WASHINGTON,
March 10, 2013
/PRNewswire-USNewswire/ -- 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 land
surface and newly improved satellite data sets.
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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."
The study was published Sunday in the journal Nature Climate Change.
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."
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 say 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."
Researchers did find found more plant growth in the boreal zone from
1982 to 1992 than from 1992 to 2011, because water limitations were
encountered in the latter two decades.
Data, results and computer codes from this study will be made
available on NASA Earth Exchange (NEX), a collaborative supercomputing
facility at Ames. NEX is designed to bring scientists together with
data, models and computing resources to accelerate research and
innovation and provide transparency.
For more information and images associated with this release, visit:
http://go.nasa.gov/12Amv2s
SOURCE NASA
CONTACT: Steve Cole,
Headquarters, Washington , +1-202-358-0918, stephen.e.cole@nasa.gov,
Kathryn Hansen , Goddard Space Flight Center, Greenbelt, Md.,
+1-301-286-1046, kathryn.h.hansen@nasa.gov, or Ruth Marlaire, Ames
Research Center, Moffett Field, Calif., +1-650-604-4709,
ruth.marlaire@nasa.gov 
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