If President Barack Obama wants to stop the descent toward dangerous global climate change, and avoid the trade anarchy that current approaches to this problem will invite, he should take Al Gore's proposal for a carbon tax and make it global. A tax on CO2 emissions -- not a cap-and-trade system -- offers the best prospect of meaningfully engaging China and the U.S., while avoiding the prospect of unhinged environmental protectionism.

China emphatically opposes a hard emissions cap on its economy. Yet China must be part of...