Giant Umbrella's Will Not Solve Global Warming

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http://ens-news.com/ens/dec2001/2001L-12-13-09.html

GIANT UMBRELLAS WILL NOT SOLVE GLOBAL WARMING

SAN FRANCISCO, California, December 13, 2001 (ENS) - Scientists have floated

a lot of wacky schemes for combating global warming, but some of these could

do more harm than good.

Among the stranger engineering schemes proposed to help reduce the effects

of global warming are lofting reflective balloons into the stratosphere or

erecting a huge parasol in orbit. By blocking some of the sunlight, these

devices would create a cooling effect to offset the warming caused by

increasing levels of greenhouse gases, supporters say.

To compensate for the climate effects of doubling the amount of carbon

dioxide in the atmosphere, the amount of sunlight striking Earth would need

to be decreased by almost 1.8 percent.

Scientists at the University of Illinois (UI) say that blocking some of the

sun's rays may not be such a cool way of counteracting climate change. The

plans could have harmful effects on agriculture and forest production, and

also could create secondary feedback mechanisms that may further change the

climate, the team says.

" The biosphere plays a very important role in determining how much carbon

dioxide is in the atmosphere, " said Wuebbles, a professor and head of

atmospheric sciences at the UI. " Through photosynthesis, carbon dioxide is

removed from the atmosphere and stored in plants. Decreasing the solar

constant by 1.8 percent could impact the amount of biomass produced, and

therefore affect how much uptake and storage of carbon dioxide occurs. "

To study the potential effects on the biosphere, Wuebbles and his

colleagues ­ Foley, a professor of atmospheric and oceanic sciences at

the University of Wisconsin at Madison, and UI graduate student Vaishali

Naik ­ used a dynamic global ecosystem model to simulate the response of

vegetation to engineered climate conditions.

The researchers projected a decrease in vegetation growth in tropical

forests and in boreal forests located in higher northern latitudes. However,

there was a slight increase in growth in the mid-latitudes.

" We think this mixed message is coming as a result of feedback mechanisms

such as changes in water stress, " Wuebbles said. " Without those feedbacks,

we would have seen a decrease in net primary production everywhere. "

Photosynthesis depends not only on atmospheric carbon dioxide and sunlight,

but also on an ample water supply, Wuebbles said.

" In water stressed regions, such as deserts, biomass is heavily dependent on

the availability of water, as well as sunlight. If you reduce the solar

radiation, there will be less evaporation from the soil, leaving more water

for plants to consume, " Wuebbles explained. " With less water stress, the

plants can grow better, creating more biomass. "