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Thread: Greenhouse Theory Question

  1. #1 Greenhouse Theory Question 
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    According to a greenhouse theory I read, visible light reaches earth's surface and is converted to long IR waves. These are absorbed, scattered, or reflected by carbon dioxide and other greenhouse gases, including water vapor. According to the theory, this process warms things up. My question: Why wouldn't the increased humidity and clouds resulting from the warming, block the sun's visible light as it heads for earth, causing less energy to be absorbed by the earth's surface, and cause a cooling process offsetting the warming process?


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  3. #2  
    Reptile Dysfunction drowsy turtle's Avatar
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    It does. This is a natural cycle in the Earth's climate:

    Greenhouse effect causes warming.
    Warming causes increased evaporation of water.
    Evaporated water forms increased numbers of clouds.
    Clouds reduce the amount of radiation reaching the surface and cause cooling effect.
    Cooling effect reduces evaporation of water.
    Less clouds formed, so more radiation reaches the surface.
    Cycle starts again.

    The greater the warming effect because of greenhouse gases, the greater the cooling effect caused by clouds. This cooling effect is, however, offset by several years. I believe it is due to start this year, or next year.

    The problem is, will the equilibrium shift?


    "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." ~ Douglas Adams
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  4. #3 Re: Greenhouse Theory Question 
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    Quote Originally Posted by williampinn
    According to a greenhouse theory I read, visible light reaches earth's surface and is converted to long IR waves. These are absorbed, scattered, or reflected by carbon dioxide and other greenhouse gases, including water vapor. According to the theory, this process warms things up. My question: Why wouldn't the increased humidity and clouds resulting from the warming, block the sun's visible light as it heads for earth, causing less energy to be absorbed by the earth's surface, and cause a cooling process offsetting the warming process?
    there are a number of such feedbacks, some positive and some negative. You have described a negative feedback.

    An example of a positive feedback is that a warmer climate allows the many tonnes of frozen tundra in the arctic to warm and decompose, releasing more greenhouse gases into the atmosphere.
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  5. #4 Re: Greenhouse Theory Question 
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    Quote Originally Posted by free radical
    Quote Originally Posted by williampinn
    According to a greenhouse theory I read, visible light reaches earth's surface and is converted to long IR waves. These are absorbed, scattered, or reflected by carbon dioxide and other greenhouse gases, including water vapor. According to the theory, this process warms things up. My question: Why wouldn't the increased humidity and clouds resulting from the warming, block the sun's visible light as it heads for earth, causing less energy to be absorbed by the earth's surface, and cause a cooling process offsetting the warming process?
    there are a number of such feedbacks, some positive and some negative. You have described a negative feedback.

    An example of a positive feedback is that a warmer climate allows the many tonnes of frozen tundra in the arctic to warm and decompose, releasing more greenhouse gases into the atmosphere.
    If what I described is a negative feedback, how would what you described be a positive feedback? Wouldn't the releasing of more greenhouse gases cause more clouds which create the cooling offset or negative feedback?
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  6. #5  
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    Quote Originally Posted by drowsy turtle
    It does. This is a natural cycle in the Earth's climate:

    Greenhouse effect causes warming.
    Warming causes increased evaporation of water.
    Evaporated water forms increased numbers of clouds.
    Clouds reduce the amount of radiation reaching the surface and cause cooling effect.
    Cooling effect reduces evaporation of water.
    Less clouds formed, so more radiation reaches the surface.
    Cycle starts again.

    The greater the warming effect because of greenhouse gases, the greater the cooling effect caused by clouds. This cooling effect is, however, offset by several years. I believe it is due to start this year, or next year.

    The problem is, will the equilibrium shift?
    Perhaps it will shift. The question then is by how much?
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  7. #6 Re: Greenhouse Theory Question 
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    Quote Originally Posted by williampinn
    Quote Originally Posted by free radical
    Quote Originally Posted by williampinn
    According to a greenhouse theory I read, visible light reaches earth's surface and is converted to long IR waves. These are absorbed, scattered, or reflected by carbon dioxide and other greenhouse gases, including water vapor. According to the theory, this process warms things up. My question: Why wouldn't the increased humidity and clouds resulting from the warming, block the sun's visible light as it heads for earth, causing less energy to be absorbed by the earth's surface, and cause a cooling process offsetting the warming process?
    there are a number of such feedbacks, some positive and some negative. You have described a negative feedback.

    An example of a positive feedback is that a warmer climate allows the many tonnes of frozen tundra in the arctic to warm and decompose, releasing more greenhouse gases into the atmosphere.
    If what I described is a negative feedback, how would what you described be a positive feedback? Wouldn't the releasing of more greenhouse gases cause more clouds which create the cooling offset or negative feedback?
    One could argue that increasing cloudcover leads to more people using fuel to warm their homes. But you would not call cloud cover a positive feedback.

    Likewise, decomposing arctic tundra is a positive feedback, not a negative feedback; whether there is a subsequent negative feedback that results is a separate issue.

    There are many feedbacks. Increased weathering is another one, as is decreased albedo.
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  8. #7 Re: Greenhouse Theory Question 
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    Quote Originally Posted by williampinn
    Wouldn't the releasing of more greenhouse gases cause more clouds which create the cooling offset or negative feedback?
    For clouds to form the relative humidity has to approach 100% locally. In fact the RH stays roughly constant as temperature increases. (The absolute humidity increases, but that's not what causes clouds.) Increasing temperature due to anthropogenic greenhouse gas emissions therefore does not necessarily increase cloud cover.
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  9. #8  
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    From my days playing SimEarth:

    Water vapor in cloud form tends to increase the albedo of a planet. Or how reflective it is. But the flip side of this is that water vapor is a greenhouse gas itself. And not all water vapor forms into clouds. So the net effect of, say, the oceans boiling off would be a net increase in planetary temperature.

    I used to have fun when my sentient insects started burning fossil fuels and the oceans boiled off and everything died. Good times
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  10. #9  
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    Quote Originally Posted by Numsgil
    From my days playing SimEarth:

    Water vapor in cloud form tends to increase the albedo of a planet. Or how reflective it is. But the flip side of this is that water vapor is a greenhouse gas itself. And not all water vapor forms into clouds. So the net effect of, say, the oceans boiling off would be a net increase in planetary temperature.

    I used to have fun when my sentient insects started burning fossil fuels and the oceans boiled off and everything died. Good times
    That seems logical if the oceans did boil off. But then the oceans never boil off, so there must be some check to how warm things can get. Some sort of negative feedback.
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  11. #10 Re: Greenhouse Theory Question 
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    Quote Originally Posted by Bunbury
    Quote Originally Posted by williampinn
    Wouldn't the releasing of more greenhouse gases cause more clouds which create the cooling offset or negative feedback?
    For clouds to form the relative humidity has to approach 100% locally. In fact the RH stays roughly constant as temperature increases. (The absolute humidity increases, but that's not what causes clouds.) Increasing temperature due to anthropogenic greenhouse gas emissions therefore does not necessarily increase cloud cover.
    What do you think causes clouds?
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  12. #11 Re: Greenhouse Theory Question 
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    Quote Originally Posted by free radical

    One could argue that increasing cloudcover leads to more people using fuel to warm their homes. But you would not call cloud cover a positive feedback.
    Why not?

    Quote Originally Posted by free radical
    Likewise, decomposing arctic tundra is a positive feedback, not a negative feedback; whether there is a subsequent negative feedback that results is a separate issue.
    Why is it a separate issue? Is there a connection or isn't there?

    Quote Originally Posted by free radical
    There are many feedbacks. Increased weathering is another one, as is decreased albedo.
    Yes, I'm sure there are many feedbacks.
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  13. #12 Re: Greenhouse Theory Question 
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    Quote Originally Posted by Bunbury
    Quote Originally Posted by williampinn
    Wouldn't the releasing of more greenhouse gases cause more clouds which create the cooling offset or negative feedback?
    For clouds to form the relative humidity has to approach 100% locally. In fact the RH stays roughly constant as temperature increases. (The absolute humidity increases, but that's not what causes clouds.) Increasing temperature due to anthropogenic greenhouse gas emissions therefore does not necessarily increase cloud cover.
    Gotta another question for you: when it comes to absorbing, reflecting or scattering different frequencies of light, what is the difference between humidity and clouds?
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  14. #13 Re: Greenhouse Theory Question 
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    Quote Originally Posted by williampinn
    What do you think causes clouds?
    Condensation of water vapor on nucleation sites, basically dust. Some have suggested cosmic rays can act as nucleation sites but this appears to be false.
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  15. #14 Re: Greenhouse Theory Question 
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    Quote Originally Posted by williampinn
    Quote Originally Posted by free radical

    One could argue that increasing cloudcover leads to more people using fuel to warm their homes. But you would not call cloud cover a positive feedback.
    Why not?

    Quote Originally Posted by free radical
    Likewise, decomposing arctic tundra is a positive feedback, not a negative feedback; whether there is a subsequent negative feedback that results is a separate issue.
    Why is it a separate issue? Is there a connection or isn't there?
    Calling it all one feedback would be like calling a biochemical pathway a reaction.
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  16. #15 Re: Greenhouse Theory Question 
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    Quote Originally Posted by Bunbury
    Quote Originally Posted by williampinn
    What do you think causes clouds?
    Condensation of water vapor on nucleation sites, basically dust. Some have suggested cosmic rays can act as nucleation sites but this appears to be false.
    I never heard of this. Why would dust need to be involved? From:
    http://www.weatherquestions.com/How_do_clouds_form.htm

    "Clouds form when rising air, through expansion, cools to the point where some of the water vapor molecules "clump together" faster than they are torn apart by their thermal energy. Some of that (invisible) water vapor condenses to form (visible) cloud droplets or ice crystals."

    Here is an interesting article on how iris clouds may actually reduce global warming:

    http://www.clean-coal.info/drupal/ua...ch_iris_effect

    What I find interesting is the claim that clouds create a net warming effect. That seems odd when you consider how clouds are actually formed: rising air that cools.
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  17. #16 Re: Greenhouse Theory Question 
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    Quote Originally Posted by free radical
    Quote Originally Posted by williampinn
    Quote Originally Posted by free radical

    One could argue that increasing cloudcover leads to more people using fuel to warm their homes. But you would not call cloud cover a positive feedback.
    Why not?

    Quote Originally Posted by free radical
    Likewise, decomposing arctic tundra is a positive feedback, not a negative feedback; whether there is a subsequent negative feedback that results is a separate issue.
    Why is it a separate issue? Is there a connection or isn't there?
    Calling it all one feedback would be like calling a biochemical pathway a reaction.
    Why? In any case the end result is a negative feedback whether it is one or more feedbacks.
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  18. #17 Re: Greenhouse Theory Question 
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    Quote Originally Posted by williampinn
    Quote Originally Posted by Bunbury
    Quote Originally Posted by williampinn
    What do you think causes clouds?
    Condensation of water vapor on nucleation sites, basically dust. Some have suggested cosmic rays can act as nucleation sites but this appears to be false.
    I never heard of this. Why would dust need to be involved? /
    You never heard of a fairly fundamental fact about climate and yet you are ready to call the IPCC report bullshit. Why should we take you seriously?

    Read this from wikipedia-
    Water requires a non-gaseous surface to make the transition from a vapour to a liquid. In the atmosphere, this surface presents itself as tiny solid or liquid particles called CCNs. When no CCNs are present, water vapour can be supercooled below 0 C (32 F) before droplets spontaneously form (this is the basis of the cloud chamber for detecting subatomic particles). In above freezing temperatures the air would have to be supersaturated to around 400% before the droplets could form.
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  19. #18 Re: Greenhouse Theory Question 
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    Quote Originally Posted by williampinn
    Quote Originally Posted by free radical
    Quote Originally Posted by williampinn
    Quote Originally Posted by free radical

    One could argue that increasing cloudcover leads to more people using fuel to warm their homes. But you would not call cloud cover a positive feedback.
    Why not?

    Quote Originally Posted by free radical
    Likewise, decomposing arctic tundra is a positive feedback, not a negative feedback; whether there is a subsequent negative feedback that results is a separate issue.
    Why is it a separate issue? Is there a connection or isn't there?
    Calling it all one feedback would be like calling a biochemical pathway a reaction.
    Why?
    I have explained this already. Are you really this daft? I suspect you are simply stubborn, but the end effect appears the same. Either you wish to comprehend or you don't, and it seems you don't.


    In any case the end result is a negative feedback whether it is one or more feedbacks
    no, one result, which is not an 'end' in any case, is a negative feedback, other results are positive feedbacks. Are you denying that Earth's climate has been variably hot then cold then hot then cold through time? There is no 'end' to the process. Greater cloud cover means more heat trapped (water vapour being an excellent blanket) as well as less photosynthesis (again increasing the CO2, another positive feedback) and greater weathering (rainfall washing carbonates to the ocean where they pull another CO2 out of the atmosphere to form bicarb), etc etc etc .... Your argument is an oversimplification.
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  20. #19  
    Forum Masters Degree Numsgil's Avatar
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    It's a terribly fascinating process. Some reactions are negative feedback, and others are positive feedback. It's a constant tug of war between competing forces, with some very chaotic end behavior. Very fun to play with
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  21. #20  
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    Quote Originally Posted by williampinn
    That seems logical if the oceans did boil off. But then the oceans never boil off, so there must be some check to how warm things can get. Some sort of negative feedback.
    just because something has never happened doesn't mean it can never happen - after all it's almost a cert that when the sun becomes a red giant there will be precious little liquid water left on earth, so at some stage in the future the oceans will start to evaporate irrevocably

    Quote Originally Posted by williampinn
    What I find interesting is the claim that clouds create a net warming effect. That seems odd when you consider how clouds are actually formed: rising air that cools.
    i suppose it all depends on the type of cloud (e.g. how high up, how thick etc.)
    surely it's a well-known fact that overcast nights usually are warmer than nights with a clear sky ?
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  22. #21 Re: Greenhouse Theory Question 
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    Quote Originally Posted by williampinn
    I never heard of this. Why would dust need to be involved?
    Relative humidity assumes there are condensation nuclei present. Without condensation nuclei, water water vapor can reach more than 300% relative humidity before there is any condensation. Usually there are plenty of nuclei to start condensation except in a few places such as the upper troposphere of Eastern subtropical Atlantic. Another odd effect is super condensation nuclei also exist that make condensation possible at less than 100% relative humidity. Common sea salt particles, which blow off wave tops or from their evaporation of fine sea water droplets, allow condensation to start at 80% relative humidity and account for more dense fogs over the ocean (e.g. "pea soup") than is possible over land.

    Freezing condensation nuclei are another type, and essential for water vapor or liquid droplets to freeze. Unlike condensation nuclei those require to freeze are actually uncommon, and clouds often contain super cooled liquid water below 0F. The amount of freezing condensation nuclei, and super cooled droplets are important to precipitation and a hazard to aircraft.

    According to a greenhouse theory I read, visible light reaches earth's surface and is converted to long IR waves. These are absorbed, scattered, or reflected by carbon dioxide and other greenhouse gases, including water vapor. According to the theory, this process warms things up. My question: Why wouldn't the increased humidity and clouds resulting from the warming, block the sun's visible light as it heads for earth, causing less energy to be absorbed by the earth's surface, and cause a cooling process offsetting the warming process?
    It's important to note that greenhouse gasses don't warm the entire atmosphere, they warm the lowest layers (where we and most other life resides), while cooling the upper layers. The observed cooling of the upper troposphere and lower stratosphere is one of the smoking guns that it's the green house gases causing the observer surface warming and not some other phenomena like a brighter sun etc.
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