This paper A lower and more constrained estimate of climate sensitivity using updated observations and detailed radiative forcing time series from Skeie et al is now in open peer review at Earth System Dynamics. They say an ECS of 1.84
See Figure E2 from the paper.
Abstract:
The equilibrium climate sensitivity (ECS) is constrained based on observed near-surface temperature change, changes in ocean heat content (OHC) and detailed radiative forcing (RF) time series from pre-industrial times to 2010 for all main anthropogenic and natural forcing mechanism.
The RF time series are linked to the observations of OHC and temperature change through an energy balance model and a stochastic model, using a Bayesian approach to estimate the ECS and other unknown parameters from the data. For the net anthropogenic RF the posterior mean in 2010 is 2.1 W m−2 with a 90% credible interval (C.I.) of 1.3 to 2.8 W m−2, excluding present day total aerosol effects (direct + indirect) stronger than −1.7 W m−2. The posterior mean of the ECS is 1.8 °C with 90% C.I. ranging from 0.9 to 3.2 °C which is tighter than most previously published estimates.
We find that using 3 OHC data sets simultaneously substantially narrows the range in ECS, while using only one set and similar time periods can produce comparable results as previously published estimates including the heavy tail in the probability function. The use of additional 10 yr of data for global mean temperature change and ocean heat content data narrow the probability density function of the ECS. In addition when data only until year 2000 is used the estimated mean of ECS is 20% higher. Explicitly accounting for internal variability widens the 90% C.I. for the ECS by 60%, while the mean ECS only becomes slightly higher.
h/t to Bishop Hill
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This is the Kubler-Ross stage known as “bargaining”.
In the limit, as they say in calculus, as time tends to infinity (or whenever) ‘climate sensitivity” will tend to 1…
Alas for climatologi$ts, the vast fluid dynamic ocean that dominates the heat cycles known as climate doesn’t have equilibrium in its résumé.
OldWeirdHarold says:
August 14, 2013 at 9:31 am
This is the Kubler-Ross stage known as “bargaining”.
######
no its called having more data.
1. 10 more years of surface data
2. 10 more years of RF
3. 10 more years of OHC
If you understand the formula for estimating ECS, its clear why the estimate is coming down and getting more narrow.
One theme of skepticism is that we need more data.
When you get more data your estimates can change. especially when you have 10 more years of OHC which is highly informative ( in the baysian sense)
[For new readers, clarify your abbreviations, please. Mod]
It seems to me that if ECS is about 1.8C, then we need to hit about 620ppm CO2 in the atmosphere to reach the fabled 2C temperature increase which the IPCC considers the safe upper limit.
Seems like we probably have a good long while before we hit 620ppm.
I believe it; 1.84 it is, and the very next time that earth’s climate is in equilibrium, we will see that for ourselves.
Unfortunately, I am planning to not be here, next time earth climate is in equilibrium.
I understand the concept of climate sensitivity but I have not explored how it is calculated. However, I get the impression that it is obtained by running the particular model. Is this right?
So does this mean that the sensitivity is model specific and with 70 plus models giving any temperature prediction you can imagine, provided it is much higher than reality, there will be 70 plus versions of climate sensitivity to choose from?
Worse than that, since the models are clearly not fit for purpose, does this mean that discussing climate sensitivity is a waste of breath?
Fitting limited period of natural warming to hypothetical radiative forcing and then calculating “climate sensitivity”.. what sensitivity is from this one?
http://www.woodfortrees.org/plot/hadcrut3vnh/from:2001/scale:500/plot/esrl-co2/from:2001/scale:1
Schrodingers Cat Yes.
What this still does not tell us is the effect of all the feedbacks in the system, both known and unknown, or even if the apparent CO2 sensitivity is an artifact of another process. At least teh sky is no longer falling faster than terminal velocity.
This is not English–
Could someone who reads “climate sensitivity-ease” summarize please?
This is consistent with the observations to date.
And observations are 1,000 times more valuable than a climate model output or theroritical guesses.
Q: How do climate modelers keep the CAGW gravy train chugging along?
A: With a tweak-tweak here,
Fudge-fudge there,
And a couple of tra-la-las,
That’s how we graph the Pause away
In the Climatists’ land of Oz.
They’re still too high the correct answer is ECS = 1.62.
Are they still assuming that 100% of the warming was caused by CO2?
Feedbacks ultimately tend to dampening, positive feedbacks are unstable and tend toward not existing. It’s highly unlikely the CS is greater than 1.2C for doubling. It is as likely the CS would go negative as it would go above that (for very long).
Mosher says
One theme of skepticism is that we need more data.
Henry says
I really do have all the data I need to make an informed decision:
it is not going to get any warmer whether you add more CO2 or not
http://blogs.24.com/henryp/2013/04/29/the-climate-is-changing/
Day by Day, basically what they are saying is that if you take into account the variability of the climate system, their best estimate (C I ) gets 60% greater. So the say .9 to 3.2 is their C I, or a total of 2.3C. 60% of that is 1.2C roughly, so the .9C and 3.2, combined would decrease and increase by approx 1.2C, where the total difference would be 3.5 instead of 2.3C. They also say that their mean estimate of 1.8C would not increase greatly, hope that helps. They did not define in the abstract, if the increase is equal on both the upper or lower, typically as we are seeing in the leaked IPCC5, they will put more of the increase on the higher side.
“Day By Day says:
August 14, 2013 at 10:10 am
This is not English–
Explicitly accounting for internal variability widens the 90% C.I. for the ECS by 60%, while the mean ECS only becomes slightly higher.
Could someone who reads “climate sensitivity-ease” summarize please?”
It means that if you take into account that climate is variable (huh, whodathought that?) the uncertainty becomes larger (surprise!) but the average sensitivity estimate barely increases.
One basic problem. The OHC values are not much more than wild guesses before 2003. So, while the effort is commendable, the result is questionable. We should have some idea in another 50 years or so when we have at least one full 60 years cycle worth of data.
Thanks to:
brian says:
August 14, 2013 at 10:28 am
and
tty says:
August 14, 2013 at 10:29 am
the combined answers gave me a clue as to what they were saying!
It’s interesting that the lower end of their estimate would require negative feedback. As time goes on estimates will continue to fall. I’m betting on a final number between .5 and 1.5.
Old Weird Harold nails it, this fictitious “constant” of climatology numeracy, is whatever the computer modeller requires to produce the desired output.
Garbage in Gospel out.
In the real world its called a fudge or wild ass guess and the mumbo jumbo of climatology numeracy ain’t working.
So now the team is walking it back hoping to approximate reality and deny their previous BS.
What is next? They will discover statistical competency?
Driving a late model sedan, hands fiercely gripping the steering wheel, he tuned the radio more finely and stepped on the gas, “I’ll show her,” he smirked silently, “we’re not lost, Carbonville will be just around that bend.” An hour later and deep in the forest, now, miles from anywhere, he glanced at the clock on the dashboard and frowned. “Better slow down,” he muttered, “might be lost.”
“What’s that? Slowing down, dear?” his wife murmured, “Possibly willing to admit that I was right — that Carbonville is NOW 100 miles in the opposite direction?”
“No!” he snapped. “I just have more data now. It makes sense to slow down.”
“Whatever you say, dear.”
Elliot, the climate sensitivity number includes feedback. If it did not it would be the same as the lab tests on CO2, which is 1C for 2xCO2.