A scientific (or empirical) skeptic is one who questions beliefs on the basis of scientific understanding. Most scientists, being scientific skeptics, test the reliability of certain kinds of claims by subjecting them to a systematic investigation using some form of the scientific method.What I think people find especially galling, is the extent to which AGW deniers are denying science. And by "science", I mean the established system upon which we all depend - especially as laypeople - for objective measurement of reality, the process of peer review and consensus building.
What I find peculiar, is the willingness of people who are not experts in climate science, to assume themselves qualified to be "skeptics" of scientific consensus. While not necessarily conspiratorial (although the climate gate thing basically went there), the phenomenon is similar. The assumption is that a bedrock component of authority, the global scientific body, is untrustworthy (likely because of personal bias), and therefore can be discounted.
This is how conspiracy theories work. The first thing you do is discount the established authority, whether the media, government, academia, or science. Once that is accomplished, you basically have free reign to argue whatever you want, facts having been "relativized". You find this again and again in a variety of areas, where quackery thrives because of a dismissal of the only established authority. Therefore, unless one is personally an expert, reality for all intents and purposes does not exist. The conversation has been removed into a vacuum of ideology.