Gas Garbage?

Remember 1999, the second-warmest year of the 20th century? (The warmest was 1998.) If the trend continues, 2000 may go down in history as another scorcher. What's turning up the heat?

Most likely it's green-house gases, such as methane and nitrous oxide, which trap heat from escaping the atmosphere. But the biggest culprit of all is carbon dioxide ([CO.sub.2]), a gas spewed into the air by human burning of fossil fuels (like oil and coal) for energy. [CO.sub.2] emissions may account for 67 percent of global warming signals, experts say.

Now the U.S. Department of Energy has offered $18 million for a [CO.sub.2] solution. One scheme: capturing and storing [CO.sub.2] underground or in the deep ocean--a strategy known as carbon sequestration.

Carbon sequestration is not new. An offshore gas rig off Norway's North Sea has been pumping [CO.sub.2] into a rock layer below the seafloor since 1996.

But scientists have proposed injecting [CO.sub.2] from energy plants and factories into coal beds, old salt mines, deep aquifers (underground water-storage units), or depleted oil or gas reservoirs. Together, these geologic formations could hold thousands of gigatons (billions of tons) of carbon dioxide. But how stable are they? Can these formations hold [CO.sub.2] for thousands of years without suddenly erupting, releasing the gas into the atmosphere and killing nearby populations? Scientists aren't sure.

Another option is to release [CO.sub.2] into the deep ocean. Pumping the gas about 1,000 meters (3,280 feet) or more below the sea's surface could prove to be a safer bet. Here the seawater is so cold and dense it would take centuries before carbon-laden water mixes with surface waters. But [CO.sub.2] could turn seawater more acidic, affecting organisms such as plankton and microbes--the base of the ocean food chain.