Landscaped Changes may Alter Climate
12/31/98
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Title: Landscaped Changes may Alter Climate
Source: Environmental News Network
Status: Copyrighted, contact source to reprint
Date: 12/31/98
Transformations in the Earth's landscape may affect climate change,
according to a climatologist from the University of Wisconsin-Madison.
From the deforestation of the Amazon to the transformation of millions of
acres of North American prairies to farmland, humans have remolded the
surface of the Earth. Those changes, scientists now suspect, may have a
significant influence on climate, changing regional weather patterns at
least, and possibly contributing to global shifts in climate.
At the fall meeting of the American Geophysical Union in San Francisco,
Calif., University of Wisconsin-Madison climatologist Jonathan Foley said
changes to the landscape, coupled with global increases in atmospheric
carbon dioxide concentrations, could be capable of remaking regional
climates by altering patterns of rainfall and temperature.
Such changes, he said, are reflected in a novel study of the Amazon Basin,
the first to simulate the combined effects on regional climate of large-
scale deforestation and increases in global concentrations of carbon
dioxide in the atmosphere. The study was conducted by Marcos Heil Costa,
now a professor at the University of Viosa in Brazil and Foley, a UW-
Madison professor of atmospheric and oceanic sciences.
"It's a safe bet to say that the future climate of the Amazon will be
determined by deforestation and carbon dioxide concentrations," Foley said
in an interview.
In the past, climate change scenarios have been linked primarily to the
increasing concentrations in the world's atmosphere of the so-called
greenhouse gases, carbon dioxide and methane, for example. But some
scientists are now beginning to examine the influence on climate of the
surface of the Earth and the collection of landscapes, such as forests,
farmland, and deserts that collectively make up what is known as the
biosphere.
The biosphere, argues Foley, probably exerts an influence on climate that
is equal to, and in some instances greater than, the accumulation of
greenhouses gases.
When you alter landscapes on a massive scale, as has happened across the
globe in the past 200 years as farms have replaced forests, basic patterns
of climate are disrupted and climatic change is set in motion.
In his study of the Amazon basin, for example, when forest is cleared and
replaced with pasture or cropland, the hydrologic cycle, where rain is
recycled back to the atmosphere through soil, trees and forest plants by
the process of evapotranspiration. That process, said Foley, is essential
to a landscape's ability to cool itself. Without it, as reflected in the
model developed by Costa and Foley, it acts together with increased
atmospheric carbon dioxide concentrations to significantly warm the
regional climate of the Amazon basin.
"If you were to cut down a big chunk of the Amazon and replace it with
grasslands and pasture, the ability of that land to cool itself off is
diminished," said Foley. "The dominating effect is cutting off
evapotranspiration. Forest (landscapes) can cool themselves off by
releasing water (to the atmosphere)."
Moreover, Foley noted that wholesale changes to the landscape can affect
climate by altering the ability of the biosphere to store carbon dioxide.
Forests and prairies, for example, have a far greater ability to store
carbon dioxide than cornfields or pasture. With deforestation, these
"sinks" are eliminated and the ability of the biosphere to absorb and
store greenhouse gases like carbon dioxide is reduced.
The supercomputer-driven model used by Costa and Foley showed that a
significant deforestation of the Amazon, combined with increased carbon
dioxide levels, would reduce annual rainfall by as much as 20 percent.
Such a reduction, in addition to environmental consequences, would have an
impact on such things as Brazil's hydroelectric capacity, a primary source
of power there.
The scale of change factored into the model of a deforested Amazon is
unlikely to occur, said Foley, because many parts of the Amazon basin
flood annually and are unlikely to be converted to farmland. However, he
said the results are important because it demonstrates how altered
landscapes can feed climate change.
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