Via Michael Tobis, it seems that Jim Manzi is generating a bit of buzz for a non-denialist challenge to the case for mitigating climate change recently published at TNR: Why the Decision to Tackle Climate Change Isn’t as Simple as Al Gore Says.
First off, let me echo others who’ve stated that it’s a pleasure to engage with someone who doesn’t typically deal in the fringe, anti-science nonsense that dominates so much of the right in American political discourse. To his credit, Jim Manzi doesn’t attempt to de-legitimize the scientific basis of anthropogenic climate change and chides his conservative colleagues for exactly that sort of tinfoil hattery.
With that said, it’s disappointing to see Manzi engaging in an only slightly less silly argument against mitigation, which utilizes a superficial gloss on some figures from the 2007 IPCC WGII Summary for Policy Makers to propose that costs incurred from unchecked warming don’t justify the cost of preventing it. This is an argument Manzi has made before in other venues, and one I’ve engaged him on previously.
Manzi’s argument can be fairly summarized as “according to the IPCC, the most warming we can realistically expect is 4°C, which will only cost ~3% global GDP using economic models like DICE, which is less than mitigating against that warming will cost according to an analysis of my choosing, ergo mitigation isn’t an optimal strategy”.
- There is only one SRES scenario that reasonably tracks real world emissions growth per observations and infrastructure legacy: A1FI.
- The “likely” temperature range for A1FI is 2.4-6.4°C.
- The high end cost of ~6°C warming in Manzi’s source is upwards of 11% global GDP, yielding a range/estimate of 1-11%/5.5% GDP, not 1-5%/3%.
- Manzi cites a third party estimate of mitigation costs as ~6% GDP for stabilization at 450 ppm, while other analyses by experts in the field put the cost far lower- e.g. 2.5% at 350-400 ppm.
- Being generous and more than splitting the difference- rather than using my own preferred analysis outright- gives a cost of 4.25% GDP for 450 ppm, compared to a non-stabilization cost of 5.5%GDP.
In short Manzi’s analysis depends on a suspiciously narrow reading and selection of source material that doesn’t hold up to even a cursory amount of scrutiny.
Further points: This simple debunking has ignored other problematic assumptions implicit in Manzi’s analysis- the absurdly conservative damages of the DICE model, for example. Notoriously, DICE shows a warming of 20°C resulting in a loss of only 50% of global GDP, a warming so extreme that it would exceed humans’ (and other mammals’) capacity to endure heat stress, resulting in mass extinction. It’s fairly safe to say that there wouldn’t even be a “Gross Domestic Product” much less one half as large as today’s 2100’s expected. Ocean acidification, non-linear ice sheet collapse and resulting sea level rise, and other costly consequences of unchecked emissions are likewise ignored by DICE. [And yes, I realize that Manzi will simply claim that the IPCC deserves a similar criticism, with which I agree- though in its defense the IPCC doesn’t attempt to hang its conclusions on such a slavish acceptance of this modeling.]
Work by others (like Annan and Hargreaves) finds losses from DICE to be understated in the AR4 compared to their own papers. This isn’t a problem with Manzi’s formulation of the issue, but is relevant to the discussion.
On a final note, it’s also disappointing to see that the pro-mitigation punditry (e.g. Klein, Plumer) don’t even appear to seriously investigate Manzi’s argument, but rather grant his flawed premises and hand-wave in favor of mitigation anyway. Or as Tobis puts it (emphasis in the original): “The answer from the punditry to Manzi is not to call the absurdly small cost into question, but to say that we should take drastic action anyway, even though the [economic] risk is trivial.” As much as I appreciate the interest of Klein and Plumer in climate issues, they do not appear to be sufficiently conversant with the relevant material to proficiently engage their opposition.