There is a new paper that is being somewhat uncritically accepted at the new Climate “Skepticism” site (and, yes, the inverted commas are necessary) and at Bishop Hill. It’s by someone called J. Ray Bates and claims to estimate climate sensitivity using two zone energy balance models. The paper essentially concludes that the method used
give low and tightly-constrained EfCS values, in the neighbourhood of 1°C
which is slightly bizarre.
Fortunately, Andrew Dessler has already provided a rebuttal to an earlier version of the paper. Essentially, the new paper is based very heavily on Lindzen & Choi (2011) which has been heavily criticised. Lindzen & Choi (2011) used sea surface temperatures and satellite measurements of the TOA flux to try and determine the feedback response. They essentially concluded that the non-Planck feedbacks were 0, or negative. However they only considered the tropics (20S – 20N) and then assumed that the non-Planck feedbacks everywhere else where 0.
The new paper tries to present a slightly more sophisticated model in which it considers two zones, but given what it assumes for the non-Planck feedbacks, it’s no surprise that it returns an effective climate sensitivity (EfCS) of about 1oC; that’s close to the value for the the non-feedback climate sensitivity. It’s fairly straightforward to illustrate why this result doesn’t make sense. Even though it is a two-zone model, it is still fundamentally an energy balance approach. You can write the basic energy balance formalism as
where is the planetary energy imbalance, is the change in anthropogenic forcing, is the change in temperature, and is the feedback response, which can be used to given the EfCS through
Today , , and . The main unknown is the initial planetary energy imbalance, but I’ve seen values between 0.08 and 0.15 Wm-2, so let’s use 0.1Wm-2. Putting these numbers in gives
which then gives an EfCS of about 2K. Of course, these numbers are ballpark figures and there are uncertainties that should also be considered, but it is still hard to justify an EfCS close to 1K. Essentially, we’ve already warmed by almost 1K, have yet to double atmospheric CO2, and still have a planetary energy imbalance that is probably greater than 0.5 Wm-2. How, then, can the EfCS be 1K? I’ve emailed the author to ask him this question. I’ve yet to get a response.