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Re: Black Soot and Snow: A Warmer Combination

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  • Mike Neuman
    The key conclusion of the study is this: Although the role of soot in altering global climate is substantial, it does not alter the fact greenhouse gases are
    Message 1 of 2 , Dec 31, 2003
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      The key conclusion of the study is this: "Although the role of soot
      in altering global climate is substantial, it does not alter the fact
      greenhouse gases are the primary cause of climate warming during the
      past century. Such gases are expected to be the largest climate
      forcing for the rest of this century."

      --- In ClimateArchive@yahoogroups.com, npat1@j... wrote:
      > December 22, 2003
      >
      > Black Soot and Snow: A Warmer Combination
      > New research from NASA scientists suggests emissions of black soot
      alter the way sunlight reflects off snow. According to a computer
      simulation, black soot may be responsible for 25 percent of observed
      global warming over the past century.
      >
      > Soot in the higher latitudes of the Earth, where ice is more
      common, absorbs more of the sun's energy and warmth than an icy,
      white background. Dark-colored black carbon, or soot, absorbs
      sunlight, while lighter colored ice reflects sunlight.
      >
      > Soot in areas with snow and ice may play an important role in
      climate change. Also, if snow- and ice-covered areas begin melting,
      the warming effect increases, as the soot becomes more concentrated
      on the snow surface. "This provides a positive feedback (i.e.
      warming); as glaciers and ice sheets melt, they tend to get even
      dirtier," said Dr. James Hansen, a researcher at NASA's Goddard
      Institute for Space Studies, New York.
      >
      > Hansen and Larissa Nazarenko, both of the Goddard Institute and
      Columbia University's Earth Institute, found soot's effect on snow
      albedo (solar energy reflected back to space), which has been
      neglected in previous studies, may be contributing to trends toward
      early springs in the Northern Hemisphere, thinning Arctic sea ice,
      melting glaciers and permafrost. Soot also is believed to play a role
      in changes in the atmosphere above the oceans and land.
      >
      > "Black carbon reduces the amount of energy reflected by snow back
      into space, thus heating the snow surface more than if there were no
      black carbon," Hansen said.
      >
      > Soot's increased absorption of solar energy is especially effective
      in warming the world's climate. "This forcing is unusually effective,
      causing twice as much global warming as a carbon-dioxide forcing of
      the same magnitude," Hansen noted.
      >
      > Hansen cautioned, although the role of soot in altering global
      climate is substantial, it does not alter the fact greenhouse gases
      are the primary cause of climate warming during the past century.
      Such gases are expected to be the largest climate forcing for the
      rest of this century.
      >
      > The researchers found that observed warming in the Northern
      Hemisphere was large in the winter and spring at middle and high
      latitudes. These observations were consistent with the researchers'
      climate model simulations, which showed some of the largest warming
      effects occurred when there was heavy snow cover and sufficient
      sunlight.
      >
      > Hansen and Nazarenko used a leading worldwide-climate computer
      model to simulate effects of greenhouse gases and other factors on
      world climate. The model incorporated data from NASA spacecraft that
      monitor the Earth's surface, vegetation, oceans and atmospheric
      qualities. The calculated global warming from soot in snow and ice,
      by itself in an 1880-2000 simulation, accounted for 25 percent of
      observed global warming. NASA's Terra and Aqua satellites are
      observing snow cover and reflectivity at multiple wavelengths, which
      allows quantitative monitoring of changing snow cover and effects of
      soot on snow.
      >
      > The research is in the paper "Soot Climate Forcing via Snow and Ice
      Albedos," appearing online this week in the Proceedings of the
      National Academy of Sciences.
      >
      > This research was funded by NASA's Earth Science Enterprise. The
      Enterprise is dedicated to understanding the Earth as an integrated
      system and applying Earth system science to improve prediction of
      climate, weather and natural hazards using the unique vantage point
      of space.
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