In a well-done piece, Paul Krugman explains the difference between a carbon tax and cap-and-trade in terms an economist understands, and in terms a politician understands. And while the former might be preferable in economic terms, a cap-and-trade system has a chance of actually happening. And that’s important:
So what I end up with is basically Martin Weitzman’s argument: it’s the nonnegligible probability of utter disaster that should dominate our policy analysis. And that argues for aggressive moves to curb emissions, soon.