Introduction

The principle of prevention, which aims at preventing the occurrence of environmental harm (rather than at remedying it), is a cornerstone of international and European environmental law. Despite being rooted in both systems, the interpretation and application of this principle differ significantly between the international legal order and one of the European Union (EU). While international law (at least in certain sectors) appears to treat the principle as a binding customary obligation, the EU’s interpretation has often relegated it to a policy guideline, limiting its direct enforceability. This post delves into these differences, examining their impact on decision-making processes within the EU and how they shape environmental governance in both international and EU contexts.

The Principle of Prevention in International Law

At the international level, the principle of prevention has evolved from a general environmental objective into a binding legal norm. Following the 1972 Stockholm Conference, which laid the foundation for modern environmental law, the principle progressively emerged as a rule of customary international law. Without entering into detail, States, based on this rule, are therefore required to adopt measures to prevent environmental damage, particularly when such harm could be irreversible or difficult to remedy and is likely to have an impact beyond their borders.

The International Court of Justice (ICJ) has further solidified this principle by emphasising its “prescriptive” nature. In its case-law, the ICJ has ruled that States must not only enact appropriate legislation but also ensure its enforcement through administrative vigilance (see, 2010 Pulp Mills case). The focus is on the due diligence required of States to prevent environmental damage, holding them accountable even in the absence of direct harm if they fail to take necessary preventive actions. In essence, the principle is forward-looking, aiming to mitigate risks before damage occurs, particularly in sensitive contexts such as marine pollution and transboundary harm.

The development of the principle of prevention reflects the international community’s increasing recognition of environmental degradation as a global issue requiring coordinated action. The Rio Declaration on Environment and Development of 1992 reinforced this approach, linking environmental protection to sustainable development. By embedding the principle of prevention in international frameworks, the global legal community has sought to create a proactive approach that anticipates environmental challenges rather than reacting to them after the damage has occurred.

Obligations Under Customary International Law

As a rule of (as least in certain sectors, like marine protection) customary international law, the principle of prevention generally obliges States (and the EU – as a subject of international law, in the frame of its environmental competences) to act with due diligence in preventing environmental damage. This means that they must adopt and enforce measures aimed at preventing the occurrence of harm, such as setting environmental standards and procedures, monitoring activities, and imposing penalties for non-compliance. The principle emphasises anticipatory action, where States must focus on the potential sources of harm rather than waiting for damage to materialise.

One key sector where this principle has been particularly emphasised is the protection of the marine environment. International treaties, such as the United Nations Convention on the Law of the Sea (UNCLOS), have underscored the importance of preventing marine pollution, for instance, from land-based activities. The International Tribunal for the Law of the Sea (ITLOS) has further reinforced this, stressing that States are obliged to prevent harm to the marine environment even if such harm has not yet occurred. The Tribunal’s 2024 Advisory Opinion on Climate Change and International Law reiterated that the Principle of Prevention is a binding customary law that requires proactive measures to mitigate environmental risks.

Moreover, the obligation to exercise due diligence does not only imply the adoption of regulations but also their effective enforcement. States are expected to oversee private and public entities within their jurisdiction, ensuring compliance with preventive environmental measures. For example, they have to monitor industrial activities, ensuring that emissions do not exceed legal limits, and that environmental impact assessments are properly conducted. Failure to do so could escalate to a violation of the primary preventive norm and, therefore, in international liability, even if the environmental damage is caused by private actors, under the jurisdiction of the State.

The Principle of Prevention in the European Union

In the EU, the Principle of Prevention is enshrined in Article 191(2) TFEU, which mandates that EU environmental policy be based on preventive action. However, unlike its international counterpart, which is in any case binding upon it, the EU’s version of the principle has been interpreted more as a policy guideline than a binding legal obligation. The Court of Justice of the European Union (CJEU) has often ruled that Article 191(2) TFEU does not impose enforceable obligations on EU institutions (above all, C-534/13, but also C-6/99). Instead, it serves as a framework for guiding environmental policy, limiting the scope of judicial review and the consequent enforcement. One could argue that it constitutes a bridge between the international obligation and the enactment of secondary EU legislation, acting as a “booster” to stimulate the adoption of preventive measures (already required under international law) through binding legal instruments.

This distinction between the international and EU approaches, in any event, creates a notable gap in the application of the principle. While international law provides a robust legal basis for prevention (binding for all States, including the EU), the EU’s reliance on the principle as a policy orientation means that it lacks the same legal force. Consequently, this limits the possibility to challenge, at EU level, actions that may fail to prioritise preventive measures, unless there is a manifest breach of proportionality or a “manifest error” in policymaking.

The EU’s legislative process reflects this challenge. Environmental protection is often a balancing act between economic development and ecological preservation. As a result, EU institutions may sometimes prioritise economic concerns, leading to weaker preventive measures. This flexibility can result in delays or inaction, particularly in sectors where environmental degradation is gradual and cumulative, such as air and water pollution.

Policy Implementation and Challenges

Despite these limitations, the principle of prevention has influenced the development of EU environmental policies, particularly in the context of preventive mechanisms such as emission standards and environmental impact assessments. EU secondary legislation often reflects and implements the principle, requiring Member States to implement (as required internationally) preventive procedures and measures such as emission limits, monitoring systems, and environmental standards for specific pollutants. This has led to the adoption of measures aimed at curbing pollution, preserving biodiversity, and preventing industrial accidents.

However, the enforceability of these measures is often contingent upon their codification in secondary legislation rather than being directly rooted in Article 191(2) TFEU. This creates a paradox: while the EU has traditionally been a strong proponent of environmental protection, its legal framework (rectius, its interpretation) does not solidly guarantee the enforceability of the “EU version” of the principle of prevention, relying instead on the discretionary powers of EU institutions in the relevant environmental policy initiatives. The limited scope for judicial review further complicates matters, as breaches of the principle of prevention at the EU level are difficult to challenge in court unless they constitute a clear violation of EU law.

A recent example is the EU’s Green Deal, which introduced ambitious environmental targets, including a “zero pollution ambition”. While the Green Deal reflects the preventive mindset, its success depends on how these ambitions are translated into binding legislation. The “do no harm” principle embedded in the Green Deal emphasises preventive action, but its practical impact will largely rely on how stringently it is implemented through secondary legislation, whose ambition – at least presently – seems to be consistently watered down or undermined.

The Future of the Principle of Prevention in the EU

As environmental challenges continue to evolve, particularly in the face of climate change and biodiversity loss, there is a growing need for the EU to strengthen its commitment to the Principle of Prevention. Scholars and environmental advocates have called for a recalibration of the EU’s approach, urging a more literal interpretation of Article 191(2) TFEU that would enhance the principle’s enforceability and ensure that preventive action becomes legally binding.

One potential solution lies in aligning the EU’s interpretation of the principle with its international counterpart, treating it not only as a policy objective but as a binding legal obligation (to which the EU is in any case subject, as an actor in the international legal order). This would require a shift in the CJEU’s approach, recognising the enforceability of Article 191(2) TFEU and integrating it more closely with international environmental norms. Doing so would enhance the EU’s environmental governance and promote greater consistency in the application of preventive measures across Member States.

Conclusion

The principle of prevention plays a vital role in both international and EU environmental law, but its legal force differs significantly between the two systems. Internationally, the principle is treated as a binding obligation, requiring States (and the EU) to adopt preventive measures to avoid environmental harm. In the EU, however, the principle functions more as a policy guideline, limiting its direct enforceability and often leaving preventive measures to the discretion of EU institutions.

To address these challenges, the EU must reconsider its approach to the principle of prevention, enhancing its legal force and ensuring that it becomes a central pillar of environmental decision-making. By aligning its interpretation with international obligations and strengthening its application in EU law, the principle of prevention can become a more effective tool for addressing the environmental crises of the 21^st century.

Posted by Francesco Maletto, Ph.D

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Bio:

Francesco Maletto was born in Italy in 1992. After graduating summa cum laude in law from the Catholic University of the Sacred Heart of Milan, he started to collaborate (from 2016 to 2021) with the environmental law department of a leading Italian law firm, qualifying as a lawyer in 2019. In 2021, he joined ClientEarth, an environmental law charity of global relevance, where he specialises on marine conservation issues, bringing strategic legal actions to increase the protection of marine biodiversity. In 2024, he obtained a Ph.D. from Maastricht University, discussing a thesis titled “Enhancing Marine Protection: The Role of Prevention in Addressing Pollution from Land-Based Sources Starting from the European Regional Experience”. He is also a teaching assistant at the Catholic University of the Sacred Heart of Milan and a member of the World Commission of Environmental Law of the International Union for the Conservation of Nature. The author works as lawyer at the environmental law charity ClientEarth. However, the present article  reflects the personal opinions of the author in his academic capacity, and does not bind ClientEarth in any way.