Oh dear, now we have three peer reviewed papers (Lindzen and Choi, Spencer and Braswell, and now Richard P. Allan) based on observations that show a net negative feedback for clouds, and a strong one at that. What will Trenberth and Dessler do next? Maybe the editor of Meteorological Applications can be persuaded to commit professional suicide and resign? The key paragraph from the new paper:
…the cloud radiative cooling effect through reflection of short wave radiation is found to dominate over the long wave heating effect, resulting in a net cooling of the climate system of −21 Wm−2.
After all the wailing and gnashing of teeth over the Spencer and Braswell paper in Remote Sensing, and the stunt pulled by its former editor who resigned saying the peer review process failed, another paper was published last week in the journal Meteorological Applications that agrees well with Spencer and Braswell.
This new paper by Richard P. Allan of the University of Reading discovers via a combination of satellite observations and models that the cooling effect of clouds far outweighs the long-wave or “greenhouse” warming effect. While Dessler and Trenberth (among others) claim clouds have an overall positive feedback warming effect upon climate due to the long-wave back-radiation, this new paper shows that clouds have a large net cooling effect by blocking incoming solar radiation and increasing radiative cooling outside the tropics. This is key, because since clouds offer a negative feedback as shown by this paper and Spencer and Braswell plus Lindzen and Choi, it throws a huge monkey wrench in climate model machinery that predict catastrophic levels of positive feedback enhanced global warming due to increased CO2.
The cooling effect is found to be -21 Watts per meter squared, more than 17 times the posited warming effect from a doubling of CO2 concentrations which is calculated to be ~ 1.2 Watts per meter squared. This -21 w/m2 figure from Richard P. Allan is in good agreement with Spencer and Braswell.
[While the -21wm2 and ~1.2 W/m2 values are correct, the comparison is wrong, and it is my mistake. The values are Top of Atmosphere and Surface, which aren’t the same. This prompts a new rule for me, I shall not publish any posts after midnight again (other than something scheduled previously during the day), because clearly I was too tired to recognize this mistake. I’ll add that I have emailed Dr. Allan regarding the question of feedback on hisfigure 7, and have not received a response. – Anthony]
Here’s the paper abstract, links to the full paper (which I located on the author’s website) follow.
Combining satellite data and models to estimate cloud radiative effect at the surface and in the atmosphere
Richard P. Allan
Abstract: Satellite measurements and numerical forecast model reanalysis data are used to compute an updated estimate of the cloud radiative effect on the global multi-annual mean radiative energy budget of the atmosphere and surface. The cloud radiative cooling effect through reflection of short wave radiation dominates over the long wave heating effect, resulting in a net cooling of the climate system of -21 Wm-2. The short wave radiative effect of cloud is primarily manifest as a reduction in the solar radiation absorbed at the surface of -53 Wm-2. Clouds impact long wave radiation by heating the moist tropical atmosphere (up to around 40 Wm-2 for global annual means) while enhancing the radiative cooling of the atmosphere over other regions, in particular higher latitudes and sub-tropical marine stratocumulus regimes. While clouds act to cool the climate system during the daytime, the cloud greenhouse effect heats the climate system at night. The influence of cloud radiative effect on determining cloud feedbacks and changes in the water cycle are discussed.
1. Introduction
Earth’s radiative energy balance (solar radiative energy absorbed and terrestrial radiation emitted to space) determines current patterns of weather and climate, the complexity of which is illuminated by satellite observations of the evolving distribution and diversity of cloud structures. Representing clouds and the physical processes responsible
for their formation and dissipation is vital in numerical weather and climate prediction, yet many approximations must be made in these detailed models of our atmosphere (e.g. Bony et al., 2006; Allan et al., 2007). Observations of cloud characteristics from satellite instruments and in situ or ground-based measurements are crucial for improving understanding of cloud processes and their impact on Earth’s radiative energy balance (Sohn, 1999; Jensen et al., 2008; Su et al., 2010). The energy exchanges associated with cloud formation and precipitation are also a key component of the global water cycle, of importance for climate change (Trenberth, 2011). In this paper, initially presented at a joint meeting of the Royal Meteorological Society and Institute of Physics on Clouds and Earth’s Radiation Balance (Barber, 2011), the utility of combining weather forecast model output with satellite data in estimating the radiative effect of cloud is highlighted. Using a combination of models and satellite data a simple question is addressed: how do clouds influence the radiative energy balance of the atmosphere and the surface.
As an example of the radiative impact of cloud, Figure 1 displays thermal infra-red and visible channel narrow-band images of the European region from the Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) on board the Meteosat-9 satellite (Schmetz et al., 2002).
In both images clouds appear bright: this denotes relatively low infra-red emission to space and relatively high reflection of visible sunlight to space. The hot, generally clear regions of northern Africa are also noticeable in both images since they are associated with substantial thermal emission to space (dark regions in the infra-red image) and high surface reflection from the desert surface (bright in the visible image). The brightest clouds in the thermal image correspond with (1) a trailing cold front extending from the coast of Norway, across Scotland and to the west of Ireland, (2) a developing low pressure system to the west of Iceland, and, (3) a low pressure system in the Mediterranean centred on Sardinia.
These are regions of ascending air with relatively high altitude, low temperature cloud tops which depress the thermal emission to space compared with surrounding regions. These features are also present in the visible image. However, many more cloud structures are also present. There is a prevalence of low altitude cloud over the oceans: this cloud contains large amounts of water droplets which are highly reflective (e.g. Stephens et al., 1978). The imagery captures the complex cellular structure of this cloud (e.g. Jensen et al., 2008) over the region surrounding the Canary Islands. These cloud types are thought to contribute strongly toward uncertainty in climate projections (Bony et al., 2006). While these clouds also strongly attenuate infra-red radiation, their impact on the thermal radiation escaping to space is modest since cloud-top temperatures are not dissimilar to the surface at night and so they do not contribute significantly to the strong natural greenhouse effect of the clear-sky atmosphere.
The altitude and optical thickness of cloud determines the overall radiative impact of cloud, a combination of the warming greenhouse effect and the surface-cooling solar
shading effect. Yet, probably an even stronger influence does not relate to the cloud itself. The time of day and time of year dictate the incident solar radiation and, therefore,
modulates the strength of the short wave reflection: clearly at night the solar influence of cloud is absent.
…
7. Conclusions
Exploiting satellite measurements and combining them with NWP models initialized through assimilation of available observations enables the effect of clouds on the Earth’s radiative energy balance at the surface and within the atmosphere to be quantified for the present day climate. Consistent with previous results (Ramanathan et al., 1989; Su et al., 2010), the cloud radiative cooling effect through reflection of short wave radiation is found
to dominate over the long wave heating effect, resulting in a net cooling of the climate system of −21 Wm−2.
The short wave radiative effect of cloud is primarily manifest as a reduction in the solar radiation absorbed at the surface of −53 Wm−2 for the global multi-annual mean. The magnitude of this effect is strongly modulated by the incoming solar radiation and the dominance of cloud short wave cooling over long wave greenhouse trapping is maximum around local noon (Nowicki and Merchant, 2004) while the cloud long wave heating effect dominates at night.
The long wave greenhouse effect of cloud measured at the top of the atmosphere is manifest primarily as a heating of the atmosphere in the moist tropics, consistent with calculations by Sohn (1999).
Over the marine stratocumulus regions and across higher latitudes the cloud-base emission to the surface becomes substantial and dominates over the reduced outgoing long wave radiation to space resulting in enhanced radiative cooling of the atmosphere and heating of the surface. The cloud radiative influence on the exchange of radiative fluxes between the atmosphere and the surface are intimately linked with the water cycle through radiativeconvective balance. While tropical, high-altitude clouds act to stabilize the atmospheric profile radiatively, clouds over polar regions tend to cool the atmosphere while heating the surface through enhanced atmospheric longwave radiative emission to the surface. In future work it would be informative to categorize these effects by cloud type further (e.g. Futyan et al., 2005) and compare with climate model simulations. These analyses are vital in constraining cloud feedback processes further and in linking to future changes in the water cycle (Stephens, 2005; Bony et al., 2006; John et al., 2009).
A particular challenge is the accurate quantification of surface radiative fluxes due to the sparse ground-based observing network (Roesch et al., 2011) and also monitoring current changes in cloud radiative effect in satellite data, reanalyses and models (Wielicki et al., 2002); combining meteorological reanalyses with satellite data and surface observations provide a vital methodology for meeting these challenges.
Abstract is here: http://onlinelibrary.wiley.com/doi/10.1002/met.285/abstract
Full paper is here: http://www.met.reading.ac.uk/~sgs02rpa/PAPERS/Allan11MA.pdf
UPDATE: Some people in comments including Dr. Roy Spencer, (and as I was writing this, Dr. Richard Allan) suggest that the paper isn’t about feedback (at least in the eyes of IPCC interpretations, but Spencer adds “it could be”). Thus I’ve removed the word from the headline to satisfy such complaints. My view is that clouds are both a feedback and a forcing. Others disagree. That’s an issue that will occupy us all for sometime I’m sure.
Regarding cloud feedbacks, here’s what I noted in the paper in section 6, near the end. Allan is referring to figure 7 which shows (a) net radiation and (b) net cloud radiative forcing:
Substantial negative anomalies in net radiative flux from ERA Interim are apparent in 1998 and 2010, both El Niño years, suggesting that the substantial re-organization of atmospheric and oceanic circulation systems act to remove energy from Earth during these periods.
You can clearly see the famous double peak in the 1998 El Niño, but it is inverted. To me that looks like a thermostat action, and not one with stuck electrical contacts, i.e. a negative feedback. I’ve also updated the text related to the incorrect comparison I made. – Anthony
Does cloud cover increase when temperatures increase?
The IPCC and the climate models in general estimate that the negative -21.0 W/m2 net cloud impact reduces to -20.0 W/m2 when temperatures increase by 1.0C. This is really the equivalent of a 5.0% reduction in cloud opacity/cover.
They also predict water vapour will increase by about 7.0% per 1.0C increase in temperatures.
So water vapour goes up by 7.0% per 1.0C but cloudiness goes down by 5.0% per 1.0C.
In practise, the climate models have a complex reaction where the height of cloud increases and the cloud fraction drops by about 1.0% resulting in the net change but I imagine this comes out of Hansen’s imagination only. It started with him.
If Hansen’s cloud numbers were correct, then his published Ice Age forcing numbers are way, way off because the 5.0C drop in temperatures in the ice ages should have resulted in a 25% increase in the cloud fraction and a decline in forcing of 5.0 W/m2 from this affect alone. Instead, he has a verty large drop in cloud cover (not exactly specified but that is how the numbers work out).
The Classius Clapeyron relation says water vapour increases by 7.0% per 1.0C increase in temperatures and clouds should increase by 2.0% to 7.0% (not decline by 5.0%). (The empirical data says water vapour increases by 4.5% per 1.0C increase and clouds are about Zero.)
Rewrite the climate models based on reality not on what you want the numbers to show.
I see that John B has posted another NASA chart that misrepresents reality by using a flat baseline. Charts like that are tantamount to lying. They deceive the eye by falsely making it appear that temperatures are rising at an accelerating rate [another hokey stick chart].
The truth is that global temperatures have been rising along a trend line going back to the LIA. Once that simple fact is understood, it logically follows that CO2 has at most an insignificant effect.
Temperatures are not accelerating. They have been rising along the same trend line since the LIA. CO2 has been ≤ 300 ppmv until very recently, thus falsifying the claim that CO2 has any more than a negligible effect, which for all practical purposes can be completely disregarded.
For normal folks, that clarification is all that is necessary to debunk the “carbon” scare.
Let’s consider this: It took a while, not a long while, but a while, to figure out this article. Who here can give an estimate of how long it would have taken arm chair warmers, main stream media, and politicians to figure out this research before they shoot from the hip? It is entirely likely that they have learned to stop here first before responding. This is what makes this blog worth reading. And I mean to say not only the post, but every comment made after the post. At WUWT, research sits down to chew it out with the public.
John B says:
September 20, 2011 at 4:53 pm
We should look at 10 year running averages, like this:
=============================================================
Truthfully, we should step back at look at the big picture…..
What moron put that “normal/zero” line way up at the very top?
….and who’s stupid enough to believe it?
http://www.daviesand.com/Choices/Precautionary_Planning/New_Data/IceCores1.gif
John B says:
September 20, 2011 at 3:02 pm
“The science is sound. Not settled, as science never is, but sound.”
No, the science of AGW is not sound, not even close. That CO2 can backscatter out going LWIR is about as close as it gets to sound, and that’s not close enough. The desire of climate scientists to view the climate purely in radiative terms has blinded them to the reality of a climate governed by the phase change of H2O.
The effect of backscattered LWIR on the cooling rate of the oceans appears to have been miscalculated. Water that is free to evaporatively cool does not respond to LWIR in the same way as rock or soil. The “Missing heat” never got trapped in the oceans.
Even ignoring this error, projected increases in CO2 do not have the ability to cause catastrophic warming on their own. Not even if we used all known fossil fuel reserves. Hence the need to invent strongly positive water vapour feedback and erase the MWP. The discussion on this thread alone should be enough to indicate that the empirical evidence for strongly positive water vapour feedback is lacking.
The CAGW hypothesis depends on strongly positive water vapour feedback. The evidence for strongly positive water vapour feed back is lacking. The science is therefore not sound.
Dave Springer said at September 20, 2011 at 9:54 am
“Extinction altitude for primary CO2 absorption band is about 2000 meters AGL. That’s what I calculated from IR spectrograph looking downward from 20 kilometers above the arctic ocean. In the IR window you see the temperature of the arctic ocean and in the CO2 absorption band you see a temperature that is 20C colder. Using dry adiabatic lapse rate of 1C per 100 meters that works out to a 2000 meter column of air beginning at sea level.”
This was in response to my question asking how high a cloud base must be to be beyond the reach of surface LWR. What this tells me then is that clouds at or above 2000 meters have no direct influence on surface temperature at night, and so the higher they are, the less heat is retained at the surface. The air column below 2000 meters that is heated by surface LWR can reach the cloud with upwelling radiation and also the reach surface with downwelling radiation, but the effect is hindered by the opacity of the atmosphere and this: There are asymmetries in the radiated heat – CO2 does not radiate at the same frequency that excites it, so heat radiated from CO2 is less effective at heating adjacent CO2. But on analysis we can say that high clouds do not retain surface heat effectively. The heat they effectively retain is above the surface by some distance that is a function of the cloud base altitude and the opacity of the lower atmosphere.
Seems simple enough, but now the sun rises and the cloud is still there, very high overhead, and it is reflecting as much light back to space as does its lower altitude neighbors except the atmosphere above it is far less opaque, and because of the altitude advantage it begins reflecting light sooner, and casting a longer shadow, prevents the sun from heating a disproportionately larger area than it will at mid day. We conclude then this: There is nothing remotely symmetrical about the heat impact of very high clouds.
So now I want to know if this study of cloud influence considers cloud base altitude as well as cloud top altitude.
whether or not the gist of this paper is about feedback or net effect, it must be obvious that the impact that clouds have on radiation balance is large compared to changes in CO2 forcing, and that this large effect is calculated as the difference of two numbers that are larger still, and have substantial uncertainties. So, the difference has uncertainties in it that are yet larger yet, and may, in fact, be the sum of two substantial uncertainties.
Lamb, many years ago, thought he had indirect evidence for long period variations in cloudiness–if so is this a driver or feedback?
Anthony says
You can clearly see the famous double peak in the 1998 El Niño, but it is inverted. To me that looks like a thermostat action, and not one with stuck electrical contacts, i.e. a negative feedback. – Anthony
———–
I find this interesting because it says, I think, that Anthony, agrees the planet is warming and that the strong 98 el niño was in response to that warming and that the el niño then acted to counteract that warming. Otherwise the use of the term “feedback” does nor make sense.
Sounds plausible and if it is true then the predicted consequence would be that the el ninos will get stronger or more frequent as the global temperature rises.
REPLY: Nope, and not interested in having you put words in my mouth based on your anonymous opinion. -Anthony
Question about positive and negative forcings – the scientists say clouds may provide positive and negative forcings but I am wondering about agricultural dust. (Maybe another AGW funding issue for some university professor) Here in Alberta, every fall I see about 1000 km of north south dust, and about 1500 km of dust east of the Rocky Mountains from the harvesting activities of farmers. This lasts for three to four weeks every year. I have observed this both driving and flying over the Canadian and US grain belts and with all the discussion of dust and clouds, I wonder what impact the annual harvest has on temperature, if any, and in what direction. In reality, I don’t think it matters but in the context of all those people concerned about the environment and “Big Oil”, I see a lot more impact from food production on the prairies than from oil development. Just asking.
Konrad says:
September 20, 2011 at 5:05 am
Those saying that this paper is not addressing the feedback issue may be missing the point. For the strongly positive water vapour feedback demanded by the IPCCs doom scenarios to work, the increased evaporation would need to be prevented from causing more clouds. This is not plausible in an atmosphere with a vertical pressure gradient.
———–
If this was an easy question to answer it would have been answered already.
It’s not easy to answer since the increase in temperature has two effects:
1. it produces an increase in evaporation therefore increasing the absolute humidity
2. It produces a reduced tendency of water vapour to condense to form rain.
Then throw in the fact that rain happens when cold air streams collide with warm air steams, causing vertical air motions.
Then add in land versus sea and latitude and spinning earth’s and the whole effect becomes impossible to decide on the back of an envelope.
So sorry, common sense is not good enough outside your personal experience.
NetDr says
A strongly negative feedback system is highly resistant to change up or down.
———
Which means you have a serious problem explaining what the set point actually is.
We know there have been hotter periods in the deep past and most recently ice ages are the norm. So it looks like this is proof that negative strong feedbacks cannot exist.
A post that contains an erroneous interpretation of a paper (which the the author of the paper points out in the comment thread, as do other climate scientists) should place the update at the top of the post, not the bottom.
LT says:
“We know there have been hotter periods in the deep past and most recently ice ages are the norm. So it looks like this is proof that negative strong feedbacks cannot exist.”
Ridiculous.
The climate alarmist positive feedback argument is always resurrected to support runaway global warming, not ice ages. And there is no ” ‘proof’ that negative strong feedbacks cannot exist.” Another ridiculous argument. Negative feedbacks are the norm. It is positive feedbacks that are highly unusual.
Really, LT, you shouldn’t pollute this excellent site with your pseudo-science. Go back to tamino where you belong, junior.
I don’t know if this is accurate, when the sky is cloudy in the winter time, it is warmer, when it is cloudy in the summer it is cooler.
What I think I am missing is what is happening on a global basis.
tall bloke
“I invite you to consider why it is that cloud amount reduced according to ISCCP data in the 80s and 90′s. I think it was due to ongoing above average solar activity”
you refer to ISCCP cloud data.
Do you accept the physical models that are used to create the cloud data. Yes, create.
That physics is RTE. And we know from that that doubling c02 gives us 3.7 additional watts for forcing..
Now, you may believe that this forcing is counter balanced by other factors. you may believe that. But every time, every single time you cite data taken from a platform in space, you tacitly accept the physical models that used to turn sensor inputs into data products.
when a sensor in space gives you a picture of a cloud, when it measures SST, when it sees ice, when it provides any data whatsoever that data goes through a physics based algorithm. That algorithm has at it heart the physics which tells us… doubling C02 gives us 3.7W of additional forcing. Again, you can argue that this forcing is balanced or offset by other mechanisms. But when you talk about satellite data you invoke the physics required to produce it. You dont get to cite that data without owning the physics that creates its.
coaldust says:
September 20, 2011 at 5:20 pm
John B says:
September 20, 2011 at 2:06 pm
Except that there has been no trend in GCRs, so even if GCRs did cause clouds to form, which is still merely conjecture, it would be irrelevant.
There is no trend in GCRs? They change with every sunspot cycle. You are assuming the average is the controlling factor, but why would it be? The are the extremes and the rate of change. These are more likely controlling. Physical phenomenon operate on local and immediate conditions, not trends or averages.
———————
Yes, they go up and down – i.e. no trend, only variations. GCRs go up and down, as do other things, so those things can’t explain the trend. So, what has shown a trend over the last couple of hundred years that might explain temperature rises?
One point and one question:
1) Negative feedback normally reduces oscillations, positive feedback increases instability and makes oscillations more likely.
2) Clouds are white at the top and dark at the bottom (own shadow). Does this mean the cloud itself is hotter at the top than at the bottom compared to the air at the same heights? Do we know? Can a cloud really store energy?
Steven Mosher says:
September 20, 2011 at 10:51 pm
Morning (here) Steve – Not sure I follow your point. Yes, in order to define what a sensor measures, we would define the measurement based on the physics. But even if the physics is correct – that does not actually make the definition or measurement totally correct. Take something with a wide range of values e.g. radiation energy from nanometers to longwave – or TSI for example – no single sensor will measure the whole range (as far as I know?) because it will lose sensitivity in some ranges/areas. Hence, a range of sensors must be added together to give the end (summary) result. I for one don’t necessarily trust all the satellite data, and has been adequately demonstrated, neither do the scientists who interpret them based on the various corrections, etc, they seem to ‘need’ to apply.
The point that accurate measurement is fundemental to observations, does seem to get lost in the science publications – with uncertainties and error bars often guessed, or left out altogether – and certainly not highlighted within conclusions!
I find it quite ridiculous that cimate science talks about 1.4w/m of forcing here and there – within a total TSI of 1000 times as much – then say that TSI only varies by a tiny amount (0.1%), which, to all intent and purpose is equivalent to the tiny anthropogenic signal they are trying to measure. How often is this highlighted within the publications? I am not saying it isn’t possible to detect such AGW signals, but it is clear (especially after the last decade) that so called natural variation could easily ‘mask’ any such signal, and in real terms, likely outweighs the effects of any anthropogenic origin. I am not suggesting all the scientists deliberately evade the uncertainty questions – but the IPCC and political proponents certainly do!
“Roy W. Spencer says:
September 20, 2011 at 4:46 am
Now, it might well be that since the average effect of clouds on the climate system in response to radiative heating by the sun is to cool the Earth, then a small increment in radiative heating (e.g. from more CO2) will ALSO result in clouds having a further increment in cooling.”
If the above statement is not true then there would be some point and mechanism between snowball earth and now when the average effect of clouds reached a maximum level of cooling.
What is that point and mechanism? I don’t think there is any theory or evidence for such.
Anthony compared in his post the -21 W/m2 net radiative effects of clouds at the top of the atmosphere (TOA; see table 1 in the paper) to 1.3 W/m2 of surface forcing due to doubled CO2. This comparison has been echoed by several commenters (e.g. TallBloke, Rob Potter).
It is apples and oranges.
The 21 W/m2 of net cloud radiative effect is in reference to having no clouds at all: What is the net effect of clouds (TOA) on the radiation balance in the current climate? It doesn’t say anything directly about the contribution of clouds to current and future changes in climate.
The 1.3 W/m2 otoh refers to the surface forcing due to a hypothetical doubling of CO2. Something entirely different. The units are the same, but that doesn’t mean that can be usefully compared, let alone be interpreted to mean what some want it to mean.
The total (natural) greenhouse effect on Earth (due to water vapor, clouds, CO2 a.o.) is about 150 W/m2. If anything, that would perhaps be a relevant number to compare the 21 W/m2 to.
I posted my reaction also on my blog http://ourchangingclimate.wordpress.com/2011/09/20/net-cloud-effect-cloud-feedback-wuwt-confused/
Bart Verheggen says:
September 20, 2011 at 12:50 pm
Tallbloke,
You wrote: “if it becomes slightly less negative, it’s still very negative, and overwhelms the effect of changes in co2. ”
No. If cloud forcing becomes less negative in response to warming, it be definition acts as a positive feedback. You’re confused by the reference point.
The IPCC scientists claim that warming due to increased co2 will cause a positive water vapour feedback. This would cause more cloud and so cooling.
But cloud cover reduced while the planet warmed 1980-1998, so the supposed water vapour feedback to increased co2 is clearly overwhelmed by some other effect QED.
If it is a solar effect (GCR’s or upper troposphere specific humidity) then these natural variations overwhelm the alleged enhanced greenhouse effect.
Your theory is crumbling Bart V.
George,
Build an electronic circuit and try it. Assuming some lagg. It’ll be underdamped. Overshoot on the way down. Overshoot even more on the way up, etc. Untill the oscillation amplitude is reaches a saturation.
Hockey Schtick says:
September 20, 2011 at 5:20 pm
Multi-institutional study group finds strong negative-feedback cooling effect from clouds
http://hockeyschtick.blogspot.com/2011/09/multi-institutional-study-group-finds.html
Dear Mr. Schtick,
It appears the Climate Process Team did not like the results they were getting and decided to stop their efforts. Alternatively, funding sources saw their results and cut funding. It appears that no work has been done on this since about 2006. Still, it is an interesting find. Thank you for the link.
@EJT
You don’t seem to understand the principles here. George is absolutely right. Negative feedback is what damps the oscillations. Positive feedback is what amplifies them. As an electronics engineer I can say it is basic stuff!
I am a little surprised Allan says the paper is not about cloud feedbacks when it mentions cloud feedbacks four times in the article, including in the abstract and the conclusion.
The abstract reads: “The influence of cloud radiative effect on determining cloud feedbacks and changes in the water cycle are discussed. ”
So is Allan now saying he did not do what the abstract says he did?
From the body of the paper:
“Thus, the radiative effect of changes in cloud cover or properties is highly sensitive not only to cloud type (height, optical thickness, extent) but also to the time of year and time of day at which the changes in cloud properties take place. This is of importance in assessing cloud climate feedbacks which contribute substantially to uncertainty in climate prediction (Bony et al., 2006).”
So is he now saying he is wrong? Is he now saying the radiative effect of cloud changes does not play a role in assessing cloud climate feedbacks?
From the conclusion: “These analyses are vital in constraining cloud feedback processes further and in linking to future changes in the water cycle (Stephens, 2005; Bony et al., 2006; John et al., 2009).”
So is Allan now saying his analysis does not “constrain cloud feedback processes?”
It is fine to say the Allan paper focuses on the radiative effects. It is wrong to say the paper does not say anything about feedbacks. It clearly does.
Perhaps this paper is just a pre-print and Allan will make corrections to it prior to publication like Dessler is doing?