Arguments
What is the net feedback from clouds?
What the science says...
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Evidence is building that net cloud feedback is likely positive and unlikely to be strongly negative. |
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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.
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
[DB] Sphaerica quite well understands both positive and negative feedbacks, including those "net" ones.
[DB] Actually, skywatcher's questions to you are both germane and on-topic. You are clearly being evasive and avoiding answering questions for which you have no substantive answer.
[DB] RW1 is clearly trolling now. His comments will be treated as such until he can offer up substantive dialogue supported by more than mere opinion and hand-waving. This has become tiresome.
For starters, the positive feedback effect of melting ice from that of leaving maximum ice cannot be equated to that of minimum ice where the climate is now (and is during every interglacial period). There just isn’t much ice left, and what is left would be very hard to melt, as most of it is located at high latitudes around the poles which are mostly dark 6 months out of the year with way below freezing temperatures. A lot of the ice is thousands of feet above sea level too where the air is significantly colder. Unless you wait a few 10s of millions of years for plate tectonics to move Antarctica and Greenland to lower latitudes (if they are even moving in that direction), no significant amount of ice is going to melt from just a few degrees rise in global average temperature. Furthermore, the high ‘sensitivity’ from glacial to interglacial is largely driven by the change in the orbit relative to the Sun, which changes the distribution of incident solar energy into the system quite dramatically (more energy is distributed to the higher latitudes in the NH summer, in particular). This combined with positive feedback effect of melting surface ice is enough to overcome the net negative feedback and cause the 5-6 C rise. The roughly +7 W/m^2 or so increase from the Sun is a minor contributor to the whole thing. We are also relatively close to the end of this interglacial period, so if anything the orbital component has already flipped back in the direction of glaciation and cooling.[DB] Now you post gibberish. It has become etremely evident that you are here simply to be argumentative, and that you simply do not have a background sufficient to realize that most of what you write above is, to put it delicately, "crap".
Please make a considered effort to ensure what you write is consistent with the known physics of climate change; your persistence in forcing physics to contort to your electronics-based interpretation of things is admirable, but misguided.
Shorter admonition: less posting, more studying.
A general note to the lay reader: RW1 has a long history here of having these exact type of interactions on many previous threads. He promulgates the same basic arguments which are promptly shown to have the same basic misunderstandings. Not liking the answers, he has even taken the propositions to other websites like Real Climate, where he was given the same answers, to which he expressed similar reluctance in believing. Let the reader beware.
[DB] "Now you're at least asking some good questions."
Actually, all parties have presented you with good questions. If you are going to participate in the dialogue here, it is incumbent upon you to formulate good answers to those questions.
[DB] Welcome to Skeptical Science! There is an immense amount of reference material discussed here and it can be a bit difficult at first to find an answer to your questions. That's why we recommend that Newcomers, Start Here and then learn The Big Picture.
I also recommend watching this video on why CO2 is the biggest climate control knob in Earth's history.
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"These effects may not have already been considered in the models."
Please use the search function to find a page on models. Likely any question you may have on climate science has already been addressed on one of the 4,700+ pages here. Thus, the search function is your friend; use it and the coppers of your pocket [your questions]...and it will line your mind with gold.
If clouds feedback were positive, we would expect:
Infinite warming, until oceans become dry.
It never has occurred in the past, even with a warmer earth.
IPCC's Climatologists should say:
We don't know everything about clouds. We need study a lot to understand the entire process. When we are sure, we are explaining step by step, showing with controlled laboratorial experiments, and calculation memory. When we can explain in details how to trigger an ice age, and an interglaciation era, we are ready to define positive or negative feedback for clouds. By now, we are closing our mouth about global warming or cooling.
Licorj - See Does positive feedback necessarily mean runaway warming. That would only be true with a feedback gain >1, which means that any increase would have an infinite effect. In reality, the law of diminshing returns means that feedbacks of a physical scale are of gain <1, with the total change in temperature being:
Total T = ΔT / (1-g)
and with the positive feedbacks providing a limited scale of amplification for any temperature change. For the current sensitivity estimate of ~3C per doubling of CO2, with an initial ΔT of ~1.1C, the gain 'g' is about 0.63.
Now as to clouds, if you have actually read the opening post (I suspect you have not), clouds are estimated to have a small positive (amplifying) contribution to the total sensitivity.
Dear KR,
First, thank you by attention, even after long time past from publication of this post. I just have realized it, after my post was sent.
I have read the post, and a lot of very interesting comments. "Clouds are estimated be small positive feedback". Ok. Estimated to be, but could be estimated to not to be... It is a game.
Excuse me by error on "INFINITE WARMING". It is clear that is not possible, otherwise, we would have free energy generation.
Backing to the clouds: I believe, of course, with less scientific based knowledge than you, that the choice on small positive feedback for cloud, taken by climate scientists was just a choice, with high level of uncertainty. So high, that choice would be NEUTRAL, or small negative feedback. In order to get the true cloud feedback, it would be need a lot of measures taken around the world, on entire troposphere, entire world, during long time. Of course it is very expensive and hard to do, maybe impossible.
Even assuming my mistake on INIFINITE WARMING, I still believe that oceans would be expected to dry, because of positive feedback, in any level.
Other expected result from feedbacks for, aerossols, cloud, water vapor, CO2, CH4, etc, would be the accuracy of models on recreating paste climates. They are all wrong, on this task. Somethings are very wron with them, and nedd to be fixed, before can tell us how will be the climate after 100 years from present day.
Why we see tomorrow's weather forecasts, and believe on it ?
Because they are correct on vaste majority of times. It is not the same case for climate models, at least, untill now.
But, this is off-topic.
[JH] Since you have provided absolutely no specific evidence to substantiate your sweeping assertions about global climate models, your assertions are merely your opinion - which carries virtually no weight on this site.
If you post similar comments in the future, they will be summarily dismissed for violating the SkS Comments Policy re sloganeering.
Please read the SkS Comments Policy and adhere to it.