Land Cover Changes Affect U.S. Summer Climate
Elvia H. Thompson |
Rob Gutro/Mike Bettwy
Goddard Space Flight Center, Greenbelt, Md.
March 23, 2004
While climate may be impacted by carbon dioxide
emissions, aerosols and other factors, a new study offers further
evidence land surface changes may also play a significant role.
The study of summer climate in the United States reported changes in
land cover, particularly vegetation, have impacted regional
temperatures and precipitation. The study used data and computer models
from NASA and other organizations such as the National Oceanic and
Atmospheric Administration (NOAA).
"The largest human impacts
on nature have occurred since the Industrial Revolution," said Somnath
Baidya Roy, a research scientist at Princeton University, N.J. Roy is
lead author of the study published in a recent issue of the Journal of
Geophysical Research-Atmospheres. Co-authors included George Hurtt,
University of New Hampshire; Christopher Weaver, Rutgers University;
and Stephen Pacala also from of Princeton.
simulated and compared past and present climates with current and
potential vegetation. This research used the NASA-funded Ecosystem
Demography computer model to trace the evolution of vegetation
distribution patterns over the U.S. for nearly 300 years. "The model is
truly a technological breakthrough and enables scientists to study the
potential impact of land use and climate change across a wide range of
scales, from individual plants to continental regions," Hurtt said.
The researchers found land cover changes produced a significant cooling
effect of more than one degree Fahrenheit in parts of the Great Plains
and Midwest as agriculture expanded and replaced grasslands. Farmlands
tend to create lower temperatures through increased evaporation. A
warming effect was found along the Atlantic coast where croplands
Compared to forests, croplands are less
efficient in transpiration; a daytime process where water evaporates
from leaves during photosynthesis and cools the air. A slight warming
effect was also observed across the Southwest, where woodlands replaced
The study found land cover changes could impact
local precipitation, but not as significantly as they affect
temperature. The relatively strong cooling over the central U.S. has
probably weakened the temperature difference between land and the Gulf
of Mexico, slowing the northern movement of weather systems and
resulting in enhanced rainfall across Texas. Consequently, the air
masses reaching the Central Lowlands region, including Illinois and
Indiana, are drier, causing rainfall reductions.
change is not uniform. Most people associate land cover change with
deforestation, but the changes in the U.S. are more complex, creating a
temperature signal that is more difficult to study," Roy said. The
forest cover in the U.S. has actually increased in the last 100 years
mainly due to farm abandonment in the East, fire suppression in the
West, and large parts of the Great Plains have been converted into
irrigated croplands, which tends to produce cooling.
research also carries additional implications. "It is important to
understand the effects of changing land cover, because it can mitigate
or exacerbate greenhouse warming," Roy said. "In the U.S. over the past
100 years, it seems to be offsetting greenhouse warming. The opposite
is probably true in most other parts of the world. This finding has
also been supported in previous research," Roy said.
Researchers relied on several computer models. These included the
Ecosystem Demography model, which incorporates data from NASA's
International Satellite Land Surface Climatology Project. The model
contains data from the Global Energy and Water Cycle Experiment. The
experiment was conceived to take advantage of environmental monitoring
satellites including NASA's Terra, Aqua, Tropical Rainfall Measuring
Mission, and ADEOS I and II. The study also used the Regional
Atmospheric Modeling System for regional climate simulations.
NASA's Earth Science 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. NASA, Princeton, and NOAA funded this research.
For information and images about this research, visit:
http://www.gsfc.nasa.gov/topstory/2004/0223landsummer.html For more information about NASA's Earth Science Enterprise on the Internet, visit:
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