One advantage of using this mainstream-science form of the zero-dimensional model is that it explicitly and separately accounts for the input signal T_ref and for any amplification of it via the gain factor μ in the amplifier, so that it is no longer possible either to ignore or to undervalue either T_ref or the feedback response to it that must arise as long as the feedback fraction β is nonzero.

It is proven below that the apportionment of the 35.4 K difference between T_ref = 252.2 K and T_eq = 287.6 K in 1850 derived earlier in our Gedankenexperiment is in fact the correct apportionment. Starting with the mainstream equation, in due time we introduce the direct or open-loop gain factor μ = 1 + ΔT_ref / T_ref. The feedback factor μβ, the product of the direct or open-loop gain factor μ and the feedback fraction β, has precisely the form that we used in deriving the feedback fraction f as 1 – (243.3 + 8.9) / 287.6 = 0.123, confirming that our apportionment was correct.

Note in passing that in official climatology f is at once the feedback fraction and the feedback factor, since official climatology implicitly (if paradoxically) assumes that the direct or open-loop gain factor μ = 1. In practice, this particular assumption leads official climatology into little error, for the amplification of emission temperature driven by the presence of the non-condensing greenhouse gases is a small fraction of that temperature.

But was it reasonable for us to assume that the 287.6 K temperature in 1850, before Man had exercised any noticeable influence on it, was an equilibrium temperature? Well, yes. We know that in the 168 years since 1850 the world has warmed by only 0.8 K or so, and official climatology attributes all of that warming to Man, not Nature.

Was it reasonable for us to start with Lacis’ implicit emission temperature of 243.3 K, reflecting their specified albedo 0.418 on a waterbelt Earth in the absence of the non-condensing greenhouse gases? Why not start with Pierrehumbert (2011), who said that a snowball Earth would have an albedo 0.6, implying an emission temperature 221.5 K? Let’s do the math. The feedback fraction f = μβ would then be 1 – (221.5 + 8.9) / 287.6 = 0.20.

Thus, from a snowball Earth to 1850, the mean feedback fraction is 0.20; from a waterbelt Earth to 1850, it is 0.12; and at today’s albedo 0.293, implying an emission temperature 255.4 K, it is 1 – (255.4 + 8.9) / 287.6 = 0.08. Which is where we came in at the beginning of this series. For you will notice that, as the great ice sheets melt, the dominance of the surface albedo feedback inexorably diminishes, whereupon the feedback fraction falls over time.

Though the surface albedo feedback may have dominated till now, what about the biggest of all the feedbacks today, the water-vapor feedback? The Clausius-Clapeyron relation implies that the space occupied by the atmosphere may (though not must) carry near-exponentially more water vapor – a greenhouse gas – as it warms. Wentz (2007) found that total column water vapor ought to increase by about 7% per Kelvin of warming. Lacis (2010) allowed for that rate of growth in saying that if one removed the non-condensing greenhouse gases from today’s atmosphere and the temperature fell by 36 K from 288 to 252 K, there would be about 10% of today’s water vapor in the atmosphere: thus, 100% / 1.07³⁶ = 9%.

Specific humidity (g kg^–1) at pressure altitudes 300, 6000 and 1000 mb

However, though the increase in column water vapor with warming is thus thought to be exponential, the consequent feedback forcing is approximately logarithmic (just as the direct CO₂ forcing is logarithmic). What is more, a substantial fraction of the consequent feedback response is offset by a reduction in the lapse-rate feedback. Accordingly, the water-vapor/lapse-rate feedback response is approximately linear.

Over the period of the NOAA record of specific humidity at three pressure altitudes (above), there was 0.8 K global warming. Therefore, Wentz would have expected an increase of about 5.5% in water vapor. Sure enough, close to the surface, where most of the water vapor is to be found, there was a trend in specific humidity of approximately that value. But the water-vapor feedback response at low altitudes is small because the air is all but saturated already.

However, at altitude, where the air is drier and the only significant warming from additional water vapor might arise, specific humidity actually fell, confirming the non-existence of the predicted tropical mid-troposphere “hot spot” that was supposed to have been driven by increased water vapor. In all, then, there is little evidence to suggest that the temperature response to increased water vapor and correspondingly diminished lapse-rate is non-linear. Other feedbacks are not large enough to make much difference even if they are non-linear.

Our method predicts 0.78 K warming from 1850-2011, and 0.75 K was observed

One commenter here has complained the Planck parameter (the quantity by which a radiative forcing in Watts per square meter is multiplied to convert it to a temperature change) is neither constant nor linear: instead, he says, it is the first derivative of a fourth-power relation, the fundamental equation of radiative transfer. Here, it is necessary to know a little calculus. Adopting the usual harmless simplifying assumption of constant unit emissivity, the first derivative, i.e. the change ΔT_ref in reference temperature per unit change ΔQ₀ in radiative flux density, is simply T_ref / (4Q₀), which is linear.

A simple approximation to integrate latitudinal variations in the Planck parameter is to take the Schlesinger ratio: i.e., the ratio of surface temperature T_S to four times the flux density Q₀ = 241.2 Watts per square meter at the emission altitude. At the 255.4 K that would prevail at the surface today without greenhouse gases or feedbacks, the Planck parameter would be 255.4 / (4 x 241.2) = 0.26 Kelvin per Watt per square meter. At today’s 288.4 K surface temperature, the Planck parameter is 288.4 / (4 x 241.2) = 0.30. Not much nonlinearity there.

It is, therefore, reasonable to assume that something like the mean feedback fraction 0.08 derived from the experiment in adding the non-condensing greenhouse gases to the atmosphere will continue to prevail. If so, the equilibrium warming to be expected from the 2.29 Watts per square meter of net industrial-era anthropogenic forcing to 2011 (IPCC, 2013, Fig. SPM.5) will be 2.29 / 3.2 / (1 – 0.08) = 0.78 K. Sure enough, the least-squares linear-regression trend on the HadCRUT4 monthly global mean surface temperature dataset since 1850-2011 (above) shows 0.75 K warming over the period.

But why do the temperature readings from the ARGO bathythermographs indicate a “radiative energy imbalance” suggesting that there is more warming in the pipeline but that the vast heat capacity of the oceans has absorbed it for now?

One possibility is that not all of the global warming since 1850 was anthropogenic. Suppose that the radiative imbalance to 2010 was 0.59 W m^–2 (Smith 2015). Warming has thus radiated 2.29 – 0.59 = 1.70 W m^–2 (74.2%) to space. Equilibrium warming arising from both anthropogenic and natural forcings to 2011 may thus eventually prove to have been 34.8% greater than the observed 0.75 K industrial-era warming to 2011: i.e., 1.0 K. If 0.78 K of that 1.0 K is anthropogenic, there is nothing to prevent the remaining 0.22 K from having occurred naturally owing to internal variability. This result is actually consistent with the supposed “consensus” proposition that more than half of all recent warming is anthropogenic.

The implication for Charney sensitivity – i.e., equilibrium sensitivity to doubled CO₂ concentration – is straightforward. The models find the CO₂ forcing to be 3.5 Watts per square meter per doubling. Dividing this by 3.2 to allow for today’s value of the Planck parameter converts that value to a reference sensitivity of 1.1 K. Then Charney sensitivity is 1.1 / (1 – 0.08) = 1.2 K. And that’s the bottom line. Not the 3.3 K mid-range estimate of the CMIP5 models. Not the 11 K imagined by Stern (2006). Just 1.2 K per CO₂ doubling. And that is nothing like enough to worry about.

None of the objections raised in response to our result has proven substantial. For instance, Yahoo Answers (even less reliable than Wikipedia) weighed in with the following delightfully fatuous answer to the question “Has Monckton found a fatal error?”

What he does is put forward the following nonsensical argument –

1. If I take the 255.4 K temperature of the earth without greenhouse gases, and I add in the 8K increase with greenhouse gases I get a temperature of 263.4 K.

2. Now, what I’m going to say is say that this total temperature (rather than just the effect of the greenhouse gases) leads to a feedback. And if I use this figure I get a feedback of 1 – (263.4 / 287.6) = 0.08.

And the problem is … how can the temperature of the planet (255.4 K) without greenhouse gases then lead to a feedback? The feedback is due to the gases themselves. You can’t argue that the feedback and hence amplified temperature due to greenhouse gases is actually due to the temperature of the planet without the greenhouse gases! What he’s done is taken the baseline on which the increase and feedback is based, and then circled back to use the baseline as the source of the increase and feedback.

So, I’m afraid it’s total crap …

The error made by Yahoo Answers lies in the false assertion that “the feedback is due to the gases themselves”. No: one must distinguish between the condensing greenhouse gases (a change in the atmospheric burden of water vapor is a feedback process) and the non-condensing greenhouse gases such as CO₂ (nearly all changes in the concentration of the non-condensing gases are forcings). All of the feedback processes listed in Table 1 would be present even in the absence of any of the non-condensing greenhouse gases.

Another objection is that perhaps official climatology makes full allowance for the feedback response to emission temperature after all. That objection may be swiftly dealt with. Here is the typically inspissate and obscurantist definition of a “climate feedback” in IPCC (2013):

Climate feedback An interaction in which a perturbation in one climate quantity causes a change in a second, and the change in the second quantity ultimately leads to an additional change in the first. A negative feedback is one in which the initial perturbation is weakened by the changes it causes; a positive feedback is one in which the initial perturbation is enhanced. In this Assessment Report, a somewhat narrower definition is often used in which the climate quantity that is perturbed is the global mean surface temperature, which in turn causes changes in the global radiation budget. In either case, the initial perturbation can either be externally forced or arise as part of internal variability.

IPCC’s definition thus explicitly excludes any possibility of a feedback response to a pre-existing temperature, such as the 255.4 K emission temperature that would prevail at the surface in the absence of any greenhouse gases or feedbacks. It was for this reason that Roy Spencer thought we must be wrong.

Our simple point remains: how can an inanimate feedback process know how to distinguish between the input emission of temperature of 255 K and a further 9 K of temperature arising from the addition of the non-condensing greenhouse gases to the atmospheric mix? How can it know it should react less to the former than to the latter, or (if IPCC’s definition is followed) not at all to the former and extravagantly to the latter? In the end, despite some valiant attempts by true-believers to complicate matters, our point is as simple – and in our submission as unanswerable – as that.