My climate science blogging brethren have been typing up a storm about Naomi Oreskes' Dec. 3 Science essay on the consensus about climate change, and amidst all the noise I missed Roger Pielke Jr.'s thoughtful take (he's quoting here in his blog from a 2001 Nature paper):

Consider once again global climate change. For many years, policy debate has centred on the degree of certainty that decision-makers ought to attach to competing visions of the future climate. Lost in this doomed enterprise is the point that climate will certainly have an increasingly strong effect on the environment and society, simply because of growing vulnerability related to factors such as population, wealth and use of land. If a goal of climate policy is to reduce the effects of climate on the environment and society, then effective action need not wait until we are more certain about details.

Seen in this light, efforts to reduce uncertainty via 'consensus science' - such as scientific assessments - are misplaced. Consensus science can provide only an illusion of certainty. When consensus is substituted for a diversity of perspectives, it may in fact unnecessarily constrain decision-makers' options. Take for example weather forecasters, who are learning that the value to society of their forecasts is enhanced when decision-makers are provided with predictions in probabilistic rather than categorical fashion and decisions are made in full view of uncertainty. As a general principle, science and technology will contribute more effectively to society's needs when decision-makers base their expectations on a full distribution of outcomes, and then make choices in the face of the resulting - perhaps considerable - uncertainty.