Today, everybody’s favorite policy for combating greenhouse gas emissions is “cap and trade,” the shorthand for a larger system of carbon emissions trading.

It works like this: countries are each permitted, via international treaty, to emit only a certain amount of carbon. They then enforce these limits by allocating carbon emissions credits to their big emitters — by auctioning them off or selling them outright. In that way, the thinking goes, emitting carbon can carry a cost more literal than the collective cost of global warming.

It seems a simple enough idea. If natural resources can be monetized, why not the pollutants they unleash? Why not turn the market, with its complex system of incentives and disincentives, to the task of regulating fossil fuel emissions? The invisible hand could save the world.