Fertilize the Ocean, Cool the Planet?

Like the leaves of New England maples, phytoplankton, the microalgae at the base of most oceanic food webs, photosynthesize when exposed to sunlight.  In the process, they absorb carbon dioxide from the atmosphere, converting it to carbohydrates and oxygen. Many phytoplankton species also release dimethyl sulfide (DMS) into the atmosphere, where it forms sulfate aerosols, which can directly reflect sunlight or increase cloud cover and reflectivity, resulting in a cooling effect. The ability of phytoplankton to draw planet-warming carbon dioxide (CO2) from the atmosphere and produce aerosols that promote further cooling has made ocean fertilization — through massive dispersal of iron sulfite and other nutrients that stimulate phytoplankton growth — an attractive geoengineering method to reduce global warming.

But undesirable climate impacts could result from such a large-scale operation, which would significantly increase emissions of DMS, the primary source of sulfate aerosol over much of the Earth’s surface, and a key player in the global climate system.  Now, in a study published in Nature’s Scientific Reports, MIT researchers found that enhanced DMS emissions, while offsetting greenhouse gas-induced warming across most of the world, would induce changes in rainfall patterns that could adversely impact water resources and livelihoods in some regions.

“Discussions of geoengineering are gaining ground recently, so it’s important to understand any unintended consequences,” says Chien Wang, a co-author of the study and a senior research scientist at MIT’s Center for Global Change Science and the Department of Earth, Atmospheric, and Planetary Sciences.  “Our work is the first in-depth analysis of ocean fertilization that has highlighted the potential danger of impacting rainfall adversely.”

Read more at Fertilize the Ocean, Cool the Planet?