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Fwd: Greenhouse gas growth rates.

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  • Mike Neuman
    ... wrote: *Hansen s notations... as always are interesting........** Global warming itself probably causes the major GHGs (CO2, N2O, and
    Message 1 of 1 , Jul 19, 2005
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      --- In Paleontology_and_Climate@yahoogroups.com, Sonya
      <msredsonya@e...> wrote:
      *Hansen's notations... as always are interesting........** "Global
      warming itself probably
      causes the major GHGs (CO2, N2O, and CH4) to increase" and I assume
      he is going for the
      thermodynamic and chemistry laws when he makes a statement of that

      Hansen, J., and Mki. Sato 2004. Greenhouse gas growth rates. Proc.
      Natl. Acad. Sci. *101*, 16109-16114, doi:10.1073/pnas.0406982101.

      * Download PDF
      (Document is 580 kB)

      Supplementary material is available.
      Click here <http://pubs.giss.nasa.gov/supplement/2004_HansenSato/>

      Abstract http://pubs.giss.nasa.gov/abstracts/2004/HansenSato.html

      We posit that feasible reversal of the growth of atmospheric CH_4
      and other trace gases would provide a vital contribution toward
      dangerous anthropogenic interference with global climate. Such trace
      reductions may allow stabilization of atmospheric CO_2 at an
      achievable level of anthropogenic CO_2 emissions, even if the added
      global warming constituting dangerous anthropogenic interference is
      as small as
      1°C. A 1°C limit on global warming, with canonical climate
      sensitivity, requires
      peak CO_2 {approx} 440 ppm if further non-CO_2 forcing is
      +0.5 W/m^2 , but peak CO_2 ? 520 ppm if further
      non-CO_2 forcing is -0.5 W/m^2 . The practical result is that
      a decline of non-CO_2 forcings allows climate forcing to be
      with a significantly higher transient level of CO_2 emissions.
      Increased "natural" emissions of CO_2 , N_2 O, and
      CH_4 are expected in response to global warming. These emissions, an
      indirect effect of all climate forcings, are small compared with
      climate forcing and occur on a time scale of a few centuries, but
      they tend to
      aggravate the task of stabilizing atmospheric composition.


      Greenhouse gas growth rates
      James Hansen* and Makiko Sato
      National Aeronautics and Space Administration Goddard Institute for
      Space Studies and Columbia University Earth Institute, 2880 Broadway,
      New York, NY 10025
      Contributed by James Hansen, September 29, 2004

      p 5 of 6
      "Summary and Implications
      CO2 Growth Rate. Annual growth of atmospheric CO2 fluctuates
      widely from year to year. It is sometimes said that meanCO2 growth
      in recent decades has been reasonably stable at1.5 or 1.6 ppmyr."

      However, the long-term near constancy of the CO2 airborne
      fraction at 60% (Fig. 5A) indicates that the more steadily changing
      fossil-fuel emissions provide a good measure of the underlying
      CO2 growth rate. Fossil-fuel emissions have increased 50% since
      1973 to 7 gigatonsyr. Thus, the underlying atmospheric CO2
      growth rate is now 7 gigatonsyr 60% 0.453 ppmgigaton 
      1.9 ppmyr. One consequence is that, unless CO2 emissions begin
      to level off soon and then decline, it will become impractical to
      additional global warming to 1°C (13).

      *GHG Feedback and Indirect Forcings. Global warming itself probably
      causes the major GHGs (CO2, N2O, and CH4) to increase, with a
      full response time that may be as long as hundreds of years. On the
      basis of paleoclimate evidence, this climate feedback is unlikely to
      cause a large nonlinear effect if additional global warming is held
      to 1°C or less.*

      CO2 Emissions. Stabilization of atmospheric composition requires
      CO2 emissions to be reduced to match the CO2 absorbed by the
      ocean and biosphere. We point out that the permitted level for the
      atmospheric CO2 amount depends sensitively on the magnitude of
      non-CO2 forcings. The corresponding CO2 emissions depend on
      the time scale considered, because of the limited ability of the ocean
      and biospheric sinks to absorb more CO2.

      For example, if non-CO2 climate forcing decreases this century
      by 0.5 Wm2, rather than increasing by 0.5 Wm2, the
      allowed CO2 emissions are higher and more plausibly attainable.
      Say, as in the alternative scenario, that the aim is to keep added
      forcing 1.5 Wm2. If non-CO2 forcings increase 0.5 Wm2, the
      remaining 1 Wm2 allowed for CO2 corresponds to CO2  69
      ppm or CO2  439 ppm. Conversely, if non-CO2 forcings
      decrease 0.5 Wm2, the 2 Wm2 allowed for CO2 correspond to
      CO2  150 ppm or CO2  520 ppm (540 ppm for IPCC CO2
      sensitivity). A different choice for the maximum forcing would
      not alter the large impact of non-CO2 forcings on the permissible
      CO2 amount.

      The near-term permitted CO2 emissions in these two cases also
      differ. If 1.6% of excess atmospheric CO2 continues to be taken up,
      as in the past half century (Fig. 5C), the case with CO2  439 ppm
      would have atmospheric CO2 being soaked up at a rate of 5.3
      gigatons of C per yr (75% of today's fossil fuel emission rate),
      whereas the case withCO2520 ppm would haveCO2 being taken
      up at a rate of 8.0 gigatons of C per yr (115% of today's emissions).
      In reality, the ability of the ocean and terrestrial biosphere to take
      upCO2 is expected to decline as anthropogenic emissions continue.
      CO2 emissions consistent with stable atmospheric composition will
      be less than the above percentages and will decline with time. The
      aim of our gedanken experiment is not to quantify allowed emissions
      but, rather, to show that non-CO2 forcings have a large impact
      on allowed CO2 emissions. If non-CO2 forcings are reduced,
      acceptable CO2 emissions in coming decades may be greater than
      commonly assumed.

      Practical Implications. The success of the Montreal Protocol in
      reversing the growth ofMPTGs, at moderate cost, suggests a similar
      approach for OTGs. The machinery in place for MPTGs could be
      used, e.g., with the World Bank supporting the phase-out of gases
      such as HFC-134a. Indeed, some of the OTGs are a consequence
      of the phase-out of MPTGs, so it is not difficult to rationalize that

      CH4 deserves special attention in efforts to stem global warming,
      for reasons given in this paper.We suggest that a reward approach
      for emission reductions, analogous to that used for MPTGs, could
      achieve much reduced CH4 emissions at low cost.

      N2O and BC aerosols are other significant climate forcings that
      have received inadequate research support and regulatory attention,
      given their potential to impact the level of constraints that will
      be needed for CO2. BC reductions are needed to counterbalance
      expected reductions of reflective aerosols and would have numerous
      other benefits (26).

      We thank Jack Kaye, Don Anderson, Phil DeCola, and Tsengdar Lee of
      the National Aeronautics and Space Administration headquarters for
      support of our research; the members of the National Oceanic and
      Atmospheric Administration Climate Monitoring and Diagnostics
      for access to current measurements of GHGs; Jean Jouzel and
      Francoise Vimeux for the Vostok ice core data; Inez Fung, Jos
      Michael Prather, and Gavin Schmidt for criticisms of the manuscript;
      Darnell Cain for technical assistance.

      Sonya mail to: <msredsonya@e...>
      PLoS Medicine http://www.plosmedicine.org
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