Scientific Uncertainty and Science-Based Precaution

The debate between advocates of the "Precautionary Principle" and those of "science-based regulation" hinges in large part on the standard of proof to be applied to the scientific evidence that a given action poses a danger of serious and irreversible environmental harm. We propose an intermediate approach, which we term "science-based precaution," intended to facilitate adaptive management of environmental issues – that is, learning through experience and experimentation.We propose that evidence justifying precautionary action must be sufficient to create a "reasonable belief" of serious and irreversible environmental danger. In other cases, in which the proponents of an action bear the burden of proof that the actions they propose will not cause environmental harm, we propose that they must make a "clear showing"to that effect. Both of these standards of proof are derived from a scale constructed from the standards of proof used in various branches of US law.The "reasonableness" standard of proof for the application of the Precautionary Principle is more cautious than the record of international efforts to protect the stratospheric ozone layer and to deal with climate change. It is analogous to the standard of proof imposed by US administrative law, and is also consistent with the position of the European Union and the holdings of the WTO Dispute Settlement Body in the beef hormones case. We further propose a Reasonableness Principle: that scientific research and technological innovations promising major benefits not be unreasonably blocked before their full implications are understood.