So how should the public and policymakers, whipsawed by debate, sort out the competing claims? "That's easy," said Dessler, co-author of Cambridge University Press's "The Science and Politics of Global Climate Change." Dessler calls for the use of "expert assessments"- panels of specialists brought together to sort out and summarize scientific information for politicians, policymakers and the public. It's a common technique on all sorts of science-policy questions.There's a really interesting point here. I agree with Pielke Sr. that assessments have to include the range of opinions held by the majority of the scientific community. If half of the community says one thing and the other half says something else, then a good assessment will include both views. My sense is that the recent AGU assessment on hurricanes failed in this regard (see also this Prometheus post).
On climate change, a number of such reviews have been done, including work by the Intergovernmental Panel on Climate Change and the National Academy of Sciences. The panels' findings have been consistent and are reflected in the key finding in the IPCC's 2001 "Climate Change: The Science": Greenhouse gas emissions are altering Earth's climate.
Pielke Sr. has a different answer- listen to more diverse scientific voices. He thinks expert panels like the IPCC are inbred, representing a narrow focus on greenhouse gases. "The public is getting a very narrow view of the breadth of issues in climate science," he said.
However, we have to be careful about including views that are "too diverse." The goal of a scientific assessment is to let policymakers know what the scientific community thinks on an issue. If 99.9% of the scientists think one thing (e.g., the Earth is warming), then should the assessment include a dissenting view held by 0.1% of the community? I would argue not. Policymakers are often unable to discern a 99.9% position from a 0.1% position, and they look to expert assessments to do just that. If they don't, then the assessment has essentially abdicated its responsibility to clarify the science for the policymakers.
Obviously, this is one of the hard choices that the authors of assessments have. They have to use their judgment about what positions are credible within the majority community and what positions are simply outliers. Writing assessments is a tricky business, but they play such a crucial role that scientific community has to continue to work hard to make them the best possible source of information for policymakers.