Deep beneath the surface of the Southern Ocean, tiny marine plankton are doing something remarkable: they're helping to form the clouds that regulate Earth's climate. A breakthrough experiment at CERN, led by researchers from the University of Helsinki, has revealed that these microscopic organisms play a far larger role in cloud formation than scientists ever suspected—possibly speeding up cloud creation by a factor of ten in some of the planet's most remote waters.
For nearly half a century, researchers theorized that marine plankton contributed to cloud formation. Now they have proof. When these plankton photosynthesize, they release dimethylsulfide (DMS), the compound responsible for the sea's distinctive smell. As DMS travels upward and oxidizes in the atmosphere, it transforms into methanesulfonic acid (MSA), a vapor that the Helsinki team's experiments show can seed clouds just as effectively as sulfuric acid—the long-understood primary driver of atmospheric particle formation.
The discovery came through the CERN CLOUD chamber, where researchers recreated the pristine, frigid conditions of remote marine air. Testing temperatures ranging from +9°C down to a bone-chilling −52°C, they found that once temperatures dropped below −10°C and even trace amounts of ammonia were present, MSA formed new aerosol particles with equal efficiency to sulfuric acid. Even more significantly, when the two compounds mixed, they reinforced each other through shared molecular clusters, accelerating particle growth across the entire temperature range.
"Clouds may form up to 10 times faster than previously thought," said Dr. Jiali Shen, one of the study's lead authors, speaking about cold ocean regions where MSA and sulfuric acid occur at similar concentrations.
This finding resolves a longstanding puzzle. Current climate models underestimate cloud-forming particle concentrations over the Southern Ocean by more than half, introducing a warm bias into predictions. The gap exists precisely because models failed to account for MSA's contribution. The Helsinki team's global simulations show that incorporating MSA strengthens particle concentrations most dramatically over the cold, unpollated ocean regions surrounding the Arctic and Antarctic—exactly where observations diverged from theory.
The timing may prove crucial. As sulfur dioxide emissions from fossil fuels continue to decline worldwide, the natural biological sources of cloud seeds from marine plankton become relatively more important. "Capturing these processes is essential if we are to reliably predict future climate," noted corresponding authors Xu-Cheng He and Katrianne Lehtipalo. The study, published in Nature, underscores the value of investing in precise atmospheric measurements—tools that help humanity see its own climate more clearly.
So the next time morning fog rolls in from a cold sea, it may carry with it the quiet, invisible work of creatures too small to see, shaping clouds that cool a warming world.