Why would melting ice caps increase global warming?

Discussion in 'Earth Science' started by nuk, May 18, 2011.

  1. nuk Registered Member

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    The standard line is that ice reflects light well, so losing the ice caps means the Earth will absorb more sunlight, and global temperatures will increase.

    But it seems to me that removing the ice caps would cool the Earth. Can anyone point out a flaw in the following reasoning?

    If the polar regions are staying at roughly constant temperatures, that means the heat flows into and out of the poles are equal. Heat flows into the poles through sunlight and from the warmer parts of the globe. Heat flows out only through radiated energy. So there must be more radiated energy being emitted by the poles than absorbed.

    Emission and absorbtion of light are directly related, so that if ice is a poor absorber of radiation, it must also be a poor emitter of radiation. So if the ice is melting, both the absorbtion and emission of light from the poles will increase. But if there's more radiation being emitted than absorbed, increasing those things would lead to a net increase in heat lost from the Earth, cooling us off.

    I assume all the scientists saying the melting ice caps will contribute to global warming know what they're talking about, but I've never heard anyone address this issue. What am I missing?
     
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  3. spidergoat Valued Senior Member

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  5. adoucette Caca Occurs Valued Senior Member

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    Not much.

    It's obviously complicated.

    What you are leaving out of the equation though is the air and wind currents that bring in warmer air and water to the Arctic.

    Ice cover is not all about direct solar radiation.

    http://nsidc.org/arcticseaicenews/2010/120610.html

    Arthur
     
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  7. Ophiolite Valued Senior Member

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    You are quite ignoring the reflection of light. Why are the interior of white cars cooler on a sunny day than black cars? Reflection. The poles stay cool in part because much of the incoming solar radiation is reflected back into space.
     
  8. nuk Registered Member

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    A black car is hotter than a white one because they absorb more radiant energy than they emitt. I'm arguing that the poles emitt more than they absorb, so a "black" pole should be cooler than a white one.

    I did consider heat flow to the poles from the rest of the Earth as a sort of black box, without worrying about the mechanisms. But perhaps if the ice caps melt, there could be less heat carried to the poles through air/water currents? That would make the poles colder, but the human-occupied parts of the world warmer.
     
  9. iceaura Valued Senior Member

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    Anything that is at a constant temperature, averaged over a long time (to settle any chemical reactions, changes of phase, etc) is ejecting exactly as much energy as it is absorbing.

    The newly dark, light-absorbent surface area around the poles will, when it stabilizes in its more absorbent new state (with the phase changes done, etc) be radiating more energy as heat than now. That means the poles will be hotter, they will be warming the moving air and water that goes elsewhere, etc.
     
  10. Fraggle Rocker Staff Member

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    24,690
    It's true that ice is an insulator, but it's an even better reflector. Ice does not cool the planet by absorbing heat from the underlying minerals and radiating it out into space. It cools the planet by reflecting sunlight out into space rather than absorbing it and convecting it down to the ground and/or water below. Without the ice covering the mineral and liquid surface of the earth, the ground and the seas will absorb more heat than they emit by radiation and reflection combined. This will contribute to the warming of the entire planetary surface.

    This is why the earth's surface temperature does not oscillate around an equilibrium point, but instead fluctuates dramatically. When it is cold and there is a large permanent icepack at the poles and on mountain ranges, it has a cooling engine to make it colder. When it is hot and there is no permanent icepack, it has a warming engine to make it hotter.

    [Note from the Linguistics Moderator: BTW, "emit" has only one T.]
     
  11. nuk Registered Member

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    But if the poles absorb more than they emit, they would have to give heat to the temperate zones through convection/conduction, which would mean that the poles would be warmer than the temperate zones.

    Thanks. I'm dependent on those squiggly red lines under my misspelled words.
     
  12. fedr808 1100101 Valued Senior Member

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    Well for one thing, ice cools the earth by absorbing solar energy. It takes a lot of energy to convert ice to water. By absorbing solar energy it is absorbing energy which would otherwise heat up the earth.

    Now guess what happens when there is no more ice left to absorb set energy.
     
  13. nuk Registered Member

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    My best idea so far is that ice might be a good absorber/emitter of infrared light. Perhaps ice reflects most of the visible light coming in from the sun but absorbs the infrared. Most of the energy the Earth emits is in the infrared, so ice might be able to reflect much of the incoming radiation while still being a good emitter. Then, if the ice melts, the liquid water would absorb more visible light, while not emitting infrared any better.
     
  14. Dinosaur Rational Skeptic Valued Senior Member

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    To some extent, melting of artic ice is an effect of global warming.

    I am not disputing its being a cause due to decreased reflection reflection of solar radiation.
     
  15. Asguard Kiss my dark side Valued Senior Member

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    Also the blanket effect.
     
  16. Trippy ALEA IACTA EST Staff Member

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    nuk;

    There seem to be three key points you're missing in amongst all of this, one of which has been addressed by other posters.

    The first is that objects in thermal equilibrium with their surroundings emit as much heat as they absorb. Objects that are colder than their surroundings absorb more heat than the emit, until they warm up. Objects that are hotter than their surroundings emit more heat than they absorb until they cool down.

    This has a couple of implications The first of which is that if you have a dark coloured object, and a light coloured object, and if those objects are otherwise identical, and are both sitting in sunlight, then the dark object will reach a higher object than the light object in order to be in equilibrium with its surroundings. This is, in essence, bvecause the light object reflects most of the incoming radiation back into the environment, and only has to warm up a little to ensure that the total out going and incoming radition is the same. The dark object, however, has to warm up a lot in order to satisfy the same condition, so the dark object gets hotter than the light object.

    Which leads us to our second point. Hot objects emit more radiation than cooler objects. This is the essence of Blackbody Radiation.
    The temperature of an object rises until the energy emitted (including reflected) by the object is the same as the energy absorbed by the object. As the temperature increases, the total amount of radiation, increases, and the frequency of the peak of the emition increases. This is why as metal heats up, it tranitions from glowing faintly cherry red, to being blindingly white hot. This is also the reason why the blue flame on your bunsen burner is a lot hotter than the yellow flame.

    And finally, we reach our third point - higher latitudes recieve less energy per unit of surface area than lower latitudes. Think of a cylinder extending from the surface of the earth, the diameter of which is such that it contains 1 unit of energy, and define that as 1 unit of area. At the equator, we're making the smallest possible cut, so we get one unit of energy per unit of area, but, as we move further north, we're effectively cutting that cylinder at steeper and steeper angles, and spreading that single unit of energy over larger and larger areas. Because of this, given the earths current orbital parameters, it is (more or less) not possible for the poles to have a higher average temperature than the equator (that's not to say that it's completely impossible, mind, it can happen, for example, if there is a high seasonal inclination involved, so that the sun spends more time over the poles, or conceivably it might happen if, for example, enough of the equator were occupied by a mountain range laden with icecaps, and a clear ocean at the poles).
     
  17. Me-Ki-Gal Banned Banned

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    Its true moisture moves with heat . We use to put foundation vents in crawl spaces as to air out the crawl space . Not now. The new technology requires us to treat like indoor space . The reason is when the weather is hot it draws moisture into the crawl space and moister is the enemy to human habitations. You can see this real good if you live in cold weather climate and have forced air heat . Just look at your fresh air duct in the winter . It will be frosted up , sometimes dripping condensation enough to cause damage .

    My non - scientific analysis :
    Ice melts , More rain , cools planet, more ice forms . Now as far as reflection goes the more clouds the more reflection, the cooler the temp . These does not take in consideration the darkening of the planet from jet contrails . People it is also cooler in the shade. How bout space debris? does that block out sun light ? Moon shadow Moon shadow
     
  18. Trippy ALEA IACTA EST Staff Member

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    nuk;
    Something else to keep in mind, is that the albedo of water is latitude dependent - water at the poles reflects more and absorbs less solar energy than water at the equator does.

    There is no (relevant) physicochemical difference between the water at the two locations, it's purely and simply to do with the angle of incidence of the sunlight.
     
  19. billvon Valued Senior Member

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    That is correct. However, it is a much better REFLECTOR of radiation.

    In other words, if the sun didn't shine on the poles, your reasoning would make sense.
     
  20. Me-Ki-Gal Banned Banned

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    would water take on mirror effect at the poles at that angle? which is more reflective than white . Lets see white is what 80% reflection and mirror I don't know 99% . That is if water takes on mirror type reflection at that angle ?
     
  21. billvon Valued Senior Member

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    12,804
    Well, the critical angle of water is about 50 degrees. If the sunlight hits a perfectly smooth water surface at an angle steeper than that most of the light is reflected.

    However, the ocean is rarely perfectly smooth. Even a little chop gives you significant changes in angle, and once you get below that 50 degree mark you absorb most of the light that hits the surface.

    Fresh snow (which is often found on top of ice) has an albedo of 50-90%; ice is around 40% and water is around 5%. So even a little deviation from a perfectly flat surface gives you a lot more absorption than snow/ice does.
     
  22. Me-Ki-Gal Banned Banned

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    4,634
    Thank you , Thank you very much
     
  23. chimpkin C'mon, get happy! Registered Senior Member

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    I see a black road and I want to paint it whi-ite
    No tar roofs anymore, I want them to turn whi-ite....

    * Grabs cordless sprayer and giant bucket of white outdoor road grade latex, gets nutty gleam in eye*

    http://www.takepart.com/node/39692/actions
     

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