Comments On A New Paper On “Climate Sensitivity” By Lin Et Al 2010

There is a new paper on the relationship of top of the atmosphere radiative forcing to the response in the annual average global surface temperature trend. Unfortunately, the paper perpetuates an archaic perspective with respect to the assessment of the climate system including the global annual averaged radiative imbalance.

The paper is

 Lin, B., Chambers, L., P. Stackhouse Jr., Wielicki, B., Hu, Y., Minnis, P., Loeb, N., Sun, W., Potter, G., Min, Q., Schuster, G., and Fan, T.-F.: Estimations of climate sensitivity based on top-of-atmosphere radiation imbalance, Atmos. Chem. Phys., 10, 1923-1930, doi:10.5194/acp-10-1923-2010, 2010

The abstract reads

“Large climate feedback uncertainties limit the accuracy in predicting the response of the Earth’s climate to the increase of CO2 concentration within the atmosphere. This study explores a potential to reduce uncertainties in climate sensitivity estimations using energy balance analysis, especially top-of-atmosphere (TOA) radiation imbalance. The time-scales studied generally cover from decade to century, that is, middle-range climate sensitivity is considered, which is directly related to the climate issue caused by atmospheric CO2 change. The significant difference between current analysis and previous energy balance models is that the current study targets at the boundary condition problem instead of solving the initial condition problem. Additionally, climate system memory and deep ocean heat transport are considered. The climate feedbacks are obtained based on the constraints of the TOA radiation imbalance and surface temperature measurements of the present climate. In this study, the TOA imbalance value of 0.85 W/m2 is used. Note that this imbalance value has large uncertainties. Based on this value, a positive climate feedback with a feedback coefficient ranging from −1.3 to −1.0 W/m2/K is found. The range of feedback coefficient is determined by climate system memory. The longer the memory, the stronger the positive feedback. The estimated time constant of the climate is large (70~120 years) mainly owing to the deep ocean heat transport, implying that the system may be not in an equilibrium state under the external forcing during the industrial era. For the doubled-CO2 climate (or 3.7 W/m2 forcing), the estimated global warming would be 3.1 K if the current estimate of 0.85 W/m2 TOA net radiative heating could be confirmed. With accurate long-term measurements of TOA radiation, the analysis method suggested by this study provides a great potential in the estimations of middle-range climate sensitivity.”

The conclusion reads

Since for the modeled climate system (or for the climate variability on time scales about a century) the climate memory is generally within 1 to 10 years, the estimated total climate feedback coefficient ftot would be in the range of −1.3 to −1.0 W/m2/K for the estimated 0.85 W/m2 TOA radiation imbalance. Thus, for the 2×CO2 climate (or 3.7 W/m2 forcing), the estimated global warming would be in the range between 2.8K to 3.7 K. Since the best estimated memory length of the climate system is about 4 years owing to the time lag of the maximum autocorrelation beyond 0 lag of the GISS surface temperature data, the best estimates of fm and ftot would be 4.8 and −1.2 W/m2/K, respectively, resulting in our estimated most likely warming of 3.1K if the radiation imbalance used is confirmed. These results are clearly in alignment with previous projections around the peaks of climate sensitivity distributions obtained from GCMs (IPCC, 2007). The difference between current estimates and previous results is that our estimates provide very straightforward physics, and have a great potential to reduce the broad range of climate predictions from GCMs.

“Because of the extreme importance of the climate energy imbalance for climate studies as shown in this report, longterm measurements of the TOA radiation with both high precision and high absolute accuracy are desperately demanded. These measurements will provide the key information to nail down the climate feedback and middle-range climate sensitivity. A great potential in accurate climate predictions, thus, could be realized. Furthermore, with long-term, accurate global energy imbalance measurements and the method suggested by this study, a physically-based tool for decisions related to global warming policies can be offered to the public and policymakers, which will have enormous socioeconomic impacts.”

The problems in this paper include:

1. What is called “climate sensitivity” is actually a “global average annual surface temperature sensitivity”.  There statement that a ” study [that] explores a potential to reduce uncertainties in climate sensitivity estimations using energy balance analysis, especially top-of-atmosphere (TOA) radiation imbalance” perpetuates the misunderstanding that this is a broad “climate” metric.

2. Another serious error in the paper is their assumption of a 0.85 Watts per meter squared top of the atmosphere radiative imbalance. However, as summarized on my weblog (see), the global annually average radiative imbalance over the last 7 years or so is much less than 0.85 Watts per meter squared. The Lin et al 2010 paper ignored this new observational diagnosis of the Earth’s energy budget.

3.  The statement in their conclusion that “[b]ecause of the extreme importance of the climate energy imbalance for climate studies as shown in this report, long term measurements of the TOA radiation with both high precision and high absolute accuracy are desperately demanded”, ignores the finding that the diagnosis of changes in ocean heat content is a much more robust metric to assess the radiative imbalance. The assessment of heat content in Joules of the ocean is an effective integrated metric of the global annual radiative imbalance, as discussed, for example, in

Ellis et al. 1978: The annual variation in the global heat balance of the Earth. J. Climate. 83, 1958-1962

Pielke Sr., R.A., 2003: Heat storage within the Earth system. Bull. Amer. Meteor. Soc., 84, 331-335.

Pielke Sr., R.A., 2008: A broader view of the role of humans in the climate system. Physics Today, 61, Vol. 11, 54-55.

It is time to scrap the use of the global annual averaged surface temperature as the metric to diagnose global warming and cooling.

4. There is no “best estimated memory length of the climate system owing to the time lag of the maximum autocorrelation beyond 0 lag of the GISS surface temperature data”.  First, the climate system is much more than just a globally averaged surface temperature. Even with respect to global annual averaged radiative imbalance, the retention of the scientifically inaccurate use of surface temperature trends (with its lags) is unnecessary.  As discussed in the papers under #3, the changes in the  ocean heat content over time, when accurately measured, provides a diagnostic of the radiative imbalance without the need for considering lags or a so-called “climate sensitivity”.

Until the climate community moves away from the surface temperature trends, with its inaccuracy and unnecessary complexity, and replaces it with the diagnosis of ocean heat content changes in Joules over time, the policy community will continue to be misled as to the actual warming and cooling of the climate system.

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