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NOAA & NCAR - Two of the nation's premier atmospheric scientists conclude ...

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  • patneuman2000
    Dec 1, 2003 Press Release 2:00 PM EST No Doubt Human Activity Is Affecting Global Climate, Top Scientists Conclude BOULDER-Two of the nation s premier
    Message 1 of 2 , Dec 15, 2004
      Dec 1, 2003 Press Release 2:00 PM EST

      "No Doubt" Human Activity Is Affecting Global Climate, Top Scientists

      BOULDER-Two of the nation's premier atmospheric scientists, after
      reviewing extensive research by their colleagues, say there is no
      longer any doubt that human activities are having measurable-and
      increasing-impacts on global climate. Their study cites atmospheric
      observations and multiple computer models to paint a detailed picture
      of climate changes likely to buffet Earth in coming decades, including
      rising temperatures and an increase in extreme weather events, such as
      flooding and drought. The study appears December 5 in Science as part
      of the journal's "State of the Planet" series.

      The coauthors-Thomas Karl, director of NOAA's National Climatic Data
      Center, and Kevin Trenberth, head of the Climate Analysis Section at
      the National Center for Atmospheric Research (NCAR)-conclude that
      industrial emissions have been the dominant influence on climate
      change for the past 50 years, overwhelming natural forces. The most
      important of these emissions is carbon dioxide, a greenhouse gas that
      traps solar radiation and warms the planet.

      "There is no doubt that the composition of the atmosphere is changing
      because of human activities, and today greenhouse gases are the
      largest human influence on global climate," they write. "The likely
      result is more frequent heat waves, droughts, extreme precipitation
      events, and related impacts, e.g., wildfires, heat stress, vegetation
      changes, and sea-level rise which will be regionally dependent."

      Karl and Trenberth estimate that, between 1990 and 2100, there is a 90
      percent probability that global temperatures will rise by 1.7 to 4.9
      degrees Celsius (3.1 to 8.9 degrees Fahrenheit), because of human
      influences on climate. Such warming would have widespread impacts on
      society and the environment, including continued melting of glaciers
      and the great ice sheets of Greenland, inundating the world's coasts.
      The authors base their estimate on computer model experiments by
      climate scientists, observations of atmospheric changes, and recorded
      climate changes over the past century.

      Carbon dioxide levels in the atmosphere have risen by 31 percent since
      preindustrial times, from 280 parts per million by volume (ppmv) to
      over 370 ppmv today. Other human activities, such as emissions of
      sulfate and soot particles and the development of urban areas, have
      significant but more localized climate impacts. Such activities may
      enhance or mask the larger-scale warming from greenhouse gases, but
      not offset it, according to the authors.

      If societies could successfully cut emissions and stabilize carbon
      dioxide levels in the atmosphere, temperatures would still increase by
      an estimated 0.5 degree C (0.9 degree F) over a period of decades,
      Karl and Trenberth warn. This is because greenhouse gases are slow to
      cycle out of the atmosphere. "Given what has happened to date and is
      projected in the future, significant further climate change is
      guaranteed," the authors state.

      If current emissions continue, the world would face the fastest rate
      of climate change in at least the last 10,000 years. This could
      potentially alter ocean current circulations and radically change
      existing climate patterns. Moreover, certain natural processes would
      tend to accelerate the warming. For example, as snow cover melts away,
      the darker land and water surface would absorb more solar radiation,
      further increasing temperatures.

      Karl and Trenberth say more research is needed to pin down both the
      global and regional impacts of climate change. Scientists, for
      example, have yet to determine the temperature impacts of increased
      cloud cover or how changes in the atmosphere will influence El NiƱo,
      the periodic warming of Pacific Ocean waters that affects weather
      patterns throughout much of the world. The authors call for multiple
      computer model studies to address the complex aspects of weather and
      climate. The models must be able to integrate all components of
      Earth's climate system-physical, chemical, and biological. This, in
      turn, will require considerable international cooperation and the
      establishment of a global climate monitoring system to collect and
      analyze data.

      "Climate change is truly a global issue, one that may prove to be
      humanity's greatest challenge," the authors conclude. "It is very
      unlikely to be adequately addressed without greatly improved
      international cooperation and action."

      -The End-

      Anatta, NCAR
      Cheryl Dybas, NSF
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