We don't live in a culture where debate has any meaning. There are rarely any "debates" when it comes to politics, which is the context of this issue.
Politicians and commentators usually simply hurl their positions at each other repeatedly, their talking points and memorized "facts" without really getting down to negating, refuting, or rebutting. Opponents ignore each other's logic and just repeat what they want to say, over and over and over.
Even if there were a "real" debate, the public doesn't give a crap. Honest debate is not valued, most people who have an interest in politics are interested mostly in "doing battle", defeating the other side. A real debate needs all parties, viewing and participating, to honestly care about the truth, care about hearing the other side out, and be comfortable with being proven wrong in some way, shape, or form.
Gore, then, has no real reason to want to debate the Lord. It would not benefit Gore or his position. It wouldn't hurt it, either. Noone would pay attention, noone would be convinced one way or another. Also, debating someone is a tacit admission of their positions merit....even if it is thought to be wrong.
African Americans don't debate White Supremacists for a reason. Gays don't debate the Westboro Baptist Church for a reason. Scientists don't debate with doctors for a reason.
Also, as stated before, these are politicians who don't really know what they are talking about. Gore shouldn't be the spearhead of the Global Climate Change movement, and the Lord shouldn't be the spearhead of the Climate Change Denier movement.
Anyone who actually cares about the truth, on either side, would be interested in a debate between two competent scientists.