Earth too warm? Bury the CO2.

Under a blazing west Texas sun, with a whiptail lizard and cattle looking on, Rebecca Smyth works with an assistant to lower a measuring line, then a hose, and finally a slender plastic capsule down an old water well 200 feet deep.

She's hoping the water samples she collects will yield clues to what is, arguably, one of mankind's most pressing environmental questions: Can nations bury their greenhouse gases?

If they can, then governments will have bought themselves a decades-long respite as they search for less carbon-intensive energy sources. If they can't, then a significant rise in global temperatures by 2100 looks inevitable, if fossil-fuel consumption continues at its current pace.

And the answer may well lie here, atop an old west Texas oil field known simply as SACROC, where more CO2 has been pumped underground over a longer period of years than anywhere else on Earth. Her efforts – and those of the rest of a small army of scientists funded by the US Department of Energy – are being closely watched. Energy companies want to know their options as Congress mulls over legislative options to global warming. Environmentalists are eager to find ways to slow the rise of greenhouse gases.

"If we don't sequester carbon from coal, we won't be able to stabilize the concentration of CO2 in the atmosphere," says John Thompson, director of the coal transition project of the Clean Air Task Force, a Boston-based environmental group. "It's the linchpin."

Admittedly, pumping huge amounts of carbon dioxide into underground caverns sounds audacious. If the US captured just 60 percent of the CO2 emitted by its coal-burning power plants and reduced it to a liquid for injection underground, the daily volume would roughly equal what the US consumes in oil each day – about 20 million barrels, according to a report by the Massachusetts Institute of Technology in Cambridge. And the risks are substantial.

Inject too much CO2 and the resulting pressure could cause earth tremors or push deep super-salty groundwater up into freshwater aquifers. Once pumped in, the CO2 may not even stay put in the sandstone formations, below layers of shale and other rock.

Nevertheless, researchers sound confident. "I grew up near Love Canal, so I know the problems of putting stuff underground," says Sue Hovorka, a research scientist at the University of Texas at Austin. "But we're cautiously optimistic this is going to work."

She is one of the scientists tracking the movement of carbon dioxide underground in the nation's first deep-sequestration experiment.

Under a torrid midday sun in the old Liberty oil field south of Houston, she is tracking the progress of about 2,000 tons of food-grade CO2 that she had injected into a well in 2004 and again last fall. Unlike SACROC (Scurry Area Canyon Reef Operators Committee), no CO2 had ever been injected here before, so it should be straightforward to track. But at the moment, Dr. Hovorka is not happy.

Nearly a mile below, her sensitive instruments are trapped in a five-inch steel pipe, and the roughnecks on the rig have spent hours trying to pull them out. A colleague opts to use small explosives to dislodge them. An hour later, the instruments are on their way to the surface and water samples are being analyzed from an adjacent well.

So far, the results are positive.

"Right now the CO2 is stored as small bubbles in the pore spaces of the sandstone," Hovorka says. "We believe it's immobilized and will sit there on a 10,000-year time frame and that when we open this well later nothing will happen. We don't expect any geysers of escaping CO2 or any of the things that people worry so much about."

The amount of potential storage is vast. Three of the five US geologic storage possibilities under review – salt basins a mile or more deep, mature oil and natural-gas reservoirs, and deep unminable coal seams – could permanently hold at least two centuries' worth of US CO2 emissions – about 6 billion metric tons a year, researchers estimate.

But many steps lie ahead. These geologic formations must be tested for environmental safety and their ability to retain CO2. New power-generation technologies that can economically capture CO2 emissions must be developed. Finally, pipelines and infrastructure must be built to collect CO2 from emitters to move it to geologic storage.

Perhaps America's best hopes for geologic sequestration lie with the sandstone formations holding super-salty groundwater here on the Texas coast – as well as the dwindling oil fields across its vast breadth, says Ian Duncan, associate director of the Bureau of Economic Geology at the University of Texas at Austin. Together, these two geological assets could hold all of America's CO2 emissions for at least the next 40 years, he estimates, enough time to help bridge the gap until solar power or other emissions-free sources of energy become common.

"The question will end up being: How much capacity can we find for injecting large amounts of CO2 over decades?" says Ernest Moniz, an MIT professor and coauthor of the March report that criticized the government for not expediting large-scale sequestration research. "Will we, for instance, be able to inject the CO2 output of 50 big power plants in the ground and have it stay there?"

High-volume CO2 injections of 1 million tons or more are expected to begin in Cranfield, Miss., later this year to push out hard-to-reach oil and to test further the feasibility of geologic storage.

Back in Snyder, Smyth keeps a lookout for rattlesnakes from under her broad-brimmed hat as she collects water samples. She'll compare them with other samples from nearby areas where CO2 is not a factor. Slight chemical differences could yield clues about whether the CO2 is staying put or expanding upward.

"We're not sure we're going to see any significant impact from CO2 here," Smyth says. "But if the impacts are going to show up anywhere in the world, they should show up here where CO2 has been injected so long." [Editor's note: The original version included a chart that contained inaccurate data.]