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Scientists: Earth will lose global protection

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  • Mike Neuman
    Scientists: Earth will lose global protection Computer model shows planets ability to fend off global warming eroding By Ian Hoffman, STAFF WRITER Inside Bay
    Message 1 of 1 , Aug 8, 2005
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      Scientists: Earth will lose global protection
      Computer model shows planets ability to fend off global warming

      By Ian Hoffman, STAFF WRITER
      Inside Bay Area

      Scientists speeding through decades by supercomputer are concluding
      that the Earths built-in resilience to global warming — the great
      carbon storage capacity of its oceans and forests — could be coming
      to an end.

      Climate researchers know the worlds plants, soils and seas recently
      have been absorbing billions of tons more carbon dioxide than in the
      past 400,000 years. This breathing biosphere in essence has kept more
      than 60 percent of human fossil-fuel emissions from trapping solar
      energy in the atmosphere and warming the planet.

      But scientists have disagreed on how much more carbon these natural
      repositories can take.

      In experiments and satellite images, increasing carbon dioxide
      appears to be fertilizing plants in North America, making them lush
      and greener in the springtime. But can humans continue relying on
      plants, bacteria and other species of land and sea to cushion the
      effects of increasing fossil-fuel burning?

      According to the most recent supercomputer simulations, the answer is

      Inez Fung, head of the University of Californias Berkeley Atmospheric
      Sciences Center, led a team peering 100 years into the future as
      humans continue expanding reliance on fossil fuels for energy. What
      they found was a slow loss of the biospheres resilience to carbon
      dioxide and accelerated globalwarming.

      The computer simulation that they used was unrealistic in some ways:
      Plants were allowed unlimited nutrients. Redwoods could grow as tall
      as they wanted, without regard for getting water to the crown.

      "There's a maximum capacity of the land. Here we're just ignoring
      that," Fung said.

      Even then, the plants ran into metabolic limits. And as summer heat
      and droughts increased, the plants cut back on their intake of carbon
      dioxide in order to save water, then turned brown and stopped
      breathing carbon dioxide altogether.

      Likewise, the upper layer of the ocean becomes warm enough that
      carbon dioxide at the surface no longer is churned down to great
      depths impeding the absorption of more carbon dioxide.

      "With the ocean, think of it as a leaky pipe," Fung said. "If you
      stuff things down faster, that leakage rate is going to slow down."

      By 2050, global temperature had risen 2.5 degrees, which ranks low
      among projections of global warming over the same period. A less
      conservative simulation, for example one with limited nitrogen or
      other nutrients in soils or more realistic tree growth, would remove
      less carbon dioxide from the air and return it more quickly as the
      plants die.

      Stanford scientist Ken Caldeira ran a climate simulation 200 years
      into the future while working at Lawrence Livermore National
      Laboratory and found a point late in the 21st century when the
      biosphere caved, clouds vanished and the temperature started soaring.

      The study by Fung's team suggests that leveling carbon dioxide
      emissions off now or at least within 30 years could preserve the
      planet's flexibility.

      "There is a window of opportunity," she said.

      Contact Ian Hoffman at ihoffman@...


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