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
Well of course clouds cause cooling! What was the 1815 ‘summer that never was’ and other post volcanic winters if not a perfectly good example that the cloud forming aerosols ejected by volcanoes affect temperature a lot.
This paper, in association with the recent CERN research, its very powerful and strongly suggests Svensmark (and Herschel centuries ago) got it right.
I think there was a famous leprechaun that said:
GK
If you are going to do modeling at all, it will be important to properly model cloud dynamics. Any pilot will tell you there are strong updrafts under big cumulus clouds. The updraft very likely continues to the top of the cloud where the upward velocity drops to zero, cooling occurs, and the velocity of the droplets subsequently becomes negative. If the droplets get big enough, you get rain falling out of the center. Cumulonimbus clouds can have a shape like a stovepipe top hat with rain falling from the center and hot moist air flowing up the walls of the stovepipe. The idea is some clouds can act more like a heat conveyor, and other clouds can act more like a blanket. It is important to distinguish between the two and accurately handle the heat flow. I think that was an important point this paper was making, if not explicitly. Using optical density alone will be insufficient for some cloud types.
Mann, Hansen, Jones et al. Back to the drawing board. Run along. Shoo
I wish someone who knew what they were talking about would draw a picture. A nice block diagram with the the blocks and energy flows properly labelled would really help.
“So does more water vapor lead to more clouds?”
Yes, but primarily where there is sufficient uplift or in regions of air mass mixing. Primarily (but not exclusively) at the ITCZ and along the various jet stream tracks.
The consequent additional uplift along the more vigorous ITCZ and jet stream tracks causes a growth in the amount of descending air elsewhere and that suppresses low cloud development especially over water in the tropics with a widening of the sub tropical high pressure cells for a general growth of the equatorial air masses at the expense of polar air masses which pushes ALL the components of the surface air pressure distribution poleward.
Perversely that then leads to MORE solar energy into the oceans in a POSITIVE feedback.
However the more vigorous ITCZ and jetstreams represent a faster water cycle which provides the negative feedback sufficient to cancel out BOTH the initial forcing from whatever cause AND the positive feedback from reduced low cloud cover in the tropics.
It all goes into reverse when there is a cooling globe.
Forgive the shaudenfreude, but its a classic case of comfirmation bias.
The heading and many of the posts clearly read this research as supporting Spencer and Lindzen in their speculations about the magnitude, and sign, of cloud FEEDBACKS in AGW.
While this is just a refinement of the total/net effect of clouds in the average climate with no climate change.
With the overall effect just -21W/m2, it would require a 10% change in cloud cover – a massive and obvious alteration – to equal the effect of rising CO2.
izen says:
September 20, 2011 at 8:49 am
With the overall effect just -21W/m2, it would require a 10% change in cloud cover – a massive and obvious alteration – to equal the effect of rising CO2.
You mean the “claimed” effect of rising CO2, don’t you?
izen,
I’d like to see where you get the figures from to the effect that it would need a 10% change in cloud cover to equal the effect of rising CO2.
Well,
I really don’t see the issue. They’re talking about the radiative contribution, not the feedback. And they reach the conclusion that clouds tend to heat the surface (please read the conclusions’ section!). So, all in all, he just confirms the IPCC report, but with a different value for the radiative contribution (and a more subtle study of spatial dependence).
It’s a bit sad that this posting is being buried beneath new ones without appropriate corrections or an update addition to correct the feedback/forcing misunderstanding and the originals inferences.
Looks like the clouds captured a La Nina in cloud radiation. It was a long time span so I wonder if it was a net La Nina. It would be interesting to run the data during different time spans and see.
BTW, everyone knows it’s a cooling during the day. I believe the issue is night vs. day and long vs. short. This appears to show that the net Night + Day is dominated by daytime cooling. The net is very far from the variation though. He had some numbers in the +100, -400 range which seem staggering. That would seem to indicate that not only is it currently dominated by cooling but it will be massively responsive to cloud cover changes. Massive negative feedback if -400 is correct.
Will peer reviewed papers like these make it to the congress and will they understand it. Probable no.
Bart Verheggen
The Allan study has suggested a somewhat higher net negative climate forcing from clouds than earlier studies (Ramanathan + Inamdar 1989, for example) , i.e. -21 Wm-2 versus -18 Wm-2.
This is good information.
Incidentally, this difference in cloud forcing of 3 Wm-2 is twice the total anthropogenic radiative forcing estimate of IPCC from 1750 to 2005 (1.6 Wm-2), so the Allan finding is significant.
The cloud feedback versus cloud forcing issue is still open, as you say, as Spencer + Braswell 2011) seem also to have concluded.
My conclusion based on the data I’ve seen would be that clouds exert a slight negative feedback with surface warming but that forcing from natural changes in cloud cover play a greater role (Palle 2005). More work is needed to identify the mechanism for these observed natural changes in cloud cover. Maybe the CLOUD experiment at CERN will give us some new data.
Max
I was surprised that this paper was mis-interpreted as suggesting negative cloud feedback. This is a basic error by the author of the post that has been highlighted by many contributors including Roy Spencer.
REPLY: Dr. Allan, thank you for visiting and for your correction. Please note that I’ve made an update to the post, removing the word negative from the headline and including why I interpreted the paper to demonstrate a negative feedback for clouds. I welcome your thoughts. It seems to me that if clouds had a positive feedback, the dips in 1998 and 2010 in your figure 7 would be peaks rather than deep valleys.
Thanks for your consideration.
– Anthony
Hector Pascal says:
September 20, 2011 at 3:03 am
Oh noes! Not another Allan from Reading. We have Allen (Perce) and Allen (JRL) already.
The latter of whom is a geologist/archaeologist of monumental standing. It’d be interesting to know what he thinks of the undebate.
I see this paper as trying to nail down the number. We can measure how much shortwave is reaching the top of the atmosphere in Wm^-2, now we need a good estimate of how much of that actually reaches the surface (and once it reaches the surface, how much is thermalized and reemited in long wave versus how much is reflected). The authors have measured the total cloud reflectance as -21W/m^2. Now we can take that number and plug it in everywhere the calculations say subtract shortwave reflected by clouds. It seems more related to answering a “what is the total albedo of the sunlight side of the Earth?” kind of question.
I don’t think the science is at all settled numerically of how the cloud cycle impacts the energy budget. That’s a very important number to have, and once someone can show that number definitively and verifiably, a major hurdle to understanding how the climate works will be overcome. Right now we are all just hand-waving. (though personally I love “hand-wavy” proofs, takes away all that rigor and mathy stuff)
EJT, you just hit on what is so confusing about talking about feedback on a blog: there are two related parameters, the open-loop gain, and the closed-loop gain. They’re related by the geometric series, so that as the negative open loop gain approaches (negative) infinity, the closed loop gain approaches zero. With time lags, the loops will oscillate at higher open-loop gain, but op amps operate quite stably with 10^5 open loop gain, because their high frequency response allows it.
What I was saying is that the closed loop gain for a negative open loop gain system can never be less than zero (you can’t get more than 1 degree of cooling in response to one degree of warming). Positive feedback is a whole nuther matter, and can run away. But that’s a another discussion entirely in the climate context.
suyts says: “I’d like to thank Dr. Spencer, also. But, Bob, you stopped in your quote too early.”
That’s why I ended with the elipse and thanked Roy for the further explanation.
As many commenters have noted, the fact that clouds have negative feedback is well known, it isn’t new information.
The issue is, does an increase in GHGs cause an increase in water vapor, which then causes either positive or negative feedback? If clouds don’t change, and if there is added water vapor in the atmosphere, the odds favor a positive feedback because water vapor is an important GHG.
But if increased water vapor then means more clouds, we may get net negative feedback because the clouds may reflect back a greater increment of energy than the increased water vapor will keep in the earth’s system.
That is why the new Carnegie paper, in conjunction with the new paper by Allen reaffirming that clouds have negative feedback, is so important. The Carnegie paper links increased evaporation with net negative feedback due to increases in reflective clouds.
We do need to keep in mind that just because this study fits with our priors — the earth has been warming at a rate well below those predicted by GC models, which incidentally have net positive feedback from more water vapor in the air — doesn’t mean that this new science is the end of the argument. We do need confirmation from more studies. That is the scientific process, or at least WAS the process before Trenberth and Mann and Jones and Briffa and Bradley etc. hijacked it.
Richard Allan says:
September 20, 2011 at 9:27 am (Edit)
I was surprised that this paper was mis-interpreted as suggesting negative cloud feedback. This is a basic error by the author of the post that has been highlighted by many contributors including Roy Spencer.
########
it is also fascinating because of what we dont see. usually you will see a whole crew of commeters pounce on the word “model”. This time they didnt.
They didnt because they thought the paper supported spencer. But it was on an entirely different topic. That misunderstanding kinda silenced the usual “models are bad” crew.
BTW I was glad to see Roy and Bart come here to correct the misunderstanding. And thank you for coming here as well.
REPLY: Thanks Mosh, I’ve responded to Dr. Allan also, and provided an update. I ask viewers to note how WUWT handles criticism from a science professional, versus say, some award winning Australian websites. -Anthony
So, how are people like this still able to publish? Are they giving their papers amusingly obscure titles to sneak them past peer review, or is this thing we call science genuinely working at last?
Correction to my last post: In this sentence, substitute the word “forcing” for the word “feedback:”
As many commenters have noted, the fact that clouds have negative feedback [no, FORCING] is well known, it isn’t new information.
I do not think it is current to say Allan’s paper is just about the forcing. Allan mentions feedbacks nine times.
I asked how clouds, which everyone seems to agree causes significant cooling as a forcing, can also cause net warming as a feedback. It seems to me the feedback is necessarily less powerful than the forcing. Unless I am reading Allan wrong, this is exactly what he is saying.
The abstract ends with this line: “The influence of cloud radiative effect on determining cloud feedbacks and changes in the water cycle are discussed.”
He concludes: “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 (the mechanism by which a positive feedback would occur), 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.”
So what I am missing? Is he not saying clouds cause a change in radiative forcing resulting in significant cooling which completely swamps the warming feedback at night? Is this not in opposition to the IPCC reports which claim a net positive (warming) feedback?
Well, I thought that adding CO2 to the atmosphere would increase temperature, result in increase in water vapor and clouds, that would have a positive feedback effect, increasing temperature further.
Call it “forcing” or ‘feedback” (who cares), this paper indicates that clouds have a significant net cooling effect. If it is true that CO2 added to the atmosphere will increase cloud cover, how do the new clouds know that they are supposed to have a net warming effect, rather than the net cooling effect of the non-CO2 generated clouds?