This is one of those times I’m really glad WiFi has been installed on passenger aircraft. After reviewing this paper at Nic Lewis’ home prior to that extraordinary meeting with climate scientists I mentioned, and expecting a leisurely writeup in about a week, Nic sends me this email which I get on the plane:
Anthony, Climate Dynamics has released my paper nearly a week earlier than they said!!
This is a significant paper. As I once read on Climate Audit:
This will set the cat amongst the pigeons
Here is the paper at Climate Dynamics: http://link.springer.com/article/10.1007/s00382-014-2342-y
The implications for climate sensitivity of AR5 forcing and heat uptake estimates
Energy budget estimates of equilibrium climate sensitivity (ECS) and transient climate response (TCR) are derived using the comprehensive 1750–2011 time series and the uncertainty ranges for forcing components provided in the Intergovernmental Panel on Climate Change Fifth Assessment Working Group I Report, along with its estimates of heat accumulation in the climate system. The resulting estimates are less dependent on global climate models and allow more realistically for forcing uncertainties than similar estimates based on forcings diagnosed from simulations by such models. Base and final periods are selected that have well matched volcanic activity and influence from internal variability. Using 1859–1882 for the base period and 1995–2011 for the final period, thus avoiding major volcanic activity, median estimates are derived for ECS of 1.64 K and for TCR of 1.33 K. ECS 17–83 and 5–95 % uncertainty ranges are 1.25–2.45 and 1.05–4.05 K; the corresponding TCR ranges are 1.05–1.80 and 0.90–2.50 K. Results using alternative well-matched base and final periods provide similar best estimates but give wider uncertainty ranges, principally reflecting smaller changes in average forcing. Uncertainty in aerosol forcing is the dominant contribution to the ECS and TCR uncertainty ranges.
A PDF file of a reformatted version of the final revised manuscript titled ‘The implications for climate sensitivity of AR5 forcing and heat uptake estimates’, with minor editing corrections, is available here: Lewis&Curry_AR5 energy budget climate sensitivity_Clim Dyn2014_accepted (reformatted, edited). This work was accepted for publication by Climate Dynamics on 13 September 2014.
A compressed zip file containing data and computer code that will generate the results in the paper is available here: AR5-EB-LewisCurry-ClimDyn-2342
Nic is preparing a discussion about the paper to post at Climate Audit, I’ll add it when it is ready – Anthony (somewhere over Canada)
When the Lewis & Crok report “A Sensitive Matter” about climate sensitivity in the IPCC Fifth Assessment Working Group 1 report (AR5) was published by the GWPF in March, various people criticised it for not being peer-reviewed. But peer review is for research papers, not for lengthy, wide-ranging review reports. The Lewis & Crok report placed considerable weight on energy budget sensitivity estimates based on the carefully considered AR5 forcing and heat uptake data, but those had been published too recently for any peer reviewed sensitivity estimates based on them to exist.
I am very pleased to say that the position has now changed. Lewis N and Curry J A: The implications for climate sensitivity of AR5 forcing and heat uptake estimates, Climate Dynamics (2014), has just been published, here. A non-paywalled version of the paper is available here, along with data and code. The paper’s results show the best (median) estimates and ‘likely’ (17–83% probability) ranges for equilibrium/effective climate sensitivity (ECS) and transient climate response (TCR) given in the Lewis & Crok report to have been slightly on the high side.
Our paper derives ECS and TCR estimates using the AR5 forcing and heat uptake estimates and uncertainty ranges. The analysis uses a global energy budget model that links ECS and TCR to changes in global mean surface temperature (GMST), radiative forcing and the rate of ocean etc. heat uptake between a base and a final period. The resulting estimates are less dependent on global climate models and allow more realistically for forcing uncertainties than similar estimates, such as those from the Otto et al (2013) paper.
Base and final periods were selected that have well matched volcanic activity and influence from internal variability, and reasonable agreement between ocean heat content datasets. The preferred pairing is 1859–1882 with 1995–2011, the longest early and late periods free of significant volcanic activity, which provide the largest change in forcing and hence the narrowest uncertainty ranges.
Table 1 gives the ECS and TCR estimates for the four base period – final period combinations used.
AR5 does not give a 95% bound for ECS, but its 90% bound of 6°C is double that of 3.0°C for our study, based on the preferred 1859–1882 and 1995–2011 periods.
Considerable care was taken to allow for all relevant uncertainties. One reviewer applauded “the very thorough analysis that has been done and the attempt at clearly and carefully accounting for uncertainties”, whilst another commented that the paper provides “a state of the art update of the energy balance estimates including a comprehensive treatment of the AR5 data and assessments”.
UPDATE2: Judith Curry weighs in. More details on the paper at