  satellite sun earth  If reducing carbon emissions fails to
stop climate change, we may one day have the option of sending
mirror-supporting satellites into space or filling the
stratosphere with light-reflecting particles to block the sun's
rays.  According to a new study, such measures could
significantly cool Earth. But researchers caution that if they
if they do not work or are suddenly halted, they could make
matters worse.  "As far as I know, this is the first century-
scale, time-dependent simulation of a geoengineering scheme,"
says Ken Caldeira, a climate scientist at the Carnegie
Institution of Washington's Department of Global Ecology in
Stanford, Calif., and senior author of the study published this
week in Proceedings of the National Academy of Sciences USA.
Geoengineering refers to activities designed to alter Earth's
climate that may include blocking the sun, large-scale
reforestation and sequestering carbon dioxide in the ocean.
First, Caldeira and his colleague, ecologist Damon Matthews, con