Precautionary Principle vs Prevention Principle: Certainty of Risk, Burden of Proof and Their Application in Indian and International Law

Both principles say 'act before the harm happens'. The difference lies in how much we know. The prevention principle applies where the risk of harm is known and its causes understood: we must take steps to avoid it. The precautionary principle applies where the risk is uncertain: where science cannot yet prove that an activity will cause serious or irreversible harm, we must still act cautiously and must not use that uncertainty as an excuse for delay. In India, the precautionary principle also shifts the burden of proof to the developer. The distinction is a favourite examination question.

1. The Prevention Principle

The prevention principle requires States and persons to prevent environmental harm rather than merely remedy it after it occurs. It rests on the recognition that environmental damage is often irreversible, and that prevention is cheaper than cure. In international law it developed from the rule that a State must not allow its territory to be used to cause significant harm to other States:

• Trail Smelter Arbitration (United States v. Canada), 1938 and 1941: Canada was held responsible for sulphur dioxide fumes from a smelter damaging crops in the United States; no State may use or permit the use of its territory so as to cause injury by fumes to another State;
• Principle 21 of the Stockholm Declaration (1972) and Principle 2 of the Rio Declaration (1992): States have the responsibility to ensure that activities within their jurisdiction or control do not cause damage to the environment of other States or areas beyond national jurisdiction; and
• Pulp Mills on the River Uruguay (Argentina v. Uruguay), ICJ 2010: the prevention principle, as a customary rule, has its origin in the due diligence required of a State, and requires an environmental impact assessment where there is a risk of significant transboundary harm.

Domestically, prevention underlies consent requirements (no discharge without prior consent under the Water and Air Acts), emission and effluent standards, EIA, siting rules and the hazardous substances rules. The risk is known (for example, untreated effluent pollutes rivers), so the law requires known preventive measures.

2. The Precautionary Principle

The precautionary principle addresses scientific uncertainty. It emerged from the German Vorsorgeprinzip in the 1970s, appeared in the Bergen Ministerial Declaration (1990), and is reflected in the UNFCCC (Article 3(3)), the Convention on Biological Diversity (preamble), and the Cartagena Protocol on Biosafety (2000). Its elements are: (i) a threat of serious or irreversible damage; (ii) lack of full scientific certainty about cause or extent; and (iii) the duty to take anticipatory, cost-effective measures despite that uncertainty.

3. The Precautionary Principle in Indian Law

In Vellore Citizens' Welfare Forum v. Union of India, (1996) 5 SCC 647, Justice Kuldip Singh held that the precautionary principle is part of the law of the land, and explained it in three parts: (i) environmental measures by the State must anticipate, prevent and attack the causes of environmental degradation; (ii) where there are threats of serious and irreversible damage, lack of scientific certainty should not be used as a reason for postponing measures; and (iii) the onus of proof is on the actor or the developer or industrialist to show that his action is environmentally benign. Notably, the first element includes prevention within the Indian formulation.

The principle has since been applied in many cases, including Narmada Bachao Andolan (2000), where the Court held that it applies where the extent of damage is unknown, not to a dam whose impacts were known; Research Foundation for Science (2005) on hazardous waste; G. Sundarrajan v. Union of India, (2013) 6 SCC 620 (Kudankulam nuclear plant), where the Court upheld the project with safeguards; and Hanuman Laxman Aroskar (2019). Section 20 of the NGT Act, 2010 makes it a statutory principle for the Tribunal.

4. Key Differences

The two are complementary: prevention deals with the known, precaution with the unknown. Precaution is sometimes described as prevention extended to situations of uncertainty. In Indian law, Vellore folded both into one formulation, but the burden-shifting element is distinctly precautionary.

5. Related Topics and Provisions