But when I was a kid, the scientific community was in consensus that global cooling was our biggest threat, from pollution. Now it's global warming, and in another generation it'll probably be global cooling again. This isn't a science issue so much as it is a social one. Scientists are just as susceptible or perhaps more so than anyone in being swept away by the inertia of positive bias. It's very difficult to dissent in a community as tightly woven as the science community has become.
Everyone pats one another on the ass to get published and to cite publications while publishing. That trends heavily towards publishing things which are guaranteed to not rock the boat, go against the current trends and to be widely difficult to disprove such as issues as nebulous as global warming. Without any 'causes', what we have are weather patters which are roughly linear going back to the ice ages and which have occurred on uninhabited planets as well.
Despite the obvious explanation that perhaps weather is cyclic, and taking into account man's minority contribution to the organic discharge of carbon on the planet, we have a frantic persuasive group demanding that this be the issue which guides our judgement, not because this issue itself has validity or provability but rather because the tertiary effects of abiding by policies guided by this doctrine will achieve the other desirable outcomes; in this case a moral support of secondary 'green' initiatives.
In that way, and I won't go too far with this parallel, the global warming debate has become a religious issue. Without proof, those who believe in it are fervent and zealous. They see proof in everything, and that reaffirms their faith. They know that if others would convert to their faith, the other problems which plague them such as conservatism of wetlands and undeveloped lands and control of pollution and emissions would also be resolved.
This is not an issue in itself, as it is a banner under which other issues are being brought. That is why the argument itself doesn't appear to make sense to outsiders to the faith, because it isn't and never has been a simple, explicable and provable thing. It's a nebulous accusation that carries the hope of people who have genuine and valid concerns, and are driven to have a cause to unite them.