Slowing Global Warming by Enhancing the Natural Sulfur Cycle

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Scientists have proposed a limited iron fertilization of the Southern Ocean as a means to stimulate the natural sulfur cycle associated with marine phytoplankton. This could result in increased cloud reflectivity that would slow down global warming and possible decrease sea level rise.

New Directions: Enhancing the natural sulfur cycle to slow global warming

Prof. Oliver Wingenter of New Mexico Tech and his colleagues propose a limited iron fertilization of the Southern Ocean as a means to stimulate the natural sulfur cycle associated with marine phytoplankton which could result in increased cloud reflectivity that would slow down global warming and possibly decrease sea level rise.

Wingenter and his research colleagues Dr. Scott M. Elliot at Los Alamos National Laboratory and Prof. Donald R. Blake at University of California, Irvine report their research findings in an article published online July 18 in the journal Atmospheric Environment, titled "New Directions: Enhancing the natural sulfur cycle to slow global warming,".

The scientists base their plan on their observations made during the Southern Ocean Iron Experiments (SOFeX) research expedition, the longest and most comprehensive ocean iron fertilization experiment to date, which was carried out in 2002 aboard three research ships in the Southern Ocean, between New Zealand and Antarctica.

During the SOFeX, two patches of the Southern Ocean approximately 100 square miles in area each were fertilized with trace amounts of iron in order to see if an increase in populations of marine, single-cell algae known as phytoplankton could be used to remove, or "sink," carbon dioxide---from the atmosphere into the deep ocean. However, the effectiveness of iron fertilization for sequestering significant amounts of atmospheric carbon dioxide is still in question.

"However, marine microorganisms not only consume inorganic carbon, but also produce and consume many climate-relevant organic gases," Wingenter continues. "The greatest climate effect of iron fertilization may be in enhancing dimethyl sulfide (DMS) production, leading to changes in the optical properties of the atmosphere and cooling of the region." Samples taken by Wingenter during SOFeX showed that the concentration of DMS increased about five times in the iron fertilized patch versus outside. Emissions of DMS are the main source of sulfate particle formation to the region and "seed" much of the cloud formation.

Wingenter and his research colleagues propose a limited fertilization of only about 2 percent of Southern Ocean---which would result in an estimated two degrees (Celsius) cooling of the region. A program of limited-scale iron fertilization in the Southern Ocean and perhaps a portion of the equatorial Pacific may have the potential to set back the tipping point of global warming from about 10 years to about 20 or more years," Wingenter estimates.

An iron-fertilization program of the scale envisioned by Wingenter and his fellow researchers would require about 30 ships, fertilizing the Southern Ocean with about 22 kilotons of iron sulfate, at an annual cost of anywhere between $10 million and $100 million, according to the article in Atmospheric Environment. Wingenter points out the plan seems doable and can be verified by satellite observations. He also points out that any unforeseen consequences would need to be monitored and that the danger is that policy makers might view proposed geo-engineering solutions an excuse not to deal with cutting back CO2 emissions.

"Our limited, two percent, fertilization of the Southern Ocean to enhance the natural sulfur cycle must be differentiated from previous plans of massive iron enhancements to sequester CO2. Full-scale iron fertilization of the Southern Ocean must be ruled out simply because major cooling of the region by increased DMS would result in a temperature drop of perhaps 10 degrees Celsius or more," Wingenter says. "Massive fertilization would severely impact not only the Southern Ocean, but also summertime temperatures and agriculture in parts of Australia, New Zealand, South Africa, Chile, and Argentina."

Wingenter, Elliot and Blake all received their Ph.D.s at the University of California, Irvine and were all former graduate students of the 1995 Nobel Laureate F. Sherwood Rowland.

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OLIVER WINGENTER
New Mexico Tech
505-835-5263
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