Climate Skeptic notes the similarity of climate models and macroeconometric models:
The climate modeling approach is so similar to that used by the CEA to score the stimulus that there is even a climate equivalent to the multiplier found in macro-economic models. In climate models, small amounts of warming from man-made CO2 are multiplied many-fold to catastrophic levels by hypothetical positive feedbacks, in the same way that the first-order effects of government spending are multiplied in Keynesian economic models. In both cases, while these multipliers are the single most important drivers of the models’ results, they also tend to be the most controversial assumptions. In an odd parallel, you can find both stimulus and climate debates arguing whether their multiplier is above or below one.
Here is my take, from “Modeling Is Not Science“:
The principal lesson to be drawn from the history of massive government programs is that those who were skeptical of those programs were entirely justified in their skepticism. Informed, articulate skepticism of the kind I counsel here is the best weapon — perhaps the only effective one — in the fight to defend what remains of liberty and property against the depredations of massive government programs.
Skepticism often is met with the claim that such-and-such a model is the “best available” on a subject. But the “best available” model — even if it is the best available one — may be terrible indeed. Relying on the “best available” model for the sake of government action is like sending an army into battle — and likely to defeat — on the basis of rumors about the enemy’s position and strength.
With respect to the economy and the climate, there are too many rumor-mongers (“scientists” with an agenda), too many gullible and compliant generals (politicians), and far too many soldiers available as cannon-fodder (the paying public).
Scientists and politicians who stand by models of unfathomably complex processes are guilty of physics envy, at best, and fraud, at worst.
Politics and Prosperity 