It's also quite long, so here's a summary of Krugman's main points:
1. Climate Change: It's happening. It's time to trust the scientists, drown out the naysaying, and tackle the problem using economic incentives.
2. Cap-and-Trade: It's the best option for a market-based solution, which is the only viable way to address greenhouse gases. An emissions tax is less flexible.
3. Cost: Cap-and-trade will slow economic growth, but only by a very small amount.
4. Conservatives: Their obstinate resistance to the science of climate change and the economic tools for tackling it does not mesh with the rest of their worldview. Whatever happened to Reagan's "magic of the marketplace?" The Republican Party's attempt to convince Americans that we can't afford to put a price on carbon is "a political ploy rather than a reasoned economic judgment."
5. China: If the world's biggest greenhouse gas emitter refuses to participate in emissions reductions, the U.S. and the E.U. should resort to carbon tariffs. Corralling global participation will be tough, but with a few key players on board, it will be doable.