SAN FRANCISCO -- In the era of fossil fuels, humans so far have tossed their garbage -- carbon dioxide -- out the window and tempted greenhouse warming. But for the closing chapter of that era, scientists envision a landscape veined in pipelines carrying greenhouse gases to the largest, deepest landfills in the world.

There, in depleted oil and gas wells and subterranean oceans of brine, scientists say they think there could be room for decades worth of carbon dioxide from burning coal, oil and natural gas.

A leading carbon-storage scientist, Lawrence Berkeley National Laboratory's Sally Benson, told scientists Monday that all available research suggests thousands of billions of tons of carbon dioxide could be shoved underground safely and securelyfor 1,000 years or more.

"Many believe the retention times could be over a million years," Benson said at the fall meeting of the American Geophysical Union, one of the world's largest scientific societies.

That would allow two of the most energy-hungry nations, China and the United States, to tap copious native supplies of coal and perhaps buy time for a shift to new, carbon-free energy sources.

Both countries are headed fast toward a coal-powered future, with utilities planning construction of as many as 174 coal-fired power plants by 2025 in the United States. In half that time, China expects to build as many as 562 coal plants, and India plans 213.

So far, virtually none of the new coal plants are expected to capture carbon-dioxide emissions. The plants could release five times the amount of carbon dioxide that nations have promised to cut under the Kyoto treaty, largely erasing the pact's effect.

But at least some of the carbon dioxide could be kept out of the atmosphere if plants could be built or retrofitted with technology for capturing carbon dioxide, then compressing it for piping or transporting to an injection well, scientists say.

Oceans and plants now absorb the majority of carbon dioxide released to the atmosphere. But a competing idea of stowing yet more of the gas deep under the sea looks remote, with some studies showing that the injected gas turns sea water into carbonic acid and kills marine life nearby. At a minimum, scientists say more research is needed.

Oil companies have been injecting carbon dioxide deep into their wells since the 1970s as a way of coaxing out more oil.

"I think it has huge potential. The main issue is cost," said Bill Carey, a Los Alamos National Laboratory geochemist who has studied a 30-year-old carbon-dioxide injection site in Texas that is the nation's oldest.

Carey found that carbon dioxide can blend with underground water and become carbonic acid, eating away at concrete seals in the oil well and possibly providing a path for leakage of the gas. That's a worry because a large gush of carbon dioxide to the surface could cause asphyxiation for humans and animals. Even a leakage rate as small as 1 percent per year is enough to produce significant global warming, making the endeavor worthless.

But scientists say the old wells, often running a mile or more in depth, appear to hold the gas securely as long as abandoned wells are plugged and the overlying rock is shown free of cracks and faults.

"It's pretty long term, probably thousands of years at the least," said geologist Scott McCallum of Oak Ridge National Laboratory. "They've been holding hydrocarbons for millions of years."

The idea works for storing natural gas in the Bay Area. Much of the region relies on a massive underground well at McDonald Island near Rio Vista for supplying its natural gas in wintertime.

But for carbon dioxide, there are only three storage plants worldwide and no incentives or taxes on carbon yet in the United States that would make it economical for power companies to capture and store their carbon dioxide.

Contact Ian Hoffman at ihoffman@angnewspapers.com