Runway Greenhouse Effect



  • Radiation Trapping by Greenhouse Gases:
    Sunlight falling on the surface of a planet is primarily in the visible part of the spectrum.
    However,the reflection of light from the surface tends to produce light of longer wavelenghth called infrared (IR) radition (also known as radiant heat;IR radition is the heat that we sense being radiated from a hot surface like a hot piece of metal).

    Now,because of thier molecular structures,certain gases like carbon dioxide and water vapor (and many others)have the property that they are essentially transparent to visible light but absorb IR radition very strongly.

    such compounds are sometimes termed greenhouse gases because,if they are present in planetary atmosphere,they absorb the scattered IR radiation and tend to raise the temperature of the atmosphere by trapping solar energy. (The analogy with a real greenhouse is imperfect because of mechanism by which a greenhouse stays warm is different,but it is sufficiently good that the name "(Planetry) Greenhouse Effect" is now the common one for this phenomenon.)


  • The Greenhouse Effect Out of Control:
    The Greenhouse effect occurs for all planetry atmospheres containing greenhouse gases,and is responsible for their being WARMER than would be in case otherwise.

    The greenhouse effect by itself could not account for the conditions that we find on Venus.However,undercertain conditions we believe the greenhouse effect can "run away".
    For example,consider the case of a planet like the Earth.The Earth has enormouse amounts of two greenhouse gases : water vapor and carbon dioxide.However,for the Earth most of the water and carbon dioxide are not in the atmosphere.The water is mostly in the oceans,and the carbon dioxide is mostly bound chemically in rocks made from compounds that chemists call carbonates (for example,limestone).

    Now suppose we increased the effectiveness of greenhouse heating of the Earth's atmosphere,for example by increasing the amount of solar radiation falling on it,or by increasing the concentration of greenhouse gases in the atmosphere (for example,by burning fossil fules,which produce water vapor and carbon dioxide as byproducts of burning).We would then expect the temperature to rise in the atmosphere.And this would be a greenhouse effect.


    ...and the Oceans Would Boil


    It would become a runaway greenhouse effect if the rising temperature approached the boiling point of water,because then the Oceans would begin to convert to water vapor,the water vapor would increase the effectiveness of heat trapping and accelerate the greenhouse effect,this would cause the temperature to rise further,thus causing the oceans to evaporate faster,this kind of runaway is also called a "positive feedback loop".

    When the oceans were gone the atmosphere would finally stabilize at a much higher temperature and at much higher density,because all the water would now be in the atmosphere.

    Venus had large amounts of water like Earth but it all boiled away.Venus is now quite dry.

    ...and the Rocks Would Sublimate

    We can envision even a further runaway stage in this scenario.
    Suppose the preceding runaway raised the temperature so high that chemical reactions begin to occur that drive the carbon dioxide from the rocks into atmosphere (the process is called sublimation;a few hundered degress Celsius would be sufficient).
    Then another runaway would occur as the carbon dioxide feeding into the atmosphere would accelerate the heating,which would in turn accelerate the transfer of carbon dioxide from the rocks to the atmosphere.


    After that the atmosphere would finaly stablize at a still heating temperature and a pressure after all the carbon dioxide had been driven from the rocks.In fact,we believe that if this sequense were to take place on the Earth,the reulting temperature and pressure of the atmosphere left behind would not be very different from that for present-day Venus:the atmospheric temperature would be hunderds of degrees Celsius and the pressure would be maybe 100 times greater than it is today.


    After we know all that things which could happen , and from Our site " Our Solar System " we invite every one to protect his environment and keep it claer and we have to be very serious with people whose use an environment false such as burning fossil fules in large volumes

    AND YOU CAN SAVE OUR EARTH BY PUTTING A TREE IN FRONT OF YOUR HOME.



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    Last Modified : 5 Sep. 2001
    Created By#C0115361 Team