Environment & the World

Friday, June 29, 2007

National Review LTE

Filed under: Climate Change, Media — Cathy @ 12:51 pm

A response to the National Review’s Cover Story on global warming.  

Dear Editor

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.

Cathy Kunkel



  1. I’m the author of the article. Thanks for your very thoughtful reply.

    A few points for you to consider:

    1. You accurately reflect the position of the IPCC that 90% confidence interval for climate sensitivity is 2 – 4.5C. As you also accurately reflect, the SPM for WG1 contains the additional confusing statement that a sensitivity below 1.5C is “very unlikely”. A couple of things to bear in mind are that: (1) this confidence interval represents a subjective statement of opinion, and is not actually derived from an underlying probability distribution, and (2) this range represents a view of uncertainty assuming that climate models can accurately predict future climate development on a multi-decadal timescale, which is a non-validated claim. I have written an article on the science behind precisely this point that you can see here:

    The reason this matters is that the range in sensitivies does not really represent the range of possible outcomes, but merely a subjective estimate of the range of possible outcomes subject to a premise that has never been validated, and therefore subject to additional, currently non-quantified, uncertainty. The actual confidence interval for sensitivity is not known.

    2. The economic studies referenced, as stated in the article, show “zero to very mild net average global economic costs through 2100”. Any costs are well within the range of uncertainty of the global climate model temperature impact prediction concatenated with the (massive) uncertainty implicit in estimating the global GDP impact of this temperature change. As also indicated in the article, these projections do justify taking action, just not the action of rapid, aggressive emissions abatement. I believe that this accurately reflects the consensus of academic economists who have conducted such modeling.

    3. Even if one were to accept your assumption that we know how to reduce the risk of negative climate change, and we do not have such knowledge for other potential disasters (which is questionable, e.g., wouldn’t investing more in AIDS reduction in Africa reduce the likelihood of further mutations arising by reducing the number of hosts through which this could occur?) , it doesn’t follow that we should take the action of forcing reductions in emissions if either: (1) the costs of avoidance outweigh the odds and time-adjusted future costs, and/or (2) there are lower costs methods of avoiding the future costs.

    Again, thanks for such a thoughtful commentary on the article.

    Best regards,
    Jim Manzi

    Comment by Jim Manzi — Friday, June 29, 2007 @ 4:06 pm

  2. In the link above I too take issue with Jim’s science (so called) and reflect on what seems to be a more likely reality. A scientific approach has not been taken but a calculating political calculation has been made. It is time for skeptic fallback position five!

    Comment by Calvin Jones — Sunday, July 1, 2007 @ 6:34 pm

  3. Thanks for taking the time to respond to my comments. I appreciate your rapid and thoughtful response.

    Comment by ckunkel — Monday, July 2, 2007 @ 2:41 pm

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