Anthropogenic global warming is not a theory being put forth, it's the logical consequence of physical principles that are well established. It's not at all like Einstein proposing General Relativity.I'm sorry to be blunt, but this is just plain wrong, and shows a profound misunderstanding of the scientific method.
First, do you think that Einstein was just making stuff up from whole cloth? No, he was working from well-established physical principles, building onto it using logical reasoning. Despite the fact that his reasoning was logical, there was still every reason for requiring verification (and indeed, Einstein insisted on it) because there could be alternative explanations.
Similarly, AGW builds on known principles like the "greenhouse effect". But the way it seeks to apply these to a hideously complex, chaotic system requires extensive verification. What's known to be true at the micro level might not be applicable to the entire system at all.
Thus, the theory of AGW is precisely like that of General Relativity in that it absolutely requires verification. (Unfortunately, it's unlike GR in that it's not so easily experimented upon)
The scientific method requires that the burden of proof is on the claimant. The one proposing a theory has the responsibility to prove it; the world at large need not disprove it. It must work this way, because it's generally not possible to prove the opposite. When you say you saw Elvis, you can't require that I prove that you didn't.
See http://en.wikipedia.org/wiki/Burden_of_proof#Burden_of_proof...
[Edit: spelling fix]
[Edit #2: I'm really dismayed to see the parent post getting up-voted. I can't fathom how you can assert that AGW is not a "theory being put forth", and thus escapes the requirement of proof.]