Can there be science-based precaution?

'Science-based precaution' is possible in logic if not in politics, and should be a normal part of risk management. It should balance the risks and benefits of innovation, or equivalently, specify the price one is willing to pay to avoid risk. The Precaution Principle states that the absence of scientific proof does not preclude precautionary action—or, in its stronger version, that it requires such action. This principle is a useful counterweight to the insistence on rigorous scientific proof, but focuses on costs and risks to the exclusion of benefits. It expresses 'look before you leap', but not 'nothing ventured, nothing gained'. To facilitate adaptive management, we propose a complementary principle: 'precautionary action should not unreasonably interfere with innovation that promises major benefits, until its dangers and benefits are well understood'. In international trade law, we propose that scientific evidence presented in support of discriminatory measures that would otherwise violate the world trade regime—such as the de facto European Union moratorium on importing genetically modified crops—be required to suffice to support a 'reasonable belief' of danger to human health or the environment.