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June 5, 2003 GLOBAL GARDEN GROWS GREENER
A NASA-Department of Energy jointly funded study concludes the
Earth has been greening over the past 20 years. As climate changed,
plants found it easier to grow.
The globally comprehensive, multi-discipline study appears in
this week's Science magazine. The article states climate changes
have provided extra doses of water, heat and sunlight in areas where
one or more of those ingredients may have been lacking. Plants
flourished in places where climatic conditions previously limited
growth.
"Our study proposes climatic changes as the leading cause for the
increases in plant growth over the last two decades, with lesser
contribution from carbon dioxide fertilization and forest
re-growth," said Ramakrishna Nemani, the study's lead author from
the University of Montana, Missoula, Mont.
From 1980 to 2000, changes to the global environment have
included two of the warmest decades in the instrumental record;
three intense El Ni¤o events in 1982-83, 1987-88 and 1997-98;
changes in tropical cloudiness and monsoon dynamics; and a 9.3
percent increase in atmospheric carbon dioxide (CO2), which in turn
affects man-made influences on climate. All these changes impact
plant growth.
Earlier studies by Ranga Myneni, Boston University (BU), and
Compton Tucker, NASA's Goddard Space Flight Center (GSFC),
Greenbelt, Md., also co-authors of the study, reported increased
growing seasons and woody biomass in northern high-latitude
forests.
Another co-author, Charles Keeling, Scripps Institution of
Oceanography, La Jolla, Calif., cautions no one knows whether these
positive impacts are due to short-term climate cycles, or
longer-term global climate changes. Also, a 36 percent increase in
global population, from 4.45 billion in 1980 to 6.08 billion in
2000, overshadows the increases in plant growth.
Nemani and colleagues constructed a global map of the Net Primary
Production (NPP) of plants from climate and satellite data of
vegetation greenness and solar radiation absorption. NPP is the
difference between the CO2 absorbed by plants during photosynthesis,
and CO2 lost by plants during respiration. NPP is the foundation for
food, fiber and fuel derived from plants, without which life on
Earth could not exist. Humans appropriate approximately 50 percent
of global NPP.
NPP globally increased on average by six percent from 1982 to
1999. Ecosystems in tropical zones and in the high latitudes of the
Northern Hemisphere accounted for 80 percent of the increase. NPP
increased significantly over 25 percent of the global vegetated
area, but decreased over seven percent of the area; illustrating how
plants respond differently depending on regional climatic
conditions.
Climatic changes, over approximately the past 20 years, tended to
be in the direction of easing climatic limits to plant growth. In
general, in areas where temperatures restricted plant growth, it
became warmer; where sunlight was needed, clouds dissipated; and
where it was too dry, it rained more. In the Amazon, plant growth
was limited by sun blocking cloud cover, but the skies have become
less cloudy. In India, where a billion people depend on rain, the
monsoon was more dependable in the 1990s than in the 1980s.
The climate data for NPP calculations came from the National
Oceanic and Atmospheric Administration (NOAA) National Center for
Environmental Prediction. Researchers used two independently derived
18-plus-year satellite datasets from the Advanced Very High
Resolution Radiometers on NOAA satellite. The team processed and
improved the data at GSFC and BU.
"Systematic observation of global vegetation is being continued
by NASA's Earth observing satellites. Earth observing satellites are
paving the way to find out if these biospheric responses are going
to hold for the future," adds Steve Running, another co-author from
the University of Montana.
NASA's Earth Science Enterprise is committed to studying the
primary causes of the Earth system variability, including both
natural and human-induced causes. ###
Contacts:
David
E. Steitz
Headquarters, Washington
(Phone:
202/358-1730)
Krishna Ramanujan
Goddard Space Flight
Center, Greenbelt, Md.
(Phone: 301/286-3026)
Mary Keller
AAAS Office of Public Programs
mkeller@aaas.org
202-326-6657
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 Global Change in NPP
Between 1982 and 1999, the climate became warmer,
wetter, and sunnier in many parts of the world. These changes
increased the overall productivity of land plants by 6 percent. This
map shows productivity increases during the time period in green,
while decreases are shown in brown. Productivity, which is the net
uptake of carbon, increased the most in tropical regions, where
climate change resulted in fewer clouds and more sunlight. Credit:
NASA Earth Observatory  20 Years of change (1980-2000)
Nearly 20 years of satellite observations of net
primary productivity reveal the seasonal and yearly cycles of
Earth's vegetation. In this animation, the dominant theme is the
shift in productivity (shades of green) between the Northern and
Southern Hemisphere over the course of a year. Hidden within this
dominant cycle are more subtle vegetation patterns: a decrease in
productivity at high latitudes of the Northern Hemisphere following
the eruption of Mt. Pinatubo in 1991, as well as global-scale
decreases in productivity during the El Ni¤o events of 1982-83,
1987-88, and 1997-98. Credit: NASA Earth Observatory  Recent Changes in NPP (2001-2002)
NASA satellites have continued to measure global
changes in NPP during 2001 and 2002, and will provide scientists
with a strong platform for understanding changes in Earth's systems
in years to come. Credit: NASA Earth Observatory
 Percent Change in Annual Global Net
Primary Productivity from 1982-1999
Percent change in annual global Net Primary
Production (NPP) change from 1982-1999. Purple represents the
highest increase (2%) in NPP per year. Areas of blue and red
represent decreasing annual NPP. Credit: University of Montana
 Three Years from SeaWiFs
NASA's Sea-viewing Wide Field-of-view Sensor
(SeaWiFS) aboard the OrbView-2 satellite has been collecting data on
plant productivity and the carbon cycle since 1997. This colorful
globe is a three-year map of continuous data showing fluctuating
areas of successful photosynthesis on land and in the oceans.
Credit: NASA/ORBIMAGE  Three Years Flat, from SeaWiFs
The following animation shows three years of
continuous SeaWiFS data (1997-2000) on a flat map of the Earth. The
smooth migration of green areas over time is a reflection of
seasonal changes in temperature and moisture. Credit: NASA/ORBIMAGE
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