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Thread: Would a warmer global temperatures incease cloud cover?

  1. #1 Would a warmer global temperatures incease cloud cover? 
    Forum Cosmic Wizard icewendigo's Avatar
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    Would a warmer global temperatures incease cloud cover?

    In other words, would more water around the globe be in conditions that foster greater/more frequent evaporation and formation of clouds?

    And if so, what effect does an increase in cloud cover has? Does it reduce temperatures on the gound(less sunlight) or trap more heat in a Green house like effect?


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  3. #2  
    WYSIWYG Moderator marnixR's Avatar
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    more cloud cover means less sunlight coming on the day side, and less heat escaping on the night side
    what the effect on the overall balance is, i don't know


    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Water vapor is considered a green house gas.

    Hawaii is an interesting place to experience this situation it's climate is modified in interesting ways due to clouds. Being close to the equator and having a mountain around makes for some interesting weather.

    I guess it would depend on how much water vapor was in the form of clouds. Based on what I read recently water vapor is a feedback loop for measuring CO2 levels but in and of itself it is not in high enough quantanties in our atmosphere to raise temperatures.

    MB ...
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    Reptile Dysfunction drowsy turtle's Avatar
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    Clouds are droplets of water vapour, or grains of ice/snow, not water vapour. Water vapour is a greenhouse gas, but clouds serve to cool the atmosphere by absorbing and re-radiating infrared radiation, largely back into space. This is why there is apparantly little concern over global warming due to water vapour.


    (the following is at least in part my own speculation, and not necessarily supported)
    Cloud cover does indeed cause an overall reduction in atmospheric temperature, which in turn causes the clouds to be lost as precipitation, following which temperatures rise again. Because of this, we might expect some natural fluctuations in temperature over the short-term as on average temperatures rise, but overall there is a trend of heating.
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  6. #5  
    Veracity Vigilante inow's Avatar
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    Also, water vapor doesn't remain in clouds for centuries (like CO2 does). Water vapor only remains in the atmosphere for 10-14 days, when it then comes down to the ground in a phenomenon scientists like to call "rain." 8)
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  7. #6  
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    iNow

    That is a somewhat facetious comment. Sure clouds produce rain. However, clouds also keep reforming. The more clouds, the more the surface of the planet is cooled. The warmer the planet, the more water vapour, which should translate into more clouds, which is a cooling effect.

    We tend to get bombarded with reports of positive feed-back mechanisms which are alarmist. Negative feed-back mechanisms, like this one, get under-reported, which is a form of academic dishonesty.

    A balanced view will look at both. The problem is that the whole global warming issue has become politicised. This leads to distortions of what should be clear cut scientific findings. Sadly, the issue has become muddied.

    Another example recently is the idea that most of the glaciers in the Himalayas will be gone by 2035. This was officially reported as a finding by the IPCC, and turns out to be a load of crap. A recent New Scientist issue reports that they were the first to report this figure, and the magazine cried 'mea culpa!' They got this as an unsupported estimate by an Indian scientist - never peer reviewed. IPCC seems somehow to have picked up the figure from the New Scientist report and made it an official finding.

    While global warming is real, it is very sad that good science gets hijacked by political activists and turned into something less than reliable. When even the IPCC cannot be trusted, where do we turn?
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  8. #7  
    Forum Isotope Bunbury's Avatar
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    It seems reasonable to assume that cloud formation is related to relative humidity. The closer to saturation the air is in a local area, the more likely it is that clouds will form. Since average relative humidity does not appear to change with temperature I would expect that rising temperatures should not produce increased cloudiness. I don't think the constancy of RH is well understood. It's an empirical observation that scientists are still trying to justify from theory, and an acknowledged risk to assume that empirical observations within a fairly narrow range can safely be extrapolated when the physics isn't understood.

    The effect of clouds is not obviously or simply a cooling effect. High level and low level clouds have opposite effects and if cloudiness were to increase for any reason the warming or cooling effect would depend on where those clouds formed as well as what type of clouds they were.
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  9. #8 Re: Would a warmer global temperatures incease cloud cover? 
    Time Lord
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    Quote Originally Posted by icewendigo
    Would a warmer global temperatures incease cloud cover?
    Yes, it should for two reasons comprising a negative feedback that should balance temperature:

    1) Heated water evaporates, producing atmospheric vapour.

    2) Heated land becomes arid, producing cloud condensate nuclei AKA cloud seeds.

    You need both to form clouds. Overall, clouds cool the Earth. Thin, high altitude clouds admit much sunlight but trap infrared radiation - a greenhouse effect. Dense low altitude clouds however reflect radiation so well they absolutely rule Earth's albedo. So while it is true that clouds in one example cause some warming, the net cooling effect times worldwide ubiquity of cloudy weather overwhelms that. Clouds counteract global warming. This is maddening to climate models because clouds, as inow pointed out, are weather not climate.

    I said warming "should" increase cloud cover because it is possible to suppress one ingredient of the cloud recipe, then no surplus of the second can form clouds on its own. Review human history's two great impressions upon the Earth:

    1) Production of various aerosols through combustion of one kind or another. Most palpably that was soot, a cloud-seeding aerosol. Such CCNs embody our traditional concept of air pollution. Mixed with humid air the particulates of man-made smoke condense water droplets into clouds - white fluffy clouds incredibly. You've surely seen how jet trails grow clouds. The effect is less stark but far greater at lower altitudes, downwind of polluting industry and even from the smoke of war. This anthropic factor can be fickle as the weather. We can and do crank it up and down at will. Since about 1970 we've worked hard to reduce this air pollution.

    2) The second great impression is agriculture, which we can't control. If pollution is anthropic weather, agriculture is anthropic climate. This is our visible footprint seen from space. Climate-wise, agriculture sequesters arid lands that would naturally provide negative warming feedback by production of windblown aerosols during drought years. Now regardless of warming we suppress dust with cover crops and irrigation, which also evapourates yet more water into the air.

    So to re-enable the balance we must either return agricultural lands to natural feedbacks, or produce/allow equivalent CCNs to compensate as we "green" the Earth. The former we can't do, or we starve. The latter flies against traditional belief that dust and smoke is bad for the environment.


    That's not the whole story, but I think it's a good outline of the climate change plot and main characters, and suggests a climax. In this story, the brave men and women fighting forest fires, and the innocent child watering a seed in the desert, are the antagonists!
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  10. #9 Re: Would a warmer global temperatures incease cloud cover? 
    Forum Isotope Bunbury's Avatar
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    Quote Originally Posted by Pong
    1) Heated water evaporates, producing atmospheric vapour.
    But as already said the RH remains constant. This is both an empirical observation and an output from climate models.

    From RC's Q&A section:
    Do models assume a constant relative humidity?

    No. Relative humidity is a diagnostic of the models’ temperature and water distribution and will vary according to the dynamics, convection etc. However, many processes that remove water from the atmosphere (i.e. cloud formation and rainfall) have a clear functional dependence on the relative humidity rather than the total amount of water (i.e. clouds form when air parcels are saturated at their local temperature, not when humidity reaches X g/m3). These leads to the phenomenon observed in the models and the real world that long-term mean relative humidity is pretty stable.
    However I'm a little troubled to also read this from NASA:

    In climate modeling, scientists have assumed that the relative humidity of the atmosphere will stay the same regardless of how the climate changes.
    So is constant RH an input or an output of climate models? Seems like a fairly significant disagreement here.

    2) Heated land becomes arid,
    Is dust from desertified land the right size for nucleation? I recall vaguely that cloud nucleation sites tend to be much smaller, and typically consist of microscopic particles such as salt crystals from the oceans. But I haven't checked.

    This from RC addresses the issue of whether clouds are a positive or negative feedback:

    In general, models suggest that they are a positive feedback – i.e. there is a relative increase in high clouds (which warm more than they cool) compared to low clouds (which cool more than they warm) – but this is quite variable among models and not very well constrained from data.
    So, although the science isn't robust, the assumption that clouds have an overall cooling effect is dubious.
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  11. #10 Re: Would a warmer global temperatures incease cloud cover? 
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    Quote Originally Posted by icewendigo
    Would a warmer global temperatures incease cloud cover?

    In other words, would more water around the globe be in conditions that foster greater/more frequent evaporation and formation of clouds?

    And if so, what effect does an increase in cloud cover has? Does it reduce temperatures on the gound(less sunlight) or trap more heat in a Green house like effect?
    I think it does. I never researched the finer points, but the theory/hypothisis sounds good to me. I read what I thought was a pretty good theory not long ago. From what I remember, it in essence went that there are two stable ranges for global temperatures. On is the ice age temperatures ranges, and the other current (last few thousand years) temperature ranges. Temperature ranges swing between one set of values to the other.

    Clouds are a primary reason for the warmer ranges staying +/- 2 C of average. The warmer we get, weather due to solar, gasses, etc, cloud cover increases and acts as a negative feedback, never allowing for a thermal runaway. Cooler temperatures cause less humidity, less clouds, and more solar radiation makes it to the surface and lower atmosphere. If you look at the various records, we have stayed withing +/- 2 C regardless of volcanic, solar, and greenhouse gas ranges.
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  12. #11  
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    This article discusse recent findings:

    Now, Amy Clement and Robert Burgman of the University of Miami and Joel Norris of the University of California-San Diego have done a statistical analysis of 55 years of cloud cover and temperature observations for the north-eastern Pacific Ocean. Their study provides the best evidence yet that low-level cloud cover decreases as temperature increases — that the feedback mechanism is positive.
    http://physicsworld.com/cws/article/news/39908
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  13. #12 Re: Would a warmer global temperatures incease cloud cover? 
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    Quote Originally Posted by Bunbury
    Is dust from desertified land the right size for nucleation? I recall vaguely that cloud nucleation sites tend to be much smaller, and typically consist of microscopic particles such as salt crystals from the oceans. But I haven't checked.
    Yes, this is why the North Pacific is relatively cloudy. You have the world's largest aerosol generator (Asia) blowing over the world's largest moisture generator (Pacific ocean). The large particles settle (notoriously around Japan - you must know about the dust masks and rich fishery), but the smaller CCNs diffuse and eventually entrain with moist Pacific air.

    Last year's dust storm in Eastern Washington State:

    Most of that crap falls out within hours. But notice some of it rises and even in this short timeframe begins to collect moisture. This lighter component diffuses and spreads much farther than the muddy rain locally reported that evening.

    What I most wished to illustrate with that image is where the dust isn't blowing from. Agriculture works to retain fertile (dusty/muddy/decomposing) topsoil with cover crops and irrigation. If nature had her way, large areas of the North American plains would have returned to dustbowl by now.

    Central Asia produces increasing volumes of fine particles, because the historic lakes and marshes are disappearing. The dried bottom of a lake has a lot of dust in it! The Asian steppes are naturally becoming desert. That's a negative feedback. That's not exactly "green" but it's good. This change has been progressing since the ice-age.

    Here's where moist air meets dry, shot west of San Fransisco:


    The streams are tracks from ships not jets. The ships mostly cough up dark diesel smoke. The scale reads 25km by the way, so just one ship lays cloud comparable to the dust storm of our first image!

    Sorry Bunbury I think that study you linked is garbage-in-garbage-out. It studied "the perfect laboratory" of historic north-eastern Pacific Ocean shipping lanes - and that picture above makes plain that ship-based observation must yield bad data. It concluded that because over 50 years cloud cover decreased while temperatures rose, absence of cloud is "positive" feedback. I'd argue cloud coverage is broken negative feedback throughout the period studied. But i guess that's just a different way of looking at feedbacks. If the climate naturally balances, than the major forces must ultimately work as negative not positive feedbacks.

    Dry and moist, clean and dusty air masses interacting over China and Sea of Japan:


    What we don't see in those above images are the everyday particles drifting up from land and sea. They comprise the real bulk in our atmosphere. Their ejection also depends on weather or anthropic action.



    A significant volume of CCN not mentioned before comes from the ocean-atmosphere interface. This is blown salt and bits of decomposed plankton. It's as fickle as weather. Winds mechanically whip it up from the water. This one's really hard to model because it depends on surface effects just molecules thick. Where the ocean bears an oil film - typically a few molecules thick - moderate wind is ineffectual. Oily water behaves quite differently. Where I live anyway the oil film is patchy and dynamic, mostly generated by marine life. For example the salmon and oolichan runs result in local waters slicked by oil from decomposing fish. I would guess that plankton blooms do the same. This suggests that warming promotes surface film, which prevents aerosol ejection to the atmosphere, so less low level clouds and more warming - a positive feedback. But I dunno its pretty complex! So many disciplines end and fail to meet in the fickle molecular ocean-atmosphere interface.

    I guess one could generalize that because warming promotes growth of ocean interface barrier, warming reduces all kinds of atmosphere-ocean exchange. Conversely warming over land destroys the land-atmosphere interface barrier (surface moisture and vegetation). I wonder, if these tend to be true/false conditions, it might help explain what Wild Cobra said about the climate having two preferred states. Dust falling in oceans is known to drive extreme marine blooms, which would be a real positive warming feedback i.e. runaway.
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  14. #13  
    Forum Radioactive Isotope skeptic's Avatar
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    Actually, dust falling into oceans is negative feed-back. Research has shown a couple of interesting things about dust.

    1. Dust layers in glacial ice cores shows that a lot of dust correlates with cooling climate.

    2. Dust contains iron, and it is the iron that stimulates phytoplankton growth. Lots of dust falling on the ocean = lots of iron as fertiliser = lots of phytoplankton growth. This was demonstrated recently, when a lot of red iron-rich dust from the Australian desert blew over the Pacific, and higher chlorophyll levels were subsequently seen using satellites.

    3. Phytoplankton blooms correlate with more low cloud formation, which means cooling. This appears to be the result of volatile organic compound produced by phytoplankton that act as cloud nucleation sites.

    4. Phytoplankton are very efficient sequesters of CO2. Thus extra phytoplankton growth reduces CO2 in the air and this trends towards atmospheric cooling.

    So if global warming results in more dust, that becomes a negative feed-back.
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  15. #14  
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    So may I kiss you then for corroborating my basic thesis that agriculture broke a natural balancing feedback?
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  16. #15 Re: Would a warmer global temperatures incease cloud cover? 
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    Quote Originally Posted by Pong
    Sorry Bunbury I think that study you linked is garbage-in-garbage-out.
    No need to apologize. I merely posted it as reference to some recent research and have no personal vesting in it. However as to its usefulness I'll take the Hadley Centre fellow's opinion that it "sheds significant light on the role of clouds" over yours that it's "garbage" if that's OK with you.

    It concluded that because over 50 years cloud cover decreased while temperatures rose, absence of cloud is "positive" feedback.
    No, it did not say that. It said that as temperatures rise water vapor rises higher in the atmosphere and forms high level clouds at the expense of low level clouds, and since high level clouds are warming the net effect is a positive feedback, i.e. more warming. I think I've mentioned this three times now in this thread. Is it that difficult to grasp?
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  17. #16  
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    Maybe I just gotta apologize more. The methodology sucks IMHO. They took 50 years of admittedly sketchy ship-based observation, and "removed errors" until it matched recent satellite observations. Then they hunted for supporting climate model and found just one single model not contradicting this decrease in cloud cover. That model, among other predictions, has CO2 increase dissipating low altitude clouds. So according to the lucky model CO2 and warming and loss of low altitude cloud comprise a "vicious cycle". Seems like echo-chamber to me. I mean, they may be kinda right, but they got there by artifice.

    EDIT: Never mind my criticism. It's useless either way.
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  18. #17  
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    Quote Originally Posted by skeptic
    iNow

    That is a somewhat facetious comment. Sure clouds produce rain. However, clouds also keep reforming. The more clouds, the more the surface of the planet is cooled. The warmer the planet, the more water vapour, which should translate into more clouds, which is a cooling effect.
    Not necessarily. Firstly the water vapor is still limited by the amount available to evaporate. Over the land there might be a net drying and less water available as things warm up.
    Next is the vertical distribution of temperature change. Since the lower atmosphere warms the most as we add green house gases, this will probably make the atmosphere less stable. A less stable atmospheric means more convective clouds which tend to take up less horizontal area than stratiform cloud forms of more a stable atmosphere.

    We tend to get bombarded with reports of positive feed-back mechanisms which are alarmist. Negative feed-back mechanisms, like this one, get under-reported, which is a form of academic dishonesty.

    A balanced view will look at both.
    And as reported in the media it's often far more complex than they are willing to try to explain to the public. But consider this for example. Increased clouds during a polar winter would obvious limit cooling and hence be a net warming. The same thing in more temperature regions with sunlight would create a net cooling at the surface.

    The problem is that the whole global warming issue has become politicised.
    Along with the media too lazy and a public too ignorant of the scientific method to tell the difference.
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  19. #18  
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    No, that's not what they did.

    They removed errors from historical records. To know how they did this and if it was legitimate we would need to read the original paper, which of course would cost money. To assume they fixed the data to meet preconceived ideas, which is what you are at least implying, is cynical and unwarranted.

    Having removed the errors they compared cloud data from sailors' observations aboard ships with satellite reports and found surprisingly good agreement.

    They correlated their cloud data with temperature data and compared results with predictions from climate models. They found that only the Hadley Centre's model from the UK Met Office came close to predicting the observational results. This suggests that the other models need improving in this area.

    I would guess that the other modelers have tweaked the cloud simulations in their models privately, but will probably not revise the public domain versions until there is further corroboration.

    Now the article I linked to was just one piece of recent research supporting the theory that clouds are a positive feedback. This does appear to be the prevailing theory although it's in need of more evidence. This is my only reason for being in this thread - to point out that the common perception that clouds are a negative feed back is probably, but not definitely, wrong. This seems to zoom right over the heads of various posters.
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  20. #19  
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    Lynx

    There is no shortage of water to form clouds. Ever heard of oceans?

    If more clouds form over oceans, they will rain when blown over land and gain altitude. This puts more water on land - some of which evaporates to form more clouds. etc.

    Bunbury.

    Yes, you posted some valid evidence. I trust you realise that it is just evidence, and the whole story is yet incomplete. Climatologists still have not worked out the full story of cloud formation and its impact on climate change.

    There is no doubt that low clouds are net cooling. High clouds may be net warming, but the total picture is not yet in.

    There is no doubt that global warming is real, and that anthropogenic causes dominate this warming. However, we are kidding ourselves if we think that it is all understood. Ditto for accepting computer models as infallible predictors of the future.
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  21. #20  
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    Quote Originally Posted by skeptic
    you posted some valid evidence. I trust you realise that it is just evidence, and the whole story is yet incomplete.
    For goodness sake, do you ever read what I write:

    "This does appear to be the prevailing theory although it's in need of more evidence."

    "So, although the science isn't robust, the assumption that clouds have an overall cooling effect is dubious."

    "It's...an acknowledged risk to assume that empirical observations within a fairly narrow range can safely be extrapolated when the physics isn't understood."

    Whereas you write:

    "The more clouds, the more the surface of the planet is cooled."

    Tell me, who is the skeptic?
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  22. #21  
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    Quote Originally Posted by Bunbury
    the common perception that clouds are a negative feed back is probably, but not definitely, wrong. This seems to zoom right over the heads of various posters.
    Yet climate must be dominated by negative feedbacks, 'else it would have self-destructed.

    I guess you could call a few things in isolation positive feedback, while in a larger picture they are part of negative feedback.
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  23. #22  
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    Quote Originally Posted by skeptic
    Lynx

    There is no shortage of water to form clouds. Ever heard of oceans?

    If more clouds form over oceans, they will rain when blown over land and gain altitude. This puts more water on land - some of which evaporates to form more clouds. etc.

    Bunbury.

    Yes, you posted some valid evidence. I trust you realise that it is just evidence, and the whole story is yet incomplete. Climatologists still have not worked out the full story of cloud formation and its impact on climate change.

    There is no doubt that low clouds are net cooling. High clouds may be net warming, but the total picture is not yet in.

    There is no doubt that global warming is real, and that anthropogenic causes dominate this warming. However, we are kidding ourselves if we think that it is all understood. Ditto for accepting computer models as infallible predictors of the future.
    Actually there is a great deal of doubt as to what percentage humans impact global warming trends. The current consensus seems to have it at 10-50% of the recent warming trend.
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  24. #23  
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    Quote Originally Posted by Pong
    Quote Originally Posted by Bunbury
    the common perception that clouds are a negative feed back is probably, but not definitely, wrong. This seems to zoom right over the heads of various posters.
    Yet climate must be dominated by negative feedbacks, 'else it would have self-destructed.

    I guess you could call a few things in isolation positive feedback, while in a larger picture they are part of negative feedback.
    Agreed. The idea that clouds on the whole increase global temperatures is not supported by physical principles. We know for a fact that clouds reflect far more solar energy back into space than is trapped by radiative forcing.
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  25. #24  
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    Clouds can be positive or negative influences on warming, depending on altitude. Low clouds are cooling. High clouds are warming.

    Current research into long term impact of cloud formation on climate change is preliminary. I will maintain my skepticism of positive feed-back for now.

    However, if the ongoing research shows that warming causes more high clouds, and hence is a positive feed-back, then I will be forced to admit that is reality. There is a lot more work to do, though, before that conclusion is forced upon us.
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  26. #25  
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    Quote Originally Posted by skeptic
    Clouds can be positive or negative influences on warming, depending on altitude. Low clouds are cooling. High clouds are warming.

    Current research into long term impact of cloud formation on climate change is preliminary. I will maintain my skepticism of positive feed-back for now.

    However, if the ongoing research shows that warming causes more high clouds, and hence is a positive feed-back, then I will be forced to admit that is reality. There is a lot more work to do, though, before that conclusion is forced upon us.
    Thank you for finally taking a skeptical position.
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  27. #26  
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    Quote Originally Posted by skeptic
    Lynx

    There is no shortage of water to form clouds. Ever heard of oceans?

    If more clouds form over oceans, they will rain when blown over land and gain altitude. This puts more water on land - some of which evaporates to form more clouds. etc.
    As your own post illustrates once you get away from land the available surface moisture has a lot to do with how much evaporates. Even near the coast this is the case, for example in Florida, which is a peninsular, gets as much as a 3rd of it's rainfall from the surface based evaporation of it's wet surface. The flood control, agriculuture and other other projects that have reduced the wetlands have had a measureable decrease on both summer rainfall amounts and reduced the number of thunderstorms.

    In other case, such as where subsidence prevails, even an ocean isn't enough to change the atmosphere. For example, I'm less than 50 miles from the very warm Arabian gulf, but living in a desert, because of the subtropical vertical descent (subsidence) common to the latitude I'm at.

    Clouds can be positive or negative influences on warming, depending on altitude. Low clouds are cooling. High clouds are warming.
    Quite right, but it also depends on vertical temperature gradient, available sunlight, available moisture, net large scale vertical motion and other factors.

    There's no cookie cutter solution that applies to the entire globe, and much like "average temperature increase," relatively meaningless without also understanding the underlying reasons and conditions that vary from region to region due to circumstance.
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