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Fwd: Methane's Impacts on Climate Change May Be Twice Previous Estimates

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  • Mike Neuman
    ... wrote: RESEARCH NEWS Methane s Impacts on Climate Change May Be Twice Previous Estimates Click here
    Message 1 of 1 , Jul 19, 2005
      --- In Paleontology_and_Climate@yahoogroups.com, Sonya
      <msredsonya@e...> wrote:

      RESEARCH NEWS

      Methane's Impacts on Climate Change May Be Twice Previous Estimates
      Click here <http://www.giss.nasa.gov/research/news/20050718/>

      July 18, 2005

      Scientists face difficult challenges in predicting and understanding
      how much
      our climate is changing. When it comes to gases that trap heat in our
      atmosphere, called greenhouse gases (GHGs), scientists typically look
      at how
      much of the gases exist in the atmosphere.

      *Image to right -- Rice Paddies in China:* This
      image shows Chinese farmers transplanting rice in paddy fields in
      Yunnan
      Province, China, July 1999. Fossil fuels, cattle, landfills and rice
      paddies are
      the main human-related sources. Previous studies have shown that new
      rice
      harvesting techniques can significantly reduce methane emissions and
      increase
      yields. *Click on image to enlarge* Credit: Changsheng Li

      However, Drew Shindell, a climatologist at NASA's Goddard Institute
      for Space
      Studies, New York, NY, believes we need to look at the GHGs when they
      are
      emitted at Earth's surface, instead of looking at the GHGs themselves
      after they
      have been mixed into the atmosphere. "The gas molecules undergo
      chemical changes
      and once they do, looking at them after they've mixed and changed in
      the
      atmosphere doesn't give an accurate picture of their effect,"
      Shindell said.
      "For example, the amount of methane in the atmosphere is affected by
      pollutants
      that change methane's chemistry, and it doesn't reflect the effects
      of methane
      on other greenhouse gases," said Shindell, "so it's not directly
      related to
      emissions, which are what we set policies for."

      Chemically reactive GHGs include methane and ozone (carbon dioxide,
      the most
      important GHG, is largely unreactive). Once methane and the molecules
      that
      create ozone are released into the air by both natural and human-
      induced
      sources, these gases mix and react together, which transforms their
      compositions. When gases are altered, their contribution to the
      greenhouse
      warming effect also shifts. So, the true effect of a single GHG
      emission on
      climate becomes very hard to single out.

      Some of the major investigations into the state of our warming planet
      come
      from a series of reports from the Intergovernmental Panel on Climate
      Change
      (IPCC) Assessment. These reports involved the work of hundreds of
      climate
      experts. The reports rely on measurements of greenhouse gases as they
      exist in
      the atmosphere, after they may have mixed with other gases. In other
      words, the
      findings in the report do not reflect the quantities that were
      actually
      emitted.

      *Image to left -- Inland Wetlands: *Sources of
      methane include natural sources like wetlands, gas hydrates in the
      ocean floor,
      permafrost, termites, oceans, freshwater bodies, and non-wetland
      soils.* Click
      on image to enlarge.* Credit: U.S. EPA, Leo Kenney, Region 1

      Shindell finds there are advantages to measuring emissions of
      greenhouse
      gases and isolating their impacts, as opposed to analyzing them after
      they have
      mixed in the atmosphere. His study on the subject was recently
      published in the
      journal Geophysical Research Letters. In the study, when the
      individual effects
      of each gas on global warming were added together, the total was
      within 10
      ercent of the impacts of all the gases mixed together. The small
      difference in
      the two amounts was a sign to Shindell that little error was
      introduced by
      separating the emissions from one another.

      After isolating each greenhouse gas and calculating the impact of
      each
      mission on our climate with a computer model, Shindell and his
      colleagues found
      some striking differences in how much these gases contribute overall
      to climate
      change.

      The leading greenhouse gases include carbon dioxide, methane, nitrous
      oxide,
      and halocarbons. These gases are called "well mixed' greenhouse gases
      because of
      their long lifetimes of a decade or more, which allows them to
      disperse evenly
      around the atmosphere. They are emitted from both man-made and
      natural sources.
      Ozone in the lower atmosphere, called tropospheric ozone, a major
      component of
      polluted air or smog that is damaging to human and ecosystem health,
      also has
      greenhouse warming effects. In the upper atmosphere, ozone protects
      life on
      Earth from the Sun's harmful ultraviolet rays.

      *According to new calculations, the impacts of methane on climate
      warming may
      be double the standard amount attributed to the gas. The new
      interpretations
      reveal methane emissions may account for a third of the climate
      warming from
      well-mixed greenhouse gases between the 1750s and today. The IPCC
      report, which
      calculates methane's affects once it exists in the atmosphere, states
      that
      methane increases in our atmosphere account for only about one sixth
      of the
      total effect of well-mixed greenhouse gases on warming*.

      *Image above:*
      Methane in the World's Atmosphere: These maps show the distribution
      of methane
      at the surface (top) and in the stratosphere (lower), calculated by a
      NASA
      computer model. Concentrations are shown in parts per million by
      volume. Methane
      is created near the surface, and it is carried into the stratosphere
      by rising
      air in the tropics. *Click on image to enlarge* Credit: GMAO Chemical
      Forecasts and GEOSâEUR"CHEM NRT Simulations for ICARTT (top) and NASA
      GSFC
      Atmospheric Chemistry and Dynamics Branch (lower)

      *Part of the reason the new calculations give a larger effect is that
      they
      include the sizeable impact of methane emissions on tropospheric
      ozone since the
      industrial revolution. Tropospheric ozone is not directly emitted,
      but is
      instead formed chemically from methane, other hydrocarbons, carbon
      monoxide and
      nitrogen oxides. The IPCC report includes the effects of tropospheric
      ozone
      increases on climate, but it is not attributed to particular sources.
      By
      categorizing the climate effects according to emissions, Shindell and
      colleagues
      found the total effects of methane emissions are substantially
      larger. In other
      words, the true source of some of the warming that is normally
      attributed to
      tropospheric ozone is really due to methane that leads to increased
      abundance of
      tropospheric ozone. According to the study, the effects of other
      pollutants were
      relatively minor. Nitrogen oxide emissions can even lead to cooling
      by fostering
      chemical reactions that destroy methane. This is partly why estimates
      based on
      the amount of methane in the atmosphere give the gas a smaller
      contribution to
      climate change. *

      *Molecule for molecule, Methane is 20 times more potent than carbon
      dioxide as
      a greenhouse gas, but CO_2 is much more abundant than methane and
      the
      predicted growth rate is far greater. Since 1750, methane
      concentrations in the
      atmosphere have more than doubled, though the rate of increase has
      slowed during
      the 1980-90s, and researchers don't understand why. Controlling
      methane could
      reap a big bang for the buck. Another bonus of this perspective is
      that in order
      to manage greenhouse gases, policy decisions must focus on cutting
      emissions,
      because that's where humans have some control. *

      *"If we control methane, which the U.S. is already starting to do,
      then we are
      likely to mitigate global warming more than one would have thought,
      so that's a
      very positive outcome," Shindell said. "Control of methane emissions
      turns out
      to be a more powerful lever to control global warming than would be
      anticipated." *

      *Sources of methane include natural sources like wetlands, gas
      hydrates in the
      ocean floor, permafrost, termites, oceans, freshwater bodies, and non-
      wetland
      soils. Fossil fuels, cattle, landfills and rice paddies are the main
      human-related sources. Previous studies have shown that new rice
      harvesting
      techniques can significantly reduce methane emissions and increase
      yields. *

      Reference

      Shindell, D.T., G. Faluvegi, N. Bell, and G.A. Schmidt 2005. An
      emissions-based view of climate forcing by methane and tropospheric
      ozone
      <http://pubs.giss.nasa.gov/abstracts/2005/ShindellFaluvegiBS.html>.
      Geophys. Res. Lett. *32*, L04803, doi:10.1029/2004GL021900.

      Media Contacts

      Krishna Ramanujan, Goddard Space Flight Center, 301-286-8955
      This page originated as a NASA portal Looking at Earth feature
      <http://www.nasa.gov/vision/earth/lookingatearth/methane.html>.

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      Page last modified: 2005-07-18




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