PRECAUTIONARY PRINCIPLE
Rosa M. Fernández Egea
1. Notion and importance
The precautionary principle applies when no conclusive scientific evidence of the presence of a threat to the environment (or to the health or life of people, animals or plants) is available, but indicators suggest the possibility of serious and irreversible environmental damage. In such cases, the precautionary principle would require action to be taken to avoid possible damage with the greatest possible diligence.
Although there is no authoritative and all-encompassing definition of this principle (Wiener, 2018, p. 175), the most used is the one that appears in Principle 15 of the Rio Declaration(1992) which defines it as follows: “In order to protect the environment, the precautionary approach shall be widely applied by States according to their capabilities. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation.”
The precautionary principle should be distinguished from the prevention principle, though not always easily done (Wiener, 2018, p. 178). The precautionary principle operates before actions or omissions that may lead to certain and undeniable damage to the environment and that must be prevented (Juste Ruiz, 2003, p. 373). At the international level, it is embodied in the obligation not to cause transboundary harm (no harm rule), the customary nature of which has been recognized by the International Court of Justice (Case concerning the Gabčíkovo-Nagymaros project -Hungary/Slovakia- of 1997). For its part, the precautionary principle is a criterion for prudent management of potential environmental risks. In this sense, the precautionary principle operates in decision-making processes in the absence of scientific evidence regarding potential threats of environmental damage or uncertainty regarding their scope. The requirement for action that anticipates likely risks (e.g., banning the use of a given product or substance whose effects are still unclear) implies a high level of protection. Setting the standard for protection at a given level will depend on each society’s tolerance regarding specific risks (“degrees of precaution”).
In this sense, it is necessary to distinguish the determination or verification of environmental risk (risk assessment), which has a fundamentally scientific basis and is materialized in environmental impact assessments, from risk management, where a balance of interests usually occurs. Depending on whether the risk is more or less feasible, the prevention principle or the precautionary principle will be used to justify the actions or omissions of the public authorities. Their margin of manoeuvre and discretionary powers, however, is sharply reduced when applying the prevention principle in the event of true risks.
2. Origin and implementation in international law
The precautionary principle, also known as the principle of caution, originated in German Law as Vorsorgeprinzip in the early 1970s, but reached international relevance in the second half of the 1980s (Baumüller, 2003, p. 25).
The 1985 Vienna Convention for the protection of the ozone layer was the first international agreement to adopt a precautionary approach to a serious environmental problem, such as the depletion of the ozone layer, by introducing this principle to its preamble (it is also present in the Montreal Protocol of 1987, that applies the Convention).
Its use and popularity grew in the 1990s and crystallised in Principle 15 of the Rio Declaration (see above). Since then, the precautionary principle has been included in many multilateral environmental agreements, including the 1992 United Nations Framework Convention on Climate Change, the 1992 Convention on Biological Diversity or the 2000 Cartagena Protocol on Biosafety.
3. Procedural scope of the precautionary principle
One of the main virtues of this principle is that those who wish to carry out an activity that may involve risks to the environment are obliged to prove that such risks are very unlikely and that the possible damage is not serious or irreversible (Doreste, 2017). In other words, there is a reversal of the burden of proof in favour of conservationist measures and policies.
However, the greatest practical potential of the precautionary principle lies precisely in the fact that it provides a basis for courts to grant interim measures. This is especially important to stop activities (whether mining concessions, massive logging or works and infrastructure) which, if undertaken, would entail serious environmental damage.
4. Its legal nature: principle or approach?
The legal nature of the precautionary principle is unclear at the international level (Advisory Opinion of the Inter-American Court of Human Rights on the Environment and Human Rights of 2017, OC-23/17, paras. 175-180). In fact, Principle 15 of the Rio Declaration includes the expression “precautionary approach” with the clear intention of removing its normative character and considering it as a merely interpretative canon.
The International Court of Justice initially denied its general customary rule nature (Gabčíkovo-Nagymaros project case – Hungary v. Slovakia – 1997), although it had admitted that this is an approach that may be required when contemplated in a treaty being implemented (Pulp Mills on the River Uruguay case -Argentina v. Uruguay- 2010, para. 164). In its most recent jurisprudence, it continues to refer to it as a “approach or principle”, but considers it as an essential content of the obligation to act with due diligence to guide States in complying with the customary duty to prevent significant damage to the environment (Advisory Opinion on States’ obligations on climate change of 2025, Pars. 293 and 294).
In European Union Law, by contrast, its binding legal nature is clear and explicitly enshrined in article 191 of the Treaty on the Functioning of the European Union (TFUE), as the “precautionary principle and preventive action”.
Although it was first introduced into the Treaty establishing the European Community (Art. 130r), after its revision by the Maastricht Treaty of 1992, the truth is that it was not defined. It was not until the European Commission’s Communication on the use of the precautionary principle of 2000 (COM/2000/0001 final), which is not limited exclusively to the environmental field, but can also be extrapolated to the areas of protection of human, animal and plant health, that it became possible to verify its virtuality. The Communication established certain guidelines for its applicability within Community Law, such as:
- The measure must be proportional to the level of protection chosen, with the option of ‘zero risk’ being discarded.
- The principle cannot be applied in a discriminatory manner.
- The potential benefits and costs of action or omission should be weighed.
- Its application should be provisional and reviewable in the light of new scientific evidence.
The precautionary principle has also been examined in EU case-law. By way of example, the General Court (formerly the Court of First Instance) has held that, in order to apply the precautionary principle, conclusive scientific evidence of the existence of a risk to the protection of health and the environment is not necessary (STPI de 11.9.2002, as. Alpharma [T-70/99], paras. 131 et seq.). However, the Court itself has considered that precautionary measures may not be adopted on the grounds of merely hypothetical risks (Judgement dated 11.9.2002, as. Pfizer v. Com [T-13/99], para. 144).
5. The precautionary principle and climate change
The precautionary principle is particularly important in the field of climate change, since it is not possible to know with certainty what specific effects of climate change are, when they will occur and to what extent, as well as the exact link between greenhouse gas emissions and the greenhouse effect phenomenon. For this reason, it is no surprising that that it is expressly mentioned and defined in Article 3.3 of the 1992 United Nations Framework Convention on Climate Change (UNFCCC): “The Parties should take precautionary measures to anticipate, prevent or minimize the causes of climate change and mitigate its adverse effects. Where there are threats of serious or irreversible damage, lack of full scientific certainty should not be used as a reason for postponing such measures, taking into account that policies and measures to deal with climate change should be cost-effective so as to ensure global benefits at the lowest possible cost.”
However, the truth is that, in the latest reports of the Intergovernmental Panel on Climate Change (IPCC), there is an increasing scientific certainty about the anthropic origin of climate change, as well as the serious risks that this phenomenon will have on the planet. Therefore, it is increasingly common to argue that it is more appropriate to consider the principle of prevention and not so much that of precaution when implementing climate policies.
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Table of Authorities
I. International Instruments and Treaties
Consolidated Version of the Treaty on the Functioning of the European Union (TFEU), Dec. 13, 2007, 2012 O.J. (C 326).
Declaration of the United Nations Conference on the Environment and Development (Rio Declaration), June 14, 1992, UN Doc. A/CONF.151/26 (vol. I).
Treaty Establishing the European Community (EC Treaty), Mar. 25, 1957.
Treaty on European Union (Maastricht Treaty), Feb. 7, 1992, 1992 O.J. (C 191).
United Nations Framework Convention on Climate Change (UNFCCC), May 9, 1992, 1771 U.N.T.S. 107.
Vienna Convention for the Protection of the Ozone Layer, Mar. 22, 1985, 1513 U.N.T.S. 293.
II. Jurisprudence and Advisory Opinions
Court of First Instance (EU): Alpharma v. Council of the European Union, Case T-70/99 [2002] ECR II-3495.
Court of First Instance (EU): Pfizer Animal Health SA v. Council of the European Union, Case T-13/99 [2002] ECR II-3305.
Inter-American Court of Human Rights (IACtHR): The Environment and Human Rights, Advisory Opinion OC-23/17, Nov. 15, 2017, Series A No. 23.
International Court of Justice (ICJ): Gabčíkovo-Nagymaros Project (Hungary v. Slovakia), Judgment, [1997] I.C.J. Rep. 7.
International Court of Justice (ICJ): Obligations of States in respect of Climate Change, Advisory Opinion, [2025] (Reference to paras. 293-294).
International Court of Justice (ICJ): Pulp Mills on the River Uruguay (Argentina v. Uruguay), Judgment, [2010] I.C.J. Rep. 14.
III. Other Official Documents
European Commission. (2000). Communication from the Commission on the precautionary principle.