I actually did call in to a syndicated right-leaning talk show about global warming - twice to the same show in fact several months apart.
Here's some advice I would give if you think of doing it yourself
1) Realize that the playing field is NOT AT ALL FAIR. This is like a verbal boxing match where your opponent has been training for years. Not only that, he is also the referee - so he can "call time-out" at any time (by going to commercial or simply cutting you off). Both times I called in, I eventually ended up talking to myself while he went on to pontificate on the air. Furthermore, he most likely has a staff that can be googling things to feed to him.
2) Listen to the show. The hosts have typical "gotcha" tricks and debating tactics that they tend to use. Be aware of these and be ready for them.
3) Hosts are no dummies -- they have to be intelligent and driven and informed and driven to talk articulately for hours a day. Don't assume that your PhD and 20 years of teaching experience will make you able to out-talk them on the air.
4) Try to keep on topic. This was one of the lessons I learned on-air. I wanted to "teach" the host and audience, but he wanted to score points by finding something that he could use to show his audience that he was better and brighter than me.
The first time I was calling specifically to address his warping of the idea of relative humidity. (Ie "warm" winter air that is still below 0C can hold more moisture than cooler air -- so "warming" can indeed lead to more snow.) I think he actually understood the topic and once he realized he couldn't buffalo me on the subject, he started shifting around to new angles to attack.
* its been cooling for the last decade (but is still much warmer than average)
* Antarctica is losing ice (only parts of it)
* NASA says 1934 was the warmest year on record (I didn't think so -- I told him I had recently seen the charts for NASA global temps and the warmest years were all more recent. It turns out 1934 was the warmest IN THE US. I wish I had that nugget at the tip of my tongue then!)
* What evidence shows that there is indeed warming going on?
* The warming is so small it doesn't matter. (even a small fever is a problem.)
* What would be so bad about warmer weather? Canada could grow more crops. Global warming is good! ...
Every time I had an answer, the target changed! The one line I wish I had been prepared to use was "I'd be happy to start discussing 'Y'. Since we are leaving topic 'X' then I will assume you agree with me that 'xxxxx' is correct."