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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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What is the net feedback from clouds?

What the science says...

Select a level... Basic Intermediate

Evidence is building that net cloud feedback is likely positive and unlikely to be strongly negative.

Climate Myth...

Clouds provide negative feedback

"Climate models used by the International Panel on Climate Change (IPCC) assume that clouds provide a large positive feedback, greatly amplifying the small warming effect of increasing CO2 content in air. Clouds have made fools of climate modelers. A detailed analysis of cloud behavior from satellite data by Dr. Roy Spencer of the University of Alabama in Huntsville shows that clouds actually provide a strong negative feedback, the opposite of that assumed by the climate modelers. The modelers confused cause and effect, thereby getting the feedback in the wrong direction." (Ken Gregory)

At a glance

What part do clouds play in your life? You might not think about that consciously, but without clouds, Earth's land masses would all be lifeless deserts. Fortunately, the laws of physics prevent such things from being the case. Clouds play that vital role of transporting water from the oceans to land. And there's plenty of them: NASA estimates that around two-thirds of the planet has cloud cover.

Clouds form when water vapour condenses and coalesces around tiny particles called aerosols. Aerosols come in many forms: common examples include dust, smoke and sulphuric acid. At low altitudes, clouds consist of minute water droplets, but high clouds form from ice crystals. Low and high clouds have different roles in regulating Earth's climate. How?

If you've ever been in the position to look down upon low cloud-tops, perhaps from a plane or a mountain-top, you'll have noticed they are a brilliant white. That whiteness is sunlight being reflected off them. In being reflected, that sunlight cannot reach Earth's surface - which is why the temperature falls when clouds roll in to replace blue skies. Under a continuous low cloud-deck, only around 30-60% of the sunlight is getting through. Low clouds literally provide a sunshade.

Not all clouds are such good sunshades. Wispy high clouds are poor reflectors of sunlight but they are very effective traps for heat coming up from below, so their net effect is to aid and abet global warming.

Cloud formation processes often take place on a localised scale. That means their detailed study involves much higher-resolution modelling than the larger-scale global climate models. Fourteen years on, since Ken Gregory of the dubiously-named Big Oil part-funded Canadian group, 'Friends of Science', opined on the matter (see myth box), big advances have been made in such modelling. Today, we far better understand the net effects of clouds in Earth's changing climate system. Confidence is now growing that changes to clouds are likely to amplify, rather than offset, human-caused global warming in the future.

Two important processes have been detected through observation and simulation of cloud behaviour in a warming world. Firstly, just like wildlife, low clouds are migrating polewards as the planet heats up. Why is that bad news? Because the subtropical and tropical regions receive the lion's share of sunshine on Earth. So less cloud in these areas means a lot more energy getting through to the surface. Secondly, we are detecting an increase in the height of the highest cloud-tops at all latitudes. That maintains their efficiency at trapping the heat coming up from below.

There's another effect we need to consider too. Our aerosol emissions have gone up massively since pre-Industrial times. This has caused cloud droplets to become both smaller and more numerous, making them even better reflectors of sunlight. Aerosols released by human activities have therefore had a cooling effect, acting as a counter-balance to a significant portion of the warming caused by greenhouse gas emissions.

But industrial aerosols are also pollutants that adversely affect human health. Having realised this, we are reducing such emissions. That in turn is lowering the reflectivity of low cloud-tops, reducing their cooling effect and therefore amplifying global warming due to rising levels of greenhouse gases.

It sometimes feels as if we are between a rock and a hard place. We'd have been better off not treating our atmosphere as a dustbin to begin with. But there's still a way to fix this and that is by reducing all emissions.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!


Further details

The IPCC's Sixth Assessment Report eloquently sums up where we are in our understanding of how clouds will affect us in a changing climate:

"One of the biggest challenges in climate science has been to predict how clouds will change in a warming world and whether those changes will amplify or partially offset the warming caused by increasing concentrations of greenhouse gases and other human activities. Scientists have made significant progress over the past decade and are now more confident that changes in clouds will amplify, rather than offset, global warming in the future."

The mistake made by our myth-provider, writing in 2009, was to leap to a conclusion without the information needed in order to do so. He is suggesting that clouds are inadequately represented in climate models, so they must have a negative effect on temperatures. Instead of making such leaps of faith, however, the specialists in cloud behaviour have recognised the challenges and met them square-on. We now know a lot more about clouds as a result.

In the at-a-glance section, we explain the important difference between high clouds and low clouds, agents of warming and cooling respectively. Careful examination of older satellite records has detected large-scale patterns of cloud change between the 1980s and 2000s (Norris et al. 2016). Observed and simulated cloud change patterns are consistent with the poleward retreat of midlatitude storm tracks, the expansion of subtropical dry zones and increasing height of the highest cloud tops at all latitudes. The main drivers of these cloud changes appear to be twofold: increasing greenhouse gas concentrations and recovery from volcanic radiative cooling. As a result, the cloud changes most consistently predicted by global climate models have indeed been occurring in nature.

With respect to the cooling low clouds, one particularly important area of study has involved marine stratocumulus cloud-decks. These are extensive, low-lying clouds with tops mostly below 2 km (7,000 ft) altitude and they are the most common cloud type on Earth. Over the oceans, stratocumulus often forms nearly unbroken decks, extending over thousands of square kilometres. Such clouds cover about 20% of the tropical oceans between 30°S and 30°N and they are especially common off the western coasts of North and South America and Africa (fig.1). That's because the surface waters of the oceans are pushed away from the western margins of continents due to the eastwards direction of Earth's spin on its axis. Taking the place of these displaced surface waters are upwelling, relatively cool waters from the ocean depths. The cool waters serve to chill the moist air above, making its water vapour content condense out into cloud-forming droplets.

 Satellite image of stratocumulus clouds.

Fig. 1: visible satellite image of part of an extensive marine stratocumulus deck off the western seaboard of North America, with Baja California easily recognisable on the right. Image: NASA.

With their highly reflective tops that block a lot of the incoming sunlight, the marine stratocumulus clouds have a very important role as climate regulators. It has long been known that increasing the area of the oceans covered by such clouds, even by just a few percent, can lead to substantial global cooling. Conversely, decreasing the area they cover can lead to substantial global warming.

Although many cloud-types are produced by convection, driven by the heated land or ocean surface, marine stratocumulus clouds are different. They are formed and maintained by turbulent overturning circulations, driven by radiative cooling at the cloud tops. It works as follows: cold air sinks, so that radiatively-cooled air makes its way down to the sea surface, picks up moisture and then brings that moisture back up, nourishing and sustaining the clouds.

Stratocumulus decks can and do break up, though. This happens when that radiative cooling at the cloud tops becomes too weak to send colder air sinking down to the surface. It can also occur when the turbulence that can entrain dry and warm air, from above the clouds into the cloud layer, becomes too strong.

The importance of such processes has been further investigated recently, using an ultra-high resolution model with a 50-metre grid size. (Schneider et al. 2019). Global climate models typically have grid sizes of tens of kilometres. At that resolution, they cannot detail such fine-scale processes. This model, by contrast, is able to resolve the individual stratocumulus updraughts and downdraughts.

 Results of modelling of marine stratocumulus behaviour.

Fig. 2: results of modelling of marine stratocumulus behaviour in a high-CO2 world. This one compares conditions at 400 ppm (present) and 1600 ppm (hopefully never, but relevant to the Palaeocene and Eocene when a super-Hothouse climate prevailed). Redrawn from Schneider et al. 2019.

The modelling shows how oceanic stratocumulus decks become unstable and break up into scattered cumulus clouds. That occurs at greenhouse gas levels of around 1,200 ppm (fig. 2). When that happens, the ocean surface below the clouds warms abruptly because the cloud shading is so diminished. In the model, the extra solar energy absorbed as stratocumulus decks break up, over an area estimated to cover about 6.5% of the globe, is enough to cause a further ~8oC of global warming. After the stratocumulus decks have broken up, they only re-form once CO2 levels have dropped substantially below the level at which the instability first occurred.

These results point to the possibility that there is a previously undiscovered, potentially strong and nonlinear feedback, lurking within the climate system. These findings may well help to solve certain palaeoclimatic problems, such as the super-Hothouse climate of the Palaeocene-Eocene, some 50 million years ago. It's been hard to fully explain that event, given that estimates of CO2 levels at the time do not exceed 2,000 ppm. Present climate models do not reach that level of warmth with that amount of CO2. But the fossil record presents hard evidence for near-tropical conditions in which crocodilians thrived - in the Arctic. Something brought about that climate shift!

The quantitative aspects of stratocumulus cloud-deck instability remain under investigation. However the phenomenon appears to be robust for the physical reasons described by Schneider and co-authors. Closer to the present, the recent acceleration of global warming may be partly due to a decrease in aerosols. Aerosols produce smaller and more numerous cloud droplets. These have the effect of increasing the reflectivity and hence albedo of low cloud-tops (fig. 3). It follows that if aerosol levels decrease, the reverse will be the case. Of considerable relevance here are the limits on the sulphur content of ship fuels, imposed by the International Maritime Organization in early 2015. These regulations were further tightened in 2020. An ongoing fall in aerosol pollution, right under the marine stratocumulus decks, would be expected to occur. As a consequence, the size and amount of cloud droplets would change, cloud top albedo would decrease and there would be increased absorption of solar energy by Earth. That would be on top of the existing greenhouse gas-caused global warming. James Hansen discussed this in a recent communication (PDF) here.

Cloud effects on Earth's radiation.

Fig. 3: NASA graphic depicting the relationship between clouds, incoming Solar radiation and long-wave Infrared (IR) radiation. High clouds composed of ice crystals reflect little sunlight but absorb and emit a significant amount of IR. Conversely low clouds, composed of water droplets, reflect a great deal of sunlight and also absorb and emit IR. Any mechanism that reduces low cloud-top albedo will therefore increase the sunlight reaching the surface, causing additional warming.

In their Sixth Assessment Report, the IPCC also points out that the concentration of aerosols in the atmosphere has markedly increased since the pre-industrial era. As a consequence, clouds now reflect more incoming Solar energy than before industrial times. In other words, aerosols released by human activities have had a cooling effect. That cooling effect has countered a lot of the warming caused by increases in greenhouse gas emissions over the last century. Nevertheless, they also state that this counter-effect is expected to diminish in the future. As air pollution controls are adopted worldwide, there will be a reduction in the amount of aerosols released into the atmosphere. Therefore, cloud-top albedo is expected to diminish. Hansen merely suggests this albedo-reduction may already be underway.

Last updated on 15 October 2023 by John Mason. View Archives

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Argument Feedback

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Additional viewing

To explore this complex topic further, this is a great TED talk by climate scientist Kate Marvel:

Denial101x video(s)

Here is the relevant lecture-video from Denial101x - Making Sense of Climate Science Denial

Additional video from the MOOC

Expert interview with Steve Sherwood

Comments

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Comments 226 to 250 out of 271:

  1. 225, RW1, Clear evasion. And gibberish.
  2. RW1 - "These things appear to be strong enough to overcome the net negative feedback operating on the system and cause significantly more change than just what the change in net incident energy alone would cause." (emphasis added) You know, that's a perfectly reasonable definition - of positive feedback. You have just invalidated your last N+ posts claiming negative feedback, RW1.
    Response:

    [DB] RW1 is clearly trolling now.  His comments will be treated as such until he can offer up substantive dialogue supported by more than mere opinion and hand-waving.  This has become tiresome.

  3. 227, RW1, What "things"? How is this any different from today? Why can it appear to cause more change in those cases, but not now?
  4. KR, "You know, that's a perfectly reasonable definition - of positive feedback." I know what you're saying, but this isn't quite what I meant. What I meant is the other things are strong enough to cause more change than the net amount of change that would result from the net negative feedback alone.
  5. Daniel Bailey - Somewhere between Groundhog Day and Whack A Mole... RW1 - I strongly suggest actually doing some reading on radiative physics. You are once again demonstrating the D-K effect.
    Response: [Sph] End italics tags fixed.
  6. RW1, I second KR's suggestion. There is a wealth of information out there to be learned. Fill in the gaps in your understanding and come back with a model which is consistent with all of the facts, not just some. [We want to discuss science here, not magic.]
  7. Sphaerica (RE: 229), "What "things"? How is this any different from today? Why can it appear to cause more change in those cases, but not now?" For starters, the positive feedback effect of melting ice from that of leaving maximum ice cannot be equated to that of minimum ice where the climate is now (and is during every interglacial period). There just isn’t much ice left, and what is left would be very hard to melt, as most of it is located at high latitudes around the poles which are mostly dark 6 months out of the year with way below freezing temperatures. A lot of the ice is thousands of feet above sea level too where the air is significantly colder. Unless you wait a few 10s of millions of years for plate tectonics to move Antarctica and Greenland to lower latitudes (if they are even moving in that direction), no significant amount of ice is going to melt from just a few degrees rise in global average temperature. Furthermore, the high ‘sensitivity’ from glacial to interglacial is largely driven by the change in the orbit relative to the Sun, which changes the distribution of incident solar energy into the system quite dramatically (more energy is distributed to the higher latitudes in the NH summer, in particular). This combined with positive feedback effect of melting surface ice is enough to overcome the net negative feedback and cause the 5-6 C rise. The roughly +7 W/m^2 or so increase from the Sun is a minor contributor to the whole thing. We are also relatively close to the end of this interglacial period, so if anything the orbital component has already flipped back in the direction of glaciation and cooling.
    Response:

    [DB] Now you post gibberish.  It has become etremely evident that you are here simply to be argumentative, and that you simply do not have a background sufficient to realize that most of what you write above is, to put it delicately, "crap".

    Please make a considered effort to ensure what you write is consistent with the known physics of climate change; your persistence in forcing physics to contort to your electronics-based interpretation of things is admirable, but misguided.

    Shorter admonition:  less posting, more studying.

    A general note to the lay reader:  RW1 has a long history here of having these exact type of interactions on many previous threads.  He promulgates the same basic arguments which are promptly shown to have the same basic misunderstandings.  Not liking the answers, he has even taken the propositions to other websites like Real Climate, where he was given the same answers, to which he expressed similar reluctance in believing.  Let the reader beware.

  8. 233, RW1, Nice try, but no. It has been very clearly calculated that the insolation and albedo changes alone are insufficient to produce the temperature swings seen between glacials and interglacials. CO2 changes are measured, and in fact are computed to account quite well for the difference when other positive feedbacks (water vapor, etc.) are added in. This would not be the case if there were a net negative cloud feedback. Goodness, you really, really want CO2 to be a non-factor, don't you? But even if your scenario were true -- why doesn't your strong net-negative cloud feedback counter the changes in insolation and ice albedo? If cloud feedbacks are driven by temperature changes, and temperatures rise, shouldn't there be more clouds, and a higher albedo -- keeping the earth covered in ice?
  9. RW1, you really are talking gibberish now. And my question was not off-topic in relation to the feedback from clouds, as palaeoclimatic variations include feedback from clouds (as I said in #221), thus constraining their magnitude. Is the total feedback demonstrated by palaeoclimate positive or negative? And remember we live on an Earth with some hefty ice sheets, sea ice and winter snowcover right now. All ready and willing to chip in on positive albedo feedback, right now. A large portion of the Greenland Ice Sheet lies below the glacier equilibrium line. Its mass balance is presently negative and accelerating negative. Do you think that all that ice is going to remain safe at high altitude under these conditions? Speaking of altitude, what was the average altitude of the Laurentide, Scandinavian or British ice sheets? Did altitude help them survive, too? I like your definition of positive feedback in #227. With a very slight alteration in wording I might use it myself... It really does totally invalidate your argument though! If your last sentence in #233 is correct, where's the cooling? #222 mc - I see, the D-K is strong with this one.
  10. Sphaerica (RE: 234), Now you're at least asking some good questions. It's late though and I need to call it night. I'll respond tomorrow.
    Response:

    [DB] "Now you're at least asking some good questions."

    Actually, all parties have presented you with good questions.  If you are going to participate in the dialogue here, it is incumbent upon you to formulate good answers to those questions.

  11. Dear all, I wanted to make another observation regarding water-vapour feedback that might not have already been discussed. If the amount of water vapour increases in the troposhere so will the specific heat capacity of the air. The change in temperature of the air as a function of altitude is governed by the adiabatic lapse rate. For dry air this turns out to be about -9.8 Kelvin per kilometre. For air of "average moisture content" (I forget what value this is) the lapse rate turns out be be around -7 Kelvin per kilometre. So I expect this value to decrease. Now, the minimum temperature found in the lower atmosphere occurs at the tropopause. This minimum temperature is a kind of compromise between heating at the Stratospheric ozone layer and the troposheric lapse rate. Any change in the latter will imply that the tropopause occurs at a higher altitude and at a greater (minimum) temperature. This will affect the amount of radiation that can be emitted from the Tropopause in a positive way. A second influence will be that, if a greater rate of condensation occurs due to increased water vapour content this will also increase the temperature of the upper troposphere, thus further enhancing the emission rate there. These effects may not have already been considered in the models. On a different matter: sometimes it is not useful to talk about radiation as though this is the main mechanism of energy exchange within the troposphere. The only radiation that is essentially transferred in the atmosphere is incoming solar radiation and up to 40 W m-2 emitted directly from the near the Earth's to clouds and back again. All other energy is transferred by thermal conduction enhanced by convection (or just convection in the case of vaporization/condensation). This does not make any difference to most of the arguments presented but one can get a clear picture of the situation.
    Response:

    [DB] Welcome to Skeptical Science!  There is an immense amount of reference material discussed here and it can be a bit difficult at first to find an answer to your questions.  That's why we recommend that Newcomers, Start Here and then learn The Big Picture.

    I also recommend watching this video on why CO2 is the biggest climate control knob in Earth's history.

    Further general questions can usually be be answered by first using the Search function in the upper left of every Skeptical Science page to see if there is already a post on it (odds are, there is).  If you still have questions, use the Search function located in the upper left of every page here at Skeptical Science and post your question on the most pertinent thread.

    All pages are live at SkS; many may be currently inactive, however.  Posting a question or comment on any will not be missed as regulars here follow the Recent Comments threads, which allows them to see every new comment that gets posted here.

    Comments primarily dealing with ideologies are frowned upon here.  SkS is on online climate science Forum in which participants can freely discuss the science of climate change and the myths promulgated by those seeking to dissemble.  All science is presented in context with links to primary sources so that the active, engaging mind can review any claims made.

    Remember to frame your questions in compliance with the Comments Policy and lastly, to use the Preview function below the comment box to ensure that any html tags you're using work properly.

    "These effects may not have already been considered in the models."

    Please use the search function to find a page on models.  Likely any question you may have on climate science has already been addressed on one of the 4,700+ pages here.  Thus, the search function is your friend; use it and the coppers of your pocket [your questions]...and it will line your mind with gold.

  12. SC1 @236, what you are describing is the Lapse Rate Feedback, a well known negative feedback. Because it is a product of increased specific humidity, it tends to correspond inversely to the Water Vapour feedback, which is positive. That is, if there is a strong water vapour feedback, then the lapse rate feedback is also expected to be strong. Correspondingly, if there is a weak water vapour feedback, the lapse rate feedback is correspondingly weak. As can be seen below, the Water Vapour feedback is stronger than the Lapse Rate feedback, so that the net effect is a positive feedback. Please note that though the tropopause does increase in altitude with a warming atmosphere, this is not due to the change in lapse rate. Water vapour, unlike CO2, is not well mixed so that it is largely confined to the lower half of the troposphere. As such, the lapse rate feedback is negligible, or even slightly positive at higher altitudes (see first link, to the IPCC AR4, for discussion).
  13. Dear All, it would be very informative if Dessler (2010) identified the mechanism by which fewer low-lying clouds would be generated if the water vapour content of the air (plus air temperature) increases. Is anyone aware of such a mechanism being mentioned in a peer-reviewed pulblication?
  14. Dear Tom, thanks very much for your quick and informative answer. Indeed I hadn't been aware that lapse-rate forcing had been treated already.
  15. SC1 @238, there are multiple ways in which clouds can interact to produce feedbacks, both positive and negative. For example, the strength of incoming Short Wave radiation varies in (approximate) proportion to the cosine of latitude. Meanwhile the greenhouse effect of clouds varies in proportion to the surface temperature. Because surface temperature declines only slightly (about 15%-20%) from equator to Arctic, while the cosine of latitude varies from 1 to 0, clouds have a net positive effect in polar regions. Because greenhouse gases reduce the temperature range from equator to pole, that increases the strength of polar cloud greenhouse effect relative to cloud albedo effect, and hence acts as a positive feedback if all else remains equal. The point here is not that this is a major effect (it probably is not), but that the interaction between clouds and radiation is subtle. Another effect, significant in the tropics is the increase in strength of convection cells, resulting in more anvil head clouds. It is not the height of the cloud base, but the cloud tops which determines the greenhouse effect of clouds, so stronger convection in the Inter Tropical Convergence Zone would probably result in a positive cloud feedback. Further, if temperature increases in a region and/or altitude faster than water vapour so that relative humidity falls, the result will be reduced cloud in that region and/or altitude. This effect can result in more high cloud and less low cloud (or the reverse) which depending on the distribution of these phenomena can result in a positive or negative net cloud feedback. Other physical mechanisms exist. So, the problem in answering your question does not lie in deducing physical mechanisms. It lies, firstly in the fact that models do not agree on the properties of clouds, so we cannot look at the models to deduce exactly which physical mechanisms will dominate with regards to clouds. Further, observations are limited in number so that it is difficult to distinguish signal from noise in this instance. While substantial mystery remains about the behaviour of clouds in a warming environment, what can be said is that both the balance of models (see graph in 237), and the balance of physical evidence (see main article) suggest a net positive feedback. That means that summed over a variety of possible cloud reactions, more possible combinations of cloud responses result in warming (models), and physical evidence suggests the actual response is a positive feedback.
  16. I'm a bit late on this. We all agree that clouds both cool by reflecting the Sun's energy and warm by 'blocking' or delaying the exit of surface emitted energy, but this is rather trival to the fundamental question of the net cloud feedback, is it not? The biggest problem is in the current climate, the net effect of clouds globally averaged is to cool by about 20 W/m^2, as is even acknowledged in papers claiming to show net positive cloud feedback (i.e. Dessler 2010), and is consistent with net negative feedback from clouds. This discrepancy would have to be explained in the context of strong net positive feedback from clouds on incremental warming, would it not? Not only is this not explained either by Dessler or anyone else to my knowledge, but without knowing physically why the net effect of clouds is to cool by 20 W/m^2 in the current climate, there is no way to know if the assessments of net positive feedback on incremental warming are accurate, let alone even physically possible. Ultimately, the fact that no one purporting evidence of net positive cloud feedback can explain this or even tries to explain it in light of the conclusions of their work, is rather telling to me how weak and unsubstantiated the case for net positive cloud feedback actually is. And while globally averaged, the water vapor concentration and water vapor feedback in response can further increase temperatures in a warmer world, it cannot be separated or isolated from the cloud feedback, as the two are constantly interacting together to maintain the current energy balance. This gets back to my point about the water vapor and cloud feedbacks already operating in a very dynamic manner in the current climate's globally averaged state from the forcing of the Sun. From this, let's look at the fundamental question of climate sensitivity, net feedback, etc. from the basic constraints dictated by conservation of energy. If the surface of the Earth is the warm by 3C, it must emit 406.6 W/m^2 from S-B (assuming an emissivity of 1 or very close to 1), which is +16.6 W/m^2 from the current global average of 390 W/m^2. Conservation of Energy dictates this +16.6 W/m^2 flux has to be entering the surface from the atmosphere on global average if it is to warm by 3C. There are really only two possible sources for this required energy flux into the surface, and that is either from the Sun via a reduced albedo or from increased atomspheric absorption (like from water vapor). If the current averaged state of the atmosphere is only going to provide +6 W/m^2 (+1.1C) from 2xCO2 (3.7 W/m^2 directly from the CO2 'forcing' and the remaining 2.3 W/m^2 from the current average opacity of the atmosphere; 3.7 W/m^2 x 0.62 = 2.3 W/m^2), where is the additional 10.6 W/m^2 needed for the 3C rise coming from? Can anyone explain and quantify the actual physics of how about a 1 C rise in temperature will change the atmosphere in a way that will further cause an additional 10.6 W/m^2 flux into the surface? If you think it will come primarily from increased water vapor, are you claiming that the water vapor absorption will increase by 10.6 W/m^2 from a 1 C rise in temperature (actually more than 10.6 W/m^2 because half of what's absorbed by the atmosphere escapes to space as part of the flux leaving at the TOA), and if so based on what data or physics? Or if you think the combined cloud feedback will cause a large portion of it, in what specific physical way? If by letting in more sunlight, how does increasing water vapor cause decreasing clouds or more transparent clouds? If by causing increased atmospheric absorption through more clouds, how is this specifically more than the incremental power reflected from the additional or thicker clouds? How is this rectified with the fact the net effect of clouds is to cool by about 20 W/m^2 in the current climate? In general there seems to be a lot of hand waving in regards to this fundamental question and answers to it tend to only be vague, generalized statements like "it comes from the all the feedbacks" or "from downward LW", etc. This kind of sloppy and incomplete scientific reasoning is not good enough. The required energy entering the surface for a 3C rise has to be coming from somewhere specific and from some specific physical process or combined processes that can be corroborated by some real, observable, quantifiable physics and data. I see mosly heuristic assumptions and more or less wild guessing dressed up as some kind of quasi 'best estimate' or 'educated guess'.
  17. Well, many people have tried to educate on the physics without success, but as to this one: "There are really only two possible sources for this required energy flux into the surface, and that is either from the Sun via a reduced albedo or from increased atomspheric absorption (like from water vapor)." That additional flux on the surface comes from increase in backradiation due to increased GHGs. It is that simple. This is not sloppy; it directly calculated from the RTEs.
  18. scaddenp, "That additional flux on the surface comes from increase in backradiation due to increased GHGs. It is that simple. This is not sloppy; it directly calculated from the RTEs." You disappoint me with your answer.
  19. Well that is the physics whether you can understand it or not.
  20. RW1 - I have responded to your post on the far more appropriate Climate Sensitivity thread. Moderators - Might I suggest that discussions of total climate sensitivity are (while related) off-topic in a thread on the specific subject of cloud feedback?
  21. ABC (Aussie) has a summary of Roger Davies (et al.) work on cloud height decrease over the last decade. From the summary: "Experts from the University of Auckland suggest the change in cloud altitude could be the Earth's way of dealing with global warming." Earth's way of dealing with global warming. We don't need mitigation; Earth's got our backs. Earth's a smart cookie. It likes us. Wants to protect us. That Pluto . . . dumb as a rock . . . living way out there at the edge . . . freezing! Isn't even smart enough to grow a coat.
  22. DSL - Strange how the Earth still got very hot in the past eh? The most likely explanation is that the lowering of cloud height is related to the ENSO trend, and the consequent top-of-the-atmosphere radiation flux over the last decade. The decade started off with weak La Nina and El Nino and finished off with strong ones, and the end of the decade was La Nina-dominant. A colder, drier atmosphere (relative to the beginning of the decade) should see less cloud formation and a lowering of cloud height. Nothing makes sense in mainstream media land, because they don't even make the effort to understand what's happening. Sad really. I'm writing up a post/rebuttal of Davies & Molloy (2012). Their findings have predictably been mangled - although a sentence in the study doesn't help.
  23. If clouds feedback were positive, we would expect:

    Infinite warming, until oceans become dry.

    It never has occurred in the past, even with a warmer earth.

    IPCC's Climatologists should say:

    We don't know everything about clouds. We need study a lot to understand the entire process. When we are sure, we are explaining step by step, showing with controlled laboratorial experiments, and calculation memory. When we can explain in details how to trigger an ice age, and an interglaciation era, we are ready to define positive or negative feedback for clouds. By now, we are closing our mouth about global warming or cooling.

  24. Licorj - See Does positive feedback necessarily mean runaway warming. That would only be true with a feedback gain >1, which means that any increase would have an infinite effect. In reality, the law of diminshing returns means that feedbacks of a physical scale are of gain <1, with the total change in temperature being:

    Total T = ΔT / (1-g)

    and with the positive feedbacks providing a limited scale of amplification for any temperature change. For the current sensitivity estimate of ~3C per doubling of CO2, with an initial ΔT of ~1.1C, the gain 'g' is about 0.63. 

    Now as to clouds, if you have actually read the opening post (I suspect you have not), clouds are estimated to have a small positive (amplifying) contribution to the total sensitivity. 

  25. Dear KR,

    First, thank you by attention, even after long time past from publication of this post. I just have realized it, after my post was sent.

    I have read the post, and a lot of very interesting comments. "Clouds are estimated be small positive feedback". Ok. Estimated to be, but could be estimated to not to be... It is a game.

    Excuse me by error on "INFINITE WARMING". It is clear that is not possible, otherwise, we would have free energy generation.

    Backing to the clouds: I believe, of course, with less scientific based knowledge than you, that the choice on small positive feedback for cloud, taken by climate scientists was just a choice, with high level of uncertainty. So high, that choice would be NEUTRAL, or small negative feedback. In order to get the true cloud feedback, it would be need a lot of measures taken around the world, on entire troposphere, entire world, during long time. Of course it is very expensive and hard to do, maybe impossible.

    Even assuming my mistake on INIFINITE WARMING, I still believe that oceans would be expected to dry, because of positive feedback, in any level.

    Other expected result from feedbacks for, aerossols, cloud, water vapor, CO2, CH4, etc, would be the accuracy of models on recreating paste climates. They are all wrong, on this task. Somethings are very wron with them, and nedd to be fixed, before can tell us how will be the climate after 100 years from present day.

    Why we see tomorrow's weather forecasts, and believe on it ?

    Because they are correct on vaste majority of times. It is not the same case for climate models, at least, untill now.

    But, this is off-topic.

    Response:

    [JH] Since you have provided absolutely no specific evidence to substantiate your sweeping assertions about global climate models, your assertions are merely your opinion - which carries virtually no weight on this site.

    If you post similar comments in the future, they will be summarily dismissed for violating the SkS Comments Policy re sloganeering.  

    Please read the SkS Comments Policy and adhere to it. 

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