Environmental law need not remain a silent witness, or even an accomplice, of the unfolding ecological crisis. It can be reclaimed as a transformative tool for reimagining the economy and advancing socio-ecological justice. The international law principle of prevention, visualised as a duty to stay within the planetary boundaries, can advance this shift.
Exposing Environmental Law as the Law of Negative Externalities
With ‘environmental law’, I refer here to the bulk of domestic, international and transnational rules, principles, standards and procedures that address the impact of human activities on the ‘environment’.
This regime is premised upon the analytical distinction between transactions and externalities. On the one hand, we find the complex of norms constituting global capitalism. On the other hand, we have a second ‘layer’ of norms whose main purpose is to mitigate the adverse consequences of these transactions on a separate legal object, the ‘environment’.
These externalities are addressed in practice with a strong emphasis on technical problem-solving and expertise, making environmental law a prominent example of managerialism as a governmental technology. Furthermore, this regime tends to prioritise the adoption of ‘market-based’ solutions to environmental problems, including the expansion of property rights to encompass both ecological ‘goods’ and ‘bads’, such as carbon emissions.
In sum, as scholars such as Julia Dehm and Vito de Lucia have demonstrated, environmental law developed along a double movement, first separating the ‘economy’ from the ‘environment’ and subsequently re-embedding the latter within the logic of economic rationality. As such, this regime is not able to remedy, but, quite the opposite, ends up reproducing the unsustainable exploitation of Planet Earth.
The Evolving Role of Prevention in the Field of Climate Change
Over the past few years, a growing awareness of the shortcomings of environmental law has prompted various attempts to reform it from below. For example, the turn to rights-based litigation in the field of climate change represents an attempt to reappropriate the foundational principles of environmental law beyond managerialism and neoliberalism, to tackle the unsustainable organisation of the economy.
Notably, climate change litigation has catalysed a reinterpretation of the public international law principle of prevention (a customary norm of international law). Today, international courts and tribunals have consistently concluded that the duty to prevent environmental harm implies a duty to mitigate greenhouse gas emissions and reach net zero. This has been recently confirmed by the International Court of Justice (ICJ), the principal judicial organ of the United Nations, in its advisory
The Court explained that each State has its individual standard of diligence, whose specific content can only be tailored on a case-by-case basis, based on the principle of common but differentiated responsibilities and respective capabilities. Nonetheless, it did not shy away from identifying a general standard of conduct under international law. It found that the individual and collective efforts of States must be directed towards limiting global warming to 1.5 °C above pre-industrial levels, as stipulated by the Paris Agreement and in line with the best available science.
Importantly, the ICJ took into account the material fact that no further expansion of the fossil fuel energy system is compatible with the ‘carbon budget’ available to remain within this critical threshold. Therefore, it concluded that
In other words, based on the logic of the principle of prevention, any diligent conduct vis-à-vis the harm caused by greenhouse gas emissions can only include the commitment to transition away from fossil fuels.
Reinterpreting the Principle of Prevention as a Duty to Stay Within the Planetary Boundaries
The above reasoning, developed in the specific context of climate change, can drive a comprehensive shift in the role of environmental law, beyond the mere governance of externalities. Moving away from a conception of the economy as a closed system operating in a vacuum, it is now possible to concretely target unsustainable economic activities, in line with the biophysical reality: the economy is not an abstraction, but an open system operating in the materially closed system of Planet Earth.
The planetary boundaries framework, which identifies nine critical global processes that regulate the stability and resilience of the Earth, represents a powerful metaphor to visualise this shift. Crossing a planetary boundary means, from an international law perspective, reaching the threshold of significant harm to the environment.
Credit: "Azote for Stockholm Resilience Centre, based on analysis in Richardson et al,2023"
Therefore, amid the current compounding and escalating ecological crises, prevention should be conceptualised as a duty to stay within the planetary boundaries. This is not mere wishful thinking or, more technically, a de lege ferenda proposal. It is an attempt to apply existing customary international law to the protection of the global environment.
At the international level, the scheme is simple: any activity – including private activities (see also paras. 252, 282, 428 of the Advisory Opinion) – that risks causing significant harm to the environment (in our case, any activity that puts pressure on one or more planetary boundaries) has to be regulated by the State that has jurisdiction or control over it, according to its required standard of care.
When a State’s conduct falls below that level of diligence and significant harm materialises (that is, the relevant planetary boundary is crossed), the State engages in international responsibility for its actions and omissions (i.e., its contribution to the materialisation of the harm to the planet). In that case, the State will have to cease the wrongful conduct, offer guarantees of non-repetition and make full reparations.
Furthermore, the implications of this rule are also significant from a local perspective. If invoked by affected individuals and communities within domestic legal orders – also in connection with existing constitutional rights with an environmental dimension – the duty to stay within planetary boundaries can ground legal resistance to specific unsustainable economic activities and the complex network of legislative and administrative instruments that secures and legitimises them.
There are good reasons to hope that the evolution of the principle of prevention that we are witnessing will strengthen the voice of those at all levels who seek to hold States and corporations accountable for their actions and inactions that continue to exacerbate the ongoing ecological crisis.
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This blog post is based on the paper to be presented at the SMART Network Symposium, Sustainability is (Still) Possible! Governing Market Actors for a Safe and Just Space, 18-19 September 2025, at the University of Turin
