The precautionary principle holds that, if the effects of a human-induced change would be very large, perhaps catastrophic, those responsible for the change must prove that it will not do harm before proceeding.

This is the reverse of the normal situation, where those who are concerned about the change would have to prove that it will do harm in order to prevent such changes going ahead.

The Precautionary principle reverses the argument of the 'Burden of Proof'. The precautionary principle argues that those responsible for an effect (global warning, climate change, enhanced greenhouse effect) have the obligation to show that what they are doing has causes no harm.