Every degree of global warming does greater damage than the previous degree, simply because small changes are easier to adjust to than large ones. Therefore, the greater the uncertainty about potential global warming, the stronger the case for doing something about it sooner rather than later.
Honest and knowledgeable opponents of doing something, such as Jim Manzi, accept this obvious point. Those, such as George Will, who use uncertainty as an argument for inaction should therefore be presumed either incompetent or dishonest.
Let’s say this one more time: There’s lots of room for argument about the details of the climiate models. And there’s some room for the argument that, if some of the economic cost of preventing further warming could instead be but into efforts to decrease vulnerability to warming — especially faster economic growth in poor low-lying countries such as Bangaladesh — total prevented damage would be greater. (The problem with that argument is that no one has proposed a plausible mechanism for making that happen, and in fact most opponents of action to prevent climate change are also fervent opponents of substantial transfers of global wealth.)
But global-warming denialism in its George Will/Sen. Inhofe version is a completely loony conspiracy theory, insisting, without evidence, that the relevant scientific community is completely corrupt and has deliberately chosen to foist a false theory on the world.