Wednesday
Aug282013
by 
Bishop Hill
Bishop Hill Masters and Dessler do climate sensitivity
Aug 28, 2013 Climate: sensitivity I chanced upon Andrew Dessler's video on climate sensitivity a few weeks ago.
At the time I sent it to Nic Lewis to see what he made of it, but I think he was away at the time and it slipped my mind. This morning, however, I was reminded of it by this response from Troy Masters. I would say that the case for low climate sensitivity is still looking pretty strong.
Reader Comments (61)
Richard Verney
I have the GISS data in front of me here.
http://data.giss.nasa.gov/gistemp/graphs_v3/Fig.A2.gif
Using the 5-year running mean (in order to filter out some of the short term variation) I observe a rise from 14.15C in 1980 to 14.59C from 2003. This increase of 0.44C is derived from data with 95% confidence limits of +/- 0.07C and is statistically significant.
Bearing this in mind, I am at a loss to understand how you can describe the data thus- "Aapart from an ENSO event, the globe does not appear to have warmed these past 33 years!"
Similarly your "no warming for 17 years" depends on using individual years instead of 5-year running means and cherrypicking an ENSO event, 1998, the third warmest year on record, as you starting point while ignoring 2005 and 2010.
I'll grant you a pause since 2003, but your 17 and 33 year pauses are not supported by the data.
Mark T.
I am doing nothing of the sort.
I am using feedback in the widely accepted use of the concept: an input has an effect (heats oceans) and produces an output (rise in temperature). That effect feeds back (clouds) and modifies the effect of input on the system. If there is a delay in each network, this will result in at least a second order system.
I am not redefining feedback. I am applying simple mathematics to a proposed feedback system, which cannot possibly work as a first order system as proposed by the proponents of the hypothesis.
Richard Verney
http://www.ssmi.com/msu/msu_time_series.html
This is the decadal trend data from the satellite record. Check the different channels and you will note that the channels sensing troposphere temperatures are rising , while those sensing stratosphere temperatures are decreasing. This is what you would expect from an atmosphere responding to increased CO2.
In the troposphere the extra CO2 increases downwelling infrared radiation and slows the cooling rate, producing a warming trend. In the stratosphere the extra CO2 increases the outward longwave radiation and has a cooling effect.
Bullshit, RCS. You are claiming feedback only exists if you have a second order system. I gave a simple first order example that proves you wrong. If you want to be taken seriously when you rightly call out the failure on the part of climate scientists to use the theory properly, you need to make sure you get the details right.
Oh, and for the record, Martin A, EM's description above is not actually a feedback system until he includes temperature causing an increase in CO2. I seriously hope you don't ever listen to his statements as any kind of legitimate source of knowledge.
Mark
Aug 29, 2013 at 11:06 PM Mark T
Don't worry. I was saying that I understood RCS's viewpoint - not that I agreed with it.
I have (or had before some of it evaporated) quite a deep knowledge of control theory - both ancient and modern - plus experience of applying it to tricky systems, so (apart from my sceptical attitude to just about everything) I'm not very likely to be mislead on things involving feedback.
Thanks, for your comments.
I have also used feedback extensively in rather tricky non-linear systems.
The point is that any system that involves significant phase shifts in the forward and backwards nets will involve a second order ODE. In the case in point, the Dessler and Spenser, the system was modelled by a first order ODE and the constant (time constant of the physical system) was called feedback.
Can a classic feedback system oscillate? Can a classic feedback system show underdamped behaviour? If they can, this cannot be described by a 1st order ODE
The examples you propose are false. One can use feedback to create a circuit that mimics a first order system over a partcular range of frequencies. This is a property of feedback that depends on near ideal behaviour of ops amps. When driven outside their ideal range, the first order approximation break down.
Actually , I find these arguments on the internet with people who claim to have profound knowledge of subjects but don't give their names rather difficult.
I at least post under my own name and my degrees and research are a matter of public record.
RCS - don't worry about the claimed degrees or the claims of expertise. They don't change whether someone's reasoning is correct or not. Just address the facts and the logic.
Martin: True. But use of a real name is much more than 'claimed degrees or the claims of expertise'. Indeed I have argued that it's most important at moments when we say something particularly stupid. The person using their real name suffers more at that point than the other type of contributor. That pain is both good for our souls and good for the quality of the blog on which it occurs, as a deterrent, the benefit also accruing to those of good faith who use a pseudonym.
In a rational world there would be some kind of quid-pro-quo for this ongoing reputation cost that works for the common good. But half a loaf is as always better than none.
"EM's description above is not actually a feedback system until he includes temperature causing an increase in CO2. I seriously hope you don't ever listen to his statements as any kind of legitimate source of knowledge."
Mark
That is exactly what happens. Increasing temperatures tend to cause release of CO2 from sinks, this then drives further warming and more CO2 release.
Cooling temperatures encourage uptake by carbon sinks, with reduced CO2 driving further temperature decrease.
With only a limited amount of carbon available for this exchange the system oscillates between two equilibria 5C apart, driven by the cyclic temperature changes due to Milankovich cycles. the change in insolation at 65N is enough to chage temperatures by ~ 1C. The feedback between temperature and CO2 amplifies this to ~ 5C
We are currently in a cooling phase of the cycle. More correctly, we were cooling until the system was disrupted by the addition of an extra 600 gigatons of CO2 from fossil fuels.
Regarding anonymity, my children are in business and prefer that Google searches of ther names do not pick up their Dad's curious hobby of arguing with climate sceptics.
I'm a retired science teacher with no public reputation, so you're not missing anything.