Taken literally, this would effectively shut down civilisation. Greenpeace, like other radical environmental organisations, seems to want a zero risk society. But some types of risk taking may lead to great rewards. Buying Microsoft or AOL shares when they first came to the market would have yielded spectacular returns, although to do so would certainly have been risky. Generally, people who buy stocks accept that the value of their investment can go down or up, but they think the risk of loss is worthwhile because on average the returns are better than safer investments such as bank accounts.
Higher returns mean more wealth and more wealth means more safety.
But coal fires themselves reduce the risk of death from hypothermia. Most definitions of the precautionary principle are less extreme than Greenpeace's. But the result is a 'principle' that is so vague as to be meaningless. Also, 'cost-effective' is a wonderfully ambiguous term, which is likely to mean different things to different people. So what this 'principle' does is to limit the circumstances under which something that is impossible can be used as a justification for not doing something else that may or may not be desirable.