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David Herring               April 23, 2003
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301/614-6219)

RELEASE:  03-41

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.

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