CO2, forcings and feedbacks

Discussion in 'Environment' started by Old Rocks, Jan 5, 2012.

  1. Old Rocks
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    Old Rocks Diamond Member

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    Atmospheric CO2: Principal Control Knob Governing Earth

    Atmospheric CO2: Principal Control Knob Governing Earth’s Temperature

    Andrew A. Lacis*, Gavin A. Schmidt, David Rind and Reto A. Ruedy
    + Author Affiliations

    NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA.

    *To whom correspondence should be addressed. E-mail: andrew.a.lacis@nasa.gov

    Abstract
    Ample physical evidence shows that carbon dioxide (CO2) is the single most important climate-relevant greenhouse gas in Earth’s atmosphere. This is because CO2, like ozone, N2O, CH4, and chlorofluorocarbons, does not condense and precipitate from the atmosphere at current climate temperatures, whereas water vapor can and does. Noncondensing greenhouse gases, which account for 25% of the total terrestrial greenhouse effect, thus serve to provide the stable temperature structure that sustains the current levels of atmospheric water vapor and clouds via feedback processes that account for the remaining 75% of the greenhouse effect. Without the radiative forcing supplied by CO2 and the other noncondensing greenhouse gases, the terrestrial greenhouse would collapse, plunging the global climate into an icebound Earth state.
     
  2. Old Rocks
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    Old Rocks Diamond Member

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    NASA GISS: CO<sub>2</sub>: The Thermostat that Controls Earth's Temperature

    Science Briefs
    CO2: The Thermostat that Controls Earth's Temperature
    By Andrew Lacis &#8212; October 2010

    A study by GISS climate scientists recently published in the journal Science shows that atmospheric CO2 operates as a thermostat to control the temperature of Earth.

    There is a close analogy to be drawn between the way an ordinary thermostat maintains the temperature of a house, and the way that atmospheric carbon dioxide (and the other minor non-condensing greenhouse gases) control the global temperature of Earth. The ordinary thermostat produces no heat of its own. Its role is to switch the furnace on and off, depending on whether the house temperature is lower or higher than the thermostat setting. If we were to carefully monitor the temperature of the house, we would see that the temperature does not stay constant at the set value, but rather exhibits a "natural variability" as the house temperature slips below the set value and then overshoots the mark with a time constant of minutes to tens of minutes, because of the thermal inertia of the house and because heating by the furnace (when it is on) is more powerful than the steady heat loss to the outdoors. If the thermostat is suddenly turned to a very high setting, the temperature will begin to rise at a rate dictated by the inertia of the house and strength of the furnace. Turning the thermostat back to normal will stop the heating.



    Figure 1. Attribution of individual atmospheric component contributions to the terrestrial greenhouse effect, separated into feedback and forcing categories. Dotted and dashed lines depict the fractional response for single-addition and single-subtraction of individual gases to either an empty or full-component reference atmosphere, respectively. Solid black lines are the scaled averages of the dashed and dotted line fractional response results. The sum of the fractional responses must add up to the total greenhouse effect. The reference model atmosphere is for 1980 conditions.
    + View larger image or PDF

    Atmospheric carbon dioxide performs a role similar to that of the house thermostat in setting the equilibrium temperature of the Earth. It differs from the house thermostat in that carbon dioxide itself is a potent greenhouse gas (GHG) warming the ground surface by means of the greenhouse effect. It is this sustained warming that enables water vapor and clouds to maintain their atmospheric distributions as the so-called feedback effects that amplify the initial warming provided by the non-condensing GHGs, and in the process, account for the bulk of the total terrestrial greenhouse effect. Since the radiative effects associated with the buildup of water vapor to near-saturation levels and the subsequent condensation into clouds are far stronger than the equilibrium level of radiative forcing by the non-condensing GHGs, this results in large local fluctuations in temperature about the global equilibrium value. Together with the similar non-linear responses involving the ocean heat capacity, the net effect is the "natural variability" that the climate system exhibits regionally, and on inter-annual and decadal timescales, whether the global equilibrium temperature of the Earth is being kept fixed, or is being forced to re-adjust in response to changes in the level of atmospheric GHGs
     
  3. Old Rocks
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  4. westwall
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    westwall USMB Mod Staff Member Gold Supporting Member Supporting Member

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    First sentence.....WHERE oh where is that evidence?
     
  5. westwall
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    westwall USMB Mod Staff Member Gold Supporting Member Supporting Member

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    Climate models are not DATA for the umpteenth time!

    This assessment comes about as the result of climate modeling experiments which show that it is the non-condensing greenhouse gases such as carbon dioxide, methane, ozone, nitrous oxide, and chlorofluorocarbons that provide the necessary atmospheric temperature structure that ultimately determines the sustainable range for atmospheric water vapor and cloud amounts, and thus controls their radiative contribution to the terrestrial greenhouse effect.
     
  6. Old Rocks
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    Old Rocks Diamond Member

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    Dr. Lacis did a presentation at the AGU Conferance. Did you miss it?
     
  7. westwall
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    westwall USMB Mod Staff Member Gold Supporting Member Supporting Member

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    Yes I did. I didn't attend the AGU conference this year as I was in Europe.
     
  8. bripat9643
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    Is that where he presented the data?
     
  9. CrusaderFrank
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    CrusaderFrank Diamond Member

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    [​IMG]
     
  10. CrusaderFrank
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    CrusaderFrank Diamond Member

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    I have peer reviewed this post and find it totally awesome.

    We have Consensus

    Science = Settled
     

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