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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.


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.

Dessler (2010) 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

This rebuttal was updated by Kyle Pressler in September 2021 to replace broken links. The updates are a result of our call for help published in May 2021.

Last updated on 25 July 2017 by skeptickev. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

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Comments 251 to 261 out of 261:

  1. Licorj - I would suggest following the links in the opening post; there is considerable evidence for a small positive cloud feedback based on observations, on constraints from other forcings and feedbacks, from paleo evidence, etc. 

    Not a "game", not a guess - a small positive feedback comes from the best estimates of the various evidence available. 

  2. Licorj @250, by "estimate", it is meant estimate based on empirical observations and predictions from models.  Both, separately, suggest that a small positive cloud feedback is more likely than not.  The uncertainty is large so that negative feedbacks are not excluded, but neither are large positive feedbacks excluded.  

    You say that to get the true cloud feedback, we need lots of measurements around the world.  Those measurements have been done.  Three examples of such measurements are linked to in the OP.  Unfortunately the measurements do not tightly constrain the result because the feedback is complicated and the observational data is noisy.

    Of course, it is always possible to avoid the whole issue by looking at empirical estimates of the net feedback from historical and paleo data.  These overwhelmingly suggest a large net positive feedback.  As these are estimates based on what has actually occured on the Earth, they of necessity include all feedbacks.  Therefore, if the cloud feedback does in fact turn out to be negative, that merely means that some other combination of feedbacks is more strongly positive than currenly estimated.

  3. On Safari, the final link to the Steven Sherwood video is broken. There appears to be a leading '/' that shouldn't be there.

  4. Speaking of clouds and manmade climate change, here’s a handy reference document recently published by the WMO…

    Humanity has a primordial fascination with clouds. The meteorological and hydrological communities have come to understand through decades of observation and research that cloud processes – from the microphysics of initial nucleation to superstorms viewed from satellites – provide vital information for weather prediction, and for precipitation in particular. Looking at clouds from a climate perspective introduces new and difficult questions that challenge our overall assumptions about how our moist, cloudy atmosphere actually works.

    Clouds are one of the main modulators of heating in the atmosphere, controlling many other aspects of the climate system. Thus, “Clouds, Circulation and Climate Sensitivity” is one of the World Climate Research Programmes (WCRP) seven Grand Challenges. These Grand Challenges represent areas of emphasis in scientific research, modelling, analysis and observations for WCRP and its affiliate projects in the coming decade.

    Understanding Clouds to Anticipate Future Climate by Sandrine Bony, Bjorn Stevens & David Carlson, Bulletin nº Vol 66 (1) – 2017

  5. Interesting paper finds "surprising" results from CERES with a negative trend of Earth Energy Imbalance as well as a negative trend of Ocean Heat Content Time Derivative :

    "Decadal Changes of the Reflected Solar Radiation and the Earth Energy Imbalance" by Dewitte , Clerbaux and Cornelis.

    Abstract: Decadal changes of the Reflected Solar Radiation (RSR) as measured by CERES from 2000 to 2018 are analysed. For both polar regions, changes of the clear-sky RSR correlate well with changes of the Sea Ice Extent. In the Arctic, sea ice is clearly melting, and as a result the earth is becoming darker under clear-sky conditions. However, the correlation between the global all-sky RSR and the polar clear-sky RSR changes is low. Moreover, the RSR and the Outgoing Longwave Radiation (OLR) changes are negatively correlated, so they partly cancel each other. The increase of the OLR is higher then the decrease of the RSR. Also the incoming solar radiation is decreasing. As a result, over the 2000–2018 period the Earth Energy Imbalance (EEI) appears to have a downward trend of −0.16 ± 0.11 W/m2dec. The EEI trend agrees with a trend of the Ocean Heat Content Time Derivative of −0.26 ± 0.06 (1 σ) W/m2dec.


    "The Earth Energy Imbalance (EEI) shows a trend of −0.16 ± 0.11 W/m2dec. The decreasing trend in EEI is in agreement with a decreasing trend of −0.26 ± 0.06 W/m2dec in the Ocean Heat Content Time Derivative (OHCTD) after 2000.
    The OHCTD over the period 1960–2015 shows three different regimes, with low OHCTD prior to 1982, rising OHCTD from 1982 to 2000, and decreasing OHCTD since 2000. These OHCTD periods correspond to periods of slow/rapid/slow surface temperature rise [16,17], to periods of strong La Ninas/El Ninos/La Ninas [14,18], and to periods of increasing/decreasing/increasing aerosol loading [19,20]. " curve: running yearly mean EEI. Green line: linear fit to running yearly mean EEI. Blue curve: 10 year running mean OHCTD. Orange curve: piecewise linear fit to OHCTD.

  6. Hefaistos @255 ,

    please comment on the Dewitte et al., 2019  paper you cite.

    My first impression of the EEI graph is (ignoring error bars) that it's very noisy.

  7. To this layman, a new report (Saint‐Lu et al 2020) seems to support Lindzen's "Iris effect" (that high cloud cover in the tropics diminish with increased temperature), but at the same time finds that high clouds have a neutral effect on global warming:

  8. Quick question on cloud feedbacks in particular and other feedbacks in particular. If every feedback we have is positive, and we know that way back in time CO2 was 30* current levels, wouldn't the earth have had runaway warming? Doesn't the fact that it didn't mean that some of the feedbacks must be negative, and indeed dominate in higher temperature regimes? What are the explanations for why 600-400 mya, there wasn't runaway warming? Was it the tilt of the earth, the sun, or some other astronomical feature that was very different, or was it a not yet understood feedback? Thanks

  9. Some feedbacks are negative, some are positive. So long as the total sum of all feedbacks is less than 1 in either direction, there can be no runaway warming or freezing. There is plenty of info on that from a variety of sources:

  10. sunnyx @258,

    The level of CO2 in the atmosphere during the early Earth is usually assumed to be very high because the sun was a lot weaker (it has been brightening by something like 5% every billion years) and we know from rocks that there was liquid water so the Earth could not have been very cold. For the period back to 500My the CO2 level can be assessed from proxy data and also modelled. This shows CO2 was a lot higher than today for most of the last 500My. The impact on the climate is a matter of how many doublings of CO2. So three or four doublings would suggest a climate something like 10ºC-13ºC warmer. But the loss of 2½% of solar heating with the weaker sun back 500My would equal perhaps two of those CO2 doublings. So much of the climate forcing of the additional CO2 was negated by there being a cooler sun.

    Changes in climate result from the feedbacks as well as the CO2/solar forcing and will not have chaned greatly. But the net feedback would have to be large to have caused a runaway warming. Imagine ECS=3ºC. That is the net feedback (the sum of positive and negative) result in trebling the temperature increase initially caused by the CO2. But that is all you get - a trebling. It would take a stonger net feedback to become runaway (actually 50% stronger).

    (The ECS=3ºC is a compound result in that the warming of the feedback itself induces feedbacks. The trebling of ECS=3ºC is equivalent to a simple feedback of 0.67. As Philippe Chantreau @259 says, the magic number to achieve runaway is 1.0, an increase on 0.67 of 50%.)

    I hope that makes sense for you.

  11. CRE / cloud radiative effect (-19Wm-2)


    ...please do not confuse with

    CRF / cloud radiative feedback (+0,42Wm-2 °C-1)                      page 74


    [BL] Links activated.

    The web software here does not automatically create links. You can do this when posting a comment by selecting the "insert" tab, selecting the text you want to use for the link, and clicking on the icon that looks like a chain link. Add the URL in the dialog box.

    Pleas also note that the Comments Policy here discourages pasting just links or images:

    No link or picture only. Any link or picture should be accompanied by text summarizing both the content of the link or picture, and showing how it is relevant to the topic of discussion. Failure to do both of these things will result in the comment being considered off topic.

    If you have a point to make, please state it, and make sure that it is on topic for the discussion.


  12. Being a layman, it seems to me that the normal water cycle cools the surface through conduction and evaporation. That energy is eventually released to the upper atmosphere through convection and condensation of cloud formation. Low warm clouds in turn will block more radiation from the sun keeping the ground cooler, negative feedback: Johannes Mulmenstadt et al 6/3/2021 paper.
    "As the atmosphere warms, part of the cloud population shifts from ice and mixed-phase (‘cold’) to liquid (‘warm’) clouds. Because warm clouds are more reflective and longer-lived, this phase change reduces the solar flux absorbed by the Earth and constitutes a negative radiative feedback."
    See an article about this paper "Cooling effect of clouds ‘underestimated’ by climate models, says new study"
    This process seems that it would cause self regulation of the temperature of the atmosphere preventing the possibility of the atmosphere from ever overheating and becoming uninhabitable, i.e. runaway warming. Maybe in a repeating cycle such as more co2=>more warming=>More h2o=>more warm cloud cover=>more cooling=>less co2=>less heating=>less h2o=>less warm cloud cover=>more heating=>more co2 and so on. This seems that it could cause long periods of heating and cooling, maybe decades.  Let me know where I'm wrong.
    I always thought it was cooler on cloudy days than sunny days.

  13. Likeitwarm  @26 :

    Yes, it seems cooler on cloudy days than sunny days ~ during daytime.

    But warmer nights, when it is cloudy.

    Overall effect, rather close to neutral.

    The paleo evidence shows no "runaway" , but it does show that the global climate can become very hot indeed.

  14. Likeitwarm:

    The paper by Mulmenstadt et al that you mention was covered in this blog post at Skeptical Science, around the time it first appeared. (SkS reposted the Carbon Brief article.)

    In that post, a key summary is:

    However, the lead author of the study tells Carbon Brief that fixing the “problem” in rainfall simulations “reduces the amount of warming predicted by the model, by about the same amount as the warming increase between CMIP5 and CMIP6”.

    So, the results are not as earth-shattering as you seem to want to imply. Uncertainties in cloud feedback are a well-known part of climate modelling and understanding, and this paper represents one more small step in helping understand the consequences.

    As for your description of the water cycle:

    • A wet surface evaporates more than a dry one. This transfers energy as latent heat into the atmosphere, and reduces the energy transfer as sensible heat (thermal energy). Thus, it priimarily changes the balance in how the energy reaches the atmosphere, not the total.
    • What evaporates evenutally condenses and falls out as precipitation, but it rarely condenses or precipitates over the location it evaporates. Most extra water vapour is transported to other regions, where it falls as precipitation.
      • Oceans receive far less water via precipitation than they lose as evaporation.
      • Land areas (mostly) are the opposite - much more precipitation than evaporation.
    • Increased evapoation does not necessarily lead to increased cloud cover at the evaporation location. Any changes in cloud type, amount, etc., are strongly depndent on when and where and how that cloud eventually forms.
      • This complexiity is why cloud feedbacks are still an area of active study.
      • The current understanding remains that clouds provide neither strong negative or positive feedback.

    As for your discussion of "runaway warming" - nobody is predicting such a result due to CO2, so you are arguing a strawman.

    And as to "self regulation of the temperature of the atmosphere" - the simple fact that climate has changed in many ways, for many reasons, over centuries and millenia is strong evidence that this is not true. Perhaps try reading the "Climate's changed before" post that reponds to our number 1 myth listed in our "Most Used Climate Myths" in the top left sidebar of all our pages.

    I have worked through some darn cold sunny days in winter - much colder than overcast days in summer - to illustrate how incomplete your cloudy/sunny day closing statement is.

  15. Bob Loblaw:

    Thanks for taking the time to point out my mis-understandings. 

    I didn't realize the article had been posted to SkS.  It was news to me.  I should have figured climate hawks like yourself would have read it. My mistake.

    I will keep reading and post any questions I might have.

    Best to you.

  16. Bob Loblaw:

    If there is no prediction of runaway heating, what is all the hub-bub about CO2?

  17. Likeitwarm: what exactly do you mean by "runaway heating"? Unless you are willing to define your term, you are playing word games.

    If CO2 content stabilizes at any point (450, 500, 600ppm, take your pick) then temperature will stablize at some new value (2, 3, 4 or more degrees warmer than it was at 300ppm CO2), and it will not continue to increase indefinitely. It will not "run away". But that new, stable temperature will have plenty of bad consequences.

    Even if we were to manage to burn every gram of fossil fuel we can find, and raise CO2 to 1200ppm or more, we still won't see a perpetually-increasing temperature. No "runaway". A new equilibrium will be found. There is no reason to expect anything like Venus.

    After all, body temperature is only 37C (98.6F), and if you get a fever and your temperature goes up to 41C and stabilizes at that point, you still run a pretty large risk of death. Your body temperature does not need to keep rising more ("runaway") to be a serious problem.

    Unless you have some other (odd) definition of "runaway".

    Should you wish to discuss "runaway greenhouse effect" myths, there are two possible threads here:

    It would be worth your time to read those posts (and possibly the comments) in full.

  18. Likeitwarm,

    The last time that CO2 was 400 ppm (It is currently 419 ppm) the sea level was over 23 meters higher than it is now.  That amount of rise would flood most of the major cities worldwide and inundate a very large fraction of the best farmland in the world.  I could go on with bad effects but those are enough to give any thinking person fits.  I note that sea level rise accelerated rapidly the last ten years and is now over 10 mm per year.   Pray that it goes back down.

  19. Bob Loblaw:

    I just meant warming to a point that causes unacceptable harm to human habitation.  Maybe "runaway" is the wrong term.  Maybe "harmfully warm" would be better.

    I'm just posting what I think to see where I'm right or wrong.  I appreciate your input.  I'm going to withhold posting until I do more reading.

  20. Likeitwarm:

    "Runaway" is very definitely the wrong term for what you are asking.

    You should start by reading the post that shows up as #3 on the list of Most Used Climate Myths (top left side bar of every screen here).

    Maybe go down the list, where you will probably continue to find material for many of the questions you seem to want to ask.

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