Tue Aug 15, 2006 8:44 AM ET
By Jason Szep
BOSTON (Reuters) - Climate change could be slowed by burying greenhouse gases blamed for global warming deep below the ocean floor under thick, cold sediment that would trap it for thousands of years, said a team of Harvard-led scientists.
The seafloor along the U.S. east and west coast is vast enough to store almost unlimited carbon dioxide emissions from U.S. coal-fired plants, said Daniel Schrag, director of Harvard's Center for the Environment.
"It would make coal a green fuel," he said in a telephone interview with Reuters.
Carbon dioxide released by burning fossil fuels is the main gas blamed for pushing up world temperatures. Many scientists say the buildup could trigger more floods, droughts, powerful storms, heat waves and rising world sea levels.
Schrag's team at Harvard and researchers at the Massachusetts Institute of Technology and Columbia University propose capturing carbon dioxide from power plants, liquefying the gas, pumping it about 2 miles under water and then injecting it below the sea floor.
Many governments and firms are already exploring ways to pump carbon dioxide under land or directly into the sea -- a process known as carbon sequestration -- to meet emissions caps set by the U.N.'s Kyoto Protocol for 35 industrial nations.
But such schemes will only help if the gas stays below the ground or the sea for hundreds of years, and studies and experiments to date indicate it may eventually leak.
Schrag said burying the gas under seafloor sediments of sand, silt and clay hundreds of meters (feet) thick at depths of 3,000 meters (9,800 ft) and very low temperatures would guarantee it would stay denser than the water above.
"The only place it can leak is deeper down," he said.
The cold temperatures and high pressures found deep below the ocean's surface would transform carbon dioxide into a solid that is stable enough to withstand even the most severe earthquakes, the researchers said in the August 7 issue of the Proceedings of the National Academy of Sciences.
Environmental group Greenpeace said it was skeptical of the benefits and urged the development of less expensive and swifter solutions to global warming such as renewable energy and conservation.
"We have real questions about this technology. It is not something that currently works or is tested," said Chris Miller, a senior Greenpeace campaigner. "We have a relatively short amount of time to begin making pretty dramatic reductions in global warming pollutants."
Managing a carbon dioxide sequestration program could also cost hundreds of billions a year, scientists say.
A 2005 U.N. report said carbon dioxide storage may provide 15-55 percent of all the cuts in greenhouse gas emissions needed until 2100 -- probably a bigger contribution than from renewable energies or from any revival of nuclear power.
But it would also likely raise the cost of generating electricity from a coal-fired power plant by at least 50 percent to $0.06-$0.10 per kilowatt hour from $0.04-$0.05 on a power plant with no filters.
"The downsides are that nobody has ever injected into those kinds of formations at those kinds of depths," said Ken Caldeira, a climate scientist at Stanford University. "There are engineering hurdles to overcome and it might not be that cheap," he said.
© Reuters 2006.