ATTP, This is a discussion of clouds

ATTP,
This is a discussion of clouds precisely because they are a very important part of the climate puzzle.
“Clearing Clouds of Uncertainty by Mark Zelinka, David Randall, Mark Webb and Steven Klein. Their commentary is really a summary of our recent understanding and – as illustrated by the figure on the right – they conclude that the evidence is converging on the cloud feedback likely being positive.”
From FAR 1990 positive but cloud feedback represented the largest source of uncertainty in climate sensitivity among atmospheric models.
To SAR Second Assessment Report; 1995), more climate models were predicting the mass of cloud liquid and ice, and generally finding negative cloud opacity feedbacks, albeit of widely differing strengths. The report concluded that it was not possible at that time to judge the sign of the net cloud feedback.
TAR 2001 …the sign of [the cloud] feedback remains unknown.
AR4 2007 it is not yet possible to assess which of the model estimates of cloud feedback is the most reliable
AR5 “The sign of the net radiative feedback due to all cloud types is…likely positive”
BUT Cloud opacity feedback “is highly uncertain”

You say,
“I don’t really see why I should be expected to post comments that are certain, but wrong.”
I repeated a fact, “Averaged globally and annually, clouds cause cooling ” from the article overview. I said in view of this,
“any increase in cloud cover should have a stronger negative than a positive effect.”
The current point of view says this is likely wrong but admit to high uncertainty still in areas like cloud opacity. There is a threefold variation in the global sensitivity parameter FAR 1990 due to
differences in cloud feedback.
This is a most important discussion which is not yet settled and needs open discussion.

 

 

  • angech says:

    Your comment is awaiting moderation.

    Izen
    The article overview states
    “Averaged globally and annually, clouds cause 18W/m2 of cooling relative to a hypothetical
    cloud-free Earth. This is the net result of a 46 W/m2 cooling from reflecting sunlight back to space (an albedo effect) partly offset by a 28 W/m2 heating due to reduced terrestrial radiation emitted to space (a greenhouse effect). The net planetary cooling provided by clouds is roughly five times as large as the planetary heating from a doubling of CO2.”
    So even though the albedo effect usually works only half the time [there is a minuscule effect for moonlight etc] it produces much more cooling in that 12 hour period than a whole 24 hours of
    cloud GH positive effect.

    “Why would the albedo negative effect be larger than the cloud GH positive effect if they increase”

    Because it is positive with more clouds. As stated above in a cloud free earth it would be 18W/M energy warmer. So if there is no effect with no cloud and 18 W/m2 cooler with current cloud it stands to reason that with more cloud from global warming there should be an increase in the cooling effect.

    The authors state,
    “The overall cloud feedback is actually the aggregate effect of several individual cloud feedbacks, commonly separated into three components: cloud amount, cloud altitude,and cloud opacity feedbacks” “Nearly all current climate models simulate an overall positive cloud feedback ”

    Despite Victor’s assertion he is referring to a decreasing amount of ice and here we are referring to an increasing amount of water vapor. Which up to this point in the climate causes cooling of a known degree. The models simulate and argue for positive feedbacks from clouds from this point on without acknowledgment of how the clouds caused cooling in the first place.
    It appears to be models all the way down with “weak further support from observations”

  • paulski0 says:

    angech,

    ATTP ” they conclude that the evidence is converging on the cloud feedback likely being positive.”
    This comment must therefore be directed at the increase in clouds, not their current status as the article demonstrates an original strong negative feedback (18W/m2).

    Positive feedback in this case refers to enhancement of warming rate due to changes in cloud behaviour in response to temperature increase.

    The -18W/m2 figure refers to the net present day radiative effect of clouds, relative to a hypothetical Earth without clouds (all else remaining the same). I guess you could argue that clouds wouldn’t exist at 0K temperature, so the “warming” to present day 288K temperature has resulted in a -18W/m2 negative feedback, but the temperature at which clouds can form is so far below 288K that it makes no sense to extrapolate a continuing increase in cloud amounts with temperature.

    It’s actually fairly easy to dispel any “intuitive” idea that cloud amounts must increase with temperature at present day levels by looking at seasonal cycles. Certainly in the Northern Hemisphere mid-latitudes, Summers are considerably less cloudy than Winters.

    Putting into numbers AR5 concluded with a best estimate of 0.6W/m2/K for net cloud feedback. That means a 1K warming from now would result in a change from -18W/m2 to -17.4W/m2 cloud radiative effect. Don’t know if it’s been done, but might be interesting to produce a diagram giving some idea of how Earth’s net cloud radiative effect, total cloud fraction, low cloud fraction varies with temperature from 0K up to 300K.

  • Magma says:

    That’s a nice commentary/short review in Nature Climate Change, open-access and well worth reading.

    I have the strong impression that much of the contrarian opinion on cloud feedback originates from the fact that when one is outdoors on a sunny day and a cloud passes in front of the sun, ground level insolation and perceived temperature quickly drop. Coupling this to the undeniable facts that it still gets cold in mid-latitude winters and major coastal cities are still above sea level, it is but series of short logical steps to the “all scientists are liars and climate change is a hoax to bring about one world government” held by many of these rather dim individuals.

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  • Eric Michel says:

    Just a quick note of thanks. Not nearly well versed enough to comment on the material, but enjoy reading and learning bits and pieces.

    Eric

    On Sat, Oct 7, 2017 at 3:02 PM, …and Then There’s Physics wrote:

    > …and Then There’s Physics posted: “A few years ago I posted a video by > Andrew Dessler that was discussing whether or not Equilibrium Climate > Sensitivity could be less than 3oC. The bottom line was that the best > estimate for ECS is about 3oC. Given that we’re quite confident about water > v” >

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  • angech,
    I don’t like having to justify moderation decisions, but I will illustrate this just this once. You said

    SInce the first effect is primary ie albedo and since this effect is negative any increase in cloud cover should have a stronger negative than a positive effect.

    Well, this is wrong, as others have indicated. Yet, you said it as if you understood this well enough to make a strong claim. I don’t really see why I should be expected to post comments that are certain, but wrong.

    Your comment is awaiting moderation.

    Overview of #cloudfeedbacks in the 5 IPCC reports & beyond [link].
    An interesting blog on this over at ATTP. “A bit more about clouds”
    This is a discussion of clouds precisely because they are a very important part of the climate puzzle.
    “Clearing Clouds of Uncertainty by Mark Zelinka, David Randall, Mark Webb and Steven Klein. Their commentary is really a summary of our recent understanding and – as illustrated by the figure on the right – they conclude that the evidence is converging on the cloud feedback likely being positive.”
    From FAR 1990 positive but cloud feedback represented the largest source of uncertainty in climate sensitivity among atmospheric models.
    To SAR Second Assessment Report; 1995), more climate models were predicting the mass of cloud liquid and ice, and generally finding negative cloud opacity feedbacks, albeit of widely differing strengths. The report concluded that it was not possible at that time to judge the sign of the net cloud feedback.
    TAR 2001 …the sign of [the cloud] feedback remains unknown.
    AR4 2007 it is not yet possible to assess which of the model estimates of cloud feedback is the most reliable
    AR5 “The sign of the net radiative feedback due to all cloud types is…likely positive”
    BUT Cloud opacity feedback “is highly uncertain”

    The article overview states
    “Averaged globally and annually, clouds cause 18W/m2 of cooling relative to a hypothetical cloud-free Earth. This is the net result of a 46 W/m2 cooling from reflecting sunlight back to space (an albedo effect) partly offset by a 28 W/m2 heating due to reduced terrestrial radiation emitted to space (a greenhouse effect). The net planetary cooling provided by clouds is roughly five times as large as the planetary heating from a doubling of CO2.”
    The albedo effect works only half the time [there is a minuscule effect for moonlight etc] yet it produces much more cooling in that 12 hour period than a whole 24 hours of cloud GH positive effect.

    “The overall cloud feedback is actually the aggregate effect of several individual cloud feedbacks, commonly separated into three components: cloud amount, cloud altitude,and cloud opacity feedbacks” “Nearly all current climate models simulate an overall positive cloud feedback ”

    Too much information. The link I had from Victor Venema has gone down but the article could have said Cloud Albedo negative effect had x5 the effect of GHG doubling. That observational was very weak and most of the proof came from climate model simulations which duh incorporate positive cloud feedbacks in the first place.

    To the amateur eye if going from no clouds to what we have causes 18 W/m2 cooling any further cloud increase should cause more cooling.
    Miraculously this article has found a new physical fact on model evidence. That clouds cool the earth as it goes to a surface temp of 14 degrees and then at that precise point start to warm the atmosphere up.
    Not on the basics of testable physics.
    I do not see a kettle of water cooling down as you get past a certain point in heating it up.
    But on the basis of models, observationally wrong and incorporating the very features the claim to be looking for.
    Science, shame.

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