A response to the National Review’s Cover Story on global warming.
I disagree with the conclusions of Jim Manzi’s recent cover article on global warming (“Game plan: what conservatives should do about global warming”), in which he argues that the economic costs of dealing with climate change do not justify the United States taking action to limit emissions.
Mr. Manzi rightly points out that estimates of climate sensitivity – how much the temperature will increase if we double atmospheric carbon dioxide levels – is uncertain; according to the Intergovernmental Panel on Climate Change, it is likely 2-4.5C, with a best estimate of 3C. Contrary to what Mr. Manzi suggests, it is very unlikely to be less than 1.5C. At the global level, economic studies, including the one cited in the article, generally show net benefits to avoiding a warming above 2-3 C, relative to not taking action.
Mr. Manzi notes that the economic model discussed in his article predicts “large negative impacts in poorer areas closer to the equator,” but he then dismisses this problem because the economic impacts to the U.S. are roughly break-even. Impacts to the developing world include increased water stress and reduced food security that is projected to impact 75-250 million people in Africa by 2020 and decreased freshwater availability in Asia that could affect a billion
people by the 2050s. U.S. national security efforts will not be made easier by a do-nothing climate policy that effectively promotes global inequality and resource conflicts.
Mr. Manzi also dismisses the threat of abrupt climate change, arguing that the probability of such an event occurring is too slim to justify worrying about it. He puts abrupt climate change in the same category with other low-probability potential disasters, such as nuclear war in Central Asia or a global disease pandemic. But the key difference between abrupt climate change and these other disasters is that we know with certainty how to reduce the risk of abrupt climate change, i.e. reduce emissions. Moreover, science provides rough estimates of how much the risk of abrupt climate change increases with higher emissions levels. Yes, there are a number of unlikely risks which we cannot prepare for, but why does this mean we should not mitigate the risks which are at least partially under our control?
Because science gives us a guide for deciding the socially acceptable level of climate risk, it makes sense to implement some sort of cap or tax to prevent exceeding that threshold. As Mr. Manzi states, “global warming is a manageable risk, not an existential crisis.” We already have the technology we need to put us on a path to stabilizing atmospheric carbon dioxide concentrations at levels that pose far less risk to world society than our present path.