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:
