Does expertise make the difference?   It depends.   When it comes to climate change, having a Ph.D. and a faculty position does not mean as much to the public as it does for researchers in other fields.

The difference?  Climate change researchers are perceived as being part of the cultural discourse rather than part of the objective science one, so if the scientist is taking a position different from yours, he is not an expert, he is just in the mud with politicians and environmental or industrial corporations trying to get money. Unfortunately, the same is true for both sides in the global warming discussion, and that is bad for science all the way around.

How is it that the public can completely disagree on matters like climate change where scientists largely agree?    That word 'consensus' seems to be understood more by people in the cultural war over climate change than others.   Merriam-Webster defines consensus as general agreement and Dictionary.com defines it as majority opinion.  Neither of those are great things in science because you can't vote on data.

Whether or not the science consensus on topics is good enough for some and not others comes down to individualistic versus egalitarian values, according to a recent study by Yale University law professor Dan Kahan, University of Oklahoma political science professor Hank Jenkins-Smith and George Washington University law professor Donald Braman.

Their study said people with individualistic values, who have a strong preference for independence and regard commerce favorably, were over 70 percentage points less likely than ones with egalitarian values, who resent economic inequality and believe industry harms the environment, to accept a scientist as an expert if the expert described climate change as an established risk.  

It isn't just climate skeptics that were skeptical of experts, though.   Egalitarian people were 50 percentage points less to accept a scientist as an expert if the scientists was described as believing evidence on climate change is unsettled.

Other politically/culturally charged issues had similar results.  In America, for example, nuclear power is a left/right position and their study found people were much more likely to see a scientist with excellent credentials as an expert only if he or she had a position that matched their own.

"These are all matters," Kahan said, "on which the National Academy of Sciences has issued 'expert consensus' reports." Using the reports as a benchmark," Kahan explained that "no cultural group in our study was more likely than any other to be 'getting it right'," i.e. correctly identifying scientific consensus on these issues. They were all just as likely to report that 'most' scientists favor the position rejected by the National Academy of Sciences expert consensus report if the report reached a conclusion contrary to their own cultural predispositions."

This tells us why brandishing a scientific consensus, aside from being a logical fallacy, doesn't settle debates - and why it needs to be eliminated from the scientific lexicon.   Once a word is emotionally charged with any kind of psychological dynamic its effectiveness is finished and 'consensus' is just that.    In climate change, the word consensus was brandished by non-scientists as a weapon, and that seemed to be fine for scientists who liked the attention their work was getting, but a backlash was inevitable.

"The problem won't be fixed by simply trying to increase trust in scientists or awareness of what scientists believe," added Braman. "To make sure people form unbiased perceptions of what scientists are discovering, it is necessary to use communication strategies that reduce the likelihood that citizens of diverse values will find scientific findings threatening to their cultural commitments."

In other words, stick to the science and leave the political and cultural grandstanding to others.  If both sides of cultural debates trust scientists again, then decisions will be based on data and not political perception - and that is good for everyone.

Citation: Dan M. Kahan, Hank Jenkins-Smith, Donald Braman, 'Cultural cognition of scientific consensus', Journal of Risk Research,  10 September 2010 DOI: 10.1080/13669877.2010.511246