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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)

The effect of clouds in a warming world is complicated. One challenge is that clouds cause both warming and cooling. Low-level clouds tend to cool by reflecting sunlight. High-level clouds tend to warm by trapping heat.

clouds

As the planet warms, clouds have a cooling effect if there are more low-level clouds or less high-level clouds.  Clouds would cause more warming if the opposite is true.  To work out the overall effect, scientists need to know which types of clouds are increasing or decreasing. 

Some climate scientists, such as Richard Lindzen and Roy Spencer, are skeptical that greenhouse gas emissions will cause dangerous warming. Their skepticism is based mainly on uncertainty related to clouds.  They believe that when it warms, low-level cloud cover increases. This would mean the Earth's overall reflectiveness would increase. This causes cooling, which would cancel out some of the warming from an increased greenhouse effect. 

However, recent evidence indicates this is not the case. Two separate studies have looked at cloud changes in the tropics and subtropics using a combination of ship-based cloud observations, satellite observations and climate models. Both found that cloud feedback in this region appears to be positive, meaning more warming.

Another study used satellite measurements of cloud cover over the entire planet to measure cloud feedback.  Although a very small negative feedback (cooling) could not be ruled out, the overall short-term global cloud feedback was probably positive (warming).  It is very unlikely that the cloud feedback will cause enough cooling to offset much of human-caused global warming.

Other studies have found that the climate models that best simulate cloud changes are the ones that find it to be a positive feedback, and thus have higher climate sensitivities.  Steven Sherwood explains one such study:

While clouds remain an uncertainty, the evidence is building that clouds will probably cause the planet to warm even further, and are very unlikely to cancel out much of human-caused global warming.  It's also important to remember that there many other feedbacks besides clouds. There is a large amount of evidence that the net feedback is positive and will amplify global warming.

Basic rebuttal written by dana1981


Update July 2015:

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

Last updated on 25 July 2017 by skeptickev. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Comments

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Comments 51 to 74 out of 74:

  1. RW1 - Re: your claim that "A very large amount (if not most) of the enhanced warming from the climate models comes from positive cloud feedback." From your link: "In AOGCMs, the water vapour feedback constitutes by far the strongest feedback" - followed by the lapse rate, and then surface albedo and clouds. "Water vapor and clouds act on time scales of hours to days." Absolutely. Which why they are strictly feedbacks, not forcings. They cannot stay out of balance long enough to affect any other feedbacks on their own.
  2. Sphaerica (RE 48), "Water vapor does not equal clouds." I never claimed that it did. "Again, no, clouds come in a distant fourth, at best, behind H2O feedbacks (water vapor), CO2 feedbacks, and albedo feedbacks." Not according the latest IPCC report, which says: "The water vapour feedback is, however, closely related to the lapse rate feedback (see above), and the two combined result in a feedback parameter of approximately 1 W m–2 °C–1, corresponding to an amplification of the basic temperature response by approximately 50%. The surface albedo feedback amplifies the basic response by about 10%, and the cloud feedback does so by 10 to 50% depending on the GCM." Clouds can be up to 50%, where as surface albedo is only about 10%.
  3. KR (RE: 51), "From your link: "In AOGCMs, the water vapour feedback constitutes by far the strongest feedback" - followed by the lapse rate, and then surface albedo and clouds." Are you not actually reading the whole section? This not what it says (or implies). The surface albedo is the smallest feedback - closer to a third of the average cloud feedback (0.26 W m-2 °C–1 vs. 0.69 W m–2 °C–1 for clouds). The water vapor feedback is directly tied to and offset by the lapse rate feedback (1.80 W m-2 °C–1 vs. -0.84 W m-2 °C–1 for the lapse rate). " 'Water vapor and clouds act on time scales of hours to days.' Absolutely. Which why they are strictly feedbacks, not forcings." Define specifically what you mean by a 'forcing'? The only true 'forcing' of the climate system is the Sun. All the other components, such as water vapor, clouds, and precipitation, are really just responding directly or indirectly to the Sun's forcing, the net effect of all of which dictate the equilibrium surface temperature. "They cannot stay out of balance long enough to affect any other feedbacks on their own." Why not? What's keeping them from staying "out of balance"?
  4. muoncounter (RE: 50), "Huh? What does that have to do with the rate at which CO2 radiative forcing increases global temperature?" I don't understand the question. Is 100 years not a significantly slower rate than hours to days?
  5. See the IPCC report for formal definition of forcing, but it is basically something can change the radiative balance independent of temperature. Only a change in forcing can change climate. The forcing in the system are solar, GHGs (which can also be a feedback, but are a forcing if changed independently of temperature -eg by release of fossil fuel), and aerosols. On a larger time scale, changes in continent distribution and in the nature of the biosphere can alter albedo so that it is also a forcing.
  6. KR (RE: 51), If water vapor is not a 'forcing' in the climate system, then how can CO2 be a 'forcing'? Are you claiming that increased water vapor in the atmosphere is not a 'forcing', but increased CO2 is a 'forcing'? This is the problem. They are both 'forcings' in the way you're using the term. The main difference is water vapor acts on much shorter time scales, but it is still a 'forcing' none the less.
  7. 52, RW1, Clouds come in ahead of albedo, and behind water vapor. I'm still not quite sure how you turn this into "A very large amount (if not most) of the enhanced warming" but I'll concede the point. Clouds are an important positive feedback in the models (but not "most"). So what's your point? 53, RW1,
    The only true 'forcing' of the climate system is the Sun.
    No. If anything, solar output is the single strongest constant in the entire system. Changes in CO2 concentrations in the atmosphere are almost certainly the primary driver as far as total change. They are tied to every major climate swing in some way, and global temperature closely tracks CO2 concentrations. Albedo is probably the primary driver as far as getting the ball rolling (and that can come from orbital forcings or aerosols -- volcanism). Water vapor and clouds are fast acting feedbacks that do not force anything on their own. But we're drifting. What is your point about clouds again? Now that you've proven that they are a strong positive feedback, why are we discussing them?
  8. 56, RW1,
    ...but increased CO2 is a 'forcing'?
    Yes, because water vapor responds quickly to changes in temperature. There's nothing anyone or anything can do to inject water vapor into the atmosphere and keep it there. The temperature will drop, and the water vapor will condense and things will return to normal. This is not the case with CO2, whether it is added anthropogenically or geologically. No matter how it gets there, once it does get there, it stays there for a very long time and it's effect forces the climate to follow suit.
  9. RW1 - "If water vapor is not a 'forcing' in the climate system, then how can CO2 be a 'forcing'? Are you claiming that increased water vapor in the atmosphere is not a 'forcing', but increased CO2 is a 'forcing'?" Not just claiming that, but stating that with plenty of evidence. CO2 has been changing due to anthropogenic emissions, while water vapor and clouds have been changing strictly due to temperature changes. This is part of the grand scheme of Cause -> Effect, RSVP; CO2 (due to our actions) is a recent cause of climate change, water vapor and clouds respond as an effect.
  10. RW1#54: "I don't understand the question." Well, you stated "Anthropogenic CO2 forcing is very gradual," I asked how you to substantiate this; you responded that "it's claimed to take about 100 years to double CO2." The time it takes to double CO2 through anthropogenic input has nothing to do with the time it takes for the forcing of CO2 already in the atmosphere to increase temperature, which is, of course, already in progress. I don't understand how you mixed up the two. See the 40 year lag thread I linked earlier for discussion of this.
  11. Sphaerica (RE: 57), "What is your point about clouds again? Now that you've proven that they are a strong positive feedback, why are we discussing them?" 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. The IPCC even says that if the cloud feedback is neutral, it would reduce the average sensitivity to 1.9 C instead of 3 C. That's a reduction of over half of the enhanced warming. If the cloud feedback was even moderately negative, the average sensitivity could easily come down to 1 C or less. In short, the cloud feedback is huge.
  12. muoncounter (RE: 60), "The time it takes to double CO2 through anthropogenic input has nothing to do with the time it takes for the forcing of CO2 already in the atmosphere to increase temperature, which is, of course, already in progress. I don't understand how you mixed up the two. See the 40 year lag thread I linked earlier for discussion of this." Sorry for the misunderstanding, but my question then is why doesn't it take 40 years for the forcing of water vapor in the atmosphere to increase (and decrease) temperature?
  13. RW1#62: "why doesn't it take 40 years for the forcing of water vapor in the atmosphere" I thought there was agreement that water vapor doesn't stay in the atmosphere that long. I don't know how things are where you live, but I wipe a lot of that water vapor off my car windows every morning. #61: "the average sensitivity could easily come down to 1 C or less." Ah, we've come full circle, as you've said that before: It's also inline with the sensitivity only being about 0.6 C . Of course, the temperature record doesn't support that contention, as we've already seen 0.8C with far less than a doubling of CO2.
  14. KR (RE: 59), "Not just claiming that, but stating that with plenty of evidence. CO2 has been changing due to anthropogenic emissions, while water vapor and clouds have been changing strictly due to temperature changes." Not necessarily strictly temperature changes, but even so, I don't see how that excludes them from being a 'forcing'. Do water vapor changes not also cause temperature changes? Do cloud changes not also cause temperature changes? Surely they do.
  15. muoncounter (RE: 62), "I thought there was agreement that water vapor doesn't stay in the atmosphere that long." It doesn't, but it also doesn't take 40 years for changes in water vapor concentration to effect changes in temperature. For example, a sunny humid day is generally warmer than a sunny dry day, all other things being equal. "Ah, we've come full circle, as you've said that before: It's also inline with the sensitivity only being about 0.6 C" That was assuming only half of the 3.7 W/m^2 from 2xCO2 is incident on the surface. For the purposes of this discussion and elsewhere here, I've accepted that the full 3.7 W/m^2 affects the surface (at least for now).
  16. RW1 - At the risk of repeating myself: Cause => Effect CO2 is a cause, changing (primarly and from anthropogenic actions) independent of temperature, while water vapor and clouds respond promptly to temperature and don't change on their own, and are hence amplifying effects of temperature change. Water vapor and clouds change in response to temperature. If you have any evidence supporting water vapor or cloud changes independent of temperature, I suggest you publish it. Nobody else has found any such evidence - I will (I believe correctly) take assertions to that effect as just wishful thinking without such evidence.
  17. RW1 - clouds are not forcing because unless you have something like GCR changing clouds, there is no way to produce a long term change in cloud cover without something else being responsible for changing the temperature. If your vision of reality is right, then you would have world with no change to GHG, solar, or aerosols, going through climate change (ie a long term change in radiative balance). Now plenty of that kind of internal variability in short time scales - weather. But no evidence whatsoever of any such change on long term.
  18. Sphaerica (RE: 58), "Yes, because water vapor responds quickly to changes in temperature. There's nothing anyone or anything can do to inject water vapor into the atmosphere and keep it there. The temperature will drop, and the water vapor will condense and things will return to normal." But what causes the temperature to drop and the water vapor to be removed from the atmosphere if water vapor is the primary amplifier of warming? "This is not the case with CO2, whether it is added anthropogenically or geologically. No matter how it gets there, once it does get there, it stays there for a very long time and it's effect forces the climate to follow suit." Yes, but I don't see how CO2's effect is fundamentally different than water vapor, especially if water vapor is the primary amplifier of warming (CO2 induced or otherwise). In other words, why would the response to water vapor warming in the system be any different than warming caused by CO2? Why would the same forces that modulate or control water vapor's radiative forcing, not modulate and control CO2's radiative forcing? The surface has no way of distinguishing where the radiative 'forcing' originated from - water vapor or CO2. All the surface 'knows' is its total energy flux, as it determines the surface temperature.
  19. The atmosphere has a temperature gradient. At a certain height, water condenses out. CO2 does not. Maximum water content in atmosphere is temperature-dependent. Maximum CO2 is not. Note that in our current AGW-world, CO2 is not a feedback. The mechanisms are too slow to have produced much GHG feedback yet.
  20. scaddenp (RE: 69), "The atmosphere has a temperature gradient. At a certain height, water condenses out. CO2 does not." I know. "Note that in our current AGW-world, CO2 is not a feedback." Agreed.
  21. RW1,
    In short, the cloud feedback is huge.
    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. 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. 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.
    But what causes the temperature to drop and the water vapor to be removed from the atmosphere if water vapor is the primary amplifier of warming?
    This question is evidence that you don't understand how things work. You need to go study more. If this were the case, the planet would never, ever cool, no matter what.
    ...but I don't see how CO2's effect is fundamentally different than water vapor..
    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. 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.
    ...why would the response to water vapor warming in the system be any different than warming caused by CO2?
    There's no difference in the warming. What is different is that the CO2 won't drop out of the atmosphere when the temperature drops (for instance, during the winter).
    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. The point is not how each one (water vapor vs. CO2) affects temperature. The point is that water vapor content is itself affected by temperature on short time scales, while CO2 is only affected on very, very long time scales. And, in fact, there is a positive CO2 feedback (such as outgassing from the ocean) that will, in the long term, increase CO2 levels even further.
  22. KR (RE: 66), "Cause => Effect CO2 is a cause, changing (primarly and from anthropogenic actions) independent of temperature, while water vapor and clouds respond promptly to temperature and don't change on their own, and are hence amplifying effects of temperature change." I think the confusion here lies somewhere in between the definition of 'forcing' and that there are many other things in the climate system, other than anthropogenic CO2 (and GHGs), that are changing and subsequently inducing new 'forcings' independent of temperature. As just one example, take the fluctuations of Arctic and Antarctic sea ice extents, which we know are largely driven by factors other than temperature (wind patterns, ocean currents, etc,). Yes, anthropogenic CO2 'forcing' is a cause and not an effect of temperature, but even without anthropogenic CO2, 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.
  23. RW1 - the answer then to "Yes, but I don't see how CO2's effect is fundamentally different than water vapor, especially if water vapor is the primary amplifier of warming (CO2 induced or otherwise)." CO2 is non-condensated gas. That is why the same forces that modulate or control water vapor's radiative forcing, do not modulate and control CO2's radiative forcing.
  24. "As just one example, take the fluctuations of Arctic and Antarctic sea ice extents, which we know are largely driven by factors other than temperature (wind patterns, ocean currents, etc,). " Splorff! Long term (30 year) change in arctic albedo is driven ultimately by change in temperature. Short term variation from year to year depends on wind/ocean etc. Oh and what is changing ocean/wind? I think it is time to come up with some evidence for unforced climate change if you are arguing about the definition of forcing.
  25. RW1 wrote: "I think the confusion here lies somewhere in between the definition of 'forcing' and that there are many other things in the climate system, other than anthropogenic CO2 (and GHGs), that are changing and subsequently inducing new 'forcings' independent of temperature. As just one example, take the fluctuations of Arctic and Antarctic sea ice extents, which we know are largely driven by factors other than temperature (wind patterns, ocean currents, etc,)."
    What boils to: - I know it is a system - I know CO2 is a factor - But the cause must be elsewhere, darn. - Let me uncouple the system and I'll tell why. Let also that the uncoupling makes Temperature an irrelevant variable to the climate system. "Why would you stop when you can rev up?" (signed: Thelma & Louise)
  26. 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.
  27. 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?
  28. 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.
  29. 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.
  30. 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.
  31. 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.
  32. 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?
  33. 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?
  34. 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.
  35. 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.
  36. 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).
  37. RW1 - it empirical support for models having feedback about right. They do the calculation properly.
  38. #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?
  39. 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?
  40. 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!).
  41. 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.
  42. 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.
  43. 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.
  44. 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.
  45. @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.
  46. 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?
  47. 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.
  48. 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?
  49. 96, RW1,
    ...the calculation for the amount of surface emitted energy absorbed by the clouds...
    Please clarify this calculation.
  50. 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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