Cloud control

Increased emissions of dimethyl sulphide by phytoplankton in a warmer world won't slow global warming.

Proc. Natl Acad. Sci. USA 104, 16004–16009 (2007)

Credit: © NOAA

The production of a sulphur-containing compound by microscopic ocean plants will not slow global warming as once thought, new research shows. Dimethyl sulphide (DMS) is produced by oceanic phytoplankton roughly in proportion to the amount of sunlight they receive. But by acting as a seed for cloud formation, DMS can slow its own formation and can also cool the climate.

Sergio Vallina from the Institut de Ciencies del Mar de Barcelona in Spain and colleagues¹ used two different models of DMS production incorporating ocean circulation to study future global emissions of the sulphide gas. They found that a 50% increase in atmospheric CO₂ resulted in a 1.2% annual increase in DMS production, but that the cooling effect of the DMS was minimal relative to the warming caused by CO₂. However, the models predicted large seasonal changes in DMS emissions — 10–20 times more in summer compared with winter — indicating that DMS regulates summertime sunlight over the ocean.

These findings suggest that although DMS production may have a considerable effect on seasonal cloud production, it does not show a significant trend over longer timescales, such as would be needed to counterbalance the warming effect of increasing atmospheric CO₂.