Ironing out Warming Wrinkles

Article excerpt

Fertilizing the oceans with iron could help block climate change - or it could make things worse

The world's oceans are buffering the effects of fossil fuel burning by absorbing up to one-third of annual carbon dioxide released annually from fossil fuels. Some scientists claim they can engineer the oceans to absorb even more carbon. Others say the scheme ignores the complexity of real world ecosystems and could have serious negative effects.

The late oceanographer John Martin was the first to suggest that fertilizing the ocean with iron, a plant nutrient required in low concentrations, could help slow climate warming. "Give me a half tanker of iron and I'll give you an ice-age," he claimed.

Follow-up experiments indicated that iron fertilization can indeed promote algae growth and draw carbon dioxide from the atmosphere. Phytoplankton, algae suspended in the ocean water, convert carbon dioxide into biomass. When the algae die, much of it, including the embodied carbon, sinks to the ocean depths where it can remain for thousands of years. In the experiments, adding iron to the water accelerated this natural carbon pump, removing additional carbon dioxide from the atmosphere.

Even though Martin and his colleagues were quick to caution that these experiments were "not intended as preliminary steps to climate manipulations," advocates say the findings demonstrate the potential for iron fertilization to slow global warming.

Other scientists warn that they know too little about the effects of fertilization to use it as a weapon in the battle against global warming. The Intergovernmental Panel on Climate Change, which developed the scientific framework for the Kyoto agreement, concluded that "iron fertilization is not a feasible mitigation tool given current knowledge of the potential ramifications."

These potential ramifications include oceanic oxygen depletion, reorganization of food webs, and changes in the phytoplankton species present.

Simply changing phytoplankton species is not as innocuous as it seems. Some changes could actually accelerate global warming.

Phytoplankton affect climate not only by taking up carbon dioxide, but also by releasing dimethyl sulfate (DMS), which is important in cloud formation. Increased cloud formation due to the release of DMS increases the amount of solar energy reflected back out of the earth's atmosphere, and reduces atmospheric warming.

The phytoplankton species Pheocystis is ideal as a global warming blocker because it produces DMS and fixes carbon. …