The precautionary principle is often underemphasized in discussions of international environmental law, but this principle is important as it shifts the burden of proof to those “proposing” the harmful activities. This shift represents a fundamental departure from traditional legal approaches that require affected parties to demonstrate harm after it has occurred. Instead, the precautionary principle prioritises foresight and responsibility, requiring states and private actors to justify potentially harmful conduct before irreversible damage is done. It is significant because it promotes preventive action before harm occurs, serving as a valuable risk-management tool against future pandemics and environmental crises. In a global context characterised by scientific complexity and long-term environmental risks, such preventive logic is essential for effective governance.
It is also viewed through a governmentality lens, as a way states manage uncertainty. From this perspective, the precautionary principle operates not only as a legal rule but also as a governance technique through which states regulate future risks and populations. However, critics argue that its reliance on the broad notion of “uncertainty” allows governments to justify far-reaching actions during crises without waiting for clear evidence, raising concerns about overreach. The one clear example would be the measures taken by the Chinese government during Covid. These measures illustrate how precautionary reasoning can be mobilised to legitimise extensive state intervention, thereby blurring the line between legitimate prevention and excessive control. This tension highlights the challenge of ensuring that precaution is applied proportionately rather than opportunistically.
Notwithstanding such critiques, the precautionary principle has gained considerable recognition within international environmental law. The precautionary principle has been “declared a general principle to guide the development of international environmental law.” This characterisation underscores its normative importance and its role in shaping the evolution of environmental governance at the international level. The principle was incorporated into the 1992 Rio Declaration as Principle 15, which states that the “lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation.” This formulation reflects a clear rejection of scientific certainty as a precondition for regulatory action and affirms the need for early intervention in the face of environmental risk.
Its incorporation “is significant as it could be argued to mark the elevation of the principle to the status of a core principle of international environmental law-making.” The Rio Declaration carries substantial persuasive authority due to its widespread acceptance by states. Through such collective endorsement, the precautionary principle has moved closer to being recognised as a standard against which state behavior is assessed.
Judicial engagement has further strengthened the principle’s standing. The ICJ in Pulp Mills recognized the precautionary approach as part of international environmental law. This demonstrates judicial recognition of the principle as a legitimate interpretive and operational tool in assessing state conduct. This acknowledgment confirms that precaution informs the interpretation of existing environmental obligations, particularly in situations involving scientific uncertainty.
State practice also plays a crucial role in reinforcing the precautionary principle. Also, the principle has been relied upon by “both Hungary over the Gabcikovo-Nagymaros project and by New Zealand in its case concerning French underground nuclear tests.” These cases illustrate how states increasingly invoke precaution to justify deviations from treaty obligations or to challenge environmentally risky activities. Such repeated invocation in contentious proceedings demonstrates that states increasingly frame their claims and defences through precaution, thereby contributing to both opinio juris and state practice.
Beyond the global framework, the precautionary principle has been institutionalised at the regional level. Apart from the international horizon, the precautionary principle finds its way into the Treaty on the Functioning of the European Union (TFEU) which states that “Union policy on the environment … shall be based on the precautionary principle”. This explicit incorporation elevates precaution to a foundational element of EU environmental law, ensuring its consistent application across regulatory and judicial processes. In addition to that, the European Commission Communication (2000) establishes that the principle should be considered “in the fields of environmental protection and human, animal and plant health.” This demonstrates the flexibility and breadth of the principle, extending its relevance beyond environmental protection to public health and food safety.
The recent advisory opinion of the International Court of Justice (ICJ) also referred to the precautionary principle as a guiding framework for interpreting and applying the most relevant legal rules. Thus, it could also be argued that the precautionary approach is an integral part of the general obligation of due diligence. By linking precaution to due diligence, international law increasingly requires states to take reasonable preventive measures rather than merely responding to harm after it occurs.
Treaty law further reflects precautionary reasoning. The United Nations Framework Convention on Climate Change (UNFCCC), obliges the party to take “precautionary measures to anticipate, prevent or minimise the causes of climate change and mitigate its adverse effects.” This obligation recognises that climate change presents complex risks that cannot wait for full scientific certainty. The same reasoning could be seen in the Bluefish Tuna case. As is growing international practice, such principles are supposed to be taken into account even when there is no conclusive evidence of a causal relationship between the inputs and the effects. This approach reinforces the preventive orientation of international environmental law.
One problem that really needs to be addressed, and could be the critique of the precautionary principle, is the lack of uniformity and consensus when it comes to its application. The absence of clear thresholds and procedural guidance creates uncertainty and leaves room for inconsistent application across jurisdictions.
In conclusion, while the precautionary principle faces criticism regarding vagueness and potential misuse, its role in international environmental law is both significant and evolving. It embodies a shift toward preventive governance, judicial interpretation, and responsible state conduct in the face of uncertainty. The challenge lies not in rejecting the principle, but in refining its application to ensure consistency, proportionality, and legitimacy.
Sources:
Harold Respicio, ‘Precautionary Principle | International Environmental Law | Public International Law’ (Respicio & Co, 6 October 2024) https://www.respicio.ph/bar/2025/political-law-and-public-international-law/public-international-law/international-environmental-law/precautionary-principle accessed 20 November 2025.
Reza Khabook, ‘Application of the Precautionary Principle in Dealing with Future Pandemic Diseases: The Dilemma of Legality and Legitimacy Under the Rule of Law’ (2024) 20 Utrecht Law Rev 10 https://utrechtlawreview.org/articles/10.36633/ulr.1079 accessed 20 November 2025.
Owen McIntyre and Thomas Mosedale, ‘The Precautionary Principle as a Norm of Customary International Law’ (1997) 9 Journal of Environmental Law 221, 229 <https://www.jstor.org/stable/4424813> accessed 13 November 2025.
Ibid.
Pulp Mills on the River Uruguay (Argentina v. Uruguay), Judgment, I.C.J. Reports 2010 (I), p. 83, para. 164.
Owen McIntyre and Thomas Mosedale, ‘The Precautionary Principle as a Norm of Customary International Law’ (1997) 9 Journal of Environmental Law 221, 231 <https://www.jstor.org/stable/4424813> accessed 13 November 2025.
Consolidated Version of the Treaty on the Functioning of the European Union [2012] OJ C326/47, art 191(2).
European Commission, Communication from the Commission on the Precautionary Principle [2000] COM (2000) 1 final.
Responsibilities and obligations of States with respect to activities in the Area, Advisory Opinion, 1 February 2011, ITLOS Reports 2011, p. 46, para. 131
United Nations Framework Convention on Climate Change (adopted 9 May 1992, entered into force 21 March 1994) (UNFCCC) art 3(3).
Southern Bluefin Tuna Cases (New Zealand v Japan; Australia v Japan) (Provisional Measures) (1999) ITLOS Reports 280.
Convention for the Protection of the Marine Environment of the North-East Atlantic (adopted 22 September 1992, entered into force 25 March 1998) art 2(2) (a).
