Why won't Al Gore debate?

Here.

Excerpt:

When Al Gore ran for U.S. senator from Tennessee he debated – repeatedly.

When he ran for president he once more debated frequently.

Why is it that as a recipient of the Nobel Prize for his theorizing about global warming Mr. Gore has refused repeated and prominently published challenges to debate this issue with scientists?

Is it possible Al thinks that the Nobel (also awarded to the late Yasser Arafat) makes him morally and scientifically impervious?

Or does he believe it would be unbearable for a Noble Prize winner to lose a debate on the issue for which he was awarded?