2007 ORAU Annual Report - Oak Ridge Associated Universities

Marvin L. Wesely Distinguished
Graduate Research Environmental
Fellowship Winners
Cynthia Randles and Colleen Iversen received the Marvin L. Wesely Distinguished Graduate Research Environmental
Fellowship (GREF) in 2006 and 2007, respectively, in recognition for their global change research. DOE’s Global Change
Education Program, which is managed by ORISE, established the Wesely award in 2003 to honor the late Dr. Marvin L.
Wesely, who was a senior meteorologist and scientist at Argonne National Laboratory and active mentor to GREF fellows.
The annual award provides distinction and visibility to the fellows’ research.
Randles Examines Impact of Soot on Global
Climate Change
Growing up, Cynthia Randles, who as a high
school student apprenticed at the Kennedy
Space Center, dreamed of one day exploring
the universe.
As an adult, Randles is more interested in exploring
the atmosphere around us as a climatologist.
A doctoral student at Princeton University’s
Atmospheric and Oceanic Sciences Program,
Randles studies how carbonaceous particles, like
soot and smoke, affect global climate change.
Carbonaceous particles are composed of lightscattering
organic carbon, or OC, and lightabsorbing
black carbon, or BC. They are critical to
the atmosphere
because they
can scatter
or absorb the
sun’s intense
rays. They can
therefore heat
the atmosphere
while at the
same time cool
the surface by
blocking the
sunlight from
reaching it.
Major sources
of OC and BC
emissions are from combustion processes, mainly
fossil-fuel burning, biofuel burning, and forest and
savannah fires such as those in South America and
southern Africa. Randles’ research involves trying
to understand how the particles might affect
global climate change, specifically how they impact
clouds and precipitation patterns.
“The aim of my research is to try and reduce uncertainties
associated with the particles’ reflective and absorption
properties by understanding how sensitive, for example,
the response of a global climate model is to these various
properties,” Randles explained.
One possible indirect effect of the particles might be
to slow global warming because of their effect on the
reflectivity of clouds. In fact, OC particles could actually
make clouds shinier and thus reflect the sun’s heat back
into space, exerting a cooling effect on the climate.
However, Randles pointed out a potential problem with
this scenario. “As we clean up the scattering particles in the
air to mitigate air pollution concerns, we may be causing
more warming if we neglect to clean up the absorbing
carbonaceous particles as well,” she said.
Iversen Sees the Forest for Its Trees
As the amount of heat-trapping gases such as carbon
dioxide (CO 2
) rise in the atmosphere due to fossil
fuel burning, forests have been seen as critical to the
absorption of CO 2
emissions. However, research that
University of Tennessee doctoral student Colleen Iversen
is pursuing indicates that carbon storage in forests might
be more complicated than was once thought.
The prevailing view amongst scientists has been that
most excess carbon taken up by forest ecosystems would
be allocated to the woody portion of the tree. However,
in the sweetgum plantation at ORNL’s forested Free-Air
CO 2
Enrichment (FACE) experiment, Iversen has found
that a significant amount of the excess carbon taken up
by the trees goes to forming fine roots, which are smaller
in diameter than the
thickness of a penny.
This phenomenon
can lead to a decline
in soil nutrients that
may prevent forests
from continuing to
take up more carbon
in response to rising
atmospheric CO 2
.
The main research objective at ORNL FACE is to
understand and to quantify how greater CO 2
emissions
might affect the Eastern deciduous forest. Iversen and the
other researchers at the ORNL FACE facility have identified
several important implications for forest responses to
elevated CO 2
.
First, less carbon may be stored as living tree matter
than originally thought because fine roots live and die in
the span of a year, whereas stem wood can last for the
lifespan of the tree (greater than 50 years). Increased root
production also leads to increased nitrogen uptake from
the soil. Because the soil contains a finite pool of nitrogen,
researchers are uncertain as to how long this imbalance
can be sustained. Finally, decomposition of the added roots
results in a greater nitrogen requirement for the microbes
that degrade them. While this could lead to less nitrogen
available for plants, it could also result in more carbon
storage in the soil.
“The way in which forests allocate biomass [living matter]
in response to rising atmospheric concentrations of CO 2
will determine whether carbon storage in forests
will mitigate some portion of fossil fuel burning,”
Iversen explained.
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