NASA is using satellite data to paint a detailed global picture of
the interplay among natural disasters, human activities and the rise
of carbon dioxide in the Earth’s atmosphere during the past 20 years.

According to a new scientific study that appears in the July issue of
the journal Global Change Biology, scientists used satellite
observations to estimate the amount of leafy cover worldwide and
sudden decreases in ‘greenness.’ Greenness is a measure of the amount
of chlorophyll in live plants.

“Green leaf cover is probably the most fragile and vulnerable piece
of Earth’s ecosystem that scientists can easily monitor during
ecological disturbances,” said Christopher Potter, a scientist at
NASA Ames Research Center, located in California’s Silicon Valley,
and the principal author of the technical paper. His co-authors
include Pang-Ning Tan, Michael Steinbach and Vipin Kumar, all of the
University of Minnesota, Minneapolis; Steven Klooster and Vanessa
Genovese, both of California State University-Monterey Bay, Seaside,
Calif.; and Ranga Myneni, Boston University, Boston.

“The new results come from a technique called ‘data mining,’ which
sorts through a huge amount of satellite and scientific data to
detect patterns and events that otherwise would have been
overlooked,” added Kumar, the principal investigator of a joint
project of the University of Minnesota, California State University
and NASA Ames to develop data-mining techniques to help Earth
scientists discover changes in the global carbon cycle and climate

The Earth’s land cover is so vast that much of it in the tropics and
the tundra is inaccessible to regular ground observations there,
according to the study’s scientists. “Many years of satellite
observations of remote areas have revealed completely new pictures of
ecological changes and disasters, but we have had to develop new
formulas to clearly reveal sudden changes in greenness over extensive
areas,” said Potter.

Detecting sudden changes from large amounts of global data required
the development of automated techniques that take into account the
timing, location and magnitude of such changes, according to Tan.

Researchers then matched abrupt changes in plant greenness with
records of large wildfires or massive crop losses to validate the
study’s conclusions. “The majority of the potential disturbance
events that caused carbon to go into the atmosphere occurred in
tropical savanna and shrub lands or in cold forest ecosystems,”
Klooster said.

Scientists define an ecological disturbance as an event that disrupts
the physical make-up of an ecosystem and how it works for longer than
one growing season of native plants. Natural disturbances may include
fires, hurricanes, floods, droughts, lava flows and ice storms. Other
natural disturbances are due to plant-eating insects and mammals, and
disease-causing microorganisms.

Human-caused disturbances could happen as a result of logging,
deforestation, draining wetlands, clearing, chemical pollution and
introducing non-native species to an area, according to scientists.

“Ecosystem disturbances can contribute to the current rise of carbon
dioxide in the atmosphere,” Potter said. Nine billion metric tons of
carbon may have moved from the Earth’s soil and surface life forms
into the atmosphere in 18 years beginning in 1982 due to wildfires
and other disturbances, according to the study. A metric ton is 2,205
pounds, equivalent to the weight of a small car. In comparison,
fossil fuel emission of carbon dioxide to the atmosphere each year
was about seven billion metric tons in 1990.

Some of the carbon dioxide that goes into the air reenters the
Earth’s biosphere when plants recover this gas during ‘natural

Scientists used the Advanced Very High Resolution Radiometer aboard
National Oceanic and Atmospheric Administration satellites to measure
monthly changes in leafy plant cover worldwide. Boston University
used unique NASA computer codes to produce global greenness values.
These codes removed interfering data from atmospheric effects. When
statistics showed there was much less greenness in specific areas
that lasted more than a year, scientists also found a high
probability of ecological disturbances.

“Watching for changes in the amount of absorption of sunlight by
green plants is an effective way to look for ecological disasters,”
Potter said. “This study was literally a proof of concept because we
learned how to use data mining to bring new knowledge out of existing
Earth observation data,” Klooster added.

Follow-up studies using much higher resolution satellite images are
likely to reveal more localized events, such as floods, hurricanes
and major logging operations, according to the study’s scientists.
“This is important because many natural disasters in remote areas are
not noticed and never recorded,” Potter explained.

“In the new era of worldwide carbon accounting and management, we
need an accurate method to tell us how much carbon dioxide is moving
from the biosphere and into the atmosphere,” Potter said. “Global
satellite images go beyond the capability of human eyesight. All we
need to do is look at the data with the proper formulas to filter out
just what we need,” he concluded.

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