I very much doubt global warming is a hoax. A majority of scientists in climatology and related fields seem to believe in global warming (though there is disagreement over many of the details, most significantly the degree and that one can vary widely.) Even if they have gotten it wrong, which is a real possibility, I very much doubt that anyone did it with intention to deceive or create a hoax.

Note that I am not making any statements one way or another about "An Inconvenient Truth" or Al Gore or his receipt of the nobel prize. What I am saying is that from my layman's perspective it seems that there is at least some truth to global warming and that even if it is indeed not true then that would be a scientific error, not a hoax.