Guest essay by Bob Irvine

A common refrain from the “settled science” community is that there is no known low sensitivity model that can produce either the total temperature rise or the general temperature profile of the last century.

This, however, is only the case if we assume that the efficacy of a GHG forcing is substantially the same as or slightly higher than the efficacy of a similar solar forcing. The lack of a successful low sensitivity model, then, should not come as too much of a surprise, as this is the position taken by all the IPCC reports, including the AR5.

There is, however, a strong physical case to be made for GHG efficacy being a lot lower than solar efficacy. The following paper published by the Wessex Institute of Technology outlines this case.

The abstract can be found at ; http://www.witpress.com/elibrary/wit-transactions-on-engineering-sciences/83/27156

A Comparison Of The Efficacy Of Greenhouse Gas Forcing And Solar Forcing

Free (open access) Paper DOI 10.2495/HT140241

R. A. Irvine

Abstract

The efficacy (E) of a forcing is a measure of its capacity to generate a temperature response in the earth’s system. Most Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models assume that the efficacy of a solar forcing is close to the efficacy of a similar sized greenhouse gas (GHG) forcing. This paper examines the possibility that a change in short wave solar forcing may more readily contribute to ocean heat content (OHC) than a similar change in long wave GHG forcing. If this hypothesis is shown to be correct, then it follows that equilibrium restoration times at the top of the atmosphere (TOA) are likely to be considerably faster, on average, for a change in GHG forcing than for a similar change in solar forcing. A crude forcings model has been developed that matches almost perfectly (R2 = 0.89) the National Oceanic and Atmospheric Administration (NOAA) temperature series from 1880 to 2010. This model is compared to and performs much better over this period than the United Kingdom Met Office’s (HadGEM2) contribution to the CMIP5 (R2 = 0.16). It is concluded, by implication that the efficacy of a GHG forcing is likely to be considerably lower than the efficacy of a similar sized solar forcing. Keywords: efficacy, forcing, greenhouse gas, solar, sensitivity, climate, model.

Free access to the paper is available by logging on at witpress.com and conducting an advanced search for “A comparison of the efficacy of greenhouse gas forcing and solar forcing” by R.A. Irvine, 2014. doi:10.2495/HT140241

The Basic Energy Model (BEM) outlined in the paper produces the following reconstruction (Fig 1). It has a low CO2 sensitivity of approximately 1.3C (CO2 doubling) or 3.5C/wm2 and a very strong correlation with the NOAA temperature series of R2=0.89. Importantly this model reproduces the current temperature hiatus which is proving to be a major problem for all the high sensitivity models used by the IPCC.

Fig 1; Low sensitivity model described in Irvine 2014 compared to NOAA temperature series

The inputs to the model are anthropogenic GHGs, solar, anthropogenic aerosols and internal variability.

The aerosol input to the model is toward the lower end, but still within the IPCC’s range. Internal variability is consistent with our current knowledge and is based on a combination of the AMO and PDO indexes. The solar input assumes a solar multiplier of some sort and is consistent with our knowledge of temperature over the last millennium as graphed in the AR5 and discussed in Yu & Luo 2014.

The physics behind the model is based on the established fact that the oceans are opaque to long wave GHG energy but are very transparent to short wave solar energy. This implies that GHG energy is returned to the atmosphere and space very quickly as latent heat of evaporation while solar energy is effectively absorbed to a depth of many meters with consequent delays in equilibrium at the Top of the Atmosphere (TOA).

The following quote from Hansen 2011, makes the obvious point that response time is proportional to climate sensitivity; ‘On a planet with no ocean or only a mixed layer ocean, the climate response time is proportional to climate sensitivity….Hansen et al 1985, show analytically, with ocean mixing approximated as a diffusive process, that the response time increases as the square of climate sensitivity.”

The case has been made at Real Climate and other places, that the top fraction of a millimetre, warmed by GHG energy, acts as a blanket to slow the cooling of the oceans or, alternatively, is thoroughly mixed by wave action to the point where it effectively has the same effect on Ocean Heat Content (OHC) as solar energy that is transported many meters into the oceans by radiation.

All these different mechanisms will have some effect, but to say they have the same effect is a huge assumption and, nearly certainly, not true. In fact, this is shown to be untrue by an experiment outlined in the paper. Basically, two tubs of warm water, one under a clear cling wrap roof and one under a reflective foil roof, are allowed to cool. In test A they are both free to evaporate and both cool at the same rate. In test B evaporation is restricted by placing cling wrap on the surface of the water in both tubs. In test B the tub under the foil sky is significantly affected by downward long wave radiation and cools more slowly.

Test B is how the IPCC models the oceans while test A indicates that long wave radiation does not significantly affect the temperature of a water body if that water is free to evaporate. I should at this point acknowledge the work of Konrad Hartmann and Roger Tattersal in developing the experiment. I have performed this experiment myself and confirmed their results.

The initial high sensitivities used by the IPCC were based on glacial maxima and volcanic measurements and are essentially based on solar forcing only. These sensitivities will, therefore, not apply to GHGs if this paper’s assumptions are correct, a position that is supported by the experiment and the accuracy of the model in Fig 1. The IPCC’s high sensitivity models are now assuming large amounts of energy are diverting to the deep ocean as an explanation of the lack of atmospheric warming. This is unlikely given the NOAA’s recent sea level budget report 2005-2012 by Eric Leuliette; http://www.star.nesdis.noaa.gov/sod/lsa/SeaLevelRise/documents/NOAA_NESDIS_Sea_Level_Rise_Budget_Report_2012.pdf

This report shows a sea level budget that is balanced since 2007 using a level or falling thermal expansion component. It is becoming increasingly obvious that no model, with a solid physical basis, can accurately track the slope of the temperature increase from 1910 to 1940, the cooling from 1940 to 1970, the slope of the increase from 1970 to 1998, and the current temperature hiatus without assuming GHG forcing efficacy is considerably lower than solar forcing efficacy.

References;

1. Yu & Luo, 2014, Effect of solar variations on particle formation and cloud condensation nuclei. Doi:10.1088/1748-9326/9/4/045004

2. Hansen, Sato, Kharecha & von Schuckman, 2011, Earth’s energy balance and implications. Atmos. Chem. Phys. Discuss, 11, 27031-27105, pp 19-21.

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