The precautionary principle was initially applied by the West German national legal system in the 1980s. The precautionary principle aims to supervise in developing and applying international environmental law where there is scientific uncertainty. Even today, it continues to generate disagreement as to its meaning and effect, as reflected in particular in the views of states and international judicial practice. On the one hand, some consider that it provides the basis for early international legal action to address highly threatening environmental issues such as chemical pollution and climate change.
The Precautionary principle has been adopted in numerous environmental treaties however the precise formulation of the Rio Declaration attracts the broadest of support. The roots of such formulation can be found in more traditional agreements that call upon parties to act and adopt decisions based on "scientific findings or methods" or 'in the light of knowledge available at the time'.
The principle states:
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."
One important landmark decision which disseminates over the proportionality principle is the Beef Hormone Case. In 1998 the then European Community invoked the principle to justify its claim that it was entitled to prohibit imports of beef produced in the United States and Canada with artificial hormones, where the impacts on human health were uncertain. The Community argued that the principle was already a general customary rule of international law or at least a general principle of law’, that it applied to both the assessment and the management of risk, and that it informed the meaning and effect of Articles 5.1 and 5.2 of the WTO’s SPS Agreement.
The United States denied that the principle represented a principle of customary international law, and preferred to characterize it as an ‘approach’ the content of which may vary from context to context.
Canada referred to a precautionary approach as ‘an emerging principle of international law, which may in the future crystallize into one of the “general principles of law recognized by civilized nations”, within the meaning of Article 38(1)(c) of the ICJ Statute’.
The WTO Appellate Body agreed with the United States and Canada and said:
" Whether it has been widely accepted by Members as a principle of general or customary international law appears less than clear. We consider, however, that it is unnecessary, and probably imprudent, for the Appellate Body in this appeal to take a position on this important, but abstract, question. We note that the Panel itself did not make any definitive finding concerning the status of the precautionary principle in international law and that the precautionary principle, at least outside the field of international environmental law, still awaits authoritative formulation."
The full link of the 70-page decision in pdf format can be found down below: