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April 22, 2003
NASA Satellite Measures Earth's Carbon Metabolism
In honor of the Earth Day celebration, NASA scientists unveiled the
first consistent and continuous global measurements of Earth's "metabolism." Data
from the Terra and Aqua satellites are helping scientists frequently
update maps of the rate at which plant life on Earth is absorbing carbon
out of the atmosphere.
Combining space-based measurements of a range of plant properties collected
by the Moderate Resolution Imaging Spectroradiometer (MODIS) with a suite
of other satellite and surface-based measurements, NASA scientists produce
composite maps of our world's "net primary production" every 8 days.
This new measurement is called net production because it indicates how
much carbon dioxide is taken in by vegetation during photosynthesis minus
how much is given off during respiration. Scientists expect this global
measure of the biological productivity of plants to yield new insights
into how the Earth's carbon
cycle works, a critical step toward solving the climate change puzzle.
The rate of carbon fixation through photosynthesis is a basic property
of life on planet Earth. It is the basis for capturing and storing the
energy that fuels our world's living systems and forms the foundation
of the food webs. The oxygen we breathe is a byproduct of this photosynthesis.
According to its creators, these new net primary productivity maps provide
a fascinating new insight into the intimate connection between the living
world and the physical world.
"We are literally watching the global garden grow," says Steve Running,
MODIS Science Team member and director of the Numerical Terradynamic
Simulation Group at the University of Montana. "We now have a regular,
consistent, calibrated and near-real-time measure of a major component
of the global carbon cycle for the first time. This measure can also
be the basis for monitoring the expansion of deserts, the effects of
droughts, and any impacts climate change may have on vegetation growth,
health, and seasonality."
On land, notes Running, photosynthesis is the foundation for agricultural
crop production, rangeland grazing capacity and forest growth. "We also
anticipate that our new productivity maps should help to significantly
improve analysis of global crop commodities."
The new maps show that the highest mid-summer productivity rates are
found at temperate latitudes with mild climates and not at tropical latitudes,
as some might have expected. However, tropical forests are more productive
over a full year because of their longer growing season. Viewing the
global maps sequentially in a 2-year
movie reveals some fantastic seasonal cycles of plant growth, especially
at high latitudes across North America, Europe, and Asia. The movie also
reveals the almost immediate response of land plants to changing daily
weather patterns.
However, plant life in the ocean is somewhat more buffered and therefore
not as directly driven by weather patterns, states Wayne Esaias, biological
oceanographer at NASA's Goddard Space Flight Center. The growth of microscopic
marine plants (phytoplankton) in the ocean responds more to seasonal
changes—currents, temperature, and sunlight. So, whereas certain
areas on land will swing abruptly from very low to very high rates of
photosynthetic activity, biological productivity in the ocean is ongoing
steadily and is spread over much wider areas.
"It doesn't surprise Earth scientists, but the public might be surprised
to learn that there is so much photosynthesis in the oceans," observes
Esaias. "When you average the productivity rates over the whole world,
the ocean is roughly equal to the land."
Esaias is examining how plant productivity rates in the ocean vary in
response to changes in the ocean's current patterns. In particular, he
says, these new primary productivity maps will help fisheries scientists
understand why there are good catches some years and poor catches in
others.
For the last two decades, using data from earlier satellite sensors,
scientists have been able to map global concentrations of chlorophyll,
the green pigment marine and land plants use for photosynthesis. But
it was still a leap for scientists to estimate how much carbon was converted
to organic material by plants—a measure now routinely provided
by the net primary productivity maps.
The new MODIS maps mark a major milestone in the careers of both Running
and Esaias—a milestone they have been working toward for more than
20 years. "As Earth systems science began in the 1980s, ecology was way
behind the atmosphere and oceans disciplines in achieving a global perspective
because our training was on single organisms (i.e., dissecting frogs
and counting dandelions), so we had no global-scale theory or measurements," states
Running. "But this new measurement attests that ecology is now catching
up in global science."
Esaias adds that this is just the first cut and there is much work left
to do to refine their maps. "The world is a big place and we are only
just beginning to fully understand and validate what we see in our data
around the globe and over time. We know we can make improvements in some
areas, but it is good to now have the global context to pull together
research that is being done locally in various regions around the world."
Launched in December 1999 and May 2002, Terra and Aqua are the flagships
of the Earth Observing System series of satellites and a central part
of NASA's Earth Science Enterprise. The mission of the Earth Science
Enterprise is to help us understand and protect our home planet.
For more information, visit:
MODIS Oceans
MODIS Land
University of
Montana Numerical Terradynamic Simulation Group
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Contacts:
David Herring
NASA GSFC
dherring@climate.gsfc.nasa.gov
(301) 614-6219
Lynn Chandler
NASA GSFC
Lynn.Chandler-1@nasa.gov
(301) 286-2806 |
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 2002 Net Primary Productivity
This false-color map represents the Earth's carbon "metabolism"—the
rate at which plants absorbed carbon out of the atmosphere. The map shows
the global, annual average of the net productivity of vegetation on land
and in the ocean during 2002. The yellow and red areas show the highest
rates, ranging from 2 to 3 kilograms of carbon taken in per square meter
per year. The green, blue, and purple shades show progressively lower
productivity.
high-resolution images
2001 medium
JPEG (100 KB)
2001 large
JPEG (1.0 MB)
2001 large
TIFF (7.2 MB)
2002 medium
JPEG (100 KB)
2002 large
JPEG (1.0 MB)
2002 large
TIFF (7.2 MB)
palette
TIFF (80 KB)
animations
small MPEG (6.6
MB)
large MPEG (20
MB)
broadcast QuickTime (300
MB)
 Seasonal Comparison of
Net Primary Productivity
In any given year, tropical rainforests are generally
the most productive places on Earth. Still, the ongoing productivity
near the sea's surface, over such a widespread area of the globe, makes
the ocean roughly as productive as the land.
high-resolution images
June medium
JPEG (120 KB)
June large
JPEG (1.6 MB)
June large
TIFF (5.8 MB)
Dec. medium
JPEG (120 KB)
Dec. large
JPEG (1.4 MB)
Dec. large
TIFF (5.6 MB)
palette
TIFF (80 KB)
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