Climate sensitivity and forcing 2 a re-evaluation of the IPCC position

Michael Davies

Junceira Cao Sertainho


21 May 2011

I ASSERT MY RIGHT UNDER THE INTELLECTUAL PROPERTY RIGHTS LAWS OF THE EUROPEAN UNION AS THE SOLE AUTHOR OF THIS WORK. I acknowledge the owners of the freely available scientific literature and various websites on which I conducted my research.

Climate sensitivity and forcing a re-evaluation of the IPCC position

Executive summary

I intend to give a new accurate interpretation of climate sensitivity in relation to insolation , CO2 and H2O forcing and Milankovitch Cycles. In doing so I will draw down on empirical evidence available in published data namely

    1. 800px-Vostok_420ky_4curves_insolation
    2. 65_Myr_Climate_Change
    3. Five_Myr_Climate_Change


The millennial scale climate of the earth appears exceedingly complex, but simple mathematical models of the temperature (not climate) of the earth can be constructed. I will use similar models to that used by the IPCC, but intend to recalculate climate sensitivity.

The conclusions in this theory substantiate claims made in my previous postings on the following blog posts

The IPCC position

extracts from

From Wikipedia, the free encyclopedia

1. Climate sensitivity is a measure of how responsive the temperature of the climate system is to a change in the radiative forcing. It is usually expressed as the temperature change associated with a doubling of the concentration of carbon dioxide in Earth’s atmosphere.

The equilibrium climate sensitivity refers to the equilibrium change in global mean near-surface air temperature that would result from a sustained doubling of the atmospheric (equivalent) CO2 concentration (ΔTx2). This value is estimated, by the IPCC Fourth Assessment Report (AR4) as likely to be in the range 2 to 4.5°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C. Values substantially higher than 4.5°C cannot be excluded, but agreement of models with observations is not as good for those values.[1] This is a slight change from the IPCC Third Assessment Report (TAR), which said it was “likely to be in the range of 1.5 to 4.5°C”.[2] More recent work continues to support a best-guess value around 3°C.[3]


2. Although climate sensitivity is usually used in the context of radiative forcing by CO2, it is thought of as a general property of the climate system: the change in surface air temperature (ΔTs) following a unit change in radiative forcing (RF) and expressed in units of °C/(W/m2). For this to be so, the measure must be independent of the nature of the forcing (e.g. from greenhouse gases or solar variation); to first order this is indeed found to be so.

For a coupled atmosphere-ocean global climate model the climate sensitivity is an emergent property: it is not a model parameter, but rather a result of a combination of model physics and parameters. By contrast, simpler energy-balance models may have climate sensitivity as an explicit paramter.

\Delta T_s = \lambda \cdot RF

The terms represented in the equation relate radiative forcing of any cause to linear changes in global surface temperature change.

It is also possible to estimate climate sensitivity from observations; however, this is difficult due to uncertainties in the forcing and temperature histories.

Climate sensitivity can be a useful summary of the sensitivity of the real climate, or of a given model climate. But it is not the same as the expected climate change at, say 2100: the TAR forecasts this to be an increase of 1.4 to 5.8°C over 1990.

3. Essentials

CO2 climate sensitivity has a component directly due to radiative forcing by CO2 (or any other change in Earth’s radiative balance), and a further contribution arising from feedbacks, positive and negative. “Without any feedbacks, a doubling of CO2 (which amounts to a forcing of 3.7 W/m2) would result in 1°C global warming, which is easy to calculate and is undisputed. The remaining uncertainty is due entirely to feedbacks in the system, namely, the water vapor feedback, the ice-albedo feedback, the cloud feedback, and the lapse rate feedback”;[6] addition of these feedbacks leads to a value of approximately 3°C ± 1.5°C.

4. Sample calculation using ice-age data

“… examine the change in temperature and solar forcing between glaciation (ice age) and interglacial (no ice age) periods. The change in temperature, revealed in ice core samples, is 5 °C, while the change in solar forcing is 7.1 W/m2. The computed climate sensitivity is therefore 5/7.1 = 0.7 K(W/m2)−1. We can use this empirically derived climate sensitivity to predict the temperature rise from a forcing of 4 W/m2, arising from a doubling of the atmospheric CO2 from pre-industrial levels. The result is a predicted temperature increase of 3 °C.”[11] Based on analysis of uncertainties in total forcing, in Antarctic cooling, and in the ratio of global to Antarctic cooling of the last glacial maximum relative to the present, Ganopolski and Schneider von Deimling (2008) infer a range of 1.3 to 6.8 °C for climate sensitivity determined by this approach.[12]

5. History of the concept

[edit] Three degrees as the consensus estimate

The standard modern estimate of climate sensitivity — 3°C, plus or minus 1.5°C — originates with a committee on anthropogenic global warming convened in 1979 by the National Academy of Sciences and chaired by Jule Charney. Only two sets of models were available; one, due to Syukuro Manabe, exhibited a climate sensitivity of 2°C, the other, due to James E. Hansen, exhibited a climate sensitivity of 4°C. “According to Manabe, Charney chose 0.5°C as a not-unreasonable margin of error, subtracted it from Manabe’s number, and added it to Hansen’s. Thus was born the 1.5°C-to-4.5°C range of likely climate sensitivity that has appeared in every greenhouse assessment since…”[13]

6. Other estimates

Idso, (1998)[14] reprinted in [15] calculated based on eight natural experiments a λ of 0.1°C/(Wm−2) resulting in a climate sensitivity of only 0.4°C for a doubling of the concentration of CO2 in the atmosphere.


Analysing the Earth as a Simple Machine

I have called my next paper Analysing the Earth as a Simple Machine, and have come to the following conclusions.


My interpretation of the above graph indicates that at current CO2 levels of 400 ppm a climate sensitivity λ of 0.2°C/(Wm−2) is indicated resulting in a temperature rise of only 0.8°C for a doubling of the concentration of CO2 in the atmosphere. This gives a predicted variation Tmax of 2 °C over each subsequent Milankovich cycle for a predicted CO2 value of 560 ppm. Furthermore a further doubling of CO2 to 1120 ppm would further decrease the sensitivity such that additional CO2 forcing is likely to be in the order of <0.5 °C. this gives a predicted total milankovitch cycle variation of <2.5 °C for a quadrupling of CO2.

Mad Mike



About madmikedavies

Retired Communications Engineer, living in Portugal. Interests are Cosmology, Earth Sciences, Organic farming, Climatology, Football, Golf, Birdwatching, and Dogs
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One Response to Climate sensitivity and forcing 2 a re-evaluation of the IPCC position

  1. Nice Blog with Excellent information


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