Excerpt: The large-scale conversion of forests to
croplands in the midwestern United States over the last century
has led to a measurable cooling of the region's climate, according
to Gordon Bonan of the National Center for Atmospheric Research
(NCAR). The new study, which appears in the June issue of the
Journal of Climate, is the first to document the link between
regional climate change and a major change in temperate forest
cover. NCAR's primary sponsor is the National Science Foundation.
"Human uses of land, especially clearing of forest for
agriculture and reforestation of abandoned farmland, are an
important cause of regional climate change," concludes Bonan. The
cooling is the result of the changeover of the region to crops,
which reflect more sunlight back into space than forests.
The impact of land-use changes on climate is currently one
of the most uncertain factors contributing to climate warming,
according to the latest report from the United Nations/World
Meteorological Organization Intergovernmental Panel on Climate
Change, issued earlier this year. Most of the work to date on this
subject has been with computer models and has focused on
deforestation in the tropics in areas such as the Amazon. Bonan's
is one of the first observational studies on the effect of
temperate forest changes on regional climate.