BIOPLAN POSTING 2001-5-17

Ken Creighton <ken.creighton@undp.org>
Sent by: owner-bioplan@undp.org
05/02/01 06:59 PM

bioplan
Ken Creighton <ken.creighton@undp.org>
Dear Bioplan readers,

While “prove” is undoubtedly a bit too strong a word for the output of a
computer model, this phenomena will likely factor into the dialog on
land use, land use change and the role of agriculture and forestry in
climate change mitigation. I wonder to what extent patch size and
patchiness of trees and agriculture on the landscape effect these
calculations? There are certainly few places on earth with less patch
diversity than the “amber waves of grain” of the American great plains.
But then again there wasn’t much patch diversity in the fire/bison
dominated prairies that they replaced, either…
More fuel for debate,

Ken
--

G. Ken Creighton, Ph.D.
UNDP Coordinator
Biodiversity Planning Support Programme
 

RESEARCHERS “PROVE”  PAST COOLING TREND CAUSED BY MOVE FROM
FORESTS TO AGRICULTURE
Science Daily
4/25/2001
Internet: http://www.sciencedaily.com/releases/2001/04/010424072410.htm

Livermore, Calif. - Researchers in Lawrence Livermore National
Laboratory's Atmospheric Science Division have demonstrated a
cooling of up to 2-degree Fahrenheit over land between 1000 and
1900 AD as a result of changes from natural vegetation, such as
forests, to agriculture. Through climate model simulations, the
LLNL research team made up of Bala Govindasamy, Ken Caldeira and
Philip Duffy, determined that a previously recognized cooling
trend up to the last century could, in part, be attributed to the
land-use change.

Previous studies had attributed cooling to natural climate
variations. The Livermore research, however, suggests that much of
this cooling could have been the result of human activity. Forests
tend to look dark from the sky, but agricultural lands, with their
amber waves of grain, tend to look much lighter. Dark colors tend
to absorb sunlight, and light colors tend to reflect sunlight back
out to space. Changing from forests to crops results in more
sunlight reflected back to space. This reflection of solar energy
to space tends to cool the Earth, especially in regions such as
the eastern and mid-western United States, where huge tracts of
land have been converted to crops. In the 20th century, some of
this cropland has been reverting back to forest, especially in the
eastern United States.

Greenhouse gas emissions in the 20th century likely overcame any
cooling trends that took place up to that time. Growing more trees
has been suggested as a way to soak up carbon dioxide, a
greenhouse gas, from the atmosphere. However, earlier studies
demonstrate that growing dark forests could actually heat the
earth's surface more because dark colors tend to absorb more
sunlight, despite the uptake of carbon dioxide.

"The Earth land surface has cooled by about 0.41 K (= by about 3/4
of a degree Fahrenheit) due to the replacement of dark forests by
lighter farms growing wheat, corn, etc.," said Caldeira, a climate
model researcher who also is co-director for the Department of
Energy's Center for Research on ocean carbon sequestration. "This
is an example of inadvertent geoengineering -- we changed the
reflectivity of the Earth and have probably caused a global
cooling in the past. This is now probably being overwhelmed by our
greenhouse gas emissions."

The research, published in the Geophysical Research Letters, also
shows a slight increase in the annual means of global and Northern
Hemisphere sea ice volumes in association with the cooling. The
simulated annual average cooling due to land-use change during
this period is almost a half a degree Fahrenheit globally, 0.66 °F
for the Northern Hemisphere and .74 °F over land.

In the simulations, land use data for 1000 AD uses potential
natural vegetation, made up mainly of forests, while data for the
1900 AD period uses standard current vegetation data, which is a
mix of forest and croplands, taken from the Community Climate
Model developed at the National Center for Atmospheric Research.
The greenhouse gas levels in both simulations are in
concentrations taken at pre-industrial levels. "The estimated
temperature change in the continental United States as a result of
change from forests to agriculture is up to a 2-degree Fahrenheit
cooling," Caldeira said. "So, when we talk about global warming,
we can no longer take for granted that this global warming is
starting from some natural climate state, undisturbed by human
activities."

Founded in 1952, Lawrence Livermore National Laboratory is a
national nuclear security laboratory, with a mission to ensure
national security and apply science and technology to the
important issues of our time. The National Nuclear Security
Administration's Lawrence Livermore National Laboratory is managed
by the University of California.
 

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