Global Warming: Gore's Credibility

I was looking at an article in the New York times about global warming, much of which is about Al Gore, and I ran across this:

“He has credibility in this community,” said Tim Killeen, the group’s president and director of the National Center for Atmospheric Research, a top group studying climate change. “There’s no question he’s read a lot and is able to respond in a very effective way.”

The "he" in this reference is Al Gore. The group referred to here is the American Geophysical Union.

Now I have to wonder how the word credibility is defined. My dictionary reveals that credible means: capable of being believed; believable; plausible; worthy of confidence; reliable. It also says about credibility: worthiness of belief. None of this reminds me of a politician, in general, and certainly it doesn't remind of this politician in particular.

I've posted several times recently about politics and public choice theory, mostly about the idea of rational ignorance and the implications of rational ignorance for our politics and our system of political economy. I think many of those implications point to reasons we should not often associate politicians with the words in the definitions just above.

I'm having some trouble understanding why a politician of Mr. Gore's standing would be seen as credible by a group of scientists. I certainly do not see Mr. Gore's views about science as "worthy of confidence," while I do have much greater confidence in Mr. Gore's ability to turn the rational ignorance of voters to his personal advantage. So, I suspect Mr. Gore has credibility with this group of scientists, not because of his wisdom with respect to science, but rather with respect to his wisdom about global science politics. And, this leads me to yet another idea from public choice. Could it be that Mr. Gore has credibility with this group of scientists because the nature of the politics of this group of scientists fits the idea of rent seeking?