio Declaration states that "States shall cooperate in a spirit of global partnership to conserve, protect and restore the health and integrity of the Earth’s ecosystem."
Crucially, Principle 7 of the Rio Declaration also introduced the concept of "common but differentiated responsibilities and respective capabilities" (CBDR-RC). This acknowledges that while all states share a responsibility to protect the environment, the primary burden should fall on developed countries, which bear greater historical responsibility for causing environmental problems and possess greater financial and technological capacity to address them (Stone, 2004).
For a global issue like climate change, which no single state can solve, the principle of cooperation is indispensable. It forms the bedrock of the entire international climate change regime. The 1992 United Nations Framework Convention on Climate Change (UNFCCC) was created as a forum for this cooperation. Its ultimate objective is the "stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system" (UNFCCC, Art 2). This goal is, by its nature, achievable only through collective action.
The 2015 Paris Agreement is the most prominent modern example of the principle of cooperation in practice. Under the Agreement, states commit to submitting nationally determined contributions (NDCs), which are their individual plans for climate action. The Agreement also establishes mechanisms for financial assistance, technology transfer, and capacity-building to support developing nations, directly reflecting the CBDR-RC principle. This "bottom-up" approach, based on voluntary pledges within a cooperative framework, was seen as the only politically viable way to achieve universal participation.
However, the principle of cooperation also faces limitations rooted in state sovereignty. The general duty to "cooperate" is a vague obligation, and states often prioritise national economic and political interests over collective environmental goals. The effectiveness of the Paris Agreement, for example, depends entirely on the ambition and implementation of the voluntary NDCs submitted by states. There is no international authority to compel a state to increase its ambition or to sanction it for failing to meet its targets. The withdrawal of the United States from the Agreement under the Trump administration, although temporary, demonstrated the fragility of a system reliant on the continued political will of sovereign states.
Conclusion
In conclusion, the principles of good neighbourliness and international cooperation provide the essential legal architecture for addressing climate change. The 'no-harm' rule, derived from good neighbourliness, establishes the fundamental obligation on states to prevent their emissions from causing damage to others, forming a basis for state responsibility. The principle of international cooperation acknowledges that this obligation cannot be fulfilled unilaterally and requires a collective, global effort, as embodied by the UNFCCC and the Paris Agreement.
However, these principles, in their customary and general form, are not sufficient to resolve the climate crisis. The traditional bilateral and causation-focused nature of the 'no-harm' rule is ill-suited to the diffuse, cumulative, and universal nature of climate change. Similarly, the principle of cooperation is frequently undermined by the primacy of state sovereignty and competing national interests, leading to a gap between the stated goals of international agreements and the level of action required. Therefore, while good neighbourliness and cooperation are the necessary starting points that give legal and moral force to climate action, their utility lies in their ability to be translated into more specific, detailed, and binding commitments within multilateral treaties. The ongoing challenge for international law is to strengthen these treaty regimes to ensure that cooperation is not merely procedural but substantive, and that the duty to prevent harm is effectively discharged for the benefit of all humankind.
References
Corfu Channel Case (United Kingdom v Albania) (Merits) [1949] ICJ Rep 4.
Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion [1996] ICJ Rep 226.
Paris Agreement (2015) Dec 1/CP.21.
Rio Declaration on Environment and Development (1992) UN Doc A/CONF.151/26 (vol. I).
Sands, P. and Peel, J. (2012) Principles of International Environmental Law. 3rd edn. Cambridge: Cambridge University Press.
Stone, C.D. (2004) ‘Common but Differentiated Responsibilities in International Law’, The American Journal of International Law, 98(2), pp. 276-301.
Declaration of the United Nations Conference on the Human Environment (Stockholm Declaration) (1972) UN Doc A/CONF.48/14/Rev.1.
Trail Smelter Arbitration (United States v Canada) (1941) 3 RIAA 1905.
United Nations Framework Convention on Climate Change (UNFCCC) (1992) 1771 UNTS 107.
Voigt, C. (2008) ‘State Responsibility for Climate Change Damages’, Nordic Journal of International Law, 77(1-2), pp. 1-22.
