NASA Scientists Discover Spring Thaw Makes a Difference
December 10, 2003
Using a suite of microwave remote sensing instruments aboard
satellites, scientists at NASAs Jet Propulsion Laboratory,
Pasadena, Calif., and the University of Montana, Missoula,
have observed a recent trend of earlier thawing across the
northern high latitudes.
This regional thawing trend, advancing almost one day a year
since 1988, has the potential to alter the cycle of
atmospheric carbon dioxide intake and release by vegetation
and soils across the region, potentially resulting in
changes in Earth's climate. The lengthening growing season
appears to be promoting more carbon uptake by the vegetation
than is being released into the atmosphere for the region.
How long this trend will occur depends on whether soils
continue to remain cold and wet.
Research scientists have been studying the freeze/thaw
dynamics in North America and Eurasias boreal forests and
tundra to decipher effects on the timing and length of the
growing season. These regions encompass almost 30 percent
of global land area. They store a major portion of Earths
carbon in vegetation,, in seasonally frozen and permafrost
soils. Large expanses of boreal forest and tundra are
underlain by permafrost, a layer of permanently frozen soil
found underneath the active, seasonally thawed soil.
"Frozen soil can store carbon for hundreds to thousands of
years," said lead author Dr. Kyle McDonald of JPL, "but when
the permafrost thaws and begins to dry out, it releases the
carbon back into the atmosphere." The concern is that
eventually carbon released from the soil will prevail over
the amount being taken in by growing plants. Carbon dioxide
levels in the atmosphere would increase at an accelerated
rate, fostering even greater warming of the region and
affecting global climate.
With help from NASA radars and other orbiting satellite
microwave remote sensing instruments, including the National
Oceanic and Atmospheric Administrations Special Scanning
Microwave/Imager, scientists can monitor growing season
dynamics of the global boreal forest and tundra daily.
These instruments sense the electrical properties of water
in the landscape, allowing scientists to determine exactly
when and where the springtime thaw occurs.
Because of the large extent and location of boreal forest
and tundra, and the global reservoir of carbon stored in
their vegetation and soils, this region is extremely
sensitive to environmental change. It has the capacity to
dramatically impact Earth's climate.
"If global climate change is happening, here's where you
would expect to see it first," McDonald said.
As the research team observed, the earlier the spring thaw
occurs, the longer the growing season. These changes appear
to be promoting plant growth for the region. The longer
growing season allows plants to remove more carbon dioxide
from the atmosphere over a longer period of time.
Carbon dioxide is an important greenhouse gas that, if left
in the atmosphere, would promote additional warming. The
plants release oxygen and store the carbon as biomass that
eventually decomposes and transfers the carbon into the
soil. Soil microbes decompose dead plant material, returning
a portion of the soil carbon back into the atmosphere. The
rate at which soil microbes decompose plant material and
release carbon to the atmosphere is also very sensitive to
temperature. It could potentially increase with warming
temperatures and longer growing seasons.
From this general study, McDonald, Dr. John Kimball of the
University of Montana, and JPLs Erika Podest have lead
three different investigations, each focusing on different
noticeable changes in the boreal region. Results of three
related papers on this research will be presented to the
American Geophysical Unions Fall Meeting this week in San
The research is funded by NASAs Earth Science Enterprise.
The Enterprise is dedicated to understanding the Earth as an
integrated system and applying Earth System Science to
improve prediction of climate, weather, and natural hazards
using the unique vantage point of space.
For more information about climate on the Internet, visit:
For information about NASAs Earth Science Enterprise on the
Internet, visit: http://www.earth.nasa.gov .
The California Institute of Technology in Pasadena manages
JPL for NASA.
For information about NASA, visit: http://www.nasa.gov.
JPL is managed for NASA by the California Institute of Technology in Pasadena