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.
