New Data: Phytoplankton Emissions Are a Major, Underestimated Source of Climate-Cooling Aerosols

For decades, climate scientists have understood that the Earth's oceans act as a massive thermal sponge, absorbing the lion's share of the heat trapped by greenhouse gases. But new data reveals that the ocean's smallest inhabitants are actively fighting back against warming through the atmosphere.[3]

A landmark study published this week in the journal Nature by the CLOUD Collaboration at CERN has fundamentally rewritten the math on marine aerosols. The research demonstrates that phytoplankton—microscopic marine algae—are producing far more heat-mitigating cloud particles than previously accounted for in global climate models.[1][2]

The findings offer a rare injection of optimism into climate projections. As humanity reduces its burning of fossil fuels, we are inadvertently removing a massive source of artificial atmospheric cooling. This new evidence suggests the marine biosphere possesses a built-in buffering capacity that may help compensate for that loss.[3]

To understand the breakthrough, one must look at how clouds form. Clouds do not materialize out of thin air; water vapor requires tiny suspended particles, known as cloud condensation nuclei (CCN), to condense around.[2]

When the concentration of these aerosol particles increases, clouds become composed of smaller, more numerous droplets. This makes the clouds physically brighter and more reflective, bouncing incoming solar radiation back into space before it can heat the Earth's surface—a phenomenon known as the aerosol cooling effect.[1][3]

Historically, the most important vapor for creating these nuclei has been sulfuric acid. Since the dawn of the Industrial Revolution, the burning of coal and oil has pumped vast quantities of sulfur dioxide into the sky, which oxidizes into sulfuric acid.[2]

This anthropogenic pollution has acted as a massive, unintentional sunshade. Climate models estimate that human-made aerosols have masked a substantial fraction of the warming that greenhouse gases would have otherwise caused.[6]

This creates a well-documented 'Catch-22' for environmental policy. As nations successfully implement clean-air regulations and scrub sulfur dioxide from power plants and shipping fuels, the artificial sunshade is being pulled away. Without it, scientists have feared a sudden, sharp spike in global temperatures.[3]

Enter the phytoplankton. These marine organisms naturally emit a gas called dimethyl sulfide (DMS), which accounts for roughly 20 percent of all atmospheric sulfur. When DMS oxidizes in the air, it produces two primary compounds: sulfuric acid (SA) and methanesulfonic acid (MSA).[1][2]

Until now, climate models largely ignored MSA, assuming that only the sulfuric acid pathway was efficient enough to drive the spontaneous formation of new particles, a process called nucleation.[2]

By recreating pristine marine atmospheric conditions inside CERN's ultra-clean CLOUD chamber, researchers discovered that models have been missing half the picture. At temperatures below -10°C, MSA is just as effective as sulfuric acid at driving particle nucleation in the presence of ammonia.[1][3]

More importantly, the two acids do not just operate in isolation—they work synergistically. The CERN experiments revealed that when MSA and SA mix, particle nucleation rates can accelerate by up to tenfold, and the subsequent growth of those particles can double, compared to sulfuric acid alone.[1][3]

This means that in cool marine environments and polar regions, the biological production of MSA is a massive, previously uncounted engine for cloud formation. 'Our model simulations indicate that MSA-driven new particle formation may account for the major missing source of marine aerosol particles in current models,' noted Jasper Kirkby, spokesperson for the CLOUD Collaboration.[2][3]

The CERN findings corroborate a growing body of evidence that marine biological cooling has been severely underestimated. In late 2024, researchers discovered that another phytoplankton emission, methanethiol (MeSH), increases the sulfate aerosol burden over the Southern Ocean by up to 70 percent, further plugging the gaps in climate models.[4][5]

While this biological thermostat provides a hopeful buffer, it is not a silver bullet. The ultimate efficacy of this natural cooling system depends entirely on the health of the phytoplankton themselves. If ocean acidification and extreme marine heatwaves disrupt these microscopic ecosystems, their ability to seed the clouds and cool the planet could collapse just when we need it most.[5][7]