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  • Pat Neuman
    Yale University Public release date: 7-Nov-2008 Contact: Janet Rettig Emanuel janet.emanuel@... 203-432-2157 Revised theory suggests carbon dioxide levels
    Message 1 of 1 , Nov 10, 2008
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      Yale University
      Public release date: 7-Nov-2008

      Contact: Janet Rettig Emanuel
      janet.emanuel@...
      203-432-2157

      Revised theory suggests carbon dioxide levels already in danger zone

      New Haven, Conn. — If climate disasters are to be averted,
      atmospheric
      carbon dioxide (CO2) must be reduced below the levels that already
      exist today, according to a study published in Open Atmospheric
      Science Journal by a group of 10 scientists from the United States,
      the United Kingdom and France.

      The authors, who include two Yale scientists, assert that to maintain
      a planet similar to that on which civilization developed, an optimum
      CO2 level would be less than 350 ppm — a dramatic change from most
      previous studies, which suggested a danger level for CO2 is likely to
      be 450 ppm or higher. Atmospheric CO2 is currently 385 parts per
      million (ppm) and is increasing by about 2 ppm each year from the
      burning of fossil fuels (coal, oil, and gas) and from the burning of
      forests.

      "This work and other recent publications suggest that we have reached
      CO2 levels that compromise the stability of the polar ice sheets,"
      said author Mark Pagani, Yale professor of geology and geophysics.
      "How fast ice sheets and sea level will respond are still poorly
      understood, but given the potential size of the disaster, I think
      it's
      best not to learn this lesson firsthand."

      The statement is based on improved data on the Earth's climate
      history
      and ongoing observations of change, especially in the polar regions.
      The authors use evidence of how the Earth responded to past changes
      of
      CO2 along with more recent patterns of climate changes to show that
      atmospheric CO2 has already entered a danger zone.

      According to the study, coal is the largest source of atmospheric CO2
      and the one that would be most practical to eliminate. Oil resources
      already may be about half depleted, depending upon the magnitude of
      undiscovered reserves, and it is still not practical to capture CO2
      emerging from vehicle tailpipes, the way it can be with coal-burning
      facilities, note the scientists. Coal, on the other hand, has larger
      reserves, and the authors conclude that "the only realistic way to
      sharply curtail CO2 emissions is phase out coal use except where CO2
      is captured and sequestered."

      In their model, with coal emissions phased out between 2010 and 2030,
      atmospheric CO2 would peak at 400-425 ppm and then slowly decline.
      The
      authors maintain that the peak CO2 level reached would depend on the
      accuracy of oil and gas reserve estimates and whether the most
      difficult to extract oil and gas is left in the ground.

      The authors suggest that reforestation of degraded land and improved
      agricultural practices that retain soil carbon could lower
      atmospheric
      CO2 by as much as 50 ppm. They also dismiss the notion of
      "geo-engineering" solutions, noting that the price of artificially
      removing 50 ppm of CO2 from the air would be about $20 trillion.

      While they note the task of moving toward an era beyond fossil fuels
      is Herculean, the authors conclude that it is feasible when compared
      with the efforts that went into World War II and that "the greatest
      danger is continued ignorance and denial, which could make tragic
      consequences unavoidable."

      "There is a bright side to this conclusion" said lead author James
      Hansen of Columbia University, "Following a path that leads to a
      lower
      CO2 amount, we can alleviate a number of problems that had begun to
      seem inevitable, such as increased storm intensities, expanded
      desertification, loss of coral reefs, and loss of mountain glaciers
      that supply fresh water to hundreds of millions of people."

      ###

      In addition to Hansen and Pagani, authors of the paper are Robert
      Berner from Yale University; Makiko Sato and Pushker Kharecha from
      the
      NASA/Goddard Institute for Space Studies and Columbia University
      Earth
      Institute; David Beerling from the University of Sheffield, UK;
      Valerie Masson-Delmotte from CEA-CNRS-Universite de Versaille, France
      Maureen Raymo from Boston University; Dana Royer from Wesleyan
      University and James C. Zachos from the University of California at
      Santa Cruz.

      Citation: Open Atmospheric Science Journal, Volume 2, 217-231 (2008)
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