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
“While clouds act to cool the climate system during the daytime, the cloud greenhouse effect heats the climate system at night.”
As I’ve been saying for years… higher nightime lows without higher daytime highs is a great boon to agriculture especially when the effect is primarily in higher latitudes. This greatly lessens the chance of unexpectedly late killer frosts in the spring and unexpectedly early killer frosts in the fall. It can spell the difference between one and two crop cycles per growing season and for more extreme places like Greenland the difference between being able to grow and harvest silage for livestock and not being able to raise livestock.
Add to this the well known benefits of CO2 enrichment in accelerating plant growth rates and making them more efficient in water use.
Then one last benefit to living things of a warmer earth is having a larger safety margin against the day when things like earth-cooling volcanic eruptions conspire with a grand solar minimum to end the current interglacial period.
At the end of the day there’s little not to love about rising atmospheric CO2. It makes for a greener earth and a greener earth is what we all want, right?
James says:
September 20, 2011 at 4:03 am
“If this were true then when the clouds covered the sun you would feel colder…oh, hang on a minute…”
And cloudy nights would feel colder than clear nights …. oh!
In the day the sun is the heat source at it it’s the earth!
Typo Correction
James says:
September 20, 2011 at 4:03 am
“If this were true then when the clouds covered the sun you would feel colder…oh, hang on a minute…”
And cloudy nights would feel colder than clear nights …. oh!
In the day the sun is the heat source at night it’s the earth!
This was actually already known, it just wasn’t widely known or promoted by the pro-AGW scientists for obvious reasons.
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.
This is an illogical result in that more clouds (also predicted) should be even more negative rather than less negative. Having this feedback be +2 W/m2 or -2 W/m2 will be a make or break feature in the global warming debate and, hence, the spirited response to Spencer and Braswell from Trenberth, Dessler and the Team.
I’m confused as to some of the details in this paper. Clearly there is not a -21 W/m^2 forcing on the climate that is unaccounted for. That level of negative forcing would bring on a severe ice age (which come from negative forcing from changes in albedo on the order of 4 W/m^2, if I’m remembering it correctly).
How is that -21 W/m^2 number reconciled with the net cloud forcing (NCF) in figure 7? If I just fit the anomalies by eye, I seem to get 0 W/m^2, except for the Pinatubo eruption and the last few years of data
Concerning the last few years, it seems to me that from the data shown in Figure 7 that the net forcing is on the order of -1 W/m^2. This would seem to be enough to counteract the equivalent forcing from greenhouse gas emission. I would imagine that this is related to the leveling off of temperature rise in that same period and also related to the increase of water in the atmosphere, as indicated by the floods and snowfall experienced globally.
Anyone who lives in a normally hot dry climate knows clouds can make a huge difference in temperatures.
When clouds occur in summer in interior Western Australia, daytime high temperatures drop from the usual 40C to 20C or less.
BTW, they are assuming clouds operate as a feedback. Clouds could equally well be a primary driver of climate (ref GCR). Although of course operating as a feedback as well.
Bart Verheggen says:
September 20, 2011 at 3:59 am
“The net radiative effect of clouds on climate has long been known to be negative (i.e. cooling). See e.g this quote from the paper: “The overall global net cloud radiative effect is one
of cooling as documented previously (Ramanathan et al., 1989).” That can be verified in any textbook on the subject and most introductions of papers on this topic.”
I’ve long suspected that the GCM authors didn’t have any basic textbook knowledge of how clouds effect the climate, or the subtleties of the water cycle in general otherwise they couldn’t have proposed their ballyhooed water vapor amplification with a straight face. Thanks you for confirming their ignorance. Spread the word.
Anthony, you’ve misunderstood the term ‘feedback’. I think you would have been better off with the notes that Richard Allan gives out for his ‘climate change’ course before jumping in at the deep end!
James says:
September 20, 2011 at 4:03 am
“If this were true then when the clouds covered the sun you would feel colder…oh, hang on a minute…”
And cloudy nights would feel colder than clear nights …. oh!
I think you meant to say that cloudy nights would feel warmer than clear nights.
Criminogenic, were not in a permanent ice age for 2 reasons:
1. if CERN is correct, then the cloud cover varies by intensity of the sun’s activity
2. cooler = less evaporation = less available water vapor for creating clouds.
Thus, in clouds, we have a self-regulating system with the absolute setting determined by the input of the sun, the relative setting determined by water vapor availability.
Bart, I see it this way.
If the net effect of a square kilometre of cloud is negative, then in a warmer world with more moisture and therefore more cloud, the feedback also has to be negative.
Put it another way. If the current cloud cover is say 20% (and is nett cooling) and a warming world will increase this to 22% then the feedback from this will be increased cooling.
While science frequently makes discoveries contrary to common sense
‘Knowledge’, here is a case where common sense was in the vanguard.
Everyone under the sun KNEW clouds have a cooling effect.
A victory for common sense and empiric data, ( I feel therefore I am.)
Yay!
A nicely modulated system!
During colder cycles:
cooler atmosphere => less ocean evaporation => less cloud cover = gradual warming
During warmer cycles:
warmer atmosphere => more ocean evaporation => more cloud cover = gradual cooling
Who’d a thunk it.
Hmm – more surface heat = warmer = more evaporation = more clouds = less heat = cooler. Limits imposed by the thermodynamics of water on Earth and what hits us from the sun. Kind of what you’d expect, unless you get reductionist science running unchecked with a healthy dose of political agenda.
Time to consign ‘climate’ to the geography books folks…about time too. How much wasted money and how much of a tarnish for Science and peer-review?
I found this statement in the abstract curious:
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.
(It’s near the end of the abstract.)
I thought clouds prevented heat loss i.e. performed as insulation or a reflector of IR if you will. I did not think that they were a source of energy — i.e. could “heat” the earth.
An interesting paper in light of the recent controversy. Looking forward to the obits…
criminogenic says:
September 20, 2011 at 3:05 am
“So if clouds are such a strong negative feedback, how come we aren’t in a permanent ice age?”
Indeed. At current CO2 level the earth, for the past several million years, has been cycling between 100,000 years of glacial advance and 10,000 years of glacial retreat. 280ppm CO2 clearly isn’t enough to keep the earth out of an ice age. The average temperature of the global ocean is 3.9C which is a reflection of the average surface temperature over the course of a full glacial/interglacial cycle.
Affirming these basic facts about the earth’s climate during the past several millions leads any reasonable, informed person to not ask “Is there too much anthropogenic CO2 in the atmosphere” but rather ask “Is there enough anthropogenic CO2 in the atmosphere?”. My feeling on the matter is that if burning fossil fuels wasn’t adding some badly needed warmth to this planet we’d have to invent some other way to do it lest the last 10,000 years of advance in human civilization be destroyed by massive glaciation over most of the northern hemisphere.
Like duh. It isn’t global warming we should be worried about – global cooling is the real destroyer of life and unless something has changed history is going to repeat itself right on time as interglacial periods haven’t lasted very long anytime in the past several million years. The current interglacial is long in tooth already and the Milankovich cycle is still advancing on the sweet spot favoring glacial advance and won’t reach it for a few thousand years yet. In the meantime the first unpredicatable perfect storm of earth-cooling volcanic eruptions during a solar grand minimum is going to be the straw that breaks the modern interglacial’s back. The modern solar maximum appears to have ended and solar physicists are now predicting a solar minumum is on the way but just how minumum is something they don’t know. If the GCR hypothesis is correct this is not good. We might want to think about sacrificing some virgins to the volcano gods just in case. I’ve got some nerdy climate boffins in mind for the role of sacrifical virgins.
David Wright@3.52
I also suspect they won’t come out with their hands up but they may well have a labyrinth of tunnels and sympathisers with spider holes. Where do you reckon we go searching first? The polar regions or the Maldives?
@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.
The Royal Meteorological Society published this paper. That will make the task of character assassination a bit more difficult for the team.
Erik Ramberg says:
September 20, 2011 at 5:44 am
“I’m confused as to some of the details in this paper. Clearly there is not a -21 W/m^2 forcing on the climate that is unaccounted for. That level of negative forcing would bring on a severe ice age (which come from negative forcing from changes in albedo on the order of 4 W/m^2, if I’m remembering it correctly).”
What you’re confused about is the behavior of systems with negative feedbacks. More clouds lowers average daily surface temperature. The lower surface temperature decreases cloud formation. Decreased cloud formation allows more daytime heating. More daytime heating produces more clouds. An equilibrium point is thereby established. The water cycle makes surface temperature self-regulating. The only “tipping point” we’re near is tipping away from the interglacial period. Snow and ice are not self-regulating. Once permanent snow cover starts advancing down northern hemisphere continents it becomes a vicious cycle where more southerly snow reflects more surface-warming sunlight and this breeds even more snow. The end result, which has happened a great many times with alarming regularity over the past several million years is the liberal northeastern United States being buried under a mile of ice – which just goes to prove that every cloud has a silver lining…
Erik Ramberg: that’s because Figure 7 is ‘anomalies’, which are changes from the average. i.e. the average (21 W m-2) has been taken away from each of those values!
This is the mistake Watts has made in this article, which should be rewritten or retracted immediately. A forcing is a change in heating – there hasn’t been a 21 W m-2 change in clouds recently, it’s just all the clouds we have today contribute 21 W m-2. If you took them away and kept everything else magically constant then you would get 21 W m-2 of warming.
If Watts wants clarification he can email Dr Allan.
The paper does NOT say that cloud FEEDBACK is negative.
Clouds are, and always have been, a negative FORCING (specifically, the negative effect on SW exceeds the positive effect on LW, with the net effect being negative). This paper attempts to quantify the net forcing effect and analyze it by time of day and location.
The question of cloud feedback is the first derivative of this net forcing with respect to changes in temperature. This raises a whole host of important questions:
– Does a change in temperature lead to more clouds or fewer?
– During the day or at night? At high or low altitudes? At high or low latitudes?
– Do individual clouds have larger water droplets or smaller?
– Is there an impact on cloud convection, evaporation or condensation?
– What is the net effect of all these (and other) possible changes?
Once those questions can be addressed, we might have a sense of whether cloud feedback is positive or negative. Until then, I’m in the “I don’t know” camp (though my uneducated guess would be that cloud feedback is probably negative).
Dave Springer:
“Like duh. It isn’t global warming we should be worried about – global cooling is the real destroyer of life ”
That’s like saying “it’s not overeating we should be worried about, but undereating?”, “it’s not underdosing we should be worried about, but overdosing?”
Philip Bradley says:
September 20, 2011 at 5:45 am
Yes, Eschenbach’s thunderstorm model accurately describes what happens daily from May through September in central Florida. Between 3 and 5 PM, the temperature can drop from 100 to 80 degrees Fahrenheit. Cloud cover alone can lower the temperature by 10 degrees. Most people do not understand this. If you haven’t lived in Florida (or the equivalent), you do not know sunshine.
I think Barghumer is correct. During the day, clouds have a net cooling effect. At night, even if clouds were a perfect insulating blanket, they could only retain what had not been reflected. So, from basic physics (conservation of energy), there doesn’t seem to be any way that clouds can increase the temperature of the earth – their net contribution must be negative. What have I missed?