There’s more to say about the latest attempt to deny the mainstream estimate of equilibrium climate sensitivity (e.g. NRC, 1979; Annan and Hargreaves, 2006; Knutti and Hegerl, 2008; Rohling et al., 2012) by Matt Ridley (remember him?) at the Wall Street Journal later. But I just wanted to point out something rather troubling about one of Ridley’s and Nic Lewis’s (the source of Ridley’s claims) citations.
Some of the best recent observationally based research also points to climate sensitivity being about 1.6°C for a doubling of CO2. An impressive study published this year by Magne Aldrin of the Norwegian Computing Center and colleagues gives a most-likely estimate of 1.6°C.
I recalled the Aldrin et al. paper from the last time it made the rounds in the “skeptic” blogosphere, when Chip Knappenberger cited it as finding a “low” climate sensitivity.
The funny thing about the Aldrin et al. paper is that it really doesn’t find a “low” ECS at all. Their main result is an ECS of 2.0°C, which is completely consistent with the IPCC AR4 range. Moreover, they caution that their main result is incomplete, because it explicitly does not account for the effect of clouds:
When cloud behavior is included as another term, the ECS increases significantly, from ~2.5°C to 3.3°C depending on the values used:
Surely this wasn’t the Aldrin et al. paper Riddley and Lewis were citing as finding an ECS of 1.6°C.
The 1.6°C value literally never appears in the text of the paper.
Of course, it was entirely possible that Aldrin had published another paper on ECS this year finding 1.6°C that I was simply unable to find. I reached out to Bishop Hill and Matt Ridley for some clarification:
I posted the following to Nic Lewis at Bishop Hill’s blog:
I think that some readers, and probably the authors of a paper themselves, might find it at least slightly misleading for you to claim findings on their behalf that the paper itself does not actually state.
The main result from Aldrin et al., as reported by Aldrin et al., is an ECS of 2.0°C. The authors caution that this result probably isn’t an apples to apples comparison to other ECS estimates due to the unaccounted for cloud term, and find that the value increases to ~2.5-3.3°C with clouds.
Rather than report either of these values, you simply claim Aldrin et al. “an impressively thorough study, gives a most likely estimate for ECS of 1.6°C…”.
Ridley likewse claims, “An impressive study published this year by Magne Aldrin of the Norwegian Computing Center and colleagues gives a most-likely estimate of 1.6°C.”
It would be easy for me to lob accusations of bad faith, as we don’t know each other and this is just the internet. Instead, I would encourage you, if your goal is to reach as wide an audience as possible, and try to make an impact beyond the “skeptic” and conservative blogospheres, to be more upfront about the scientific literature about ECS.
Ignoring the two main findings of a paper for values that you’re either estimating from a curve or are creating yourself based on data not used by the paper will be seen by at least some people to be misleading. Claiming that ECS cannot be estimated by paleo data is absurd, especially when so many are aware of efforts like the PALAEOSENS project and various paleoclimatic intercomparison groups.
I won’t attempt to read minds or divine motivations. I will simply suggest that what you have been doing thus far will cause some people to dismiss what you’re trying to say due to perceived dishonesty.
I hope you take this criticism in the constructive context in which it is being offered. There will be plenty of time for name-calling and insults later.
Aldrin, M., M. Holden, P. Guttorp, R. B. Skeie, G. Myhre, and T. K. Berntsen (2012), Bayesian estimation of climate sensitivity based on a simple climate model fitted to observations of hemispheric temperatures and global ocean heat content, Environmetrics, 23(3), 253–271, doi:10.1002/env.2140.
- Annan, J. D., and J. C. Hargreaves (2006), Using multiple observationally-based constraints to estimate climate sensitivity, Geophys. Res. Lett., 33, 4 PP., doi:200610.1029/2005GL025259.
- Knutti, R., and G. C. Hegerl (2008), The equilibrium sensitivity of the Earth’s temperature to radiation changes, Nature Geoscience, 1(11), 735–743, doi:10.1038/ngeo337.
- National Research Council (1979), Carbon Dioxide and Climate: A Scientific Assessment. Washington, DC: The National Academies Press.
- Rohling, E.J., et al. (2012), Making sense of palaeoclimate sensitivity, Nature, 491(7426), 683–691, doi:10.1038/nature11574.