Rhoda - have you read Clive Best's blogposts on the subject? Basically his point is that sensitivity as defined is a model construct that cannot be measured. And he suggests changing the definition so that it can be measured empirically and gives his calculation.

http://clivebest.com/blog/?p=5746 , plus later posts where he calculates TCR and ECS empirically

I find the ins and outs of climate sensitivity too complicated to understand but I realise that the current debate of how to interpret thermometer data has to be a step in the right direction. Using proxy data where they get wildly differing values depending upon which geological era they look at indictes there was a lot more going on during those periods than CO2. How they expect to extract useful data without knowing all the other variables is beyond me.

So it's a good thing they're settling down to chew over modern data. I assume each year adds more clarity.

What bemuses me is how they think we can react to AGW if we don't know whether it will be so low as to be beneficial or so high it would probably be disasterous. Officially they may have ruled out the super high values but the climatati are happier letting high sensitivity values slide in the media than even the low end of the official IPCC range.

sorry Rhoida and Martin A....Clive Best has already chased down that rabbit hole....but feel free to ignore me

I'm one of those, probably like Martin A, who often points out that TCR or ECR are abstracts from the models.

The translation of this is:

Climate Sensitivity=
"Our model says that if CO2 goes up by x, then temperature will go up by y."

The advanced interpretation is that x and y are small increments such that it tells you the slope on the curve. But that is still just the output of the computer model. Climate sensitivity is not some special new variable that you can claim to measure with a new satellite or another device that does consist of
a) A thermometer and
b) A clock.

Once this is realised, the jaundiced will also realise that "climate sensitivity" can be a useful 'framing' ruse, in that you appear, perhaps unwittingly, to be accepting precepts that that the modeller may not wish to see debated.

that should be:
"a new satellite or another device that does NOT consist of
a) A thermometer and
b) A clock."

The whole idea of climate sensitivity revolves around the notion that if the the climate warms then inevitably there will be consequences like melting snow and ice and increased water vapour caused by the increased temperature.The melting snow and ice would mean less albedo and hence were a positive feedback whereas water vapour would provide clouds which are a both a positive and negative feedback. It has a ring of truth about it, but as rhoda points out is it in fact true? Is it in fact that same as your Mum's admonition not to go out in cold weather with your hair wet because "You'll catch your death of cold."? Plausible but not backed up by the observations.

Arrehenius seems to have been the progenitor of this idea in his 1896 paper in which he proposed an ECS of 5-6C. In a, now unfashionable, climate science discussion Angstrom argued that the absorption rate for CO2 used by Arrehnius was too high, which Arrhenius dismissed in 1900, but by 1906 produced a paper accepting that the "science wasn't settled" in 1906 and revised his forecasts down to 2.1C. As far as I can make out this is where it all started, but is it true? Will there be positive feedbacks through increased water vapour?

For my part I'm firmly in the "don't know" camp, it is persuasive that there will be an increase in water vapour, but from what I've read around the subject no one has any realistic notion of how the clouds will behave in terms of absorption of outgoing absorption of radiation or albedo for incoming radiation - which, from memory, clouds account for around 79 Watt/m^2. More water vapour means more clouds which if they increased by say 10%, and the relationship between clouds and their albedo effect is linear, would mean a reduction of around 8W/m^2 in the incoming radiation - which looks like a pretty large negative feedback to me.

The other problem I have is the intractability of the climate sensitivity numbers to research. The range used by the IPCC has remained pretty well within the educated guess made by the Charney Report based on the Manabe (2C ECS) and Hansen (4C, no surprise there, ECS) models of 1.5C (subtracting 0.5C from Manabe) to 4C (adding 0.5C to Hansen) with a probable ECS of 3C (the middle number no less!). That they correctly defined numbers by guessing the range from two models has to be highly improbable, but the work of thousands of climate scientists over the 34 years from the Charney Report through to AR5 hasn't dented this number, except that in AR5 they can't agree what the most likely ECS.

So here's my problem. It is difficult to see how people paid to know these things all accept ECS and are all wrong. That isn't very likely and it is unlikely to the point of impossibility I'm having insights that the scientists wouldn't have considered themselves and have easily understandable answers to. I just can't find them.

A further problem for me is that if the climate sensitivity is indeed 3C and temperature rose naturally by 1C in the past why didn't the climate system produce water vapour then? The water doesn't know where the heat comes
from before producing the water vapour does it? So, where in the paleoclimate records are there rises of 1C followed by rises of 3C and melting of the icecaps?

And finally another piece of climate science ignorance I'd like to be relieved of is this:

Heat ------->water vapour--------->more heat-------->must give more water vapour------->must give more heat.....

What stabilises the climate once we get into that cycle?

Rhoda,

My take and therefore entirely off-the-wall is that Nic L's approach is consistent with others based on energy balance. The theory is that there is a net input of energy into the system and the imbalance will represent CO2 warming and feedbacks. The actual measurement of the imbalance is being attempted at the top of atmosphere by satellites (3) but by measurement of OHC etc by Nic L. As Martin A has pointed out on other threads, the calibration of the satellites requires adjustment but its actual accuracy is good (declared by Willis E!). The adjustment applied is from modelled expectations. Its measurements over time show no trend.

Now if there was a trend upward then that could be seen to match the upward trend of CO2 and warming. It follows that if the trend were down then that could be construed as cooling while CO2 increases. Now, between those two, a zero trend, to my logic, would suggest nothing is happening and if so, the imbalance is actually zero. That would match the temperature trend over the satellite period but not the CO2 trend.

My conclusion from that is that the theory is wrong and that the satellite adjustment is made to match the theory and not the observations. (This, of course, leads to a search for 'missing heat'.) Now, if nothing is happening, TCR is 1 (its a multiplier). Currently, TCR calculations are trending to 1.

But I am unsure if I am right and expect someone can blow a hole in this.

Mar 21, 2014 at 2:58 PM | Registered Commenter Martin A

I had intended to write a discussion piece on sensitivity based on rhoda's questions on one of the blogs, can't remember which one, but I had to spend some time in Paris and have only just got back. (I had intended to call it Sense and Sensitivity - 2 no sense in re-inventing a perfect wheel!). One of the posts on the blog, I believe by "not yet banned" tried to explain TCR and ECS by analogy to a boiling kettle. 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.

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, so what the climate scientists are saying is that the water will go above 100C because of positive feedbacks. 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.

I more inclined to believe your last post as being the most likely case, and that an increase in (temporarily) retained heat will increase cloud cover which already reflects 80w/m^2 out of 340W/m^2 and will cool the earth. But what do I know against the mass of clisci opinion? Nothing.

This brought me back to rhoda's and Martin A's position and led me to ask myself, do the climate scientists really believe that the climate system is a 5 billion year old kettle with a blocked spout and a sealed lid? How likely is that?

Thanks for setting me straight on the loop gain issue, I should know these things.