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Re: Paleoclimate and CO2

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  • tom_c2k6
    ... Ok, but how do they know that the 5,000 year warming that follows ice ages isn t all, or nearly all, due to the same factors that caused the first 800
    Message 1 of 5 , Aug 1, 2006
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      --- In globalwarming@yahoogroups.com, lasallia <no_reply@...> wrote:
      >From the RealClimate website:
      >"The reason has to do with the fact that the warmings
      >take about 5000 years to be complete.
      >The lag is only 800 years.
      >All that the lag shows is that CO2 did not cause
      >the first 800 years of warming, out of the 5000 year trend.
      >The other 4200 years of warming
      >could in fact have been caused by CO2,
      >as far as we can tell from this ice core data."

      Ok, but how do they know that the 5,000 year warming that follows ice
      ages isn't all, or nearly all, due to the same factors that caused
      the first 800 years of the warming? (Earth receiving more direct
      sunlight via orbital changes/Milankovitch effect) After all, it is a
      100,000 year cycle we're talking about. They say CO2 'could' have
      been the cause after 800 years of warming. But why would one assume
      or suspect that a warming that occurs with a periodicity of ~100,000
      years take only 800 or so to complete? Wouldn't it seem much more
      plausible that a warm up related to something as monumental as
      changes in the planet's orbit take several thousand years? Why should
      CO2 be the suspect when there really isn't any evidence to support
      the suspicion? Total CO2 concentrations, both natural and man-made,
      only amount to about 0.035% of the atmosphere here on Earth. On Venus
      I can understand, as Venus' atmosphere is something like 97% CO2.
      Quite a big difference from 0.035.

      http://upload.wikimedia.org/wikipedia/en/c/c2/Vostok-ice-core-
      petit.png

      or, if the long url above breaks apart:
      http://tinyurl.com/qbdd6

      Tom

      --- In globalwarming@yahoogroups.com, lasallia <no_reply@...> wrote:

      From the RealClimate website:
      http://www.realclimate.org/index.php?p=13

      This is an issue that is often misunderstood in the public sphere and
      media, so it is worth spending some time to explain it and clarify
      it. At least three careful ice core studies have shown that CO2
      starts to rise about 800 years (600-1000 years) after Antarctic
      temperature during glacial terminations. These terminations are
      pronounced warming periods that mark the ends of the ice ages that
      happen every 100,000 years or so.

      Does this prove that CO2 doesn't cause global warming? The answer is
      no.

      The reason has to do with the fact that the warmings take about 5000
      years to be complete. The lag is only 800 years. All that the lag
      shows is that CO2 did not cause the first 800 years of warming, out
      of the 5000 year trend. The other 4200 years of warming could in fact
      have been caused by CO2, as far as we can tell from this ice core
      data.

      The 4200 years of warming make up about 5/6 of the total warming. So
      CO2 could have caused the last 5/6 of the warming, but could not have
      caused the first 1/6 of the warming.

      It comes as no surprise that other factors besides CO2 affect
      climate. Changes in the amount of summer sunshine, due to changes in
      the Earth's orbit around the sun that happen every 21,000 years, have
      long been known to affect the comings and goings of ice ages.
      Atlantic ocean circulation slowdowns are thought to warm Antarctica,
      also.

      From studying all the available data (not just ice cores), the
      probable sequence of events at a termination goes something like
      this. Some (currently unknown) process causes Antarctica and the
      surrounding ocean to warm. This process also causes CO2 to start
      rising, about 800 years later. Then CO2 further warms the whole
      planet, because of its heat-trapping properties. This leads to even
      further CO2 release. So CO2 during ice ages should be thought of as
      a "feedback", much like the feedback that results from putting a
      microphone too near to a loudspeaker.

      In other words, CO2 does not initiate the warmings, but acts as an
      amplifier once they are underway. From model estimates, CO2 (along
      with other greenhouse gases CH4 and N2O) causes about half of the
      full glacial-to-interglacial warming.

      So, in summary, the lag of CO2 behind temperature doesn't tell us
      much about global warming. [But it may give us a very interesting
      clue about why CO2 rises at the ends of ice ages. The 800-year lag is
      about the amount of time required to flush out the deep ocean through
      natural ocean currents. So CO2 might be stored in the deep ocean
      during ice ages, and then get released when the climate warms.]

      To read more about CO2 and ice cores, see Caillon et al., 2003,
      Science magazine

      Guest Contributor: Jeff Severinghaus
      Professor of Geosciences
      Scripps Institution of Oceanography
      University of California, San Diego.

      From the RealClimate website:
      http://www.realclimate.org/index.php?p=13
      -
    • lasallia
      Why should CO2 be the suspect when there really isn t any evidence to support the suspicion? Total CO2 concentrations, both natural and man- made, only amount
      Message 2 of 5 , Aug 2, 2006
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        Why should CO2 be the suspect when there really isn't any evidence to
        support the suspicion? Total CO2 concentrations, both natural and man-
        made, only amount to about 0.035% of the atmosphere here on Earth. On
        Venus I can understand, as Venus' atmosphere is something like 97% CO2.
        > Quite a big difference from 0.035.
        >

        Carbon dioxide is the suspect because we know it's properties. I think
        you'll find there is an equally big temperature difference between
        Earth and Venus too. (By equally, I do not mean to imply correlation.)

        Sal
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