Laughable modeling study claims: in the middle of 'the pause', 'climate is starting to change faster'

David A,

Climate sensitivity “emerges” in the models based on CO2 sensitivity.

That would be CO2 forcing you’re talking about. Climate sensitivity is often expressed in terms or the system response to CO2 forcing, net feedbacks, which is called equilibrium climate sensitivity, or ECS. However, climate sensitivity can be, and is used, to refer to the system response to ANY external forcing: http://www.iac.ethz.ch/people/knuttir/papers/knutti08natgeo.pdf
Introduction, with ECS expressed as an explicit function of response to CO2 forcing:
When the radiation balance of the Earth is perturbed, the global surface temperature will warm and adjust to a new equilibrium state. But by how much? The answer to this seemingly basic but important question turns out to be a tricky one. It is determined by a number termed equilibrium climate sensitivity, the global mean surface warming in response to a doubling of the atmospheric CO2 concentration after the system has reached a new steady state. Climate sensitivity cannot be measured directly, but it can be estimated from comprehensive climate models. It can also be estimated from climate change over the twentieth century or from short-term climate variations such as volcanic eruptions, both of which were observed instrumentally, and from climate changes over the Earth’s history that have been reconstructed from palaeoclimatic data. Many model-simulated aspects of climate change scale approximately linearly with climate sensitivity, which is therefore sometimes seen as the ‘magic number’ of a model. This view is too simplistic and misses many important spatial and temporal aspects of climate change. Nevertheless, climate sensitivity is the largest source of uncertainty in projections of climate change beyond a few decades 1–3 and is therefore an important diagnostic in climate modelling 4,5.
My emphasis, from which it could not be any more clear to me that we do not know what the true response to CO2 forcing will be. ERGO, sensitivity is not dialled into the models according to some memo from Soros or Gore — something one might have expected to have found in the emails stolen from U. of E. Anglia, but are notably absent, yes?
The IPCC itself publishes a RANGE, which as of AR5 stands at 1.5-4.5 K/2xCO2. This is because the GCMs return different values in their response to the exact same past observed CO2 levels, and projected future levels as used as modelling assumptions by each RCP scenario.
The paper continues by describing the more general case of forcings, and system response (sensitivity) to them:
The concept of radiative forcing, feedbacks and temperature response is illustrated in Fig. 1. Anthropogenic emissions of greenhouse gases, aerosol precursors and other substances, as well as natural changes in solar irradiance and volcanic eruptions, affect the amount of radiation that is reflected, transmitted and absorbed by the atmosphere. This externally imposed (naturally or human-induced) energy imbalance on the system, such as the increased long-wave absorption caused by the emission of anthropogenic CO2, is termed radiative forcing (∆F). In a simple global energy balance model, the difference between these (positive) radiative perturbations ∆F and the increased outgoing long-wave radiation that is assumed to be proportional to the surface warming ∆T leads to an increased heat flux ∆Q in the system, such that ∆Q = ∆F − λ∆ T (1) Heat is taken up largely by the ocean, which leads to increasing ocean temperatures 6.
The changes in outgoing long-wave radiation that balance the change in forcing are influenced by climate feedbacks. For a constant forcing, the system eventually approaches a new equilibrium where the heat uptake ∆Q is zero and the radiative forcing is balanced by additional emitted long-wave radiation. Terminology varies, but commonly the ratio of forcing and equilibrium temperature change λ = ∆F/∆T is defined as the climate feedback parameter (in Wm−2 °C−1), its inverse S ′ = 1/λ = ∆T/∆F the climate sensitivity parameter (in °C W − 1 m 2 ) and S = ∆T 2 × CO2 the equilibrium climate sensitivity, the equilibrium global average temperature change for a doubling (usually relative to pre-industrial) of the atmospheric CO 2 concentration, which corresponds to a long-wave forcing of about 3.7 W m − 2 (ref. 7).
My emphasis again: terminology varies. Annoying, and the source of much evident confusion on top of general confusion, or in your case, what I suspect to be deliberate misunderstanding. (How do YOU like it when others appeal to motive, hmmm?)
Attempting to set aside the polemic for a moment, the key takeaway is this relationship …
λ = ∆F/∆T
… often used to quantify the equilbrium response to ANY forcing. For the record, the canonical value usually used is 0.8 Wm−2 °C−1, though I’ve seen values as low as 0.7. 0.75 is also common. The copypasta is getting longish here, but I want to finish this section because it ties things together into a more complete thought:
The beauty of this simple conceptual model of radiative forcing and climate sensitivity (equation (1)) is that the equilibrium warming is proportional to the radiative forcing and is readily computed as a function of the current CO 2 relative to the pre-industrial CO 2 : ∆ T = S ln(CO2 /CO2( t =1750) )/ln2. The total forcing is assumed to be the sum of all individual forcings. The sensitivity S can also be phrased as 8–10 S = ∆ T0 /(1 − f ) (2) where f is the feedback factor amplifying (if 0 < f < 1) or damping the initial blackbody response of ∆ T0 = 1.2 °C for a CO2 doubling. The total feedback can be phrased as the sum of all individual feedbacks 9 (see Fig. 2; examples of feedbacks are increases in the greenhouse gas water vapour with warming; other feedbacks are associated with changes in lapse rate, albedo and clouds). To first order, the feedbacks are independent of T, yielding a climate sensitivity that is constant over time and similar between many forcings. The global temperature response from different forcings is therefore approximately additive 11 . However, detailed studies find that some feedbacks will change with the climate state 12–14 , which means that the assumption of a linear feedback term λ∆ T is valid only for perturbations of a few degrees. There is a difference in the sensitivity to radiative forcing for different forcing mechanisms which has been phrased as their ‘efficacy’ 7,15. These effects are represented poorly or not at all in simple climate models 16. A more detailed discussion of the concepts and the history is given in refs 5, 7, 17–20.
Note that the concept of climate sensitivity does not quantify carbon-cycle feedbacks; it measures only the equilibrium surface response to a specified CO 2 forcing. The timescale for reaching equilibrium is a few decades to centuries and increases strongly with sensitivity 21 . The transient climate response (TCR, defined as the warming at the point of CO 2 doubling in a model simulation in which CO 2 increases at 1% yr − 1 ) is a measure of the rate of warming while climate change is evolving, and it therefore depends on the ocean heat uptake ∆ Q . The dependence of TCR on sensitivity decreases for high sensitivities 9,22,23.
The bolding is again mine. It’s been argued by some — not that I would name names — that all models are poor, even the non-simple ones. My response to that is that the climate system is unarguably complex, and simple, naive, willfully ignorant arguments about the very complex models used to project what it might do in the future if all other assumptions are correct — which they’ll never be — is stupidly simplistic.
Smart people who persist in over-simplifying the argument this way are being extremely dishonest. Don’t be that guy.