Global garden grows greenerJune 6,
2003
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 Niño 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.
NASA/Goddard Space Flight
Center--EOS Project Science Office |
Print this page
E-mail this page to a
friend
