What started out as a well-supported observation that the earth was starting to slowly warm...
Actually that's just the recent history, going back to, say, the early '80s. The dogma before then was that human action was forcing the next Ice Age early, particularly through sulfur dioxide emissions from burning coal increasing the reflectivity of clouds. And it was a very big thing, e.g. strongly influencing the science fiction of the time.
While your characterization of the environmentalists is more or less accurate (except that they've been pushing this since the '60s or so and they're essentially a religious cult) I think you've constructed a straw man for the "other side". Ignoring the tiny fraction of people who are Objectivists let alone the small fraction who are that sort of extreme libertarian, your idea that the other side blindly trusts "mega-corporations" is entirely without foundation.
Seriously, do you think we're that stupid or naive? Suffix something with big- or mega- and we're less inclined to view it favorably, let alone trust it. Although we at least (mostly) don't object to the very ideas of capitalism or profit, so corporation are not born with some form of Original Sin.