Mix UN/IPCC consensus driven politics with science the animal you get is anything but science.
The genesis of the UN/IPCC's current uncertainty guidance paper comes from the concepts expressed in this paper authored by Steven Schneider (one of the historical heavy lifters in the anthropogenic global warming crew) on the subject of how uncertainty should be expressed in IPCC papers:
http://stephenschneider.stanford.edu/Publications/PDF_Papers/UncertaintiesGuidanceFinal2.pdf
"A final note before turning to the specific recommendations themselves-the paper assumes that for most instances in the TAR, a "Bayesian" or "subjective" characterization of probability will be the most appropriate (see, e.g., Edwards, 1992, for a philosophical basis for Baysian methods; for applications of Bayesian methods, see e.g., Anderson, 1998; Howard et al., 1972). The Bayesian paradigm is a formal and rigorous language to communicate uncertainty. In it, a "prior" belief about a probability distribution (typically based on existing evidence) can be updated by new evidence, which causes a revision of the prior, producing a so-called "posterior" probability. Applying the paradigm in the assessment process involves combining individual authors' (and reviewers') Bayesian assessments of probability distributions and would lead to the following interpretation of probability statements: the probability of an event is the degree of belief that exists among lead authors and reviewers that the event will occur, given the observations, modeling results, and theory currently available. When complex systems are the topic, both prior and updated probability distributions usually contain a high degree of (informed) subjectivity. Thus in the TAR, we expect Bayesian approaches to be what is most often meant when probabilities are attached to outcomes with an inherent component of subjectivity or to an assessment of the state of the science from which confidence characterisations are offered."
And the intent of the use of such terms:
"It is certainly true that "science" itself strives for objective empirical information to test theory and models. But at the same time "science for policy" must be recognized as a different enterprise than "science" itself, since science for policy (e.g., Ravetz, 1986) involves being responsive to policymakers' needs for expert judgment at a particular time, given the information currently available, even if those judgments involve a considerable degree of subjectivity. "
The same Steven Schneider responsible for this quote:
"On the one hand, as scientists we are ethically bound to the scientific method, in effect promising to tell the truth, the whole truth, and nothing but - which means that we must include all the doubts, the caveats, the ifs, ands, and buts. On the other hand, we are not just scientists but human beings as well. And like most people we'd like to see the world a better place, which in this context translates into our working to reduce the risk of potentially disastrous climatic change. To do that we need to get some broadbased support, to capture the public's imagination. That, of course, entails getting loads of media coverage. So we have to offer up scary scenarios, make simplified, dramatic statements, and make little mention of any doubts we might have. This 'double ethical bind' we frequently find ourselves in cannot be solved by any formula. Each of us has to decide what the right balance is between being effective and being honest. I hope that means being both."
(Steven Schneider, Quoted in Discover, pp. 45-48, Oct. 1989; and (American Physical Society, APS News August/September 1996).
Interesting you should bring up my old nemesis Steven Schneider... I became a pariah in graduate school for being my impertinent public disagreement with a professor who quoted him (”To do that we need to get some broadbased support, to capture the public’s imagination. That, of course, entails getting loads of media coverage. So we have to offer up scary scenarios, make simplified, dramatic statements, and make little mention of any doubts we might have.”)
You are aware, no doubt, of Dr. Schneider’s earlier comments on climate.