Geronimo:

> The only way I could conceive of the kettle having
positive feedbacks was if the spout was blocked and the
lid sealed, when the increased pressure would allow the
temperature to rise above 100C.

Another one who doesn't understand feedback. I'm beginning to wonder if anyone here apart from MartinA understand what feedback is.

As I said in another thread, I marvel at your ability to 'know' that the standard view of climate science is wrong despite lacking an understanding of something as basic as feedback. How can you have a view on the correctness of climate sensitivity estimates without such an understanding? I also wonder why a population that says that its position is 'all about the science' would fail to correct your errors before I do.

"I disagree with this analogy because actually we know that the "natural" temperature increase without positive feedbacks is 1.2C from the S-B equation"

But unfortunately the simplistic radiation balance doesn't represent the Earth's atmosphere (Heat rises - so a natural negative feedback). Also to me it seems obvious the water cycle acts as an obvious negative feedback to heating in the Earth's atmosphere. Water vapour/clouds stop the highs getting as high and the lows as low. Just look at the sahara and Singapore.

And on the point of climate sensitivity I also believe it is a meaningless concept. You can linearise any problem to give a first order straight line solution. In fact it tends to be necessary to solve lots of problems analytically, but obviously not important if you want to iterate our problem using a computer model.

Rob, not sure whether you're taking issue with me or not, but there's little in what you've said I disagree with. There appear to be a dichotomy with "climate sensitivity". On the one hand it is reasonable to assume a warmer world will give rise to more water vapour, and from what I've read everyone agrees that it will cause more heat to be retained in the atmosphere - the so called positive feedback. They do take account of clouds but really have not the faintest idea what the effects of cloud albedo will be as there is no real understanding of the cloud "life cycle" for want of a better term.

In short there must be some response to increased water vapour but it seems to me that if the scientists wanted to forecast a cooler world they could point out that the water vapour would cause more clouds and the earth with cool dramatically with the same authority as they're forecasting an ECS of 3C. In other words I don't believe there is any foundation to the forecast ECS and it appears there's a growing number of scientists who, while not exactly agreeing with me, are having doubts about the numbers they've been using to make their "predictions".

Rob Burton said:

> Heat rises - so a natural negative feedback

Is convection in and of itself a negative feedback as Rob suggests? To act as a feeback, increased convection would either have to reduce absorbed solar radiation or increase outgoing IR radiation. Clearly convection plays a part in cloud formation and aerosol distribution which affect radiation flows but these are side effects (and possibly +ve or -ve feedbacks) of convection; convection itself doesn't seem to be acting as a -ve feedback. So can convection lead directly to increased IR radiation to space?

My understanding is as follows.

Climate Sensitivity λ is the infinitesimal change in surface temperature DT to an (infinitesimal) increase in forcing DS.

So DT = λDS units of λ are deg.cm2/watts

The temperature response of the climate is non linear and λ does indeed also depend on T. We know this is the case because of Stefan Boltzman's law. If there are no climate feedbacks then

S = εσT^4

So DS/DT = 4εσT^3 and λ = 1/4εσT^3 = 3.5W/m2 for ε = 0.6

This tells us that if the earth's temperature rises by 1 degree C the surface will on average radiate an extra 3.5 W/m2.

The greenhouse gas effect from CO2 is due to the absorption of IR photons that fall into hundreds of very narrow wavelength lines centered mainly around 15 microns. Even at 280ppm many of these lines are already saturated and increasing concentration has no effect. It is only the lines at the side of the bands where absorption increases. This raises the altitude in the atmosphere where photons in these narrow frequencies can escape to space. These photons have less energy than before because they now originate from colder air due to the lapse rate. Therefore the final result of increasing slightly the CO2 concentration is that there is a tiny reduction in outgoing IR resulting in a tiny energy imbalance with the incoming solar radiation. As a result of this imbalance the surface warms up a little so that the same OLR as before is restored.

The calculation of this reduction in OLR (or energy imbalance) can be done - for example using MODTRAN under the assumption that nothing else changes and in particular that the lapse rate remains constant. The result of these calculations is a net "forcing" from increased CO2 of S = 5.3ln(C/C0), where C0 is the start concentration and C is the final concentration of CO2.

Now it is easy to calculate what the most people mean by "climate sensitivity", which is the temperature rise caused by a doubling of CO2. The reduction in OLR (called forcing by IPCC) is simply 5.3ln(2) = 3.7 W/m2. Therefore the change in temperature of the surface needed to restore energy balance is 3.7/3.5 or about 1.1C

This is Equilibrium Climate Sensitivity (ECS) because it is the temperature change that restores energy balance. Climate models predict higher values of ECS because they also have built in feedbacks for H2O, clouds and lapse rate changes. They also use aerosols to fine tune their outputs to match observed temperature data. The effects of aerosols is still rather uncertain.

Transient Climate Response (TCR) was introduced because the oceans take many tens of years to reach an energy balance. If you try to boil a pan of water with a candle then it takes a long time to warm up! The oceans have a huge heat capacity and it could even be that the oceans will never reach equilibrium but instead just change currents and heat flow rates to the poles. GCMs however do model the ocean in vertical layers and predict how energy eventually balances. These models give a "relaxation" time of about 60 years to reach an equilibrium.

The IPCC define TCR as “Transient climate response (TCR) is defined as the average temperature response over a twenty-year period centered at CO2 doubling in a transient simulation with CO2 increasing at 1% per year". TCR is a result of pure model simulations and different climate models predict different values of TCR. TCR is calculated in the models by holding all other external forcing constant while drip feeding in CO2. That is why IPCC give a spread of values for TCR from 1.5 to 4.5C. This spread is really due to the different handling of feedbacks in each model.

This definition of TCR cannot be measured without using a model. Nic Lewis tries to measure TCR directly but he still has to rely on CMIP5 forcing to let him untangle a "measurement" from the temperature data. This is because it is not just CO2 which is changing but also CH4, NO2 etc and the IPCC definition excludes them. The modelers are then able to criticise Tim because his result according to them, doesn't handle aerosols or the other GHGs properly. Only their models are a correct description of the complex phenomena involved. This is a catch-22 situation we are in. Climate science has become a closed shop where only an elite few with access to complex black-box models are qualified to tell the world how CO2 effects climate. Don't forget also that any large software code always has bugs.

The only way out of this situation is to redefine TCR so that it is independent of models. That is why I proposed a different definition as follows. “Transient climate response (TCR) is defined as the measured average temperature response over a twenty-year period centered on the observed CO2 doubling.” This then would simply be the observed temperature upon CO2 levels reaching 560ppm. It represents the full anthropogenic effect of human activity resulting in CO2 doubling including man's effect on aerosols, CH4, NO2 etc.

The remarkable fact is that there is a near perfect cancelation in AR5 between aerosol cooling and the "other" GHGs. CMIP5 net forcing is near as damn it a perfect fit to a pure CO2 forcing ! - see graph here

You don't need the models at all to measure TCR !

Clive Best:

> TCR is a result of pure model simulations and different
> climate models predict different values of TCR. TCR is
> calculated in the models by holding all other external
> forcing constant while drip feeding in CO2. That is why
> IPCC give a spread of values for TCR from 1.5 to 4.5C.
> This spread is really due to the different handling of
> feedbacks in each model.

Is that so? The IPCC assesses many different estimates of sensitivity and GCMs are only one source of estimates. You ignore estimates resulting from paleo studies.

Chandra,

Paleo estimates are for ECS rather than TCR.
They too also heavily dependant on climate models.

geronimo - "In the post nyb suggested putting heat under a kettle of water would cause the temperature of the water to increase and that the pre-boiling point of the kettle was TCR while ECS was the boiling point."

Nope - read my comment again! No boiling in my comment:

//
For the sake of simplicity, lets assume you are running a tight ship and only put it on a very low gas which is insufficient to induce boiling.
//
Mar 12, 2014 at 11:55 PM | Unregistered Commenter not banned yet
Thread "Myles out of line"

Clive Best - thanks for sharing the info. on TCR definition. I hadn't seen that so I searched for a reference which pulled up Nic Lewis's reply to you at Climate Audit:

//
Clive,

I agree with your sentiments, but the problem is that in reality there are many drivers of surface temperature change – isolating just the effect of CO2 is not practical. However, if one converts the total effects of all greenhouse gases, aerosols, etc. into an equivalent increase in CO2 concentration (by reference to their effective radiative forcing RF, that from a doubling of CO2 being F2xCO2), then what you suggest would be pretty much in line with the generic definition of TCR in Section 10.8.1 of AR5 WGI:

“TCR was originally defined as the warming at the time of CO2 doubling (i.e., after 70 years) in a 1% yr–1 increasing CO2 experiment (see Hegerl et al., 2007b), but like ECS, it can also be thought of as a generic property of the climate system that determines the global temperature response ΔT to any gradual increase in RF, ΔF, taking place over an approximately 70-year time scale, normalized by the ratio of the forcing change to the forcing due to doubling CO2, F2×CO2: TCR = F2×CO2 ΔT/ΔF”
//
niclewis Posted Mar 11, 2014 at 6:34 AM
Thread "Does “Inhomogeneous forcing and transient climate sensitivity” by Drew Shindell make sense?"

Mar 24, 2014 at 1:19 PM | Unregistered CommenterChandra

All I as saying there is that if say the sun heats up the ground the hot air rises to be replaced by cooler air from elsewhere. A Sea Breeze is a very good example of cooler sea air coming in to cool the coast on an otherwise hot sunny day.

Mar 24, 2014 at 1:19 PM | Unregistered CommenterChandra

The whole convection cycle is the main driver of how energy moves around the atmosphere and eventually leaves it. It is involved in both moving energy from the Tropics to the Poles and also in moving energy from the ground to the Tropopause. It then involves the important role of gas/liquid H2O and CO2 in particular which emit in the IR and are effective in emitting this radiation high up in the atmosphere into space to remove the energy that was initially absorbed by the Earth primarily by the ground and sea.

@not banned yet,

and my reply to him was....:

Nic,

I don’t think you quite understood what I was suggesting. You cannot “measure” effective forcing. You can measure CO2 levels in the atmosphere and you can measure the rise in surface temperatures. For everything else you need models. CO2 levels are also an indirect measure of methane emissions and aerosol emissions since they are all related to fossil fuel usage and to the human activity enabled by fossil fuels (such as intensive farming, chemical industry etc.) So why not aim for a simple separation between theoretical physics (models) and experimental physics (measurements) ? Otherwise climate science models are basically unfalsifiable.

The IPCC definition of TCR as it stands is an unmeasurable quantity. Natural variation acts over periods of decades whether it is due to PDO/AMO, due to solar variability or both. It is likely that natural variability is currently in a negative phase resulting in the hiatus in warming.

What we need to do is place experiment back in the prime role like any normal branch of physics and NOT the inverse. TCR should therefore be defined as the measured response to CO2 which includes both anthropogenic and natural effects. Models should then be developed whose goal is to explain the measurements and then make predictions which can then be tested by expriment.

I have been told by Ed Hawkins that climate science is an observational science like astronomy. This week we have experimental evidence for a theoretical prediction of gravity waves caused by inflation after the big bang.

That is the way science should work !

Clive - thanks for the additional comment. Just to clarify - my interest was the specific, referenced IPCC definiton of TCR.

"The uninterestingly hemionymous "Martin A" " - anyone know what that means?

More to the point, why would you be interested in what Monckton says?

It's a very interesting post if you've been puzzled, as I have about some of then problems with TCR and ECS. Basically what I got from it is that in the equation for ECS:

TΔ = 5.35 x λ x ln (2)

The value of λ is time dependent, in other word it changes over time, which had puzzled because the TCR also has the term λ in it and was clearly a different number. The rest of it kinda solves other issues I have not come to grips with associated with the timescales. What I couldn't and still don't understand is the process of getting from 1.2C to 3C increase in global temperature, over what timescales this was supposed to happen, because it can't be instantaneous as it requires a build up of water vapour in physical terms. and none of the terms in the equation for ECS deal seemed to deal with this issue (if you assume, as I did, that λ is a constant). What he's saying, I think, is that λ changes over time and it will take 1000 -3000 years to reach the 3C ECS value of λ = 0..8, and the IPCC know it and have kept it buried in WG1.

If that's true then it's scandalous.

A propos of Monckton I believe he's no fool, but I don't like his abrasive faux intellectual abuse, like referring to someone who asks a polite question as "uninterestingly hemionymous" because he detects you might be challenging his sermon on the question of transubstantiation or some other secret of faith.

notyet banned: "Nope - read my comment again! No boiling in my comment:"

I apologise unreservedly I did it from memory and believe I said so, but still I should have checked.

Yes Martin, I stand corrected. But I'd be surprised if you learnt anything new from his response.