Lists of skeptical scientists
There have frequently been lists of scientists published who are skeptical of AGW. For example, Senator Inhofe once publised a list of 400 "prominent scientists disputing man-made global warming claims". Among these 400 "prominent scientists":
84 have either taken money from, or are connected to, fossil fuel industries, or think tanks started by those industries.
49 are retired
44 are television weathermen
20 are economists
70 have no apparent expertise in climate science
Several supposed skeptics have publicly stated that they are very concerned about global warming, and support efforts to address it. One claims he was duped into signing the list and regrets it.
Even if every name on the list were a climate scientist, there are approximately 20,000 climate scientists in the American Geophysical Union, so 400 would be rougly 2% of the climate scientist population. And this disregards the fact that most of the names on Inhofe's list are not climate scientists. In short, Inhofe's list essentially shows that less than 1% of climate scientists are skeptical of AGW.
Another frequently cited list is the Oregon Petition, which recently published a second version of their list. The fact that they created an entirely new version rather than continuing to add to their original list raises some questions. The reason for the abandonment of the original list was that many signatures were found to be fraudulent.
"Several environmental groups questioned dozens of the names: "Perry S. Mason" (the fictitious lawyer?), "Michael J. Fox" (the actor?), "Robert C. Byrd" (the senator?), "John C. Grisham" (the lawyer-author?). And then there's the Spice Girl, a k a. Geraldine Halliwell: The petition listed "Dr. Geri Halliwell" and "Dr. Halliwell."
The original version contained approximately 17,000 signatures and the newly released version contains 31,000 signatures. However, it's important to note that in addition to the apparent ease of adding false signatures to this list, the only requirement of signatories is to have any kind of college science degree. In other words, a guy who got a bachelor's degree in biology 40 years ago and knows absolutely nothing about global warming can sign the Oregon Petition.
Even disregarding the obviously weak signature criteria, consider the fact that in the USA there are tens of millions of people with bachelor's (or better) degrees in science. If just 10% of the US population has such a degree (according to the US census, 25% of Americans have a bachelor's degree or better), then the 31,000 names on the Oregon Petition make up ~0.1% of the pool of possible signatories. So what exactly is one-tenth of one percent supposed to prove?
Essentially the only purpose of these lists is to confuse people into thinking there is no consensus on the subject, because 400 and 31,000 sound like large numbers. In reality, even disregarding the many flaws with these lists, these are fractions of a percent of their respective populations.