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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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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 76 to 100 out of 271:

  1. RW1 - Let's stay with the standard definitions, OK? Variation: Periodic (seasons) or aperiodic (ENSO) internal variations in climate that when averaged do not demonstrate a trend. Forcing: Factor that change from causes external to the climate system, causing trends in temperature. This includes Milankovich orbital changes, insolation, volcanic aerosols, land usage, and anthropogenic CO2. Feedback: Amplifying or dampening response to climate changes, reactions to long term temperature trends, for example clouds, water vapor, ice coverage/albedo, and long term CO2/ocean/weathering interactions. --- Back to the thread topic, clouds. Both direct evidence and paleo records indicate that the climate sensitivity is around 3C for a CO2 doubling, and that the cloud feedback is most likely somewhat positive. Slightly negative has not been ruled out, but it's not the mean estimate, either. Strongly negative cloud feedback is extremely unlikely based upon the 3C sensitivity estimate. Several people (Lindzen, Spencer) have postulated that clouds might change independently from temperature, and can thus be considered a forcing - none of them have presented any physical mechanism whereby this might happen. Lacking that, clouds must be considered a feedback only, not a forcing.
  2. 72, RW1,
    ...the climate is frequently perturbed by new 'forcings' - not all of which are due to temperature changes, yet the globally averaged temperature remains very, very stable.
    Can you provide examples of specific forcings that have occurred in the last century (or millenium), to which the climate has resisted change?
  3. 61, RW1, Somehow I missed this one:
    Because if a lot of the enhanced warming comes from positive cloud feedback, and the cloud feedback is NOT really positive - but negative (even slightly negative), it is going to reduce the projected amount of warming significantly.
    That's a gigantic if. If the moon were made of green cheese, NASA could feed the world. So you're hanging your hat on the guess that all of the climate scientists in the world got something very, very wrong... just because they admit that it's an area of uncertainty? Except that their estimates are not based on guesses, they're based on science. All you've offered to support a contrary view is conjecture.
  4. Sphaerica (RE: 71), "You love to exaggerate things. The cloud feedback is important, not huge. It's more important if it is neutral or negative, but you've shown no evidence other than that you think common sense says so, while hundreds of climate scientists think otherwise. But even if you proved clouds to be a weak negative feedback, it would reduce sensitivity to anywhere from 1.9 to 3.4 (versus 3 to 4.5), given that 3 is the current best estimate, but also at the low end of the range. Even 1.9 is very, very bad, especially since we're currently taking no action to avoid it." I'm I the only one who has actually read this section in the IPCC report that I linked regarding this? It clearly says the average sensitivity of the model predictions with no cloud feedback drops to 1.9 C. That is greater than half of all the enhanced warming, so I stand by my statement that clouds are a "huge" component. If the cloud feedback is negative, it would reduce the sensitivity significantly. "But first you need to submit some evidence beyond your "plain, everyman logic" to prove that clouds are even a neutral feedback, let alone negative." I have presented quite a bit of evidence beyond just "plain, everyman logic". In case you missed it, I started out in the thread by presenting some calculations that are directly inconsistent with positive cloud feedback, especially given the albedo has not decreased. And many other lines of evidence as well. "And that evidence has to contradict all of this evidence to the contrary. I'm afraid a sensitivity below 3˚C is very, very unlikely." How can they claim a sensitivity of 3 C is so likely when they also claim there is great uncertainty in regards to the cloud feedback, which accounts for more than half of the enhanced warming by their own numbers. That seems like an oxymoron to me. If this were the case, the planet would never, ever cool, no matter what." How do you figure? Surely there are a multitude of other influences other than just water vapor and clouds. "Because water vapor will increase or decrease in the atmosphere fairly quickly in response to temperature. Raise the temperature, raise the water vapor. Lower the temperature, lower the water vapor.". Water vapor is an amplifier of temperature - meaning if the temperature goes up, the water vapor goes up, and then the increased water vapor causes the temperature to go up even more and so forth. This means something other than water vapor is causing the temperature to decrease. "CO2, on the other hand, will stay in the atmosphere for hundreds of years, even if, for example, a large volcanic eruption temporarily lowers temperatures." Yes, I know. I'm quite aware that the added CO2 has a 'permanent' or long-term staying effect unlike water vapor. I don't see how this contradicts anything of mine. Remember, I don't dispute a likelihood of some effect - just the magnitude. "[Why would the same forces that modulate or control water vapor's radiative forcing, not modulate and control CO2's radiative forcing?] There are no such forces for either. This isn't a human designed system with controls and balances. It's nature, and it's (fortunately) got a simple balance to it, and one that should be very hard to shove, but we've found a way to do it." Just stating there are "no such forces" and "a simple balance" isn't even remotely good enough. If you don't know the primary mechanism (or mechanisms) that drive the current energy balance that results in such high stability, you can't accurately predict how the system will respond to any perturbation - anthropogenic or otherwise.
  5. If you have access you may want to refer to Observational and Model Evidence for Positive Low-Level Cloud Feedback: Amy C. Clement, Robert Burgman and Joel R. Norris (2009).
    Response: [DB] For those troubled by access issues, Harvard has an open copy here.
  6. 79, RW1,
    ...some calculations that are directly inconsistent with positive cloud feedback...
    For the life of me, I can't figure out what the point is to all of your calculations. I can mostly follow them, but they're such a convoluted morass of numbers that I can't figure out what the final, meaningful result is supposed to be. Could you perhaps bother to actually make a point? Simply saying "clouds will be negative, look I have lots of numbers" doesn't cut it. Exactly what numbers are we supposed to take away from that mess? You also confuse matters by trying to infer things like reflectivity of clouds when inbound radiation is primarily (but not totally) in the visible spectrum, while outbound radiation leans more to LW. Reflectivity for things like clouds are dependent on the wavelength, so right there most of your calculations appear to be invalid (I say appear, because quite honestly, you present them in such a confused jumble, pulling in numbers willy nilly without clear attribution, that it's given me a headache trying to sort out what you did, and eventually I gave up... I don't have the time to sort through it if you don't have the time to present it with more clarity).
    These calculations are consistent with general observations - that is cloudy days are usually cooler than sunny days.
    No, really? I wonder why climate scientists never thought of that.
    The opposite would be the case if clouds blocked more energy than they reflect away (cloudy days would be warmer than sunny days).
    Again, you are ignoring wavelengths, as well as temperatures and seasons. Cloudy days in winter are warmer than summer, because of the radiation from the clouds. And as I've already explained, there are different types of clouds, with varying reflectivity. Clouds at night warm the surface while having no cooling effect whatsoever. High clouds made of ice reflect almost nothing, but trap IR. Finally, all of this is beside the point. No one has ever said that clouds can only warm, or can't reflect inbound radiation. This has all been taken into account, so your efforts to put complex numbers on it looks to me like a very well dressed strawman. What happens going forward depends on what sorts of clouds form more or less in a warmed climate. The question is, will warming generate more low clouds which reflect more than they absorb, or more high clouds which absorb and barely reflect? Your numbers do nothing to address this. Meanwhile, you completely avoided my main point, which is that many, many lines of evidence, including current observations, paleohistory and models, all point to a sensitivity of 3˚C or greater. Every one of those studies argues strongly against your inferred and mainly hoped for negative cloud feedback. You have a large body of evidence that you need to refute with something more than a pile of convoluted numbers.
  7. Sphaerica (RE: 78), "That's a gigantic if. If the moon were made of green cheese, NASA could feed the world." And you're accuse me of exaggerating things. "So you're hanging your hat on the guess that all of the climate scientists in the world got something very, very wrong... just because they admit that it's an area of uncertainty?" Not just an area of uncertainty but a significant area of uncertainty. But far from it, I'm hanging my hat on a critical examination of the evidence, data and logic - much of which I've presented here. Is it just a coincidence that whether or not sensitivity is very high or benignly low hangs mostly on the cloud feedback, and those claiming a high sensitivity are also claiming significant uncertainty for the cloud feedback, while those claiming a low sensitivity are not? Is it also it yet another coincidence that net negative cloud feedback is consistent with how the incident energy on the surface from the Sun is responded to in the system, while positive cloud feedback is not?
  8. How long will you wait with warming trucking along consistent with a climate sensitivity of 3 not 2, before you would be prepared to say just maybe the models are calculating feedback the correct way? 10 years, 30, 60?
  9. Sphaerica (RE: 81), "For the life of me, I can't figure out what the point is to all of your calculations. I can mostly follow them, but they're such a convoluted morass of numbers that I can't figure out what the final, meaningful result is supposed to be." The numbers are showing that in the aggregate, additional clouds reflect more energy back out to space than they trap or block from the surface. That for each additional m^2 of cloud cover, there is loss of about 10-12 W/m^2. Sorry if I didn't make that clear. "Again, you are ignoring wavelengths," I don't see how. A watt is watt, regardless of whether it's SW or LW. "as well as temperatures and seasons. Cloudy days in winter are warmer than summer, because of the radiation from the clouds. And as I've already explained, there are different types of clouds, with varying reflectivity. Clouds at night warm the surface while having no cooling effect whatsoever. High clouds made of ice reflect almost nothing, but trap IR." I'm well aware of all these things. The data is globally averaged, so all of these effects (differences between night and day, types of clouds etc.) are accounted for in the numbers. "Finally, all of this is beside the point. No one has ever said that clouds can only warm, or can't reflect inbound radiation. This has all been taken into account, so your efforts to put complex numbers on it looks to me like a very well dressed strawman. What happens going forward depends on what sorts of clouds form more or less in a warmed climate. The question is, will warming generate more low clouds which reflect more than they absorb, or more high clouds which absorb and barely reflect? Your numbers do nothing to address this." Not by themselves - no, but they do suggest that in aggregate the net effect of clouds is to cool rather than warm, which is much more consistent with negative feedback, especially given the albedo hasn't decreased (or has even slightly increased). But you are correct in that the issue is more complicated than this, which is why it has to be carefully weighed will all the other evidence. This is also why understanding the role clouds play in maintaining the energy balance is so important to understanding cloud behavior and ultimately whether or not they primarily act to amplify or attenuate warming.
  10. scaddenp (RE: 83) "How long will you wait with warming trucking along consistent with a climate sensitivity of 3 not 2, before you would be prepared to say just maybe the models are calculating feedback the correct way? 10 years, 30, 60?" Well, I don't agree that the warming we've seen so far is consistent with a sensitivity of 3 C, but that's an issue for another thread. I don't want to delve into that here.
  11. Sphaerica (RE: 81) "Reflectivity for things like clouds are dependent on the wavelength, so right there most of your calculations appear to be invalid" Trenberth is showing 79 W/m^2 of incoming solar energy is reflected off of clouds back out to space. The energy coming in from the Sun is SW radiation, so the 79 W/m^2 reflected back out is SW radiation. "(I say appear, because quite honestly, you present them in such a confused jumble, pulling in numbers willy nilly without clear attribution, that it's given me a headache trying to sort out what you did, and eventually I gave up... I don't have the time to sort through it if you don't have the time to present it with more clarity)" What part isn't clear? The ISCCP data says clouds cover 66.7% of the surface on average. I rounded this up to 0.67. There is 341 W/m^2 from the Sun incident on the Earth, so 67% of that is 228 W/m^2 incident on clouds, 79 W/m^2 of which is reflected away for a net reflectance of 35% or 0.35 (79 is 35% of 228) per m^2 of cloud cover. I then used the same method for the clear sky and subtracted the difference of the weighted averages for the net of 51 W/m^2 (after my slight error correction later in the thread in post 45).
  12. RW1 - it empirical support for models having feedback about right. They do the calculation properly.
  13. #86 RW1 at 14:29 PM on 21 April, 2011 Trenberth is showing 79 W/m^2 of incoming solar energy is reflected off of clouds back out to space Something does not add up here. Global cloud fraction is more than 0.6 while average incoming shortwave radiation is 341 W/m2. Trenberth's 79 W/m2 implies an average cloud albedo smaller than 0.39. On the other hand it seems to be more than 0.42 (Han 1998, Table 1. pp. 1525). Solution?
  14. 82, RW1,
    And you're accuse me of exaggerating things.
    But my hyperbole is intended to poke fun at your hypoerbole. You've arbitrarily focused on the cloud feedback as uncertain, which is true, but it's not that uncertain, and very, very few people are arguing that it will be negative. The negative lapse rate feedback is also uncertain. What if that turns out to be wrong? The pace and extent of positive CO2 feedbacks are uncertain. What if they're faster, and greater? The pace of future anthropogenic CO2 generation is also uncertain, and with people like you trying to influence the debate, it's unlikely to go down, but very likely to go up. The rate of Arctic ice melt is exceeding predictions and increasing that positive feedback. There are lots of uncertainties. Picking just one from the bunch, and then exaggerating the chance that the error is in the direction that you'd like it to be, is not logical, especially when the aggregate of all uncertainties has more chance of being net positive than negative.
    ...a significant area of uncertainty...
    Exaggeration, in particular in the wrong direction... it is uncertain both ways, and unlikely to deviate so far from expectations as to make a that large of a difference. I would point out that your cherished 1.9˚C sensitivity, the lowest you claim one could reasonably get, is still dangerously high.
    ...on a critical examination of the evidence, data and logic - much of which I've presented here...
    To me you've completely failed to present your case, but I'll give you the benefit of the doubt and think that the failing lies only in your presentation and not your numbers, because as I've already said, trying to sort through your steps is like trying to read a Chinese assembly manual for a nuclear reactor, translated by a Swede into Slavic using a base 9 number system. I hate to suggest it, but perhaps if you went through the numbers again, but in less of a jumble, one could sort out what you are doing, and where you are going. It is almost impossible to see where you have made inappropriate assumptions (such as assuming the cloud reflectivity for SW radiation is the same as for LW radiation) with the way you've written it up. When you introduce a new number, be clear about where you've gotten it. When you come up with a result, be clear about what it represents. Most importantly, when you come up with something that somehow supports your assertions, point it out. Before you even start, state what you are trying to derive. I still cannot figure out which numbers support your position, or how and why, and which ones are just intermediate steps.
    Is it just a coincidence that...
    Is it also it yet another coincidence that...
    And what is this supposed to be implying?
  15. 82, RW1,
    I don't see how. A watt is watt, regardless of whether it's SW or LW.
    !?!?!?!?!????? If you don't get this, you have a huge, huge hole in your understanding. You need to know this. It's critical to everything. As I have said repeatedly, you have a lot of studying to do. One can't even discuss this with you if you don't know why that statement demonstrates a horrible lack of understanding of the system.
    I'm well aware of all these things.
    But you choose to simply ignore them, and focus on the behavior of clouds on a sunny day, as if that is the only way that they operate.
    ...they do suggest that in aggregate the net effect of clouds is to cool rather than warm...
    You say this, but you have not actually demonstrated it, both because your numbers are unclear, and they contain at least one critical flaw (SW vs. LW distinction), and probably many others.
    But you are correct in that the issue is more complicated than this, which is why it has to be carefully weighed will all the other evidence.
    And yet twice you have ignored my demonstration of the long list of other evidence which points to climate sensitivity being at lease 3˚C, and therefore supports the contention that the models have the cloud feedback right, or at least that the net effect of all feedbacks points to 3˚C, even if the cloud feedback is lower than expected (or negative!).
  16. 82, RW1,
    ...so the 79 W/m^2 reflected back out is SW radiation.
    But you appear later to use this result to compute reflectivity for LW radiation from the ground up. Forgive me if I'm mistaken, but as I've said repeatedly... sorting through your swarm of calculations is a nightmare.
  17. 88, BP,
    Trenberth's 79 W/m2 implies an average cloud albedo smaller than 0.39.
    He took his numbers primarily (not completely) from the ERBE and CERES satellites, so they are unlikely to be wrong. I'd suggest that of that 341, since 78 is absorbed by the atmosphere, only 263 is available to be reflected (although this is a gross estimate, since it's more complex than that). If one assumes a cloud cover of .66 then 174 of that 263 is subject to cloud cover. 79 reflected from 174 gives .45, which is well within the ranges given by Hansen 1998 -- even at the upper end.
  18. RW1, Let me summarize my understanding of your logic. 1. Your personal calculations about clouds, based purely on Trenberth's "Global Energy Flows" diagram, "suggest that in aggregate the net effect of clouds is to cool rather than warm." (you haven't actually made this case, but it's your main premise). 2. The scientists behind the models admit that the cloud feedbacks are uncertain, vary between models, and provide an important positive feedback (no need to exaggerate this further... leave it at "important"). 3. Your assumption is that since you've "proven" that clouds cool rather than warm, a positive feedback is impossible (despite your lack of understanding of the physics behind how the clouds work on atmospheric temperatures, how they form, and how their formation will be affected by rising temperatures, and the fact that not all clouds are created equal). 4. Completely eliminating all positive feedback from clouds reduces estimated sensitivity from 3.1 to 1.9. 5. You think the reduction is so great that 1.9 isn't a problem -- it's not a dangerously high amount of warming. 6. You discount the fact that the lapse rate feedback might not be as great as estimated, or that CO2 and albedo feedbacks might be greater or kick in sooner than estimated, or that anthropogenic CO2 additions could actually increase with human population growth and expanding industrialization. 7. You discount the fact that other studies point to a climate sensitivity of 3+, which imply that that the cloud feedback estimates are either correct, or that any error is offset by underestimations of other positive feedbacks (or over-estimation of the lapse rate negative feedback). 8. You discount the fact that we've already seen the climate warm by 0.8˚C this century without a noticeable negative cloud feedback, i.e. that the climate is obviously sensitive enough to swing 0.8˚C in a mere 100 years (0.6˚C of that in only the last 30 years) despite your proposed fast acting negative cloud feedback.
  19. RW1 Sphaerica - "Again, you are ignoring wavelengths," RW1 - "I don't see how. A watt is watt, regardless of whether it's SW or LW." What!?! You feel that somehow the wavelength dependent behavior of clouds is irrelevant? I hate to put this so strongly, but you've just skipped one of the most important points about cloud feedback. Abandon all science here! You have also made an unsupported statement that scientists stating minimal cloud feedback depend on high uncertainties, while those stating strongly negative don't. Please present some citations on that, as that does not match anything I have seen in the literature. I would also encourage you to look at (and perhaps post upon) the How sensitive is our climate thread - the 3C figure for doubling CO2 is strongly supported, with a distribution tail much larger on the high side. Sensitivity cannot be much lower given historic and paleo data (which incorporate all feedbacks including clouds), but it could be considerably higher, and personally I don't consider depending on the low sensitivity to be a good bet. Really, RW1, you're pushing an idea not supported by the data - it's really sounding like wishful thinking.
  20. @Berényi Péter #88 @Sphaerica #92 Please, Sphaerica, don't reply to that master of word tricks, as he/she has and wield the ability to induce mistakes departing of his/her owns. @Berényi Péter #88
    Something does not add up here.
    Yes, your knowledge on the subject: You are simply playing with planetary albedo, cloud albedo and the part of planetary albedo that is provided by clouds. To explain it in a way a child of 10 could understand (change of voice) you are saying that every and all of the beams that the sun uses to give light and to warm the earth must find a cloud in their way, but all of us know that there are aplenty days the sun shines and there is no cloud in sight, isn't it truth, kids? -Yay! (back to normal voice)
    Solution?
    Thinking it better before posting with links to literature. This was just one more of "yours", like your magical UV-A beams, your dwelling in exclusively polar regions and a lot of quackery that you have been adding to a lot of posts in this site in recent days and that you don't even bother to reply, once spotted. I ask now the moderators what is the style or applicable rules to use with all this cases, that is, to deal with people that uses the disinformation technique that can be compared with a person constantly going to the woods and coming back bringing in his arms any sort of sticks and lumber, in order to put all that rubbish on different places of the tracks in an effort to derail the passing convoys, claiming in the seldom case of achieving such goal that the act is evidence of the nonexistence of a railroad system and that, in the worst scenario, a stick is better technology than a locomotive. What can we do? Tell me, please.
  21. Sphaerica (RE: 90), "!?!?!?!?!????? If you don't get this, you have a huge, huge hole in your understanding. You need to know this. It's critical to everything." I mean in terms of energy lost or retained in the system, a watt is watt. That's all. "You say this, but you have not actually demonstrated it, both because your numbers are unclear, and they contain at least one critical flaw (SW vs. LW distinction), and probably many others." The incoming energy from the Sun (341 W/m^2) is all SW radiation. The 79 W/m^2 is the cloud portion of the albedo, which is the incoming SW radiation that is reflected back out to space off of clouds. The energy trapped or retained by the clouds is LW radiation emitted from the surface (396 W/m^2) absorbed by the clouds, half of which is emitted downward toward the surface. The downward emitted amount represents the amount of energy the clouds are trapping or retaining in the system. What I've shown is - using Trenberth's numbers at least, the amount of surface emitted energy clouds retain is less than the amount of incoming energy they reflect away. This means the net effect of clouds is to cool. If the net effect of clouds is to warm, the opposite would be the case - the clouds would retain more surface emitted energy than they reflect away. Does this explain it better?
  22. Sphaerica (RE: 91), "But you appear later to use this result to compute reflectivity for LW radiation from the ground up. Forgive me if I'm mistaken, but as I've said repeatedly... sorting through your swarm of calculations is a nightmare." No, the calculation for the amount of surface emitted energy absorbed by the clouds just happened to come out about the same as the 79 W/m^2 Trenberth designates as being reflected away. Pure coincidence - nothing more. The difference between the weighted average values came out to be 0.20 and 396 x 0.20 = 79.2, which I just rounded to an even 79 - that's all.
  23. 96, RW1,
    ...emitted from the surface (396 W/m^2) absorbed by the clouds, half of which is emitted downward toward the surface.
    How do you get "half?" Citation, please.
    What I've shown is - using Trenberth's numbers at least, the amount of surface emitted energy clouds retain is less than the amount of incoming energy they reflect away
    I don't see this, or how you could arrive at this. Trenberth's own diagram does not distinguish between back radiation from clouds versus the atmosphere. Can you clarify how you arrive at that part of your calculation?
  24. 96, RW1,
    ...the calculation for the amount of surface emitted energy absorbed by the clouds...
    Please clarify this calculation.
  25. Sphaerica (RE: 93), "Let me summarize my understanding of your logic. 1. Your personal calculations about clouds, based purely on Trenberth's "Global Energy Flows" diagram, "suggest that in aggregate the net effect of clouds is to cool rather than warm." (you haven't actually made this case, but it's your main premise)." Yes. "2. The scientists behind the models admit that the cloud feedbacks are uncertain, vary between models, and provide an important positive feedback (no need to exaggerate this further... leave it at "important"). Correct. The exact wording in the IPCC report is "significant uncertainties, in particular, are associated with representation of clouds, and in the resulting cloud responses to climate change." "3. Your assumption is that since you've "proven" that clouds cool rather than warm, a positive feedback is impossible (despite your lack of understanding of the physics behind how the clouds work on atmospheric temperatures, how they form, and how their formation will be affected by rising temperatures, and the fact that not all clouds are created equal)." No, I've made no claim that anything is impossible. I've presented several lines of evidence and logic against positive cloud feedback. The calculations using Trenberth's numbers are one piece of evidence among many in support of negative cloud feedback, but the calculations in and of themselves do not 'prove' that the cloud feedback is negative. 4. Completely eliminating all positive feedback from clouds reduces estimated sensitivity from 3.1 to 1.9. Yes, 1.9 C for neutral cloud feedback. What they don't show is how much less the sensitivity would be with even a slightly negative cloud feedback.

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