The problem of what to do with the world's growing supply of atmospheric carbon dioxide, a major culprit in global warming, is one of energetic debate among today's scientists. Many of the potential methods for removing CO2 and storing, or sequestering, it elsewhere are still very much in the preliminary planning stages. And in two reports published in today's issue of Science, researchers are urging even more investigation into the potentially deleterious effects of two such plans.

Removing CO2 from the atmosphere and injecting it directly into the deep ocean was first proposed 25 years ago. Though scientists have since performed experiments to try to determine the behavior of CO2 in the deep ocean, Brad Seibel of the Monterey Bay Aquarium Research Institute (MBARI) and Patrick Walsh of the University of Miami caution that the possible adverse biological effects on deep-sea creatures must be considered.

"Many deep-sea organisms are extremely sensitive to environmental change," Seibel says. "We need more studies to characterize the extent and methods of carbon dioxide injection to predict the broader consequences on deep-sea ecosystems and the global biogeochemical cycles dependent on them." The authors estimate that ocean sequestration of sufficient CO2 to return atmospheric levels to twice the pre-industrial level would lower the pH of the entire ocean by 0.1 in less than a decade. This drop would be significant, they note, because organisms that dwell in the deep sea are highly sensitive to modest pH changes.

In the second report, Sallie Chisholm of the Massachusetts Institute of Technology and her colleagues discredit ocean fertilization as a suitable means of sequestering CO2. This theory exploits the natural biological pump already present in the oceans to remove excess atmospheric CO2. By fertilizing the world's oceans with iron, the theory goes, phytoplankton near the sea surface will be able to absorb more CO2, thereby removing it from the atmosphere and storing it in the ocean's interior. But the authors suggest that large-scale ocean fertilization is neither as feasible nor as controllable as some of its proponents have suggested. Indeed, even the cumulative effects of many small-scale fertilizationsfour of which have been the focus of experiments over the past decadewould result in large-scale consequences, they conclude.