Amplified Greenhouse Effect Shifts North's Growing Seasons   
       
   March 10, 2013: Vegetation growth at Earth's northern latitudes increasingly   
   resembles lusher latitudes to the south, according to a NASA-funded study   
   based on a 30-year record of ground-based and satellite data sets.   
       
   In a paper published Sunday, March 10, in the journal Nature Climate Change,   
   an international team of university and NASA scientists examined the   
   relationship between changes in surface temperature and vegetation growth from   
   45 degrees north latitude to the Arctic Ocean. Results show temperature and   
   vegetation growth at northern latitudes now resemble those found 4 degrees to   
   6 degrees of latitude farther south as recently as 1982.   
       
   "Higher northern latitudes are getting warmer, Arctic sea ice and the duration   
   of snow cover are diminishing, the growing season is getting longer and plants   
   are growing more," said Ranga Myneni of Boston University's Department of   
   Earth and Environment. "In the north's Arctic and boreal areas, the   
   characteristics of the seasons are changing, leading to great disruptions for   
   plants and related ecosystems."   
       
   http://www.nasa.gov/images/content/733096main_Northern_ndvi_FINAL.jpg   
       
   Of the 10 million square miles (26 million square kilometers) of northern   
   vegetated lands, 34 to 41 percent showed increases in plant growth (green and   
   blue), 3 to 5 percent showed decreases in plant growth (orange and red), and   
   51 to 62 percent showed no changes (yellow) over the past 30 years. Satellite   
   data in this visualization are from AVHRR and MODIS. Credit: NASA's Goddard   
   Space Flight Center Scientific Visualization Studio   
   Myneni and colleagues used satellite data to quantify vegetation changes at   
   different latitudes from 1982 to 2011. Data used in this study came from   
   NOAA's Advanced Very High Resolution Radiometers (AVHRR) onboard a series of   
   polar-orbiting satellites and NASA's Moderate Resolution Imaging   
   Spectroradiometer (MODIS) instruments on the Terra and Aqua satellites.   
       
   As a result of enhanced warming and a longer growing season, large patches of   
   vigorously productive vegetation now span a third of the northern landscape,   
   or more than 3.5 million square miles (9 million square kilometers). That is   
   an area about equal to the contiguous United States. This landscape resembles   
   what was found 250 to 430 miles (400 to 700 kilometers) to the south in 1982.   
       
   "It's like Winnipeg, Manitoba, moving to Minneapolis-Saint Paul in only 30   
   years," said co-author Compton Tucker of NASA's Goddard Space Flight Center in   
   Greenbelt, Md.   
       
   The Arctic's greenness is visible on the ground as an increasing abundance of   
   tall shrubs and trees in locations all over the circumpolar Arctic. Greening   
   in the adjacent boreal areas is more pronounced in Eurasia than in North   
   America.   
       
   An amplified greenhouse effect is driving the changes, according to Myneni.   
   Increased concentrations of heat-trapping gasses, such as water vapor, carbon   
   dioxide and methane, cause Earth's surface, ocean and lower atmosphere to   
   warm. Warming reduces the extent of polar sea ice and snow cover, and, in   
   turn, the darker ocean and land surfaces absorb more solar energy, thus   
   further heating the air above them.   
       
   "This sets in motion a cycle of positive reinforcement between warming and   
   loss of sea ice and snow cover, which we call the amplified greenhouse   
   effect," Myneni said. "The greenhouse effect could be further amplified in the   
   future as soils in the north thaw, releasing potentially significant amounts   
   of carbon dioxide and methane."   
       
   http://www.nasa.gov/images/content/733085main_26-palsa-mire.jpg   
       
   Trees take hold as permafrost thaws near the Altai Mountains in Russia.   
   Credit: Terry Callaghan, EU-Interact/Sergey Kirpotin, Tomsk State University   
   To find out what is in store for future decades, the team analyzed 17 climate   
   models. These models show that increased temperatures in Arctic and boreal   
   regions would be the equivalent of a 20-degree latitude shift by the end of   
   this century relative to a period of comparison from 1951-1980. However,   
   researchers note that plant growth in the north may not continue on its   
   current trajectory. The ramifications of an amplified greenhouse effect, such   
   as frequent forest fires, outbreak of pest infestations and summertime   
   droughts, may slow plant growth. Also, warmer temperatures alone in the boreal   
   zone do not guarantee more plant growth, which also depends on the   
   availability of water and sunlight.   
       
   "Satellite data identify areas in the boreal zone that are warmer and dryer   
   and other areas that are warmer and wetter," said co-author Ramakrishna Nemani   
   of NASA's Ames Research Center in Moffett Field, Calif. "Only the warmer and   
   wetter areas support more growth."   
       
   "We found more plant growth in the boreal zone from 1982 to 1992 than from   
   1992 to 2011, because water limitations were encountered in the later two   
   decades of our study," said co-author Sangram Ganguly of the Bay Area   
   Environmental Research Institute and NASA Ames.   
       
   Data, results and computer codes from this study will be made available on   
   NASA Earth Exchange (NEX), a collaborative supercomputing facility at Ames   
   Research Center, Moffett Field, Calif. NEX is designed to bring scientists   
   together with data, models and computing resources to accelerate research and   
   innovation and provide transparency.   
       
       
   Author: Kathryn Hansen| Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.9   
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