The Cloud Radiative Effect (CRE)

Guest Post by Willis Eschenbach

[UPDATE: An alert commenter, Ken Gregory, has pointed out that in addition to the temperature affecting the CRE, it is also affected by the changing solar radiation. He is correct that I did not control for this. SO … I need to go off and re-think and then re-do the entire analysis. In the meantime, in the immortal words of RMN, my analysis below is no longer operative. Bad Willis, no cookies … but that’s the nature of science. Thanks, Ken, for pointing out my error. -w.]

[UPDATE: See the subsequent post here. -w.]

Figuring that it was about time I did some more scientific shovel-work, I downloaded the full ten-year CERES monthly satellite 1° x 1° radiation dataset (link below). I also got the Reynolds monthly Sea Surface Temperature 1° x 1° dataset, and the GHCN monthly 1° x 1° land dataset. This gave me nominally complete ten-year gridded data for the ten-year period from March 2000 through February 2010 for both the temperature and the radiation.

Among the CERES datasets are  the shortwave-, longwave-, and net- cloud radiation effect (CRE). Clouds affect the radiation in a couple of ways. First, clouds reflect sunlight so they have a big cooling effect by cutting the downwelling shortwave radiation. In addition, however, they are basically perfect blackbodies for longwave radiation, so at the same time, they warm the surface by increasing the downwelling longwave radiation. And of course, at any instant, you have the net of the two, which is either a net cooling effect (minus) or a warming effect (plus). All of these are measured in watts per square metre (“W/m2”).

So without further ado, Figure 1 shows the net cloud radiative effect (CRE) from the ten years of CERES data. It shows, for each area of the earth, what happens when there are clouds.

net cloud radiative effect ceresFigure 1. Net cloud radiative effect (CRE). Red and orange areas show where clouds warm the earth, while yellow, green, and blue show areas where clouds cool the earth. The map shows that if there is a cloud at a certain area, how much it will affect the net annual radiation on average.

Note that in some areas, particularly over the land, the net effect of the clouds is positive. Overall, however, as our common experience suggests, the clouds generally cool the earth. But this doesn’t answer the interesting question—what happens to the clouds when the earth warms up? Will the warming cloud feedback predominate, or will the clouds cool the earth? It turns out that the CERES data plus the earth temperature data is enough to answer that question.

What I’ve done in Figure 2 below is to calculate the trend for each gridcell. The meaning of the trend value is, if the surface temperature goes up by a degree, what do the clouds do to the radiation? I used standard linear regression for the analysis,. It’s a first cut, more sophisticated methods would likely show more. As is always true in the best kind of science, there were a number of surprises to me in the chart.

change in cloud radiative effect per increase temperatureFigure 2. Slope of the trend line of the net cloud radiative effect as a function of temperature. This give us the nature of the cloud response to surface warming in different areas of the world. This is what is commonly known as “cloud feedback”, although it is actually an active thermoregulatory effect rather than a simple linear feedback.

The first surprise to me is the size of the variation in cloud response. In some areas, a 1° rise in temperature causes 20 extra W/m2 of downwelling energy, a strong warming effect … and in other areas for each 1° fall in temperatures, you get the same 20 extra watts of downwelling energy. I didn’t expect that much difference.

The second surprise was the difference in the polar regions. Antarctica itself is cooled slightly by clouds. But when temperatures rise in the Southern Ocean around Antarctica, the clouds cut down the incoming radiation by a large amount. And conversely, when the temperatures in the Southern Ocean fall, the clouds provide lots of extra warmth. This may be why the Antarctic and Arctic areas have responded so differently to the overall slight warming of the globe over the last century.

The third surprise was the existence of fairly small areas where the cloud response is strongly positive. It is surely not coincidental that one of these is in the area of the generation of the El Nino/La Nina events, near the Equator on the west side of South America.

One thing that did not surprise me is that the reaction of the clouds in the area of the Inter-Tropical Convergence Zone (ITCZ) in the Pacific. This is the greenish band about 10° North of the Equator across the Pacific and across the Atlantic. In this area, as I’ve shown in a variety of ways, the cumulus clouds strongly oppose the rising temperature.

Finally, there’s one more oddity. This is the fact that overall, as an area-weighted average trend, for every degree the globe warms, the warming is strongly opposed by the cloud radiation effect. The action of the clouds reduces the downwelling radiation by 3 W/m2 for every degree the planet warms … in IPCC terminology, this is not only a negative feedback, but a strong negative feedback.

And the cooling effect of the clouds is even stronger in the ITCZ. There, for every degree it warms, the downwelling radiation drops by ten W/m2 or so …

I think, although I’m by no means sure, that this is the first global observational analysis of the size of the so-called “cloud feedback”. It shows that the cloud feedback is strongly negative overall, -3 W/m2 for each degree of warming. In addition, in the critical control areas such as the ITCZ, the cooling effect is much larger, 10 W/m2 or so. Finally, it shows a very strong negative cloud feedback, 20 W/m2 or more, in the area of the Southern Ocean

Like I said … lots of surprises. All comment welcome, and please remember, this is a first cut at the data.



Land Temperature Data: From KNMI, in the “Land” temperature section, identified as the “CPC GHCN/CAMS t2m analysis 1.0°”.

Sea Temperature Data: Again from KNMI, in the “SST” temperature section, identified as the “1° Reynolds OI v2 SST, v1”.

Once you click on the observations you want, at the bottom of the succeeding page is a link to a NetCDF (.nc) file containing all of the data.

CERES Data: From NASA (offline now, likely the Gov’t shutdown), identified as “”

If you don’t want to mess with the underlying datasets, I have collated the CERES and the temperature datasets into a series of arrays in R, that are 180 row x 360 column x 120 layers (months) in size. They are available here, along with the corresponding arrays for the surface temperatures, and a landmask and a seamask file. WARNING—Be aware that this is a large file (168 Mb).

The file is an R “Save()” file named “CERES long”, so it is loaded as follows:

> mytest=load("CERES long")

> mytest

[1] "toa_sw_clr"  "toa_sw_all"  "toa_lw_clr"  "toa_lw_all"  "toa_net_clr" "toa_net_all" "cre_sw" "cre_lw" "cre_net" "solar" "landmaskarr" "seamaskarr"  "allt"<

In the naming, “toa” is Top Of Atmosphere, “sw” is shortwave, and “lw” is long-wave; “all” is all-sky, “clr” is clearsky; “cre” is cloud radiative effect, “solar” is downwelling solar”, and “allt” is all the temperature records (land and sea).

The R program I used is here  … but I must warn you that far from being user-friendly, it is actively user-aggressive. Plus it has lots of dead code. Also, none of my programs ever run start to finish, they are run in chunks as needed. However, the functions work, and the mapping section (search for “MAPSTART”) works.


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I think the inverse relation would be interesting too: what is the change in temperature for a given change in clouds?

Willis Eschenbach

lsvalgaard says:
October 3, 2013 at 9:42 pm

I think the inverse relation would be interesting too: what is the change in temperature for a given change in clouds?

Good question … that and many other questions will likely get answered when I have more time. Scientific shovel-work is a slow process, particularly since I have to make it up as I go along. Or perhaps someone will download the files and beat on them and find a host of new things.

Roger Dewhurst

Willis, you are a glutton for punishment!!!!!!!!

Paging the IPCC…
According to the lead author on clouds for AR5: “IPCC hasn’t done a good job on clouds before,” says clouds lead author Piers Forster of the University of Leeds, UK. “They were a big unknown in modelling warming.” In 2007, it was uncertain even whether clouds cooled or warmed the planet overall. “But we now believe that they are a positive feedback on temperature,” he says. “Their warming effect will intensify with global warming.”

Matt Farrell

Wow amazing work, should try and get funding and turn it into a proper paper. Would heads turn if it passes Peer-review

Well, this could be the start of something big. Great going, Willis. 🙂

gopal panicker

areas under clouds should be cooler than otherwise during the day…and warmer at night…but since cloud cover changes all the time….good luck with the calculations

Very interesting Willis, although I’m maybe not so much surprised by the results, because I already tryied to incorporate the data into my 1° gridded global insolation semiempiric model I’m working on (although I still didn’t make the nice visualizations you have), it is very nice piece of work. My preliminary findings are simmilar, and I also find big differences between ocean and landmass regions (especially the high albedo ones) and between southern and nothern hemisphere, but I never got the idea to try determine any cloud feedback – very seminal! Thank you.

Peter Miller

Assuming you are correct, this makes the IPCC totally redundant – negative cloud feedback buries the AGW concept and highly negative cloud feedback makes it a laughable concept.
The trolls will not like this.


Supposedly, lower altitude clouds are a negative forcing (increasing the albedo of the Earth), while high altitude clouds are a positive forcing, helping to trap IR radiation. I’m not sure that I buy the latter, particularly if they are high-altitude ice crystals (i.e. noctilucent clouds, jet trails etc.).
Dr. Joel Norris of the Scripps Institution of Oceanography made a presentation at the Fermilab Colloquium on May 12, 2010 titled “Cloud Feedbacks on Climate: A Challenging Scientific Problem” It is very interesting, among the points he made were:
a) it is very difficult to differentiate between cloud cover and snow-ground cover by satellite;
b) many factors are involved, including cloud height and depth, and
c) nobody really knows how clouds impact climate, and the climatologists have done a lousy job of factoring in the effects of clouds.
The presentation is archived at
By all means, mine this storehouse of information! Prof. Richard Lindzen gave a real barn-burner on Feb 10, 2010!

Leonard Lane

Nice work Willis. The dark blue in the southern seas around Antarctica seems to explain much. Strong negative feed back here verified by a cooling south polar area. Since both the southern continent and its surrounding seas are cooling this is a very interesting result ignored, or only rarely mentioned, by the warmists. Meanwhile, they focus on the Arctic where the results appear mixed with warming at the highest latitude changing to cooling a distance south. Fascinating results and the wonderful insight and hard work producing them is wonderful. Thank you.


Henrik Svensmark has had some thoughts about cosmic rays and clouds. It would be interesting to know if a relation to cosmic ray impingement can be quantified into a temperature or net energy quantity from the clouds created.


I have been married for 30 years (to 3 separate women) but I can honestly say “I LOVE YOU”!!!!
I love to send your posts to my tree-hugging friends here in Seattle. It irritates them to no end. One day they are going to wake up and realize they can no longer justify their existence based on the horrors of climate change..
Keep up the good work!!

Willis – I think your study suffers from what may be a completely invalid assumption: You assume that clouds change in reaction to temperature. Reality may be that clouds change for other reasons. I read Leif’s comment as saying this, if rather obliquely.
There is a parallel in this between your study and the IPCC report: The IPCC assume that temperature is driven by CO2, but when they try to evaluate the climate’s sensitivity to CO2 they get a wide range of values, and that range even changes over time. The reason for the high range is that temperature is driven mainly by other factors. In other words, when they take the ratio of two factors to determine sensitivity they are using two factors that are at best only weakly related. You report “The first surprise to me is the size of the variation in cloud response“. I suspect that the reason for the size of the variation is simple: clouds are not in fact driven by temperature, so you too are using two factors that are at best only weakly related.

Dr Burns

“ our common experience suggests, the clouds generally cool the earth. ”
When a cloud passes in front of the sun, the temperature falls. However clear nights are always colder than cloudy nights. The explanations for these effects are fairly obvious.
How do clouds cause warming during the day ?

I recommend you this video. A lecture from Graeme Stephens about the clouds. Don’t miss the end, questions and answers (from min. 50)
– Is the planet characterized by a sensitivity to a forcing?
– I don’t think one number characterizes the system as a whole. I think you would find the sensitivity is different in the tropics and somewhere else.
– I don’t know what the real world would do (as a response to a forcing)
– I understand the convenience of this metrics, but we tend to get lot to much into it.


“OLR has – over the globe – decreased over 10 years. This is a result of the El-Nino phase – at the start of the measurement period we were coming out of a large El-Nino event, and at the end of the measurement period we were in a La Nina event.”

John West

@ Mike Jonas
I find it easier to swallow an increase in temperature increasing evaporation thereby increasing cloud cover in a manner that produces net cooling (think thunderhead formation on a hot summer day) than a slowing of cooling increasing evaporation in a manner that produces more slowing to cooling to the point of catastrophic warming.

Willis, this is one of your most interesting posts ever. This is an area in which I have seen very few people doing any work. For this amazing effort, you deserve to receive massive Big-Oil funding!
I wonder, if you turned it into a paper whether it would pass Peer (Pal)-reviw?


Getting a lot of cloud lately. As I don’t sleep much these days I distract myself on my night time walk abouts by looking at the thermometer stuck on the outside of my kitchen window. I HAVE seen night time temperatures increase, but only when there was a clear sky the previous afternoon and evening. In other words temperature had dropped well below that daytime maximum. When a layer of 10/10 cloud then arrives overhead, the temperature climbs. I have NEVER observed cloud covered night time temperatures exceed the previous days sunshine temperature level. I have observed a SMALL night time increase if previous day was also cloud covered, but this was usually when wind speed and direction changed.
I make no claims as to the accuracy of my kitchen window thermometer. I check it against this site which is about 400 yards from my house.
I have great difficulty in understanding how clouds can make the ground warmer. Where did the extra energy come from? I have recorded small temperature increases from scattered light through the cloud during the day. That increase could on occasion remain through the following night. But that increase was never as much as a clear sky sunshine temperature.


Evidence of positive feedback is probably not what most people here want to hear.

Geoff Sherrington

We think alike, but you are well ahead on translating into words. One of my early blogs, about 2005, asked if it is warmer or cooler if a cloud comes between you and the sun when you are on the Antarctic ice shelf. Nobody ventured an answer and I have not been there.
Leif asked my question before I could cut in.
Are you confident using GHCN land temperatures? I wonder what your nice graphic would look like if you could grid the raw values for T.7.

james b

High pressure means less clouds, low pressure more clouds.
High pressure in summer gives warmer temps, high pressure in winter gives colder temps.
The opposite for winter.
So clouds can give both higher and lower temps, mainly depending on season, thereby to a large degree cancelling each other out during the course of a year.
Perhaps the picture would become clearer if you showed NH winter with SH summer, and vice versa…


Don’t tell too many alarmists, they will start ‘adjusting’ the data.

Negative feedback! Cool!!

Keith Minto

Willis, have got into it yet, but there are two Fig 1’s.
[Thanks, Keith, fixed. -w.]

Pat Smith

Roy Spencer has just posted a similar piece of work.

Your post at October 4, 2013 at 12:22 am says in total

Evidence of positive feedback is probably not what most people here want to hear.

Willis concludes the CERES data indicates a net strong negative cloud feedback.
What you or others may think people “want to hear” is not relevant.


Richard111 says:
October 4, 2013 at 12:18 am
Clouds contain condensed water and are formed within air masses saturated with the most important radiative gas in our atmosphere, water vapour. They emit LWIR. Incident LWIR can slow the cooling rate of most materials. Land under cloud cools more slowly and this effect is most notable at night.
The oceans however are an entirely different issue. To judge the effect of clouds over the ocean you would need a high resolution plot of down welling LWIR with a simultaneous plot of sea surface temperature below the skin evaporation layer at 5 min increments for night time only. I have not seen data of this type.


Hi Willis
What I like about your excellent articles is the clear writing, easy to follow, backed with solid science and solid reasoning.
England is for significant part of the year is a cloudy country. This moderates average daily maximum-minimum temperature difference to about 5C in the winter months and for the rest of the year the difference is mostly below or just above 10C, as shown here:

RC Saumarez

If the CERES data is monthly samples, How are those samples generated?


I think the real issue with the whole Global Warming/CO2 thing is that it is easy to prove that Clouds are by far the major influence of earth temperatures – including ENSO – that we have.
It’s simple: More clouds = higher albedo = lower temperatures.
So in order to model the temperature you HAVE to accurately model the clouds. The IPCC try to apply a delicate radiative equation to a situation where they have no idea what the albedo will be from hour to hour, week to week, year to year.
Modelling a system with variable albedo without modelling the cause of the abedo change is futile. Every time you see a cloud move the IPCC models are invalidated.

Very interesting post, Willis
However, the general assumption is that changes to clouds are a feedback to warming, and all GCM models assume this. What if changes to cloud cover are also caused by natural processes independent of CO2 ? For example ENSO is known to change cloud cover. This is the elephant in the room IMHO, which can also explain the observed hiatus in warming.
The global average (cooling) radiative forcing of clouds is about -21 W/m2 and the Earth has about 68% cloud cover. So if cloud cover reduces by just 2% the radiative forcing increases by 0.45 W/m2. For comparison the increase in radiative forcing from CO2 since 1950 is about the same size.

Has no-one done such basic figure bashing before? What are tehy doing with their grant money?


Good work. Two comments you said;
‘I think, although I’m by no means sure, that this is the first global observational analysis of the size of the so-called “cloud feedback”. It shows that the cloud feedback is strongly negative overall, -3 W/m2 for each degree of warming. In addition, in the critical control areas such as the ITCZ, the cooling effect is much larger, 10 W/m2 or so. Finally, it shows a very strong negative cloud feedback, 20 W/m2 or more, in the area of the Southern Ocean.”
Surely this is a very well studied area, after all the IPCC have been doing assessments for many years and clouds have always been a bone of contention. Difficult to believe that there aren’t a pile of papers out there on this. If not it seems an extreme dereliction of science.
Point two. At the start of the 19th century many parts of the world-Britain amongst them-had a fog of pollution-artists came to London to paint the sunrises. Sun levels have notably increased over the last century. More sun generally equals more warmth. More sun and changes in cloud levels (and types?) surely account for much of the temperature changes we can observe?

Claude Harvey

What I can say for sure about clouds is that they screwed up every grand engineering attempt to replace power plant cooling towers with “spray ponds” with which I was ever associated.
It was relatively easy to predict the heat rejection performance of either forced or natural draft cooling towers using only ambient temperature and humidity as the major external variables. I never saw anyone get it right for spray ponds.
The problem with spray ponds was that radiative heat transfer at night was such a huge portion of their overall heat rejection performance. On cloudless nights they dumped heat like a house afire. On cloudy nights the awful things just sat there grinning at you.


They were on the same track with ERBE:
Willis, please stop saying things like this: “In addition, however, they [the clouds] are basically perfect blackbodies for longwave radiation, so at the same time, they warm the surface by increasing the downwelling longwave radiation.” No. Their presence reduces the steepness of the temperature profile from the surface up by being warmer than the sky and thus disrupts the rate of heat loss from the surface. And this surely does not include just radiative heat loss. They intercept some of the outgoing thermal radiation from the surface heading for space by absorbing it and warming slightly from it, thus reducing the emission to space. This is the LWIR effect of clouds. From the link above: “In the longwave, clouds generally reduce the radiation emission to space (…)” You make it sound like it’s the downwelling radiation from the cooler clouds/atmosphere that do the actual (direct) warming of the already warmer surface. You know this isn’t possible. No, it’s the cloud temperature compared to the sky temperature that matters. Basic heat transfer.

Suggestions in this thread that variations in cloud cover have little effect on temperature are ill founded. Pinker et al. (2005) found a radiative forcing of 3 W/m2 from a naturally-occurring decrease in cloud cover from 1983-2001, intriguingly coincident with the positive phase of the PDO, and inadvertently indicating that the cloud feedback may be negative, and perhaps strongly so. Yet without assuming a strongly positive (i.e. temperature-amplifying) cloud feedback the IPCC cannot maintain the sensitivity interval [1.5, 4.5] K with which its 1990 report began and with which its 2013 report concludes.
Determining the influence of cloud variability on climate is not easy. The radiative effect of clouds is strongly altitude-dependent and the CERES data are poorly resolved vertically. The causes of cloud-cover variability are unknown. The cosmic-ray effect may have an underlying long-term influence. There may even be some influence from our minuscule alteration in the atmospheric composition. And the climate object behaves chaotically. It may, therefore, be impossible to determine even the sign of the cloud feedback, let alone its magnitude: but without determining it one can only guess (poorly) at climate sensitivity.

Old England

If you were wrong and the effect of clouds was to amplify warming you can bet that there would already have been funded papers finding this and trumpeted with big press releases. I can’t believe that well funded climate scientists haven’t played around with this data for some time looking for a way to show it proves positive feedbacks from water vapour (clouds).
In the absence of those ‘papers’ and press releases I would put money on it that you are on the right track.

Berényi Péter

How can satellites possibly measure downwelling thermal radiation flux?
BTW, clouds are only part of the story. There is also the so called “water vapor feedback”, which is supposed to be strong positive and operates even under clear skies, when relative humidity never gets saturated at any height.
However, I am not sure at all it is as simple as that. Water vapor, unlike carbon dioxide is not a well mixed greenhouse gas, its atmospheric distribution is fractal-like with huge differences in absolute humidity in adjacent air parcels at any scale. Now, the so called “greenhouse effect” is not generated by average concentration of GHGs, but by Planck weighted average optical depth in the thermal IR frequency range. The latter quantity is a monotonic function of the former in case of well mixed absorbers, but it is not the case for not well mixed ones.
The most one can tell about average optical thickness in water vapor absorption bands is it either increases or decreases with increasing average total column water vapor content, depending on higher moments of its distribution. A thin metal plate may be opaque while a wire fence, containing the same amount of metal per unit surface area is almost completely transparent.

I am not sure exactly what you have done here but I suspect you may have used seasonal temperature changes to derive the cloud feedback value. There are large regional variations in cloud cover – for example the monsoon seasons. The value of -3 W/m2/deg.C looks to be way too large to me. The Planck response to warming (negative feedback) is only -3.5 W/m2/deg.C.
I also think that clouds must act as a negative feedback. Otherwise how has the earth avoided runaway heating over the last 4 billion years to retain its oceans ?
Lord Monckton is also correct that cloud feedback are the largest uncertainty for all models in determining climate sensitivity.


Dr Burns says:
How do clouds cause warming during the day ?
1. When clouds form, latent heat is released, in all directions.
2. Clouds also slow down convection cooling, hence you can get a build up of energy below the clouds
All this is dependent of cloud level and ‘other stuff’ like: dew points, lapse rate (moisture content) pressure /temperature differences, sideways air currents (wind) etc etc.
We still have a LOT to learn about this stuff.
The science is far from settled.



Evidence of positive feedback is probably not what most people here want to hear.

how did you come to this conclusion? Did Willis cherry pick something? Say what. Or did you find Evidence of positive feedback somewhere? Post a link to it. As an engineer I would be very interested to see it because the climate doesn’t behave as if there is some. You know, one may get huge profits out of using positive feedbacks the right way.


What we need to realise is that EVERYTHING in the atmosphere is driven by pressure gradients, (both horizontal and vertical, which in turn can be driven by a variety of factors. Ultimately, the vertical atmospheric pressure gradient is and the fact that the Earth rotates (shh..don’t tell Trenberth) causing continually changing temperature and pressure fluctuations is what drives the climate.
The atmospheric pressure gradient only allows just so much energy to be stored, and as soon as that is reached at any altitude, the atmosphere will try to balance itself.
The atmosphere is actually a “net cooling” mechanism.
There is no blanket around the Earth


Monckton of Brenchley says:
“Determining the influence of cloud variability on climate is not easy. The radiative effect of clouds is strongly altitude-dependent and the CERES data are poorly resolved vertically. ”
Mr. Monckton, just took the words out of my mouth. Not only altitude dependent it is greatly dependent on general humidity of areas. An overview of chart one leads you to the conclusion that where CRE is positive and orange/red generally, is also is areas of low population/agriculture, not always (India) but generally. Australia, Antarctica, western N.A., North Africa/Middle East, Greenland. Why? Just below average humidity? Also of higher altitudes? Seems to be one, or the other, or both.
Increased radiation is not immediately bad, depends on whether it is night or day and where if it affects the general world population. Two graphs of the diurnal differences may show a completely different picture.


Simon says:
“Evidence of positive feedback is probably not what most people here want to hear.”
Its a good thing that this points to rather large negative feedbacks then, isn’t it ! 🙂


By the way, Willis.. Nice start ! 🙂


Willis is there a way to distinguish between cloud cover induced cooling/warming in the data for clouds that are “just there” and those that produce precipitation over their area? From your contributions regarding the tropical thunderstorm cycle we know that the evaporation/precipitation cycle is particular in regulating local heat phenomena.


Rabe says:
Yeah, imagine if you could harness the hypothetical CO2 radiation feedback.
A perpetual motion machine with unlimited capacity so long as we keep burning carbon fuels 🙂


Glancing at figure 1, the map of CRE (cloud radiative effect) I have the impression that the dark blue regions, the regions of largest negative CRE, are also the regions which in recent years seem to consistently show the biggest temperature anomalies – either warmer (e.g. off the north east coast of the USA, North Pacific) or colder (North Pacific, South Pacific, Peruvian coast La Nina upwelling region).