In a meta discussion about AGW, Eric Raymond writes about how the term scientific consensus is used in public science debates. He seems to misunderstand it, and think it is an ‘appeal to authority’ type of argument and thus a sign that the party that raises it has no more convincing arguments.
It certainly can be that sort of poor argument, but typically when raised by scientists it is something different. The scientific consensus on a topic is mentioned as a shorthand way of communicating what’s understood by scientists working the field to the public. Scientists are trying to communicate that certain things are known, and that contrary arguments that pick one or two studies and argue that the contrary opinion is *really* true or at least that no consensus exists are misleading. Either the study is part of a technical debate in the field among researchers who all understand and believe the consensus that is being misconstrued or too much weight is being given to the opinion of a rare contrarian.
The contrarians can be further divided into 1) cranks of various sorts and 2) scientists working on a contrary idea who understand that the evidence still favors the consensus but hope to make discoveries that will eventually tip the balance of evidence in favor of their idea. The second scientist will happily talk up his idea if asked about it, but if asked about the consensus will acknowledge that it is currently overall the best explanation.
So scientists will mention the scientific consensus on an issue to the public to ground the discussion with the fundamentals of what is known. With the fundamentals set down, scientists can then explain the details of how things are known, what discussions within the field are about, or discuss contrarians.