On the Limits of Expert Credibility: Theory and an Application to Climate Change

I present a model in which a voter cannot learn the consensus opinion of experts. In the model a journalist reports on an unknown state to a voter who makes a policy decision. The journalist’s report consists of the opinion of a single neutral expert and a rejoinder by an opposition party. At some cost, the party may hire a credible expert to comment on its behalf. The more uniform is expert opinion, the more informative is the report of a single expert, and hence the greater is the opposition party’s incentive to hire its own expert. When experts are divided, equilibrium reports are more informative than the neutral expert’s opinion. When experts are nearly unanimous, no informative equilibrium exists. Stronger consensus among experts can therefore lead to weaker consensus among citizens. I apply the model to climate change and other cases in which scientific consensus has not led to public consensus.