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David E. Steitz
Headquarters, Washington               June 5, 2003
(Phone: 202/358-1730)

Krishna Ramanujan
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301/286-3026)

RELEASE: 03-182

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 Nino 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.

For information about the research on the Internet, visit:

http://www.gsfc.nasa.gov/topstory/2003/0530earthgreen.html

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