Saturday, March 29, 2014

New paper finds climate sensitivity to CO2 is ~27% less than claimed by IPCC

A paper published today in Climate Dynamics uses ocean heat content data to estimate climate sensitivity from a doubling of CO2 levels at a likely range of 1.5 - 2.9 C [midrange = 2.2 C], which is 27% less than the midrange 3C* [1.5C - 4.5C] estimated in the forthcoming IPCC Report. Furthermore, the paper finds climate models overestimate sensitivity to radiative forcing by almost a factor of two [1.7X, 1.16 Wm−2K−1 vs 2.05 Wm−2K−1]

The paper is written by lukewarmist & blogger Troy Masters, and utilizes ocean heat content data from Levitus et al 2012 paper, which found the oceans have warmed only 0.09C over the past 55 yearsas well as ARGO float data. The paper, however, does not consider changes in solar activity, cloudiness, ocean and atmospheric oscillations, or other natural variability in the analysis, and states aerosol forcing is very uncertain. If any of these factors also played a role, estimates of climate sensitivity to CO2 could fall even further.

The forthcoming IPCC report is already outdated and dead on arrival, since it does not incorporate multiple publications of lower estimates of transient and equilibrium climate sensitivity published after the cut-off date for inclusion, including this new paper and several others. Thus, all of the impact analyses and policy recommendations are also obsolete and exaggerated. 

*Note: The IPCC has discontinued use of a midrange value for equilibrium climate sensitivity in the new report, however, 3C is the mean of the "likely" range reported of 1.5-4.5C.

Climate Dynamics

April 2014, Volume 42, Issue 7-8, pp 2173-2181

Climate sensitivity is estimated based on 0–2,000 m ocean heat content and surface temperature observations from the second half of the 20th century and first decade of the 21st century, using a simple energy balance model and the change in the rate of ocean heat uptake to determine the radiative restoration strength over this time period. The relationship between this 30–50 year radiative restoration strength and longer term effective sensitivity is investigated using an ensemble of 32 model configurations from the Coupled Model Intercomparison Project phase 5 (CMIP5), suggesting a strong correlation between the two. The mean radiative restoration strength over this period for the CMIP5 members examined is 1.16 Wm−2K−1, compared to 2.05 Wm−2K−1 from the observations. This suggests that temperature in these CMIP5 models may be too sensitive to perturbations in radiative forcing, although this depends on the actual magnitude of the anthropogenic aerosol forcing in the modern period. The potential change in the radiative restoration strength over longer timescales is also considered, resulting in a likely (67 %) range of 1.5–2.9 K [midrange 2.2C] for equilibrium climate sensitivity, and a 90 % confidence interval of 1.2–5.1 K.



  1. In 2007, Stephen Schwartz of Brookhaven Laboratory arrived at the same estimated range in the revised version of the following paper. I don't have the reference to the revised version but it is online.

    Dr. Schwartz also used oceanic data. The caveat here is the uncertainty in the evidence arising from poor sampling of ocean temperatures until recently.

    Schwartz S. E., Heat capacity, time constant, and sensitivity of Earth’s climate system. J. Geophys. Res., 112, D24S05 (2007)

    1. Thanks - I assume you're referring to this one:

  2. Masters has used the median estimate for the ECS range for this paper of 1.98 C according to the below post, lowering it below the "mid-range" value of 2.2 C mentioned above.
    "Clearly, the median estimate for ECS of 1.98K seems to match some other observationally-based estimates with a lower sensitivity"