Now that Al Gore and the International Panel on Climate Change have won the Nobel Peace Prize, it's time to be thinking very concretely about the best steps for reducing the harms associated with climate change. An international agreement for greenhouse gas reductions, including all the major contributors, would clearly be in the world's interest. China (now the world's leading contributor in terms of annual emissions) must be included, along with the United States (the world's second leading annual contributor, and still the leading contributor, by far, to the existing "stock").

Because of the nature of the problem, a partial approach, limited to (say) the United States and Europe, will do very little to slow warming by 2100. By itself, the Kyoto Protocol would have made only a small dent (according to one estimate, a reduction of warming, by 2100, of merely 0.03 C). Much publicity has been given to the United States' refusal to ratify Kyoto, and to our growing emissions. But emissions increases are much more rapid in the developing world, above all China, whose annual emissions will soon dwarf, and not merely exceed, those of the United States.

A serious and insufficiently appreciated problem is that while China and the U.S. would probably have to spend a great deal to produce significant reductions, both nations perceive themselves as facing lower risks than much of the rest of the world. India and African nations are far more vulnerable. And of course the United States has been unwilling to make serious commitments if China does not--and China is not at all likely to make such commitments without significant steps from the United States. (It is not clear that China will reduce its emissions even if the United States does so.)

It follows that a key task for the next president will be to develop a) a sensible, cost-effective plan for the United Sates alongside b) strategies to convince China (and other developing countries) to participate. We now know enough to produce a) (probably some kind of cap-and-trade approach--but a) will do very little good without b). In the long run, China, and not the United States, is likely to be the most serious obstacle to a sensible plan for greenhouse gas reductions.

--Cass R. Sunstein