Some sense about sensitivity

Excerpts from The Register, coverage of the Nic Lewis paper.

This graph below from Bishop Hill shows that it isn’t just one paper, but several now that show lower climate sensitivity to a doubling of CO2.

Sensitivity_lewis_outlier

The IPCC’s 2-4.5 deg claimed sensitivity range is shown as the shaded area.

===============================================================

More and more likely that double CO2 means <2°C: New study

Yes, it warms the planet – just not as much as thought

The results of a new approach to calculating the effect of CO2 – using empirical observations – suggest it has a lower impact on the climate than previously thought, and its effects are being over-estimated by the IPCC.

Publishing in the American Meterological Society’s Journal of Climate, a new paper called An improved, objective Bayesian, approach for applying optimal fingerprint techniques to estimate climate sensitivity, Nicholas Lewis applies objective Bayesian techniques and uses more up-to-date observational data to derive his conclusions.

Very few people disagree with the basic fact that the greenhouse gas CO2 warms the climate, but without some kind of positive feedback mechanism, it doesn’t add very much: around 1°C-1.2°C per doubling of CO2. (See this discussion on no-feedback sensitivity). The global warming “crisis” emerged from a belief that small rises in CO2 concentrations result in large knock-on effects, or strong positive feedbacks. These remain conjectural, as the forcings and feedbacks are poorly understood. Just how much of an effect does a rise in CO2 have – a little, or a lot? Hence the importance of new and better studies in the area of climate science dealing with “attribution”.

Lewis finds that in recent years neither the global temperature nor ocean heat uptake have changed very much, while CO2 concentrations have continued to rise. Therefore, the climate sensitivity must be lower.

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Full article here: http://www.theregister.co.uk/2013/04/22/climate_sensitivity_down_down/

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I think it is also important to keep reminding people that the IPCC claimed, as the very foundation of the agw theory, that there was a proven causal correlation between CO2 and temperatures. But finally, circa 2004 the ipcc was forced to retract their claim. Al Gore later repeated the bogus ipcc claim in his 2005 movie, see an outstanding rebuttal of Al Gore’s dishonestly in this clip:

Rud Istvan

There is another, Annan and Hargreaves 2009. They derived a mode of 1.9 twice in the course of using informed priors to constrain the ECS sensitivity tail. See figure 1. And NEVER mentioned the fact once in the paper or in the abstract, which is perhaps why it is obscure. Why they did not mentionn the mode? Perhaps because their 2006 GRL paper using uniformed priors contributed to the mainstream ( but wrong) ECS consensus of 3, and these two authors were (until Annan broke ranks in 2012 over the temperature pause) part of the Climate Club.

Patrick

“Yes, it warms the planet – ”
No it does not!

Kasuha

The longer the warming is “on hold” while CO2 concentrations rise, the lower value comes out of statistical analysis. Even Nic Lewis gets the lowest value only after processing up to date data. So it’s both better analytical methods and time what is finally proving what skeptics had “gut feeling” about for a long time.

Jeff L

It is interesting that if you just take pre-industrial temps & pre-industrial CO2 concentrations , along with current temps & current CO@ concentrations & don’t assume anything other than the change in temps is a function of the change in CO2 & fit these observations , I calculate a sensitivity of 1.5 °C/ doubling , which sits right in the middle of all the above estimates.
See :
http://wattsupwiththat.com/2013/04/18/numeracy-in-climate-discussions-how-long-ill-it-take-to-get-a-6c-rise-in-temperature/
and
http://wattsupwiththat.com/2013/04/18/numeracy-in-climate-discussions-how-long-ill-it-take-to-get-a-6c-rise-in-temperature/#comment-1279353
fore relevant math.

Latitude

assuming all this is true…….1 degree above the little ice age?
but what happened too spring coming sooner? all the banana plantations in Cleveland??

Another hugh crack in the Berlin Wall of climate denial.

DesertYote

Hmmm, so a 1 C raise in average global temp causes a doubling of CO2.

Jimmy Haigh.

One of the things I remember about physics from school was that the specific heat capacity of water is so much higher than just about any other substance. Given that there is so much water in the oceans, and to paraphrase Hilary… does the atmosphere really matter?

Kasuha:
At April 24, 2013 at 8:56 am you say

The longer the warming is “on hold” while CO2 concentrations rise, the lower value comes out of statistical analysis. Even Nic Lewis gets the lowest value only after processing up to date data. So it’s both better analytical methods and time what is finally proving what skeptics had “gut feeling” about for a long time.

No, not “gut feeling”. Empirical determinations which climastrologists have ignored..
As the above article says, no feedback sensitivity is “around 1°C-1.2°C per doubling of CO2.”
So
If feedbacks are positive then the sensitivity will be more than ” around 1°C-1.2°C per doubling of CO2″
and
If feedbacks are negative then the sensitivity will be less than ” around 1°C-1.2°C per doubling of CO2″.
All the values cited in the above article are amendments to model-derived values which assume positive feedbacks.
But empirical measurements indicate the feedbacks are negative so the climate sensitivity is less than 1°C.

Climate sensitivity less than 1°C is indicated by the studies of
Idso from surface measurements
http://www.warwickhughes.com/papers/Idso_CR_1998.pdf
and Lindzen & Choi from ERBE satelite data
http://www.drroyspencer.com/Lindzen-and-Choi-GRL-2009.pdf
and Gregory from balloon radiosonde data
http://www.friendsofscience.org/assets/documents/OLR&NGF_June2011.pdf
Negative feedbacks mean that the man-made global warming from man’s emissions of greenhouse gases (GHG) would be much smaller than natural fluctuations in global temperature so it would be physically impossible to detect the man-made global warming.
Of course, human activities have some effect on global temperature for several reasons. For example, cities are warmer than the land around them, so cities cause some warming. But the temperature rise from cities is too small to be detected when averaged over the entire surface of the planet, although this global warming from cities can be estimated by measuring the warming of all cities and their areas.
Similarly, the global warming from man’s GHG emissions would be too small to be detected. Indeed, because climate sensitivity is less than 1°C for a doubling of CO2 equivalent, it is physically impossible for the man-made global warming to be large enough to be detected. If something exists but is too small to be detected then it only has an abstract existence; it does not have a discernible existence that has effects (observation of the effects would be its detection).
Richard

OldWeirdHarold

Gosh. A consensus of models.

Dave

– using empirical observations –!!!!!????!!!??
Can we, at least, use a computer model to decide if that’s a good idea?

Theo Goodwin

“The results of a new approach to calculating the effect of CO2 – using empirical observations – suggest it has a lower impact on the climate than previously thought, and its effects are being over-estimated by the IPCC.”
I find that paragraph screamingly funny. My hat is off to you, Anthony.
No doubt the trolls will soon arrive and begin their pontifications about Trenberth’s unobservable observables in the deep ocean.

Beta Blocker

Were Jane Austen alive today, would she be writing Sense and Sensitivity, a novel set in the modern era about climate scientists and their relationships to their acolytes in politics and in the press?

Theo Goodwin

Beta Blocker says:
April 24, 2013 at 10:34 am
The heroine is attending a conference on CAGW and finds that a comment she made during a seminar attracts the attention of a notable climate scientist that she greatly admires. (This adaptation is going to be difficult.)

‘Jeff L says
April 24, 2013 at 9:00 am
It is interesting that if you just take pre-industrial temps & pre-industrial CO2 concentrations , along with current temps & current CO@ concentrations & don’t assume anything other than the change in temps is a function of the change in CO2 & fit these observations , I calculate a sensitivity of 1.5 °C/ doubling , which sits right in the middle of all the above estimates.”
Yup. That is a good starting point for the debate.
There other thing you can see is that arguments over the temperature record don’t play a big role in the estimate.
Other thing to consider is that c02 forcing is not 100% of the change in forcing.. so you need to add in all the other forcing ( neg and positive)..
Bottom line. Arrehenius predicted that increasing c02 would raise temperatures. The evidence suggests he was right. pretty damn simple. Now he predicted 5C.. the evidence suggests his estimate was high.

If CO2 concentration in the early 1700’s was about 280 ppm, and currently 390, gives ratio of 1.4.
CET across two 50 year periods
http://www.vukcevic.talktalk.net/CET1690-1960.htm
here temperature difference is 0.6 degree C.
Thus doubling of CO2 with a linear law gives sensitivity of 0.84C as shown here http://www.vukcevic.talktalk.net/CO2-S.gif
Logarithmic law would produce a bit less.

Richard M

Since we are just coming off the top of natural cyclic warming based on the oceans I suspect we will see the actual sensitivity to increases in CO2 come in much lower. Probably less than .5°C at our current global temperature. Keep in mind that sensitivity is probably different at different global temperatures and is not linear in nature.

@ Theo Goodwin,
Thank you for mentioning Trenberth and his “unobservable observables in the deep ocean.”
“There’s heat in the oceans, heat in the rivers,
Heat in the lakes, and heat in the sea,
Big grants are waiting for men who find it,
But only a travesty’s waiting for me.”
Val Doonican’s version is here:

Cheers,
Neil

RHL

Re Beta Blocker comment about Jane Austen, Nic Lewis lives in Bath where Austen lived for a while. Many of her novels revolve around life in Bath. The Jane Austen museum is there. There are Roman bath ruins in Bath and those baths must have been quite pleasant since the world was warmer during the Roman Period. Probably similar to today’s temps.

Without reading all of those papers, I suspect that they assume that all or virtually all warming is caused by CO2. This would make their numbers more like an upper bound than an estimate.
Apart from the obvious mistreatment of UHE (UHI), It is disgraceful that the IPCC justifies its very high ECS (sensitivity) estimate by “finding” still-not-understood indirect effects such as “cloud feedback” in order to make the numbers add up. At the same time, they dismiss the possibility that there could be any indirect effects related to solar activity, in spite of a known mechanism and concrete experimental evidence (Svensmark). Peer-reviewed, too. The unequal treatment is unjustifiable extreme confirmation bias at best.
On UHI – it is often stated that the urban areas are a very small part of the world’s surface, so can’t have a significant effect on global temperature. That’s not the point. The point is that the majority of thermometers are in or near urban/developed areas, so their UHE component gets extrapolated over a large proportion of the world’s area.

Dr Burns

If atmospheric CO2 levels are an effect rather than a cause of warming, there is a 99% probability that climate sensitivity calculations are b.s.

Christopher Hanley

As a layman I don’t understand how climate sensitivity can be determined using observations since all the forcing factors (e.g. clouds) are so poorly understood.
Nonetheless I can see how a maximum figure can be inferred from observations by assuming all of the observed warming since, say, 1950 was due to increased CO2.
From The Register article: ” … any changes will be slow, giving policy makers and technologists a long time to prepare, and develop economical low-carbon alternatives … “.
As always the assumption seems to be that a warmer CO2 enriched atmosphere is something to be avoided merely because it is not ‘naturally’ induced.

Christopher Hanley:
I write in hope of helping. At April 24, 2013 at 2:43 pm you say

As a layman I don’t understand how climate sensitivity can be determined using observations since all the forcing factors (e.g. clouds) are so poorly understood.

As a start for a “layman” I suggest that you start by reading Idso’s 8 “natural experiments”.
It is a technical paper but I suspect you will find it is understandable.
It can be read at
http://www.warwickhughes.com/papers/Idso_CR_1998.pdf
Richard

Bill Illis

You need the initial CO2 forcing of 3.7 W/m2 (and add in another 0.5 W/m2 for the other GHGs) plus feedbacks of over 2.2 W/m2/K to get to 3.0C per doubling.
http://www.ipcc.ch/publications_and_data/ar4/wg1/en/figure-8-14.html
If the feedbacks are less than 2.2 W/m2, then we come in right around the current estimates of close to 1.5 C per doubling.
http://s24.postimg.org/7jjj2kcgl/Feedback_Strength.png
So let’s look at the net Radiative forcing to date (2.28 W/m2 in IPCC AR5 in 2012) and assume the feedbacks are operating as expected (0.7C temperature rise at over 2.2 W/m2/K feedbacks),
There is a lot of expected forcings and feedbacks producing almost net energy accumulation or increased OLR to space.
http://s10.postimg.org/vf4h3oizd/Net_Forcing_Feedbacks_Energy_Going.png
2.67 W/m2 is nowhere to be found meaning (either the GHG forcing numbers are wrong, the aerosols negative is much larger than is currently estimated, the feedbacks are actually negative – meaning cloud feedback is strongly negative given there does appear to be some positive water vapor feedback).
http://s15.postimg.org/5ot9zkocr/Net_Forcing_Heat_Accum_vs_Missing_Energy.png

Brianp

But the real question is it enough to stop the next ice age

Matthew R Marler

Steve Mosher: Arrehenius predicted that increasing c02 would raise temperatures. The evidence suggests he was right.
I wonder sometimes whether there was anything important Arrhenius didn’t know, and what that might be.

tokyoboy

Mike Jonas says: April 24, 2013 at 2:39 pm
“……….The point is that the majority of thermometers are in or near urban/developed areas, so their UHE component gets extrapolated over a large proportion of the world’s area.”
Completely agree.

Rob JM

There was a large 0.9W/m2 forcing in a short 13 year time period due to a 5% reduction in cloud cover between 1987 and 2000 (ISCCP). Temps increased by 0.3W/m2 as a result
Therefore Climate sensitivity is less than 0.4W/m2. Close to neutal feedback is the maximum you can have!
And remember the recent paper that found that CO2 forcing may only be half as much as what is accepted currently!

knr

‘using empirical observations ‘ you see that is where they went wrong , by failing to rely on model ‘data ‘ and ignoring reality they proved themselves unworthy of being called climate ‘scientists’

Rhoda R

Mr, Courtney, thank you for that link. Like Mr. Hanley, I’ve been having problems understanding that.

Rhoda R:
Glad it helped.
This, of course, is the great value of WUWT: we can all learn from each other.
And it is why I an so angered by trolls.
I learn most by discussion with those who disagree with me. It is when somebody gives me a new, idea, opinion and/or information that I change my view, opinion or understanding. So, as with all who want to learn, I enjoy debate. But trolls don’t want anyone to learn: they want to push their agenda. So trolls try to stifle debate by whatever means they can.
The free exchange of information and the cut-and-thrust of ideas is how we learn. And WUWT has such a wide range of people that each of us has good chance of learning something each day (assuming we can stomp on the trolls), and it is a bad day when I don’t learn something from WUWT.
Richard

thingadonta

“The global warming “crisis” emerged from a belief that small rises in CO2 concentrations result in large knock-on effects, or strong positive feedbacks”.
I suppose the IPCC couldn’t also consider that the sun could also have strong knock-on effects, or strong positive feedbacks?. Even been outside our a cloudy cool morning, where the sun drives off the clouds and then afterwards it gets warmer? Too simple for the modellers to understand.

richard verney

For all of those who consider that the MWP is real (and global), what does that tell us about climate sensitivity to CO2?
Ditto, the Minoan and Roman warm period.
If one looks at the satelitte data there is no first order correlation between temperature anomaly and CO2.
Indeed, as Eric Simpson says: April 24, 2013 at 8:43 am, in fact there is no first order correlation between temperature anomaly and CO2 in any of our temperature data sets.
All of this suggests that climate sensitivity is so small that it cannot be measured given the tolerances of the equipement and data sets available to us.

Ian W

vukcevic says:
April 24, 2013 at 11:18 am
If CO2 concentration in the early 1700’s was about 280 ppm, and currently 390, gives ratio of 1.4.

That is if you believe the ice cores and not the actual measurements of chemists. The collation by Beck of routine measurements of CO2 made by various scientists would appear to show that the ice cores are a very poor proxy due to diffusion of gas in the ice and effects of the drilling of the core and depressurization. Yet for some reason routine measures by Nobel Laureate chemists are thrown out in favor of the claims of ice core bubbles.

michaelspj

And what’s so new about correcting for empirical observations?
http://www.int-res.com/articles/cr2003/23/c023p001.pdf

Jeff Alberts

stan stendera says:
April 24, 2013 at 9:08 am
Another hugh crack in the Berlin Wall of climate denial.

I’m afraid I’m not acquainted with Hugh, er, Mr. Crack. Sounds like an eminent climate scientist, no doubt.

Theo Goodwin

richardscourtney says:
April 24, 2013 at 2:55 pm
Do you mean to suggest that climate sensitivity can be determined before (independently of) the forcings and feedbacks calculation has been completed? That would imply that changes in the amount of water vapor in the atmosphere have no effect on climate sensitivity, just to take one example of a feedback.

Girma

Communicating Climate Science
Mojib Latif
Figure:
http://orssengo.com/GlobalWarming/ClimateModelGmst.gif
There is a broad scientific consensus that the climate of the 21st century will warm in response to the anthropogenic emission of greenhouse gases (GHGs) into the atmosphere, but by how much remains highly uncertain. This is due to three factors: natural variability, model error, and emission scenario uncertainty. We as climate scientists should stress this uncertainty when talking to the public. Dealing with uncertainty is an integral part of our daily life, and we are used to assess the risk of certain steps we take. Nobody would board, for instance, an aircraft that will crash with a probability of only ten percent. Emphasizing in the public discourse too much the consensus – which is an artificial construct – can be very dangerous, and the climate research community can lose its credibility when not clearly stating publicly the uncertainties.
Atmospheric carbon dioxide (CO2) levels have skyrocketed since the start of industrialization and reached values unprecedented in man’s history. The globally averaged surface air temperature of the planet has warmed during the 20th century, global sea level has risen, and many mountain glaciers and Arctic sea ice have considerably retreated. There is overwhelming scientific evidence that a significant share of 20th century warming is driven by the increase of GHGs. They will continue to accumulate in the atmosphere over the next years and possibly even decades, which together with the inertia of the climate system will support further warming. But what else do we really know about the climate of the 20th and 21st century?
Surface air temperature (SAT) during the 20th century displays a gradual warming and superimposed short-term fluctuations (the figure shows observed annual Northern Hemisphere and Arctic SAT as red lines). The upward trend contains the climate response to enhanced atmospheric GHG levels but also a natural component. The temperature ups and downs around the trend – which are particularly pronounced in the Arctic – mostly reflects natural variability. The scientific challenge is to quantify the anthropogenic signal in the presence of the background climate noise. Natural climate variations are of two types, external and internal. External fluctuations need a forcing, a change in the boundary conditions. Volcanic eruptions and fluctuations in solar output are examples. The Philippine volcano Mt. Pinatubo, for instance, caused a short-lived drop of global SAT in 1991; and an increase of the solar radiation reaching the earth may have contributed to the mid-century warming during 1930-1940. The anthropogenic influence is also considered as external.
One way to estimate the external contribution to the 20th century SAT change is to run climate models with observed natural and anthropogenic forcing. The average over all IPCC models is the consensus (black lines). The spread (gray shading), however, is large, partly because natural variability can be also produced internally by the climate system itself. A well-known example of an internal fluctuation is El Niño, a warming of the Equatorial Pacific occurring on average about every 4 years. The record event of 1997/1998 “helped” to make 1998 the warmest year to date globally . The last year also happened to be an El Niño year, which supported, for instance, weak Atlantic hurricane activity. The event still persists and was partly responsible for January 2010 being one of the warmest Januarys on record. Different initial states yield different realizations of internal variability in models even under identical external forcing, one reason for the spread, as integrations are performed in ensemble mode with different start conditions.
To some extent, we need to “ignore” the natural fluctuations, if we want to “see” the human influence on climate. Had forecasters extrapolated the mid-century warming into the future, they would have predicted far more warming than actually occurred. Likewise, the subsequent cooling trend, if used as the basis for a long-range forecast could have erroneously supported the idea of a rapidly approaching ice age. The detection of the anthropogenic climate signal thus requires at least the analysis of long records, because we can be easily fooled by the natural fluctuations, and we need to understand their dynamics to better estimate the internal noise level.
The spread also reflects model error. Climate models are based on basic physical principles. As such they are fundamentally different to empirical models which are used, for instance, in economic forecasting. Climate models, however, are far away from being perfect. Errors in annual mean SAT, for instance, typically amount to several degrees in some regions . Limitations in computer resources dictate the use of either reduced or relatively coarse-resolution models. As a consequence many important processes cannot be explicitly simulated; they must be parameterized. Some processes like cloud formation or some radiation processes are not completely understood and differently represented in the models, which adds to the uncertainty.
One way to compare models is by means of the climate sensitivity which is defined as the equilibrium change in globally averaged SAT in response to a doubling of the pre-industrial atmospheric CO2 concentration (from 280 to 560ppm ). IPCC AR4 stated that the value ‘…is likely to be in the range 2°C to 4.5°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C’. In the IPCC definition likely refers to an outcome or result when its likelihood is greater than 66% probable. Very unlikely means a probability of less than ten percent. Thus there is a non negligible probability that the climate sensitivity is either considerably smaller or larger than 3°C. Apparently, just communicating the consensus, the best estimate, is inappropriate. The uncertainty in climate sensitivity itself is in my opinion a good reason to demand reductions of global GHG emissions, because the possibility of ‘a dangerous interference with the climate system’ cannot be ruled out with high confidence.
To predict the future climate we have to consider both natural variability and anthropogenic forcing. The latter is taken into account by assuming scenarios about future GHG and aerosol emissions. The scenarios cover a wide range of the main driving forces of future emissions, from demographic to technological and economic developments. IPCC AR4 published only climate projections based on such scenarios with no attempt to take account of the likely evolution of the natural variability. This by definition yields relatively smooth trajectories if the results are averaged over many models. In the real world, the natural variations will introduce a large degree of irregularity, and even short-term cooling may occur during the next years . This could have been explained better to the public, as in some media reports the existence of Global Warming has been questioned after for more than ten years no global SAT record has been observed. Had we emphasized more the uncertainty, that debate which confused many people could have been avoided. Albert Einstein once said that we should make ‘things as simple as possible, but not simpler’.
Mojib Latif is a Professor of Climate Physics at Kiel University and Head of the Ocean Circulation and Climate Dynamics Division of the Helmholtz Centre for Ocean Research, Germany. He is Contributing Author of the IPCC Reports 2001 (TAR) and 2007 (AR4).

Girma

Latif, M., Uncertainty in climate change projections, Journal
of Geochemical Exploration (2010), doi: 10.1016/j.gexplo.2010.09.011
http://oceanrep.geomar.de/9199/1/JGE.pdf

Janice Moore

AND NOW! for something completely different!
“Were Jane Austen alive today, would she be writing Sense and Sensitivity… .” [Betablocker @ 1034] LOL, maybe, but I think she might be more likely to write:
Pride and Prejudice in the 21st Century
This time, instead of prideful Mr. Darcy with his nose in the air, it would be Algore, but, he wouldn’t be a truly noble person underneath, misunderstood due to Miss Elizabeth Bennet’s prejudice. The prejudice would come in in the biased “research” of an obscure cult who followed the teachings of the Pirate Arrrrrhenius whose parrot informed him of everything he knew. It would be a story of greed and lust for power, where the Wickhams of the world use specious arguments and downright falsehoods to woo gullible liberals whose feelings determine their every decision. The romance would be between the two Bennet sisters and the two Andrews brothers, (sister1-brother1 and s2-b2), all four are brilliant scientists teaching at WUWT University. Sister 1 is gregarious and outgoing, while sister 2 is… . And… what? Oh, sorry. Just when the story was getting good, we must PAUSE… perhaps, for a very long time… .
And (having glanced above), a Snake Oil salesperson named “Girma” would appear from time to time (and turn out, in the end, to be Algore’s mother).
Oh, and, Mrs. Bennet, the clown of the story, would be a composite character based on two or three of our favorite trolls and Mr. Bennet, the dry wit, would get the final line:
“For what do we live, but to make sport [of our detractors’ rhetoric], and laugh at the[ir speculations] in turn?”

DaveA

I’m not taking this blog seriously until you start expressing sensitivity in Hiroshima bombs a second.

Janice Moore

Thanks for the laugh, DaveA.
I also found out from that article that “humans live at the Earth’s surface.”
Aaaaand who posted it? (brrrrrrrrrr- drum roll) …. Dana Nuccatelli! (on 4/24/13)

Ian W says:
April 24, 2013 at 6:33 pm
@vukcevic: That is if you believe the ice cores and not the actual measurements of chemists.
No I don’t believe any of it, least that CO2 has much of a role, particularly if one compares oceans and atmosphere in mass and the thermal capacity.
On decadal and century time scale (excluding the long term Milankovic cycles) only oceans can move global temperature above and beyond solar variability. In turn this only can be achieved by the geo-tectonics impacting on the intensity of ocean currents.
Question still to be resolved: degree of the solar contribution via- and ex- TSI, .

richard verney

Ian W says:
April 24, 2013 at 6:33 pm
////////////////////////////////
further to the point made by Ian.
I have commented many tiimes on this old experiment data. I have suggested that those experiments should today be replicated, ie., use the same equipment, take the samples in the same manner from the same location at the same time of year.
It would be interesting to see how data extracted from such replicated experimentation compares with the original results.

Theo Goodwin:
At April 24, 2013 at 7:13 pm you refer to my post April 24, 2013 at 2:55 pm then ask me

Do you mean to suggest that climate sensitivity can be determined before (independently of) the forcings and feedbacks calculation has been completed? That would imply that changes in the amount of water vapor in the atmosphere have no effect on climate sensitivity, just to take one example of a feedback.

I try to state what I mean, and I don’t “mean to suggest” except by accident.
I suggested no such thing!
My post you are questioning said

As a start for a “layman” I suggest that you start by reading Idso’s 8 “natural experiments”.
It is a technical paper but I suspect you will find it is understandable.
It can be read at
http://www.warwickhughes.com/papers/Idso_CR_1998.pdf

If you had read it then you would have seen that Idso determines the temperature response to a change in radiative forcing. He achieves this by 8 different methods, and he obtains a similar result from each method.
Climate sensitivity is the temperature response from a change to radiative forcing provided by a doubling of atmospheric CO2 equivalent. The direct change to radiative forcing from altered atmospheric CO2 concentration is calculable from fundamental physics and is not disputed. However, that does not permit a calculation of the climate sensitivity.
The climate system responds to a change in radiative forcing in many ways. These changes provide ‘feedbacks’. And if the feedbacks are positive then the change in temperature will be greater than expected for a change in radiative forcing. But if the feedbacks are negative then the change in temperature will be less than expected for a change in radiative forcing.
Any feedbacks – including induced atmospheric moisture – will affect the observed temperature response to a change in radiative forcing.
Therefore, an empirical measurement of climate sensitivity requires a determination of the net effect of all feedbacks: it is not – and does not need to be – any knowledge of individual feedbacks. Simply, it is a measurement of how temperature changes in response to a change in radiative forcing and it includes all effects of all feedbacks.
That measured net feedback effect can be applied to the direct change to radiative forcing from altered atmospheric CO2 concentration which is calculated from fundamental physics, and the result is an empirical indication of climate sensitivity.
Idso made the determination of net feedbacks in 8 different ways and obtained a similar result in each case. He concluded

These studies all suggest that a 300 to 600 ppm doubling of the atmosphere’s CO2 concentration could raise the planet’s mean surface air temperature by only about 0.4°C.

This conclusion is similar to that of Lindzen& Choi from ERBE satellite data and of Gregory from balloon radiosonde data: they each found a climate sensitivity value of ~0.4°C per doubling of CO2 equivalent as a global average.
I mentioned and explained the implications of this in my post at April 24, 2013 at 9:35 am
http://wattsupwiththat.com/2013/04/24/some-sense-about-sensitivity/#comment-1286120
Richard

I know there is a lot of debate about climate sensitivity, but I want to add something new to the discussion. I thought it might be useful to take a step back for a moment and look at the big picture. If we accept that Earth’s climate has changed dramatically in the past, which it has, then isn’t this the strongest evidence we have for a higher climate sensitivity? If the Earth’s climate had remained relatively stable over millions of years, then this would tend to suggest a low sensitivity. But we know it hasn’t.
50 million years ago there was no ice at either pole and crocodiles lived off the coast of Greenland (bones from these animals have been found there) along with a variety of subtropical plants (fossils have also been found). A cimate sensitivity of 2C per doubling of CO2 will not create a warm enough habitat for crocodiles in the arctic. This would suggest that our models are not sensitive enough to forcing of CO2.
Any thoughts?

Rachel:
re your post at April 25, 2013 at 4:40 am .
Your entire argument relies on an assumption that global temperature is determined by climate sensitivity to CO2.
If climate sensitivity to CO2 is low then your assumption is wrong. End of.
Richard

Bill Illis

Rachel says:
April 25, 2013 at 4:40 am
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I am not aware of any crocodiles in Greenland from the Eocene but what you are probably thinking of is this period, 94 Mya to about 60 Mya. Crocodile fossils have been found originating from this period in the Arctic on both sides of the warm inland sea which covered North America from Texas to Inuvik at the time.
It is highly likely that a small gulf stream-like ocean current flowed up this inland sea to the Arctic ocean given the way ocean currents organize themselves today (which is how the crocodiles got up there and who knows what they did in the 6 months of no sunlight – reptiles need to warm up in the sun for example – they probably migrated south down the inland sea in the winter months).
http://upload.wikimedia.org/wikipedia/commons/6/64/94_mya_Texas_Geology.JPG
Obviously, it was warmer then, maybe up to 9.0C globally but note how much of the continents were flooded by shallow ocean (much of our oil comes from this period when shallow oceans covered 30% of the continents). Does it need to caused by CO2 or can the continental alignments and the shallow oceans increase temperatures by 9.0C on their own, leaving no highly reflective glacial ice at the same time further increasing the Earth’s temperature?