"When I was six years old, there were conflicting theories about how babies were born. Somebody said a stork brought them. Another guy said your parents bought them at the hospital. Another said girls had some kind of flap between their legs that babies came out of, and something about penises.
The last one definitely seemed the least likely. But by time we reached 11, a consensus had been reached for the vagina-penis theory. Nobody was still going around talking about storks!"
Notes: Now here's a metaphor for scientific inquiry -- the search for truth and evaluation of alternative hypotheses -- with which anybody can identify!
Open-minded skeptics -- i.e. all good scientists -- continue to evaluate new evidence as it comes in, within the context of the entire body of evidence.
In contrast, closed-minded skeptics -- aka "deniers" -- cling to early hypothese, such as "it's the sun," cosmic rays, volcanoes, etc., long after these hypothese have been discarded by the scientific community due to overwhelming evidence to the contrary.
Here are two tests for determing whether somebody is an open-minded climate change skeptic or has slipped into denial:
1) are they considering the entire body of evidence, or just cherry-picking certain parts that support their pre-disposition? (See for example "The earth is cooling")
2) are they subjecting the alternative hypothese ("It's the sun, etc.") and evidence to the same level of scrutiny they apply to mainstream science (e.g. the IPCC)?
No? Then your dealing with climate change denial, not skepticism.
But scientists are human, and denial is a universal human tendency when faced with something unpleasant. Sometimes good scientists (usually late in life) get "stuck" in certain positions, and -- whether for professional or socio-psychological reasons -- simply can't easily say "I've seen the new evidence, and I've changed my mind."
Others cling to earlier views for a different reason: political beliefs that embody such strongly-held values (e.g. all government regulation is so bad") that they cannot accept evidence that appears to point in another direction. See "My only tool is a hammer".
Bite Source: Bill Maher. The full monologue can be viewed here http://www.youtube.com/watch?v=0OwFSLm4pII (warning: gratuitous profanity ahead)
Image Source: here