A policy tool for curbing global warming could potentially wreak havoc on the oceans if instituted with no restrictions, warns an MIT professor in the October 12 issue of Science.

Carbon trading, an innovative feature of the Kyoto Protocol on climate change, provides a mechanism for countries to meet reduced emission targets. Under the proposed policy, a country that exceeds its limit in emissions of the principal greenhouse gas, carbon dioxide, could fulfill its commitment by purchasing “carbon credits” from a country that emits less than its quota.

Carbon credits could also be purchased from companies that develop ways to remove carbon from the atmosphere. And therein lies the hitch, says Sallie Chisholm, MIT professor of biology and civil and environmental engineering.

Fertilizing the High Seas

One potential technique for removing atmospheric carbon involves fertilizing the oceans. As pilot experiments over the last ten years have shown, fertilization can increase the number of tiny organisms, or phytoplankton, that remove carbon dioxide from the atmosphere as part of their normal growth. Some of those organisms fall to the bottom of the sea or are eaten and fall to the bottom as fecal matter, essentially moving carbon out of the air and into the deep.

Entrepreneurs watching these developments have concluded that fertilizing large patches of ocean might therefore be profitable if carbon trading is instituted.

“Proponents claim that ocean fertilization is an easily controlled, verifiable process that mimics nature; and that it is an environmentally benign, long-term solution to atmospheric CO2 accumulation,” write Chisholm and co-authors Paul G. Falkowski of Rutgers University and John J. Cullen of Dalhousie University in Canada.

“These claims are, quite simply, not true.”

Ocean fertilization is not easily controlled, say the researchers. “A fertilized patch in turbulent ocean currents is not like a plot of land. The oceans are a fluid medium, beyond our control.”

How Green Is It?

Chisholm is particularly critical of claims that ocean fertilization is environmentally benign. “What really surprises me is that they’re ignoring the results of years of research on aquatic ecosystems,” including the negative effects of nutrient enrichment in lakes and coastal waters.

Many studies have shown that over-stimulated plant growth can lead to oxygen depletion and the elimination of species vital to the food web. If oceanic food webs were to be significantly altered, the results “could be very damaging to the global oceans.”

Chisholm emphasizes that she’s not against individual experiments in which ocean fertilization is used as a tool for studying the ocean’s response to enrichment. Such experiments have already yielded “very exciting results that have contributed to our understanding of the role of the oceans in the global carbon cycle and in regulating climate.”

But “we are against the large-scale implementation of ocean fertilization as a carbon sequestration option,” she says.

Closing the Door

Commercial implementation of ocean fertilization techniques is not imminent, but interest is growing. About seven patents have been filed on different techniques, and at least three small companies have been established. Chisholm herself recently talked to a representative from Mitsubishi Heavy Industries. “So many large companies are watching with interest,” she says.

Although Chisholm notes that fertilizing a relatively small patch of water would not by itself change the ecology of the oceans, she fears a potential slippery slope. “If it’s profitable for one, it would be profitable for many, leading to exploitation and a classic tragedy of the commons,” she says.

“One simple way to avert this potential tragedy is to remove the profit incentive for manipulation of the ocean common,” she writes in Science.“We suggest that ocean fertilization in the open seas, or territorial waters, should never become eligible for carbon credits.”