Efficacy Of Green House Gas Forcing Compared To Solar Forcing

Guest post by Bob Irvine

SUMMARY

This paper outlines an idea or hypothesis that should be discussed. This idea has the huge advantage of being supported by all the available data both from over the last thousand years or more, the last 60 or 70 years and the last 20 years.

We have a chance here to solve the global  warming debate and standoff.  It is quite possible that both sides of the debate have some truth on their side.  I believe there is a strong case that the climate sensitivity or temperature response to a given forcing not only depends on the size of that forcing but also on the nature of that forcing.  I have attempted to mount a case for the idea that a given  LONG WAVE  GHG forcing will have considerably lower temperature response than a similar SHORT WAVE solar forcing.

The alarmists may well be correct.  There is a lot of evidence from the Last Glacial Maxima and Volcanoes and other areas that climate sensitivity is quite high (about 0.8, i.e. requil. T=0.8xrF).  Certainly, this can be seen on geological scales.  These estimates are based on Short Wave Solar Forcings.  The trouble starts when they try to apply these high sensitivities to the enormous increase in Long Wave GHG forcing that has occurred in the last 60 or 70 years.  They mistakenly assume that a given GHG forcing will have the same equilibrium temperature response as a similar Solar Forcing and then find it difficult or impossible to make the meagre temperature response over recent years fit their high sensitivities.

The riddle is neatly solved if we accept the concept of “Effective Climate Forcing”. In other words, we accept that a given Long Wave GHG Forcing has a lower climate sensitivity than a similar Short Wave Solar Forcing. It is in fact intuitively unlikely that these two forcings have the same efficacy as is assumed by the IPCC and others.

INTRODUCTION

The efficacy of a given forcing is an estimate of its efficiency in provoking an equilibrium temperature response in the earth’s system. The IPCC and others assume that a given change in GHG forcing will produce a temperature response that is approximately equal to the temperature response from a similar change in solar forcing.

That this is not necessarily the case is discussed in the literature. Joshi et al 2003, Hansen and Nazarenko 2004 and Shine et al 2003 all conclude that the same forcing can have a different temperature response depending on its nature or geographic location.

Forster and Taylor 2006, “Climate Forcings and Climate Sensitivities Diagnosed from Coupled Climate Model Integrations “ make the case that ”Effective Climate Forcing” is a much more useful way of estimating climate sensitivity than conventional; one size fits all, Radiative Forcing. They make their case succinctly in the following quote;

“Imagine, for example, that the atmosphere alone (perhaps through some cloud change unrelated to any surface temperature response) quickly responds to a large radiative forcing to restore the flux imbalance at the TOA (Top Of Atmosphere), yielding a small effective climate forcing. In this case the ocean would never get a chance to respond to the initial Radiative forcing, so the resulting climate response would be small and this would be consistent with our diagnosed “effective climate forcing” rather than the conventional “Radiative forcing.”

In the quote above a shorter response time at the TOA produces a lower climate sensitivity. Hansen, Sato and Kharecha confirm and support this in their paper “Earth’s Energy Imbalance and Implications”, by saying

“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.”

If it can be shown that the restoration of the flux imbalance at the TOA is quicker for a perturbation in GHG forcing than it is for a similar perturbation in solar forcing, then this would imply a lower climate sensitivity for GHG forcing than solar forcing.

DISCUSSION

It is in fact intuitively unlikely that the earth’s system would respond in almost exactly the same way to a change in Long Wave GHG forcing as it would to a change in Short Wave solar forcing, as the IPCC and others assume.

It is established physics that Long wave Radiation from GHGs only penetrates the oceans to a depth of a fraction of a millimetre. The oceans are virtually opaque to these wave lengths. Short Wave solar radiation, on the other hand, penetrates the ocean to a depth of 10 meters or more and it is counter intuitive to assume that this established fact would have close to zero effect on flux imbalance restoration times at the TOA.

Despite this matter being pivotal to any understanding of the earth’s climate response to increasing Anthropogenic GHGs (AGHG), I have been unable to find any literature supporting the IPCC’s position that solar forcing and GHG forcing have the same efficacy after the ocean/ atmosphere interface has been considered. The references mentioned by the IPCC in their reports only refer to the global nature of the two forcings and only take into account feedbacks that are related to a temperature response. These do not apply in this case. Basically, the fact that the oceans are opaque to GHGs is due to the nature of the forcing and not accounted for if the feedbacks considered are only related to a temperature response. Similarly, to assume, as the IPCC does, that GHG forcing and Solar forcing have the same “effective climate forcing” simply because they are both global in nature, also, does not take account of the opaqueness of the oceans to the wave length reemitted by GHGs.

The blogosphere does make an attempt at explaining the IPCC’s position. The only defence I am aware of is that the top fraction of a millimetre of the ocean is heated up by the Long Wave Radiation (LWR) reemitted by GHGs. This then acts as a blanket slowing the release of energy from the ocean, thereby effectively warming the ocean by nearly exactly the same amount as a similar solar forcing that penetrates the ocean to a depth of 10 meters or more.

Not only is it highly improbable that these two entirely different mechanisms would have almost exactly the same effect on OHC (Ocean Heat Content), but it can be shown by means of a simple experiment, (Appendix 1), that nearly all the Long Wave GHG energy is returned almost immediately to the atmosphere and space as latent heat of evaporation. It, therefore, has little effect on OHC. It is, also, likely that the restoration of the flux imbalance at the TOA is quicker for a perturbation in GHG forcing than it is for a similar perturbation in solar forcing.

It is apparent that the situation described in the Forster and Taylor (2006) quote above is relevant to GHG forcing. In short, the” Effective Climate Forcing” of a GHG change is likely to be considerably less than the “Effective Climate Forcing” of a similar solar change.

CORROBORATION

It is an intriguing possibility that both sides of the Global Warming debate could be correct to some extent. The IPCC and others estimate climate sensitivity by reference to three factors, none of which apply to climate sensitivity derived from a GHG forcing.

These three factors are;

1. They use “Absolute Radiative Forcing” instead of “Effective Radiative Forcing” (Forster and Gregory 2006)
2. They use sensitivities based on Solar Forcing which clearly do not apply to GHG Forcing. For example, sensitivities calculated from the Last Glacial Maxima (LGM) or volcanoes are essentially based on Solar Forcing and, therefore, do not apply to GHG Forcing. (Annan & Hargreaves 2006).
3. They use feedbacks that are dependent on an initial temperature response and, therefore, do not take account of the opaqueness of the oceans to Long Wave Radiation from GHGs. (All the Global Climate Models , GCMS)

The IPCC and others may have produced some good science that gives reasonably accurate climate sensitivity estimates for a change in solar forcing. Unfortunately, these are unlikely to apply to a GHG Forcing.

Interestingly, Idso 98 uses real world experiments that, largely, do apply to GHG Forcing and their climate sensitivity is considerably lower than the IPCC’s consensus.

The sceptics, on the other hand, are fairly obviously quite correct when they say that the high sensitivities postulated by the alarmists do not fit with the measured temperature record of the 20^th and 21^st century.

The best way to show this lack of correlation is to compare the amount of energy put into the system by human GHGs, as represented by equilibrium temperature, with actual temperature as measured in the thermometer age since 1880.

The green line in Fig. 1 equates to a sensitivity of 0.8 (rT = 0.8 x rF) which gives an equilibrium temperature increase of 3.0°C for a doubling of human CO₂, the IPCC’s central position. In 2010 the difference between the green line and blue line (actual temperature) was an unlikely 1.4°C. If present trends continue, as is likely, that gap would be close to 2.0°C in 5 years’ time.

FIG, 1 The IPCC’s upper (purple), central (green) and lower (red) equilibrium temperature predictions using their climate sensitivity to forcing. The forcings were calculated for all the human GHGs using concentrations given in 4AR and the generally accepted conversion formula, rF=5.35xln(C/C_o) WM^-2 where C is current concentration and C_O is starting concentration. These are compared with actual temperature (blue). For comparison purposes all graphs were zeroed in 1880.

NOTE; It is generally believed that equilibrium temperatures are approximately 1.5 times transient temperatures (4AR) and that aerosol cooling has masked any human induced GHG warming. These are the two factors the alarmists use to attempt to explain the gap between reality and the IPCC’s calculated equilibrium temperatures from AGHGs.

There are also major inconsistencies with the Ipcc’s explanation for the warming from 1910 to 1940. Bob Tisdale discusses these inconsistencies at WUWT on the 20^th April 2013.

The only realistic explanation for this lack of correlation ( FIG, 1) is that the IPCC’s sensitivities are far too high and that the “Effective Radiative Forcing” for Long Wave GHGs is considerably lower than the “Effective Radiative Forcing “ for Short Wave solar.

APPENDIX 1

This experiment is attributed to Tallbloke and shows unequivocally that Long Wave radiation from GHGs has little or no effect on Ocean Heat Content. Short Wave Solar radiation, on the other hand, penetrates the oceans to a depth of ten meters or more and, therefore, adds significantly to OHC.

Konrad: Empirical test of ocean cooling and back radiation theory

Posted: August 25, 2011 by tallbloke in atmosphere, climate, Energy, Ocean dynamics

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Some background –

Willis Eschenbach had a guest posting over at WUWT in which he claimed that LWIR could heat Earth’s oceans. Myself and several others on the thread contended that this LWIR was likely to be stopped by the evaporative skin layer and would not slow the exit of heat from the oceans. Numerous requests for empirical evidence to support Willis’s claim only resulted in one inapplicable study used by the “Hockey Team” to support such claims. After several hundred comments without empirical evidence being offered, I gave up reading and designed and conducted an empirical experiment that shows that any effect of backscattered LWIR on the cooling rate of water would be negligible.

What follows is an edited version of the experiment design and results as posted on the WUWT thread. I would encourage others to conduct similar experiments to check my results. The equipment required is not overly expensive and the results can be observed in minutes. The results appear to show the measurable difference between reflecting LWIR back to warm water when it is free to evaporatively cool and when it can only cool through conduction and radiation.

What is required –

– Two identical probe type digital thermometers with 0.1 degree resolution

– Two identical insulated water containers. I used rectangular 200ml Tupperware style containers, insulated on their base and sides with foil and Styrofoam. I cut away the clip on rim from each lid to create a frame to clip down cling film for Test B of the experiment.

– One IR reflector. I used an A4 sheet of 10mm Styrofoam with aluminium foil attached with spray adhesive.

– One IR window. I built an A4 size “picture frame” of 10mm square balsa wood strips and stretched cling film over it.

– One 1 litre measuring jug

– Two small identical computer fans. I used Suron 50mm centrifugal blowers powered by a 6v gel cell battery

– Extra cling film

– Optional extras – kitchen timer, an A4 ”dark cool sky” panel of matt black aluminium with peltier cooling, glamorous lab assistant of choice.

What to do –

– Position probe thermometers in identical positions in both water containers. I placed the tips 10mm below the water line by drilling force fit holes in the sides of the containers.

– Position IR reflector and IR window 50mm above either water container. You may need to build two Styrofoam side walls, but air must be free to move over the surface of the water. (The use of the IR window is to ensure that air flow is similar over each water container.)

– Position the computer fans to blow across the water surface of each container, but do not turn on.

– Fill jug with warm water, stir, then fill each water container from the bucket. I used water around 40C as the ceiling was around 18C not a 3k sky.

– When and equal amount of water is in each container, turn on the computer fans.

– Observe the temperature change over time for each tank. Less than half an hour is required for such a small amount of water. You should observe that both tanks cool a the same rate (TEST A).

– Now the important bit – Repeat the experiment, but this time lay a small sheet of cling wrap on the surface of the water in each water tank. This allows cooling through radiation and conduction but prevents evaporation. You do not need the computer fans on in this test. You should be able to observe that while both containers cool slower than before, water under the IR reflector cools slowest (TEST B).

Interpretation –

In TEST A the water cools more quickly, however the two water containers temperatures remain very close to each other over time. This indicates that backscattered LWIR has a very limited effect on the rate of cooling for water when it is free to evaporatively cool.

In TEST B both water containers cool more slowly than test A, but a divergence in temperature between the two water containers is readily detectable. The container under the foil sky cools more slowly than that under the cling wrap sky. This indicates that backscattered LWIR from a warm material can slow the rate at which that material cools, if radiation and conduction are the only methods for cooling.

Test A represents the evaporative cooling conditions in the real oceans. Test B represents how the climate scientists have modelled the oceans with regard to backscattered LWIR. From what I have observed, backscattered LWIR can slow the rate at which substances cool. However in the case of liquid water that is free to cool evaporatively this effect is dramatically reduced. It would appear that including the oceans in the percentage of Earth’s surface that could be affected by backscattered LWIR may be a serious error. Earth’s oceans cover 71% of the planets surface. If backscattered LWIR cannot measurably affect liquid water, then CO2 cannot cause dangerous or catastrophic global warming.

I have conducted further tests using a “cold sky” panel cooled with ice water over the top of the cling film IR window. While the temperature divergence in the evaporation restricted test B does not appear faster, it does appear to diverge for longer.

I would encourage others to conduct similar empirical experiments and share their observations. I would be interested in comments in further experimental design, or empirical evidence related to the LWIR question.

Typical TEST A

Typical TEST B