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« The Iris Hypothesis from the archives | Main | Diary dates, daily edition »

Iris hypothesis bridges model-observation gap

Some months ago I picked up wind of a new paper that was going to provide some support for Richard Lindzen's Iris Hypothesis - the idea that in a warming planet there would be reduced levels of cirrus cloud, which would allow the extra heat to escape from Earth.

The paper in question seems to be this one, published in Nature Geoscience. The authors are Bjorn Stevens and Thorsten Mauritzen, the former the author of a much-discussed paper on aerosols and the latter best known for his paper on the subject of GCM tuning.

Here's the abstract:

Missing iris effect as a possible cause of muted hydrological change and high climate sensitivity in models

Equilibrium climate sensitivity to a doubling of CO2 falls between 2.0 and 4.6 K in current climate models, and they suggest a weak increase in global mean precipitation. Inferences from the observational record, however, place climate sensitivity near the lower end of this range and indicate that models underestimate some of the changes in the hydrological cycle. These discrepancies raise the possibility that important feedbacks are missing from the models. A controversial hypothesis suggests that the dry and clear regions of the tropical atmosphere expand in a warming climate and thereby allow more infrared radiation to escape to space. This so-called iris effect could constitute a negative feedback that is not included in climate models. We find that inclusion of such an effect in a climate model moves the simulated responses of both temperature and the hydrological cycle to rising atmospheric greenhouse gas concentrations closer to observations. Alternative suggestions for shortcomings of models — such as aerosol cooling, volcanic eruptions or insufficient ocean heat uptake — may explain a slow observed transient warming relative to models, but not the observed enhancement of the hydrological cycle. We propose that, if precipitating convective clouds are more likely to cluster into larger clouds as temperatures rise, this process could constitute a plausible physical mechanism for an iris effect.

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Reader Comments (40)

"..would allow the extra heat to escape to Earth."

From Earth, or, to space.
[Amended. Thanks. BH]

Apr 21, 2015 at 8:44 AM | Unregistered CommenterJoe Public

This is a very interesting paper. The authors seem to be proposing a smaller 'iris effect' than Lindzen, but it's interesting that they see improvements in the hydrological cycle as well as effects on the rate of warming.

Apr 21, 2015 at 8:55 AM | Registered CommenterRichard Betts

More unfounded rubbish from the world of modelling.

Look, they have a model which runs hot (as they all do) so they think to themselves: This idea of an iris from prof Lindzen (whom I much respect) will give us the opportunity to add another tuning parameter to our model. This tuning parameter will be a negative feedback so it will reduce the uselesness of our models. Wow, great idea§ Do we need to empirically show proof of this mechanism? No no we never show proof of our tuning parameters. Great let's write a paper.

and then along comes model man Betts. " it's interesting that they see improvements in the hydrological cycle as well as effects on the rate of warming." WTF.

Apr 21, 2015 at 9:02 AM | Unregistered CommenterStephen Richards

I have to agree with Ken Rice here: Eventually, science self-corrects.

Apr 21, 2015 at 9:04 AM | Unregistered CommenterRichard Tol

"These discrepancies raise the possibility that important feedbacks are musing from the models."

Another blinding glimpse of the bleeding obvious !

Apr 21, 2015 at 9:07 AM | Unregistered CommenterGeospeculator

I'm pleased to see that someone has decided to take Lindzen's hypothesis seriously.
Whether this paper turns out to be "significant" or not at least a well-qualified voice that dissents from the "consensus" is being considered worthy of being listened to.
I've said it before (and will probably end up saying it again) the best thing that could happen to climate science is for it to divorce itself from its own environmental activist wing, ignore (or where necessary, publicly correct the excessive alarmism of) the eco-extremists and the UN politicians, and just get on with the science.
Climatology is still in its infancy as virtually every new paper that appears proves. We need to let it grow up to be a big boy before we start taking its pronouncements as gospel.

Apr 21, 2015 at 9:18 AM | Registered CommenterMike Jackson

Richard Betts

".... they see improvements in the hydrological cycle......"

Richard, I take it you mean improvements in the "modelled" hydrological cycle? What are the improvements? What sort of magnitude? Significant?

Apr 21, 2015 at 9:20 AM | Registered CommenterGreen Sand

"I have to agree with Ken Rice here: Eventually, science self-corrects." Nice of you t cite Ken as the author of this idea, but I suspect it was familiar to the scientific community long before Ken Khao came kicking and screaming into the world.

Having said that, and it is indeed true that at some point into the future we'll have a better handle on climate science the problems don't lie there the lie in the here and now. Although I believe I'm seeing a lot of back peddling in the scientific community on the potential catastrophes, there is no such back peddling in their camp followers. Bob Ward and his ilk are still peddling the "We're all doomed" variety of the message.

Even if the scientists were to pull back today, it will take years for the politicians to admit they've been throwing public money at, and threatening our energy security because of, a non-problem. So it will correct for sure, but it's not going to be a Damascen moment for the politicos.

Apr 21, 2015 at 9:21 AM | Unregistered Commentergeronimo

@Richard Tol (pace Ken Rice?)

Eventually, science self-corrects.
So that's alright then. Let's just bumble along with the craven scientists who allow politicians to get away with hosing money at a non-problem and making their mates wealthy. We'll just sit back and let it all happen until it 'self-corrects'. /s

Update: The quote is from Ghost Stories for Darwin: The Science of Variation and the Politics of Diversity
By Banu Subramaniam

Apr 21, 2015 at 9:34 AM | Registered CommenterHarry Passfield

If the models run too hot ( and scientists accept this...) then it's a very good approach to look for the reasons! The result of the paper reduces ECS of the used model (ECHAM6) from 2.81 to 2.21 (!). It would be helpfull if one reads at least the free Supps before posting an opinion?

Apr 21, 2015 at 9:39 AM | Unregistered CommenterFrank

@Harry P
eventually may not be soon enough

if this paper stands, a lot of people will owe Dick Lindzen an apology or two

Apr 21, 2015 at 9:57 AM | Unregistered CommenterRichard Tol

if this paper stands, a lot of people will owe Dick Lindzen an apology or two
Which, I surmise, is why there will be those in and adjacent to the climate "community" (the aforementioned Bob Ward springs instantly to mind but there will be others) who will not follow Frank's very sensible advice but will have already started scripting their loud and ill-informed opposition to this paper.
Anyone care to take bets?

Apr 21, 2015 at 10:18 AM | Registered CommenterMike Jackson

All very well, but they haven't the faintest idea why Cirrus clouds form at 8 - 10 km in the first place, or why other, non-convective clouds have set top surface altitudes.

If they had done some very simple basic analysis of the real IR Physics, they would have realised that the water cycle reduces (on average, perhaps over 100s of years) the warming effect of all minor, well-mixed GHGs to exactly zero.

However, your veteran correspondent, brain the size of a planet, isn't expecting any praise from all those, 97% so I am told, of the lesser intellects who toil away in the cesspit of failed IPCC pseudoscience!

Apr 21, 2015 at 10:49 AM | Unregistered CommenterNCC 1701E

From the abstract: "A controversial hypothesis ..."

Sheesh, who are these people to decide what is controversial, and what exactly is the scientific measure of controversy?

Climate science is lousy with this kind of statement against anything not politically correct enough.

Apr 21, 2015 at 11:15 AM | Unregistered CommenterMikky

I'm really getting the hang of this.

From the arguments I have read on this blog climate sensitivity is somewhere between -10 and +10 plus or minus 9.

Can't wait to tell the dog. He loves science.

Apr 21, 2015 at 11:22 AM | Unregistered Commenteresmiff

Over at Climate Audit Nic Lewis, in the 3rd of his discussions of his Ringberg presentation, includes a discussion of the impact of the Iris effect on ECS assessments.

Apr 21, 2015 at 11:30 AM | Unregistered Commenterrogue

We all know that water evapourating convects to form clouds, which reduce the input of energy to the surface. High level clouds can reduce energy loss so reducing them increases radiation away. Nature's thermostat.

Apr 21, 2015 at 12:05 PM | Unregistered CommenterJohn Marshall

Has climate science redefined tipping point? A point at which the climate, tips itself, back towards normal?

Obviously even if proved correct, climate science could feed itself for years, simply by arguing about the concept of normal. They have been doing it for 30 years already, so they are beginning to get quite good at it.

Apr 21, 2015 at 12:21 PM | Unregistered CommenterGolf Charlie

O Master, this is a major perturbation of the chaotic nonlinear coupled climate models. How should we change our response here in the UK to the changes in the consequential climate change catastrophe. Will it mean more rain or less rain, more gales or fewer gales, more hot spells or fewer, more cold spells or fewer, more cloud or less cloud. How will the catastrophe change? How should our response plan change? Should we spend more quickly or slowly, should we decarbonise faster or more slowly, this is urgent, we need to know. More wind turbines or more solar farms? What should the new balance be? What if it's still wrong?

Be calm grasshopper, frack for gas and build nuclear and gas turbine power stations for when that that should be isn't and that that shouldn't be is. The road to energy harmony is unchanged by such manipulations of the models. Om!!!

Apr 21, 2015 at 12:21 PM | Unregistered Commenterson of mulder

Golf Charlie: but what is normal? Could it be that “normal” is the few million years of the age of the dinosaurs, when it was a lot hotter than it is, now? Or perhaps in the depths of the Ice Age, when it was a lot, lot colder than now? How can humans, who have been active (rather than just living) on this planet but a few tens – perhaps hundreds – of thousands of years determine what is “normal” for a planet that has had a life hundreds of thousands times longer?

It is all a bit strange, the insistence on referring to something that we have precious little experience of, and almost no comparison with, as “normal”. It is like saying that the global “climate” that existed between 9 o’clock in the morning and midday, last Thursday was the epitome of normal, and we should endeavour to stabilise the world’s climate to that paradigm.

Apr 21, 2015 at 1:08 PM | Registered CommenterRadical Rodent

Climate Models:

One day there will be a perfect working models of the climate of the planet. Today's modellers have absolutely no idea what that model will look like and no idea what parts will be needed to complete it or how close they are to finding and understanding all those parts. However modellers just can not stop making models and using them to predict something which, whatever else it might be; is no guide to future climate.

Apr 21, 2015 at 1:39 PM | Registered CommenterDung

Richard Betts
Are you permitted to discuss this on here as you are a Civil Servant as you have pointed out previously?

If the answer is No which I'm surmising it will be then comments such as the one you have made could be considered as deliberately disruptive.

Apr 21, 2015 at 2:09 PM | Unregistered CommenterSandyS

Refer to Rule #1 of ClimateScience(TM):

Any scientific finding must be either "worse than we thought", or "of no significance".

Apr 21, 2015 at 2:19 PM | Unregistered CommenterGeckko

Just one more epicycle and we'll have it nailed.

- The Climate Modelling Community

Apr 21, 2015 at 2:23 PM | Unregistered CommenterBloke in Central Illinois

Based on this Max Planck Institute report announcing the paper :Missing iris-effect as a possible cause of muted hydrological change and high climate sensitivity in models

I'll not hold my breath.

The above link says

Notably, and in contrast to some well known early studies, the present study also finds that other processes act to limit the ability of a possible iris effect to explain a suprisingly low (less than 2 K) sensitivity of warming to a doubling of atmospheric CO2.

It sounds like the carrot for skeptics is to trim climate sensitivity a little bit more. The stick to beat them with is in all but ruling out 'surprisingly low' figures for sensitivity.

Apr 21, 2015 at 2:41 PM | Unregistered CommenterGareth

Radical Rodent 1:08 The concept of "normal" in climate science.

After 30 years of argument, climate science has not reached a conclusion. This has at least 2 important consequences.

1. It can always (for at least another 30 years) be argued that what we are experiencing now is radically different, compared to previous, due to man's interference.

2. More research is needed. Go to step 1

Apr 21, 2015 at 3:58 PM | Unregistered CommenterGolf Charlie

97% of all climate alchemists can dance on one pin called the Enhanced GHE.

In the land of the one legged, only the man with two legs can boot the rest up the arras........

Apr 21, 2015 at 4:07 PM | Unregistered CommenterNCC 1701E

Golf Charlie: I suspect that, in 30 years, the climatastrologists of the time (should they still exist – indeed should any civilization still exist; it is a bit presumptuous to assume that nothing will change), they will be saying things along the line of: “No, no. We never said the world was warming. Find one paper where that was stated… See! All you can produce is newspaper cuttings! We are definitely going to freeze!” In other words, much the same as they are now saying about the 1970s oncoming ice-age scare. The only difference is that, once on the internet, nothing is lost.

I suspect that one reason the sceptics are making such heavy weather of the argument is that there is an implicit agreement that there is a “normal” climate, despite the fact that there has never been any definition of what a “normal” climate should be – the only point being that it is not the climate that we have now, nor is it the one that is forecast to be. Perhaps we should be trying to get the Climate “Scientists” to define precisely what the climate should be, as that is really the only way that we may work towards its realisation.

Apr 21, 2015 at 4:27 PM | Registered CommenterRadical Rodent

Each and every sensitivity set on edge like quills upon the fretful porpentine.

Apr 21, 2015 at 5:30 PM | Unregistered Commenterkim


Yes, I am able to discuss this, it's a purely scientific topic and nothing at all to do with the election.

Apr 21, 2015 at 9:19 PM | Registered CommenterRichard Betts


"Richard Betts
Are you permitted to discuss this on here as you are a Civil Servant as you have pointed out previously?"

I know of no law that inhibits civil servants discussing scientific papers in public, which one is that? In any event Richard was commenting on it rather than discussing it. He seems to be getting a hard time here recently, have I missed something?

Apr 21, 2015 at 10:21 PM | Unregistered Commentergeronimo

Radical Rodent, before we were able to measure accurately, our best indicators were that Easter was freezing last year, my birthday was warmer, and that repair on the rotten fence post shoul be okay until next autumn, unless it gets too windy. Oh, and important stuff like the planted crop harvest in summer, and the size of the apple harvest following the spring frost.

Those on the west coast of south america, knew for hundreds of years, that some years, the fish did not appear. Its true significance on the worlds climate, or what causes it, has yet to be blamed on CO2, so therefore, is of no interest to adequately funded climate science.

Also, there are no polar bears in the Galapogos.

Apr 21, 2015 at 10:36 PM | Unregistered CommenterGolf Charlie

You all must remember that Lindzen was taught incorrect Physics by Goody so believes the Enhanced GHE hoax.

Apr 22, 2015 at 7:34 AM | Unregistered CommenterNCC 1701E

Big Boobed Amazing Brunette Fucking. Russian old & young. Cute young pregnant girl. Young Faith Daniels Gagged. VL and VG. hot teens by Fra1

Apr 22, 2015 at 7:47 AM | Unregistered Commenterjkrolluikenshutters

Plus one in support of what Golf Charlie just said.


Apr 22, 2015 at 7:49 AM | Unregistered CommenterMailman

@ jkroll.... What evidence do you have that someone has made a big boob here, and when you refer to "hot teems" are you talking about temperature increases in excess of 13 deg c ?

Apr 22, 2015 at 8:16 AM | Unregistered CommenterHyperthermania

Richard Betts: "Yes, I am able to discuss this, it's a purely scientific topic and nothing at all to do with the election."

As far as I know every political party in the election, bar UKIP, says we must spend many £billions to completely change the way our civilisation works based on the work (propaganda?) of the self styled "climate change" consensus, which includes Mr Betts. This paper may change that consensus, so is of considerable significance in the election. That is the consequence of scientists becoming advocates of policy, or failing to correct advocates, activists and politicians.

Apr 22, 2015 at 9:42 AM | Unregistered CommenterBudgie

IRIS, bah, the junior varsity.

Apr 22, 2015 at 4:08 PM | Unregistered Commenterkim

Lindzen's Iris posited that increased global warming from increased CO2 (kim and kith can now leave the room) would result in a decrease in tropical cloudiness. The smaller amount of tropical cloudiness would increase the ability of IR radiation from the surface to escape to space which would compensate for the increase in surface temperature driven by the increase in greenhouse gases

What Steven's has done (see Andy Dessler's comment @ realclimate) is to add something that Lindzen forgot. If there is less cloudiness, then the surface will be exposed to more sunlight and warm. On net, depending on the models used, there may be a small iris effect, but nothing of the sort that Lindzen claimed.

Apr 24, 2015 at 5:03 PM | Unregistered CommenterEli Rabett

"there may be a small iris effect"

The model used in the paper with the Iris x 1.0 effect goes from 2.8C to 2.2C ECS, a reduction of 22%. Nice to know that 22% reductions are 'small'.

It's a bonus that modelling an effect similar to what Lindzen postulated manages to:
1. Improve model vs observations for precipitation
2. Explain away the mystery of the missing tropical tropospheric hotspot.
3. Improve modeling of long-wavelenth sensitivity.
4. Getting actual temperature trends closer to observations.

This is a Ginzu knife explanation. It slices, it dices, it does everything ...

A few more small reductions and the model ECS will line up with reality!

May 5, 2015 at 10:12 AM | Unregistered CommenterPJ

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