Here is the quotation:
"Finally, on the ultimate excuse for draconian technocratic controls, the threat of global warming, Friedman was skeptical of climate models. In an interview published in Inside the Economist's Mind, by Paul A. Samuelson and William A. Barnett, Friedman drew a comparison between climate models and the sorts of large macroeconomic models that were discredited three decades ago.
The one place where you seem to be having that kind of modeling now is in the debate about global warming. And those models seem to be very unreliable and inaccurate. But if you think of physics, they usually have models with only a few equations. In any event, if you have a lot of equations, you ought to be able to draw implications from them that are capable of being understood. You should not present the model and say, now it's up to you to test. I think the person who produces the model has some obligation to state what evidence would contradict it."