I think peoples' decision about whether to accept or resist the AGW proposition is being complicated by an implicit negotiation over political power that's inevitably attached to that decision.

Because the scientific projections are still vague, people feel as if their decision about whether to believe in AGW is underdetermined by the evidence, in such a way that political actors in the future will feel entitled to retrospectively interpret their decision for purposes of political precedent. ("Were they forced by the evidence, or did they feel weak enough that they made a concession they didn't have to make?") And the precedent won't be induced in terms of the mental states that a perfect decision theorist, thinking about the AGW mitigation decision problem, would have had. The precedent will be in terms of the mental states that a normal non-scientifically-trained (but politically active) human would have had. One of those mental states would be uncertainty about whether scientists (unconsciously intuited as potentially colluding with, and/or hoping to become, power-grubbing environmental regulators) are just making AGW up. In that context, agreeing that AGW is probably real feels like ceding one's right of objection to whatever seizures of power someone's found some vague scientific way of justifying.

It becomes a signaling game, in which each choice of belief will be understood as exactly how you would communicate a particular choice of political move, and the costs of making the wrong political move feel very high. So the belief decisions and the political actions become tangled up.

Roughly, people have no way of saying:

I believe that in terms of pure decision theory, the predicted AGW damage and costs of further investigation and costs of delay are high enough that mitigation attempts should start now. But I don't want to give up my {economic privileges / substantive national sovereignty / chance to get the standard of living of past carbon-emitting nations} without a fight, because I don't want groups in the future like {scientists / profit-hating hippie tree-huggers / freedom-hating U.N. environmental bureaucrats / greedy unfair first-world hypocrites} to think I'll just roll over when they try to impose concessions on me, in the name of premises that will feel psychologically as though they might just as well have been made up. In that future situation, it will be important for me to be able to credibly threaten outrage at being forced into such concessions. But as long as nobody else is going to take me for their fool, the sacrifices needed to prevent AGW are fine with me; we could start today.

So instead, they say:

I believe that the case for AGW isn't strong enough. I demand clearer proof.

If it were possible to negotiate separately about AGW action and about precedents of policy concessions to e.g. scientists' claims, then you might see less decision-theoretic insanity around the AGW action question itself.

(Note - most of this analysis is not on the basis of such data as opinion polls or controlled studies. It's just from introspecting on my experience of attempting to empathize with the state of mind of AGW disputants, as recalled mostly from Internet forums.)