What's the Difference between a Skeptic and a Denier?
The denier has made up his mind that anthropogenic (human-caused) global warming isn't happening. He rejects any scientific evidence supporting AGW, and blindly accepts any evidence, pseudo-evidence, emotional appeal, or unsupported argument that opposes AGW. Scientifically disproving his argument won't sway him.
The skeptic doesn't believe something just because the establishment says it's so. He needs to personally examine the evidence, and won't believe it until he can prove it for himself.
The skeptic is pro-science, exactly the type of person who moves science forward. The denier is anti-science, but may hide behind the term "skeptic" the same way a creationist hides behind the term "intelligent design."
Dr. Richard Muller is a skeptic. The Berkeley physicist criticized errors he saw in Al Gore's movie, "An Inconvenient Truth" He criticized the scientists involved in the so-called "climategate scandal." He vocally criticized the "hockey stick" graph that climate scientists have used to show the sharp increase in temperature in the past few decades.