I always chuckle when I read someone that says "No credible scientists claim....." or "All credible scientists support..."
What credible in this context means is, "The ones that support the point I am trying to make".
In science just like in everything else, opinions are interesting and possible even useful. But science is considered good if it stands up to scrutiny, data and results can be reproduced independently, etc. Lots of good scientists have screwy opinions, and lots of folks with great opinions and insight haven't got a clue about scientific method.
At least, credible sources tell me so.;)
If you were a scientist that was genuinely concerned about a possible ecological disaster, you might take the same tactic just so your information wouldn't be buried back on page 23.
There are a number of scientists that the deniers employ whose credibility is questionable. Seemingly, some of these scientists are able to provide their considered analysis based on who is paying the tab. This is not a new phenomenon. There are/have been failed scientists that found being a paid shill pays well.
Consider this to be the context by which I mean 'credible' scientist.
Perhaps not the best example, but Dr. Laura Schlessinger gives personal advice on her radio show. Sure she's a doctor. But she is no more qualified to provide personal advice than you or I. She received her Ph.D. in physiology. But she uses her professional title to create the illusion that she is qualified to offer professional advice.
In my work I work with a lot of scientists (none climate related) and if they had made some of the mistakes which have been made by the current global warming scientist, they would be out of work. That doesn't mean it is not happening it only means it leads to a lot of questions.
And when you look at who is footing the tab on the deniers camp, one should be skeptical of their motives. I'm not going to say that some scientists on the global warming side don't have an self serving interest either (securing grants, recognition....), but the community is by definition self policing.
Deniers are actually performing within parameters of the scientific community. They challenge theories and question the findings. However they generally take pot shots at the global warming theories and don't engage in a public debate with the global warming community.
I would like to see a public debate between the two camps. Each side gets to pick their panel. And then have a series of public debates.
As for corporations supporting the deniers, I am sure you would not expect them to support the contrarians as it would be against their interest. The contrarians are for the most part supported by carbon credit managers, liberal governments and liberal colleges.