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
As Ursus noted earlier, Richard P. Allan is well connected in Climate circles. His CV suggests that he is active with the IPCC and has been doing this work for some time. He did his undergraduate work at the Univeristy of East Anglia. Perhaps Paul Dennis can comment. I suspect he does not see his research as supportive of Spencer & Braswell and Lindzen and Choi – hence all the red in the diagrams.
Bart Verheggen has a point which I think was overlooked. As he stated, the paper didn’t address feedbacks.
1. If a doubling of CO2 would increase temperatures 1 C, and you get additional clouds increasing earth’s albedo and reducing temperatures to an increase of only 0.5 C, you’d have a negative feedback from clouds- total warming is less than the 1 C solely from CO2.
2. If a doubling of CO2 would increase temperatures 1C, and you get additional water vapor increasing temperatures a additional 1C, and additionl clouds reducing temperatures 0.6 C,
you get a warming of 1C from CO2, 1C from water vapor, and minus 0.6 C from clouds, for a net increase of 1.4 C- an increase of 0.4 C over the 1C CO2 doubling with NO feedbacks. Verheggen should have added the qualifier- net feedback from water vapor and clouds- rather than just clouds, but he’s correct that the paper didn’t specify whether situation 1 or situation 2 holds.
My money is on situation 1.
Isn’t this actually the 4th new paper which says that clouds have negative feedback, and that increasing water vapor in the atmosphere produces cooling, not warming?
The Carnegie Institute sponsored a very recent paper which finds that trees produce net cooling because they release water vapor, and this water vapor creates more clouds, which reflect more light back to space.
Go to Carnegie’s website, look around, and you will come to this (Wed. Sept. 14 release):
————–
Water evaporated from trees cools global climate (headline)
Washington, DC — Scientists have long debated about the impact on global climate of water evaporated from vegetation. New research from Carnegie’s Global Ecology department concludes that evaporated water helps cool the earth as a whole, not just the local area of evaporation, demonstrating that evaporation of water from trees and lakes could have a cooling effect on the entire atmosphere. These findings, published September 14 in Environmental Research Letters, have major implications for land-use decision making.
…The researchers even thought it was possible that evaporation could have a warming effect on global climate, because water vapor acts as a greenhouse gas in the atmosphere. Also, the energy taken up in evaporating water is released back into the environment when the water vapor condenses and returns to earth, mostly as rain. Globally, this cycle of evaporation and condensation moves energy around, but cannot create or destroy energy. So, evaporation cannot directly affect the global balance of energy on our planet.
…Using a climate model, they found that increased evaporation actually had an overall cooling effect on the global climate.
Increased evaporation tends to cause clouds to form low in the atmosphere, which act to reflect the sun’s warming rays back out into space. This has a cooling influence.
————–
Isn’t it time to have a climate scientist or statistician with an open mind write a review article, including all these new articles, comparing them with the Trenberth attempt to put a finger in the breaking dike? Is Steve McIntyre or Ross McKittrick available?
Now, how do we get so that these things can be understood by Joe Sixpack. Oh, wait…..
Jeff L
“if the Svenmark / cosmic ray hypothesis is correct, it explain why solar effects dominate : “hot” sun = less clouds = warmer temps; “cool” sun = more clouds = cooler temps.”
Good point but the Svensmark hypothesis doesn’t explain how cosmic rays can alter the vertical temperature profile of the atmosphere and cause a redistribution of the surface air pressure of the type observed.
I prefer the idea that cloudiness and albedo changes are a result of latitudinal shifting of the cloud areas rather than simply the presence of more condensation nuclei.
The fact that GCRs increase whilst the sun is less active could well just be a fortuitous correlation with little (but maybe some) climate effect.
It’s official: this is the wettest summer since 1906
Wednesday 31 August 2011
This summer has been the wettest since 1906, with 10cm more rain than in average years, the KNMI weather bureau said on Wednesday.
In total, 35 cm of rain fell in June, July and August, with July particularly wet, the KNMI said.
This contrasts with the dry spring – the driest of the past century with just 4.9 cm of rain, compared with 17.2 cm in a normal year.
http://www.dutchnews.nl/news/archives/2011/08/its_official_this_is_the_wette.php
Dry spring = less clouds = higher temperatures
Wet summer = more clouds = lower temperatures
http://www.knmi.nl/klimatologie/grafieken/jaar/index.cgi?station=260&graphtype=anomalie&element=tg
http://www.knmi.nl/klimatologie/grafieken/jaar/index.cgi?station=260&graphtype=lopend&element=tg
The sun was there, just behind the clouds.
Solar panels provide more energy on sunny days or cloudy days?
I thought the consensus say that clouds are a positive feedback because higher temperatures lead to more clouds which lead to more heat retained because the clouds absorb LW radiation emitted by the earth. If this paper is correct and clouds offer net cooling (SW reflection outweighs radiative effects by day) then surely clouds must actually be a negative feedback to increased temperatures not a positive one? In any case, if the net cooling effect is greater than previously thought then isn’t the energy budget now incorrect?
I’ve looked at clouds from both sides now. Time to send in the clowns.
Reading the blog comments, the IPCC stuff, and this paper, it appears that clouds do not add to the radiation budget.
The IPCC ,Trenberth, Dessler team appear to believe that if AGW is happening, then clouds might increase and increase the effect of AGW, or clouds might decrease and increase the effect of AGW.
Have I got this right?
(not really bothered by the way)
“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.”
And yet, while temperatures have been increasing, cloudiness has been decreasing. Contrary to what the models and the IPCC predict. Could it be that temperature is not the primary factor forcing cloudiness? Could it be that some other mechanism is at work? Is it just possible that someone got it backwards, that cloudiness is forcing temperature?
Bill Illis says:
September 20, 2011 at 5:43 am
“The climate models project that this -21 W/m2 (might be as high as -30 W/m2) and project that it will turn into -20 W/m2 in a doubling scenario. So it is projected as a net +1.0 W/m2 feedback, about half of the feedbacks shown by the IPCC in its most recent report. ”
I note that you don’t specifically say that it is *cloud* cooling that the models project will fall by 1.0 W/m^2 in response to CO2-concentration doubling–for all that is apparent from what you say, the 1.0 W/m^2 could instead be the net of (1) *increased* cooling by clouds and (2) increased heating due to a greater optical-depth contribution by water vapor (as opposed to droplets).
Is there a primary source relatively understandable to us laymen that tells whether the models project (1) increased cloud cover and/or (2) decreased cooling by *clouds* and/or (3) increased greenhouse effect from water *vapor* in response to increased CO2 concentration?
In other words, I keep reading on the blogs what the models are doing, but I don’t as a layman have any good way to develop confidence in those descriptions, and it would be helpful to many of us more-casual observers to find something that explains the models but is not so opaque and jargon-prone as to require a prohibitive amount of time for a layman to decode. Does anyone know of such a source?
I think you guys arguing forcing / feedbacks is sort of ridiculous and off point. True, it should read forcing, Anthony should change it, but on a complex climate system forgings lead to feedbacks, both known and unknown.
The point is -21 W/M2 is a very large number. So a very small change has a large impact on the global radiation budget. It is foolish to think that cloud cover does not vary and is constant in a dynamic atmosphere.
Just to reiterate, this paper does not say what Anthony thought it said.
Clouds are a negative forcing, as was well known all along. Allen has just produced a slightly different number for that forcing.
No rebuttal required.
Over the last few years this issue has become the Achilles heal of the AGW belief. I was expecting something more close to neutral myself but -21? Holy hole in the theory Batman. Good to see real science being done. I am predicting a “ignore it and hope it goes away” attitude from the media.
Here is a video showing Ken Caldiera, one of the authors of the new study showing that increasing water vapor in the atmosphere causes net cooling by causing increasing cloud formation:
Let me chime in with the people who pointed out that this isn’t feedback. Negative feedback is when the clouds respond to temperature, not to another stimulus, such as ionizing radiation. Furthermore, it’s mathematically impossible for negative feedback to have an effect greater than the original effect. It’s impossible to create a feedback system that cools in net in response to warming.
To RobB (7:59 AM):
Yes, you are correct about negative, not positive feedback. See Caldiera video just above.
John says:
September 20, 2011 at 7:43 am
Isn’t it time to have a climate scientist or statistician with an open mind write a review article, including all these new articles, comparing them with the Trenberth attempt to put a finger in the breaking dike?
That was what most people thought the UN IPCC was going to do. However, as history has shown, the process itself is flawed. It is very unlikely that a lead author is going to point out work that contradicts their own, at least not in a favorable light. This leads to resignations from the IPCC of folks with more central and/or skeptical positions, which skews the results over time.
Thus, the IPCC concludes with great certainty that warming is caused by CO2, while downplaying the almost complete lack of understanding of the effects of clouds. Expect the next IPCC report to say we understand the clouds, they have a positive feedback effect, and we are very certain of this, because anyone that says otherwise is rubbish.
BargHumer says:
September 20, 2011 at 6:08 am
@Dave Springer
“While clouds act to cool the climate system during the daytime, the cloud greenhouse effect heats the climate system at night.”
How can this be true? There is no energy or energy source to heat the earth at night? only to retain more of what was there in the day time.
This is now getting confusing. Note that in the top two lines the phrase “climate system at night” is used and in the second 2 lines the phrase “heat the earth at night” is used.
Are these two phrases meant to describe the same thing or not? Maybe, but I can’t tell. Not being able to tell, clouds the meaning (pun intended). The discussion, so far, has many such problems and, thus, has collapsed like a glob of warmed Jell-O.
Anthony, I am afraid that those who are saying you have misinterpreted the results of this paper are correct. The main result is about the effect of all the clouds on the radiation coming in to the earth, not feedback.
However, there is in fact a suggestion of negative feedback where this is discussed in sec 6.
“Substantial negative anomalies in net radiative flux from ERA Interim are apparent in 1998 and 2010, both El Ni˜no years, suggesting that the substantial re-organization of atmospheric and
oceanic circulation systems act to remove energy from Earth during these periods.”
You can also see this in fig 7. There are dips in the cloud forcing in the hot El Nino years of 1998 and 2010, showing that when the earth is hotter it loses more heat, ie negative feedback.
So in the end I think you are right – the paper does show negative cloud feedback!
I see that the CAGW rent-a-mob have been instructed to jump on this thread. At least it stops them bullying scientists, I suppose.
In this thread the opacity of the atmosphere to LW has been mentioned, and the role of clouds at trapping nighttime heat has been offered. This has to mean that the altitude of the cloud base comes in to play and so I can ask this question: Because of the atmospheric opacity, at what altitude must a cloud be to stop trapping night time heat? This would be the altitude at which the cloud is invisible to surface LW radiation, and obviously, the reverse would be true – the cloud generated LW radiation is invisible to the surface.
If the answer is the altitude does not matter then one has to ask if the atmosphere is actually opaque to LW radiation.
I’ve not seen any mention of vertical distribution in any of this.
ChE. It isn’t mathematically impossible to have -ve feedback >1, but it would result in an oscillating system. Agree that what is quoted in the main post does not focus on feedback numbers.
PaulM says:
September 20, 2011 at 8:13 am
Anthony, I am afraid that those who are saying you have misinterpreted the results of this paper are correct.
If you watch the video above, you will see that the study says the effect of increased evaporation is both local cooling AND global cooling.
AGW and the GCM all are based on the assumption that increased evaporation will cause local cooling BUT global warming.
The difference between the points of view is AND in the first, and BUT in the second. If the AND is true, AGW is not possible and the theory collapses, if the cooling effect is of any size.
The reason is that CO2 itself has very little warming effect. AGW and the GCM’s attribute most of the warming to increased evaporation and the net GHG effect of increased water vapor in the atmosphere.
However, if the effect of increased evaporation is a net cooling, as the study shows, then AGW is wrong and CO2 does not explain the warming post 1980. Something other than CO2 must have caused the warming and climate science will have to go back to the drawing board and figure it out.
I don’t understand how there can be any question about this. Some fairly simple observations (I know, observation of physical reality has to take second place to computer models…) should give enough clue:
From underneath the clouds, at ground level, as a cloud covers the sun, you feel cold. This really is telling you that the radiation from the sun is no longer reaching ground level. This can be confirmed by looking at the output of a solar panel, it drops drastically when a cloud obscures the sun. Again a strong indication that radiation is no longer reaching ground level.
So where is all that radiation/energy going? Well its possible that it is being absorbed by the cloud itself, except that as you observer the cloud from above, it is pretty evident that it is reflecting an awful lot of energy. It’s very bright, and its white, which s telling you that it is reflecting all the energy equally (at least in the visible spectrum). I suppose that you might think that ou its outwards journey it is being absorbed by the atmosphere, but having not been absorbed and re-radiated at a different wavelength we have to assume that the atmosphere remains as transparent on the way out, as it was on the way in. Besides, from space the cloud still appears white and bright.
Anyone arguing that cloud in itself does anything other than cool the earth is a crackpot.
The only remaining question is does increasing temperature cause more clouds?
Well, the models, and observation (that pesky physical reality stuff again!) tell us that increasing temperature increases the level of water vapor in the atmosphere.
So does more water vapor lead to more clouds?
I want to see the grant submission to ask for a few million to investigate that idea! 🙂