WOODS HOLE - It reads more like science fiction than any real solution to global warming: Fertilizing the sea to create plankton blooms that suck heat-trapping carbon dioxide out of the air.
Yet two US companies are moving toward doing just that by sprinkling particles of iron over vast swaths of the ocean.
As few viable solutions emerge to slow global warming, some scientists say such measures may become increasingly necessary, although they warn that far more research needs to be done to understand the effectiveness and ecological impact of such plans.
"Climate change is presenting us with immense challenges and we have to be prepared for international calls for drastic action," said John J. Cullen of Dalhousie University's Department of Oceanography in Canada. "With iron fertilization, the scientific community has got to provide a clear understanding of the risks and benefits."
Cullen was one of about 100 scientists, environmentalists, economists, and regulators from around the world who attended a two-day conference last week on iron fertilization at the Woods Hole Oceanographic Institution, to catch up on and debate the scientific and policy consequences of ocean fertilization.
While participants clashed over what the environmental impact of iron seeding will be, one clear policy problem emerged: If a company wants to seed the high seas, there is extraordinarily little that scientists - or governments - can do to stop them. Few enforceable treaties exist in international waters and if a company wanted to avoid them, it would be easy to do so.
Iron seeding is just one of several "geo-engineering" schemes emerging as the world fails to adequately rein in emissions of greenhouse gases from cars, factories, and power plants.
Some scientists have suggested erecting giant mirrors above the earth to reflect the sun's energy. Others want to drop sulfur particles from high altitude balloons to do the same. Already, governments are planting trees to absorb carbon dioxide and are injecting heat-trapping gases deep into the earth to be locked away for hundreds of years or more. Others suggest seeding the ocean with nitrogen, another limiting nutrient in parts of the sea.
Iron seeding is a particularly attractive proposal to fight global warming because a small amount of the inexpensive nutrient could result in enormous blooms of microscopic vegetation known as phytoplankton.
Iron already fertilizes portions of the world's seas, carried there by dust storms. But the vast Southern Ocean that surrounds Antarctica, as well as other regions of the world, are missing the iron dust. Throw enough in during the right season, scientists largely agree, and phytoplankton will grow to absorb carbon dioxide from the atmosphere.
The question is what will happen next.
Scientists know that when phytoplankton are eaten or die, their organic debris rains down deeper into the ocean. Some of it is consumed by other organisms, but some amount - and there is enormous uncertainty about how much - will make it to deep ocean waters and won't resurface for decades, centuries, or even thousands of years.
Some scientists believe the blooms could provide enough food for fish stocks to increase, and others say a gas released by phytoplankton creates aerosol particles that can reflect the sun's energy and reduce global warming.
But it's unclear if iron seeding really works, or if the problems it may unintentionally create will outweigh its benefits.
"Every choice we make - every single one - will have a consequence," said Paul G. Falkowski, of Rutgers University.
There have been 11 large-scale iron seeding experiments in the last 15 years, and while all resulted in plankton blooms, they provide no clear consensus of how much carbon actually makes it to the deep ocean. Scientists worry that a powerful greenhouse gas called nitrous oxide will be released as organic matter decomposes in the sea, counteracting the absorption benefit. Some say that over time and with many large-scale iron fertilization projects, oxygen could be depleted in the deep ocean, possibly killing some fish.
"I can predict with confidence there will be more dead fish with iron fertilization," Cullen said. "What I can't do is predict how many more."
Debate or not, companies are moving forward. Businesses are increasingly compensating for the greenhouse gas pollution they create by paying to reduce emissions elsewhere. Planktos Inc. and Climos, the two US companies that are pursuing iron seeding projects, could make millions by selling these credits.
Planktos, based in San Francisco, had planned to release up to 100 tons of iron in the Pacific Ocean 350 miles west of the Galapagos Islands. In May, it was told by the US Environmental Protection Agency that if it were using a US flagged ship, it might need a permit under the Ocean Dumping Act. Planktos postponed the plan.
Officials from Climos, also in San Francisco, said they do not plan any large iron seeding trips within the next year. At the conference, they said they are working with scientists to create a "best practice" blueprint before moving forward.
But some conference participants said a key problem still remains: There is no regulatory scheme to verify how much carbon makes it to the ocean depths nor to ensure that iron-seeding companies are not harming the environment.
While the United States could require a US-flagged ship to conduct an environmental review of any iron seeding project, a company could merely re-flag the vessel from a country that is unlikely to require the same. An international anti-dumping treaty known as the London Convention issued a statement of concern in June about iron fertilization, calling for more research.
"These types of proposals are multiplying around the world, and there is no structure in place to evaluate if any of them work," said Lisa Speer, director of the water and oceans program for the Natural Resources Defense Council who attended the meeting. "People are going after these gigantic projects without any thoughtful, rational process."
Beth Daley can be reached at email@example.com