Promising Remedy for Global Warming: Bury That Greenhouse Gas
You’ve heard plenty about how a buildup of carbon dioxide in the air is promoting global warming, and how industry might be told to cut back its emissions.
But have you heard about stuffing the gas in the ocean? How about piping it into oil fields, coal seams or deep deposits of briny water?
That’s called carbon sequestration: disposing of carbon dioxide after it’s produced, rather than trying to hold down the production in the first place. It’s not a new idea, although it hasn’t gotten much public attention in the United States.
Lately, however, interest in sequestration has been growing. The Energy Department is spending some $29 million to study it this year, more than twice last year’s total, and it has asked for 50% more next year. Secretary Bill Richardson added sequestration to his climate-change strategy last summer.
“Look at the really long term--30, 50 or 70 years into the future,” Richardson said. “Carbon sequestration could offer one of the best options for reducing the buildup of greenhouse gases, not only in this country but in China, India and elsewhere.”
Both China and India have coal reserves that could produce lots of carbon dioxide if burned without controls. Developing nations are being asked to limit their future greenhouse gas emissions as they expand their economies.
The future of carbon sequestration should interest anybody who pays for electricity. Power plants produce about one-third of this country’s man-made carbon dioxide emissions. The costs of extracting carbon dioxide from smokestack gases--a big technical challenge--and transporting the gas to a final resting place would make electricity more expensive.
The Energy Department hopes to find technologies that cost $10 per ton of stored carbon, which might add 2% to 5% to consumer electric bills.
Nobody is talking about abandoning the better-known prescriptions for cutting back on carbon dioxide: Use energy more efficiently so power plants and vehicles needn’t burn so much coal and gasoline, and put more emphasis on alternative energy sources.
But the world might also need the carbon-storage approach to reach greenhouse gas goals, researchers say, and it’s time to start studying it.
The wide-ranging menu of approaches includes some that might become useful within 10 to 15 years, and others that would take longer, says Doug Carter, who directs the Office of Planning and Environmental Analysis in the Energy Department.
The nearer-term strategies can help pay for themselves by producing a useful product, he said.
Here are some of the strategies under study:
* Oil fields:
Injecting carbon dioxide into oil fields could help get oil out. In the porous earth where oil reserves lie, the gas would make isolated globs of oil swell and connect and also make the liquid thinner. Both would help shoo the oil toward recovery wells.
Oil workers already inject carbon dioxide underground to help oil recovery, but they focus on getting the most oil for the least carbon dioxide. For gas storage, “we’d want to completely flip that around,” said Sally Benson, a researcher at the Lawrence Berkeley National Laboratory. Current industry know-how would give a start on developing this approach, she said.
* Coal seams:
A good shot of carbon dioxide might produce a benefit from coal seams that are too deep to mine. Molecules of methane cling to coal, but carbon dioxide bumps them off and takes their place. So injecting the greenhouse gas might turn these useless seams into sources of natural gas. The idea is under study.
* The soil:
Plants snatch carbon dioxide from the air and transport some of the carbon to their roots, providing a natural underground storage. So campaigns to plant trees or save or replace forests, for example, promote that process as well as providing an ecological payoff.
* Deep underground:
Some strategies are more like going to the dump. The only payoff is the disposal.
In the North Sea off Norway, workers extract carbon dioxide from the natural gas they produce. Then, instead of letting it escape into the air, they inject it into porous sandstone some 3,000 feet below the floor of the ocean. They have been doing this since 1996 and avoiding Norway’s tax on carbon dioxide emissions.
On land, scientists are thinking about pumping carbon dioxide into deep deposits of briny water, more than 2,000 feet down, which are useless for drinking water. The deposits would have to be encased by rock that wouldn’t let the gas escape. Natural carbon dioxide deposits have remained underground for eons--a good indication that pumped gas could remain trapped basically forever, Benson said.
Injection into briny deposits may eventually become a favorite strategy in the United States, Benson said, because such deposits are widespread across the country. So gas from smokestacks wouldn’t have to be transported very far before it’s stored. However, research into this option is still in its infancy in the United States.
* The ocean:
This is the most controversial of the carbon-storage proposals.
One approach is to pipe liquid carbon dioxide to depths below about 3,300 feet.
At some depths it would remain a liquid and dissolve. If injected very deep, it would end up on the ocean floor as ice-like chunks, the result of a chemical reaction with the water. That would keep the carbon dioxide locked up for an unknown length of time before it dissolved.
The potential of the ocean to absorb the gas is immense. Since the mid-1700s, atmospheric concentrations of carbon dioxide have risen about 30%; if you took all the gas needed to fully double the old level and stuck it in the ocean, it would raise the ocean’s concentration by only 2%.
But what would ocean disposal mean for underwater life?
“I think it’s a very dangerous idea,” said Dan Lashof, a senior scientist at the Natural Resources Defense Council, an advocacy group. “The environmental risks associated with large-scale ocean disposal have not been assessed really at all.”
Lashof said he doesn’t reject the general idea of carbon sequestration, but “ocean disposal is probably the last place I’d look for it to be successful.”
Carbon dioxide changes the pH of seawater, making it more acidic. Scientists say they don’t yet know how the pH change from large-scale disposal would affect ocean life.
Next year an international team of researchers plans to dangle a steel pipeline an inch or two in diameter from a barge off the Kona coast of Hawaii. They want to see what happens when they dribble liquid carbon dioxide into the ocean about a half-mile deep. Where does the carbon dioxide go? What happens to the pH in the area?
Scientists will look for an effect on ocean life, but the experiment will probably be too brief and small scale to cause any disturbance, said Howard Herzog of the Massachusetts Institute of Technology, one of the project’s planners.
If large-scale injection became a reality, about one-fifth of the injected amount would eventually return to the atmosphere, Herzog said. But that would take several centuries to 1,000 years.
By then, the world will almost certainly have left fossil fuels and their carbon dioxide emissions behind. With luck, the gas seeping out of the ocean would be just a ghostly breath of history.
* On the Net:
Energy Department site about carbon sequestration: https://www.fe.doe.gov/coal_power/sequestration
Information on the Hawaii experiment: https://www.co2experiment.org
International Energy Agency greenhouse gas Web page: https://www.ieagreen.org.uk
