A comment from Tel late last year was so surgically cutting, it’s worthy of it’s own post. Un-Skeptical Science was trying to explain why climate sensitivity is high. The post includes formula’s and fancy graphs, and looks authoritative — yet underlying everything are errors of reasoning that nullify all the points that rest upon them. Things like assumptions about linearity (which means more or less, they make the mistake of assuming that all forcings and feedbacks operate at similar ratios and strengths when the planet is an iceball as they do when Earth hits a rare warm phase). An unmeasureable variable is the telltale signature of a fudge-factor. It is what you make of it. Fits better in a course analyzing postmodernistic intertexuality of Swahili neo-linguists.
Guest Post by Tel
This “Skeptical Science” post is an excellent choice to show how little credibility there is in the whole feedback house of cards:
It’s important to note that the surface temperature change is proportional to the sensitivity and radiative forcing (in W m-2), regardless of the source of the energy imbalance. The climate sensitivity to different radiative forcings differs depending on the efficacy of the forcing, but the climate is not significantly more sensitive to other radiative forcings besides greenhouse gases.
So sensitivity is all the same regardless of the forcing, but at the same time, it might be different thanks to an “efficacy” which means whatever you want it to mean, in order for everything to have the same sensitivity. Hmmmm, right I think I’ve got it. So what are the units of “efficacy”? Oh, it doesn’t have any units, it is unitless because all factors are scaled relative to CO2 forcing… except we have some of those forcings being solar radiation, others being a gas, and others as particulate matter. What sort of unitless scaling factor can relate particulate counts to solar radiation? Why, CO2 of course! Is that the LOG of CO2 vs the LOG of solar radiation (presumably giving an answer in decibels)? Maybe it is the small signal gain based on the first derivative about some arbitrary operating point? Who knows, who cares, just blurt some numbers on the table, no one is about to check any of this.
In other words, if you argue that the Earth has a low climate sensitivity to CO2, you are also arguing for a low climate sensitivity to other influences such as solar irradiance, orbital changes, and volcanic emissions.
Unless you happen to argue for different “efficacy” factors, in which case you get any result you feel like getting.
In fact, as shown in Figure 1, the climate is less sensitive to changes in solar activity than greenhouse gases.
So some forcings are more equal than others, makes sense. Solidarnosk comrade, we will outlast them.
Thus when arguing for low climate sensitivity, it becomes difficult to explain past climate changes. For example, between glacial and interglacial periods, the planet’s average temperature changes on the order of 6°C (more like 8-10°C in the Antarctic). If the climate sensitivity is low, for example due to increasing low-lying cloud cover reflecting more sunlight as a response to global warming, then how can these large past climate changes be explained?
Well, the easiest way to explain it would be that the system is nonlinear so there’s no reason to presume sensitivity is the same as it was during the last glaciation. But with all of these excellent “efficacy” fudge factors (all of which probably are also nonlinear) we could comfortably explain anything at all. Really. So let’s go over those units again
People write learned papers about this $#!+ such as the following:
We use a global climate model to compare the effectiveness of many climate forcing agents for producing climate change. We find a substantial range in the “efficacy” of different forcings, where the efficacy is the global temperature response per unit forcing relative to the response to CO2 forcing.
You heard it, “per unit of forcing”. Under the IPCC system of units, forcing is a fundamental unit and well established property of all matter (a bit like mass, but only special people can measure it). The units of forcing are CO2’s. By gum, what I can’t understand is why I ever sat through high school science.