Carbon dioxide emissions are stoking the greenhouse effect that threatens to warm the world, melt the ice caps, raise the sea level, and derange entire ecosystems. To avoid that fate, we have three choices: burn less fossil fuel, develop carbon-free energy sources, or capture the excess carbon dioxide and bury it. Some say we should do all three.

But the last idea, in particular, called carbon sequestration, has captured the imagination of many and inspired several far-out schemes.

Carbon Sequestration

Photo: California EPA

Goal: Bioengineer microbes to remove carbon dioxide from the air and slow global warming

Why it's a Loser: Even the grandest biological carbon sequestration schemes can't make a real dent in global warming. In addition, such projects mask the real problem—overdependence on fossil fuels

Organization: Institute for Biological Energy Alternatives, backed by the U.S. Department of Energy

Center of Activity: Institute for Biological Energy Alternatives, Rockville, Md., and the Department of Energy's Hanford Site in Washington

Number of People on the Project: About 10, set to rise to about 25

Budget: US $12 million over about four years