From: baalke@zagami.jpl.nasa.gov   
      
   Elvia Thompson   
   Headquarters, Washington              December 10, 2002   
   (Phone: 202/358-1696)   
      
   Lisa Townsend   
   NASA Jet Propulsion Laboratory, Pasadena, Calif.   
   (Phone: 818/393-5464)   
      
   Release: 03-404   
      
   NASA SCIENTISTS DISCOVER SPRING THAW MAKES A DIFFERENCE   
      
        Using a suite of microwave remote sensing instruments   
   aboard satellites, scientists at NASA's Jet Propulsion   
   Laboratory (JPL), Pasadena, Calif., and the University of   
   Montana, Missoula, have observed a recent trend of earlier   
   thawing across the northern high latitudes.   
      
   This regional thawing trend, advancing almost one day a year   
   since 1988, has the potential to alter the cycle of   
   atmospheric carbon dioxide intake and release by vegetation   
   and soils across the region, potentially resulting in changes   
   in Earth's climate. The lengthening growing season appears to   
   be promoting more carbon uptake by the vegetation than is   
   being released into the atmosphere for the region. How long   
   this trend will occur depends on whether soils continue to   
   remain cold and wet.   
      
   Research scientists have been studying freeze/thaw dynamics in   
   North America and Eurasia's boreal forests and tundra to   
   decipher effects on the timing and length of the growing   
   season. These regions encompass almost 30 percent of global   
   land area. They store a major portion of Earth's carbon in   
   vegetation, in seasonally frozen and permafrost soils. Large   
   expanses of boreal forest and tundra are underlain by   
   permafrost, a layer of permanently frozen soil found   
   underneath the active, seasonally thawed soil.   
      
   "Frozen soil can store carbon for hundreds to thousands of   
   years," said lead author Dr. Kyle McDonald of JPL, "but when   
   the permafrost thaws and begins to dry out, it releases the   
   carbon back into the atmosphere." The concern is that   
   eventually carbon released from the soil will prevail over the   
   amount being taken in by growing plants. Carbon dioxide levels   
   in the atmosphere would increase at an accelerated rate,   
   fostering even greater warming of the region and affecting   
   global climate.   
      
   With help from NASA radars and other orbiting satellite   
   microwave remote sensing instruments, including the National   
   Oceanic and Atmospheric Administration's Special Scanning   
   Microwave/Imager, scientists can monitor growing season   
   dynamics of the global boreal forest and tundra daily. These   
   instruments sense the electrical properties of water in the   
   landscape, allowing scientists to determine exactly when and   
   where the springtime thaw occurs.   
      
   Because of the large extent and location of boreal forest and   
   tundra, and the global reservoir of carbon stored in their   
   vegetation and soils, this region is extremely sensitive to   
   environmental change. It has the capacity to dramatically   
   impact Earth's climate.   
      
   "If global climate change is happening, here's where you would   
   expect to see it first," McDonald said.   
      
   As the research team observed, the earlier the spring thaw   
   occurs, the longer the growing season. These changes appear to   
   be promoting plant growth for the region. The longer growing   
   season allows plants to remove more carbon dioxide from the   
   atmosphere over a longer period of time.   
      
   Carbon dioxide is an important greenhouse gas that, if left in   
   the atmosphere, would promote additional warming. The plants   
   release oxygen and store the carbon as biomass that eventually   
   decomposes and transfers the carbon into the soil. Soil   
   microbes decompose dead plant material, returning a portion of   
   the soil carbon back into the atmosphere. The rate which soil   
   microbes decompose plant material and release carbon to the   
   atmosphere is also very sensitive to temperature. It could   
   potentially increase with warming temperatures and longer   
   growing seasons.   
      
   >From this general study, McDonald, Dr. John Kimball of the   
   University of Montana, and JPL's Erika Podest have lead three   
   different investigations, each focusing on different   
   noticeable changes in the boreal region. Results of three   
   related papers on this research will be presented to the   
   American Geophysical Union's Fall Meeting this week in San   
   Francisco.   
      
   The research is 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. The California Institute of   
   Technology, Pasadena, manages JPL for NASA.   
      
   For more information about climate on the Internet, visit:   
      
   http://www.gsfc.nasa.gov/topstory/2003/1210landfreeze.html   
      
   For information about NASA's Earth Science Enterprise on the   
   Internet, visit:   
      
   http://www.earth.nasa.gov   
      
      
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