The analogy is bad.
The Earth's climate is a complicated black box. We know much of the science. We know much of the physics; we don't know all the various pieces and how they interact with enough precision. But we're getting better.
Economics models are an attempt to explain large-scale human behavior in an economy. It's not physics - it's herd mentality. Fundamentally, economics attempts to apply mathematics to one of the social sciences. It's much less deterministic than a physical system.
Even though the climate models are still young, they're actually very good. And getting better all the time. What economic model from even 5 years ago would have predicted the Great Recession? What economic model can predict the state of the world economy in 30 years with any confidence? I'd have much more confidence in the prediction of the state of the climate from present models.
You can even play with some of them on your own PC or Mac (courtesy of your nemesis James Hansen's group ;-) - http://edgcm.columbia.edu/software2/
FWIW.
Cheers,
Scott.
