The American Clean Energy and Security Act (ACES) -- the bill that would impose a cap and trade regime for U.S. carbon emissions -- has passed the House of Representatives. Was it worth it? Well, on its own, ACES will in no sense make the world a cooler place. Other nations will help themselves to more coal, like bad kids on Christmas morning. An American cap and trade bill will have a meaningful impact only if it induces other nations to follow suit. So the hope -- plausible if not irresistible, I think -- is that passing climate-change legislation will be a powerful gesture before December's United Nations climate change conference.
But even if the Copenhagen Conference produces a meaningful consensus on climate change, will it matter? Jim Manzi does not think so. He runs some numbers, in response to a post I wrote yesterday, and concludes that even if you eliminate all the costs of global warming in the next century, the economic benefits would be negligible -- and certainly disproportionate to the hysterical rhetoric you hear from the left.
It's possible to quibble with Manzi's data. (More recent temperature estimates than the IPCC's exist: You can check out the work of MIT's Joint Program on Global Change for more.) Or, one might suggest that the factual uncertainty here suggests erring on the side of caution. (If Manzi is right, your children will enjoy a 1% increase in consumption. If Manzi is wrong, your children will know a world with fewer island nations.) But I don't think making a compelling case for regulating carbon emissions requires diving down that empirical rabbit hole. Even if we assume that the worldwide future economic benefits from cap and trade are tiny -- and, on the flipside, assume that the average economic costs of global warming are small -- the critical consideration is where those costs and benefits fall.
The big costs of global warming will fall overwhelmingly on developing nations with dense, coastal populations. You can be a realist about those costs -- why on earth should America care what happens to Bangladesh? -- but the costs are still real. They are also, by and large, not costs for which the developing world is responsible.
And they are big. Manzi cites the most recent Intergovernmental Panel on Climate Change report for his high-end estimate that "economic damages from [a temperature increase of 4 degrees celsius] are equal to 5% of [global] GDP." True fact. But the same report says that, in Africa, the cost of adapting to rising sea level alone "could amount to at least 5-10% of Gross Domestic Product." A one-meter rise in sea level will destroy 1,000 square kilometers of farmland in Bangladesh. And you don't even need to consider the tediously debated issue of sea level to indulge in a little hysteria: Temperature increases could help cut crop yields in agriculture-dependent South Asia by 30% come the middle of the 21st century.
I don't think this is hysterical or even controversial: Travel to South Asia and you can watch it happen now. The question is just how it enters the policy calculus. And why shouldn't it?