One of the hallmarks of conspiracy theories is that they imagine huge numbers of people to act in ways that contradict their own interests, and for them to all do it with perfect (or near-perfect) levels of secrecy.
The idea that there's more money to be made shilling against burning petroleum than there is shilling for it is simply farfetched. And leaving that aspect out of it for the moment, what scientists want more than anything is to see the scientific consensus overturned. When that happens it's like a gold strike: everyone rushes to the new fields and tries to stake his claim.
Once upon a time there was something called the "Central Dogma of Molecular Biology" (it was actually called the "central dogma"): DNA makes RNA, and RNA makes proteins. Except then Howard Temin and David Baltimore discovered reverse transcriptase, which explained how RNA from retroviruses were able to alter host DNA. Their reward for finding an exception to the dogma? A Nobel Prize, and a brand new area for research and technological development. Reverse transcriptase made the highly sensitive and accurate PCR test possible.
Any scientist who can conclusively disprove AGW would be able to dine out on that for the rest of his life. He would go down in history as one of the greatest benefactors of the human race. Most importantly, everyone would think he was waaay smarter than the other scientists.
People don't understand the function of scientific consensus. It doesn't represent a final version of the Truth; it represents a division between things statements that can be stipulated for the time being without recapitulating the entire lie of evidence (e.g. that matter is made up of atoms) and things that require citation of specific evidence (e.g. that there are stable elements with atomic numbers > 118).