From Ocean Plankton to Clouds

PSI researchers help uncover a major natural source of cloud-forming particles over the Southern Ocean

Tiny marine organisms may have a much larger influence on Earth's climate than previously thought. Scientists from the CERN CLOUD collaboration, including researchers from the Paul Scherrer Institute (PSI), have shown that methanesulfonic acid (MSA) — a compound produced when emissions from ocean phytoplankton are oxidized in the atmosphere — plays a key role in the formation and growth of cloud-forming particles.

The discovery helps explain a long-standing mystery in climate science: why global climate models consistently underestimate cloud-forming particles over the Southern Ocean surrounding Antarctica and in the cold upper atmosphere above the world's oceans. These regions are among the most pristine environments on Earth and play an important role in regulating the planet's climate.

Atmospheric aerosol particles help regulate climate by influencing both sunlight and cloud formation. Until now, sulfuric acid was considered the primary driver of new particle formation. The new study reveals that MSA can be equally effective at low temperatures and works together with sulfuric acid to substantially enhance particle production in cold marine environments.

Using the ultra-clean CLOUD chamber at CERN, the researchers investigated particle formation under realistic atmospheric conditions. The experiments showed that MSA can dramatically increase the formation and growth of new particles, helping them reach sizes capable of acting as cloud condensation nuclei.

PSI scientists from the Laboratory of Atmospheric Chemistry played a central role in the project. They contributed advanced aerosol measurements, chemical analysis, and atmospheric modelling that helped identify the molecular mechanisms behind particle formation and quantify their global climate impact. Global simulations performed within the CLOUD collaboration indicate that MSA is a major source of cloud-forming particles over the Southern Ocean, both today and under pre-industrial conditions.

The findings suggest that natural marine ecosystems generate more cloud-forming particles than previously recognized. A stronger natural aerosol background could mean that the cooling effect attributed to human-made aerosols has been overestimated, with implications for estimates of climate sensitivity and future warming.

The study highlights a previously underappreciated connection between ocean biology, atmospheric chemistry, and cloud formation, demonstrating that emissions from marine phytoplankton help sustain clouds over some of the most remote regions of the planet.