- Everybody talks about climate feedbacks, but what are they, really? And where did the expression ΔTs = λRF actually come from?
- After two decades of wrestling with this issue, I’m not sure how useful the concept of “feedback” is in the context of the climate system.
- We already saw what kind of trouble we can get into on the thread on CO2 no feedback sensitivity, which is supposed to be the easy part of the problem.
- The problem flat out isn’t linear, and attempting to do a nonlinear control theory analysis is pretty hopeless, as illustrated by the Aires and Rossow paper.
- At best, it seems like the concept is useful as a conceptual aid in thinking about a complex system. Various metrics like ΔTs = λRF or the partial derivatives may have some use in comparing climate models with each other or with observations, but it may not say much about feedback.
- So is this concept useful? If not, can it be salvaged?
- Or are there better ways to try to understand the whole system, something from dynamical systems theory, entropy extremals, etc?
torsdag 30 december 2010
Climate Feedbacks with Nothing Real to Feed On
Without anything real to feed on because of deep snow, deer are now starving to death...
IPCC climate alarmism is based on a climate sensitivity of 3 C from doubled CO2, presented as the result of feedbacks starting with an initial value of 1 C.
In a survey of IPCC climate science, (former) IPCC scientist Judith Curry has now come to the basic question of Climate Feedbacks:
We read that Curry poses questions but we see nothing in the direction of answers.
Curry asks the logical question: If now both the sign and magnitude of feedbacks are
impossible to determine, why was the concept introduced at all?
Because it served IPCC climate alarmism, of course, but there is one important element to understand: Feedbacks need something to feed on, an initial perturbation which can be magnified by positive feedback. So what was then the initial perturbation and how could it be identified by IPCC if nothing else could?
The answer is given in my recent post Definition vs Axiom and Consensus in Climate Science
showing that the initial value to feed on by IPCC is stated to be 1 C, referred to as no-feedback climate sensitivity.
So how is then the initial value of 1 C as no-feedback climate sensitivity determined? By experiments? No, that is impossible. By a theory starting with some assumptions which can be verified? No, nobody knows such a theory.
What remains is to take 1 C as a definition of no-feedback sensitivity to be computed by a
direct application of Stefan-Boltzmann's Black-Body Radiation Law with certain data ("radiative forcing" of 4 W/m2), which invariably gives 1 C.
The advantage of a definition is that full consensus can be reached: It is pointless to question if there are 100 centimeters on a 1 meter. It is pointless to question a no-feedback climate sensitivity of 1 C computed from Stefan-Boltzmann's Law with certain data. That would be like questioning that there are 200 centimeters on 2 meters.
IPCC thus can safely state that there is full consensus about a no-feedback climate sensitivity of 1 C, because it is a definition.
So, a definition is wonderful in the sense that full consensus can be reached as concerns its validity. But the full consensus and absolute truth of a definition does not come without a serious drawback: A definition says nothing about reality.
If we understand this, we understand that the IPCC feedbacks have nothing real to feed on, and
thus cannot say anything about any reality. Curry has understood this, maybe. Anyone else?
For example, what about Lindzen and Spencer? Are they happy to twist, like IPCC, a definition into a potentially alarming physical fact of 1 C, and then have to argue that negative feedback can diminish it to a harmless 0.5 C, using an argument that can easily be questioned? Is this clever? Is it science?
It must be possible for a scientist to understand if a certain statement is a definition, which is true by its construction independent of any reality. Or if it is a statement about reality which may be true or false depending on the reality and therefore can be questioned, because perceptions of reality can differ and thus possibly prevent full consensus.