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The Human Contribution To Atmosphere Circulation Changes

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  • Pat Neuman
    The Human Contribution To Atmosphere Circulation Changes by Staff Writers Virginia Key FL (SPX) May 05, 2006 A new study published in this week s issue of
    Message 1 of 1 , May 4, 2006
      The Human Contribution To Atmosphere Circulation Changes

      by Staff Writers
      Virginia Key FL (SPX) May 05, 2006
      A new study published in this week's issue of Nature is the first to
      show that human activity is altering the circulation of the tropical
      atmosphere and ocean through global warming.
      Scientists widely agree that the climate has warmed over the past
      century and that human activities, such as burning fossil fuels,
      have significantly contributed to this global warming.

      This study tapped historical records that date back to the mid-19th
      century as well as simple theory and state-of-the-art computer model
      simulations to detect and attribute these climate changes.

      The conclusion was that the principal loop of winds that drives
      climate and ocean behavior across the tropical Pacific is slowing
      down and causing the climate to drift towards a more El Niño-like
      state. This could have important implications for the frequency and
      intensity of future El Niño events and biological productivity in
      tropical oceans.

      In their paper, titled "Weakening of Tropical Pacific Atmospheric
      Circulation Due to Anthropogenic Forcing," the researchers identify
      a 3.5 percent weakening that has occurred since the mid-1800s in
      this air system known as the Walker circulation. They also cite
      evidence that it may weaken another 10 percent by 2100.

      "There is an indication that the slowdown may be intensifying," said
      Dr. Gabriel A. Vecchi, lead author from NOAA's Geophysical Fluid
      Dynamics Laboratory. "The trend since World War II is larger than
      that over the entire record, and the long-term trend is larger than
      what is expected from natural climate variability. This is why we
      employed a very long observational record — to be able to accurately
      detect and attribute these changes."

      The study does send mixed signals on the future of El Niño/La
      Niña. "While we can't predict with certainty how the frequency or
      intensity of El Niño-related weather events will respond to global
      warming, our study does suggest that the climate as a whole is
      slowly moving towards a more El Niño-like state," said Dr. Brian
      Soden, a co-author from the University of Miami Rosenstiel School of
      Marine and Atmospheric Science.

      "Additionally, this slowdown has modified the structure and
      circulation of the tropical Pacific Ocean, which is a source of
      nutrients to one of the most biologically productive regions of the
      world's oceans. This has implications to the well-being and
      proliferation of marine life in tropical oceans."

      "The Walker circulation is fundamental to climate throughout the
      globe: its variations are closely linked to those of the El
      Niño/Southern Oscillation and monsoonal circulations over adjacent
      continents, and variations in its intensity and structure affect
      climate all over the globe," wrote Vecchi, Soden, and their co-
      authors Andrew T. Wittenberg, Isaac M. Held, Ants Leetmaa, and
      Matthew J. Harrison, also from the NOAA Geophysical Fluid Dynamics
      Laboratory in Princeton, N.J. The Walker circulation spans almost
      half the circumference of the Earth.

      This study found a weakening of the Walker circulation in historical
      observations that corresponds closely to what theoretical and
      modeling studies expect from an increase in greenhouse gases. This
      agreement provides increased confidence in model projections of
      future climate change in the tropics.

      Rosenstiel School is part of the University of Miami and, since its
      founding in the 1940s, has grown into one of the world's premier
      marine and atmospheric research institutions.

      An Envisat image of La Nina in February 2006.

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