Plankton emissions directly seed clouds over the open ocean
Beneath the open ocean, invisible to the eye, microscopic plankton have long been quietly authoring the clouds above them. A landmark study from CERN's CLOUD experiment has now illuminated the mechanism: plankton emissions decompose into methanesulfonic acid, a compound that seeds aerosol particles and, in turn, the clouds that regulate Earth's climate. What once seemed a minor biochemical footnote has emerged as a critical thread connecting ocean life to atmospheric behavior — a reminder that the living and the elemental are never truly separate.
- For decades, the origin of cloud-seeding particles over the open ocean defied explanation, leaving a conspicuous gap in climate science's understanding of marine weather systems.
- CERN's CLOUD experiment has now closed that gap, providing the first direct experimental evidence that methanesulfonic acid — born from decomposing plankton — actively drives aerosol particle nucleation at scales far greater than models assumed.
- The discovery sends tremors through climate modeling: if ocean biology is a primary engine of cloud formation, then declining plankton populations from warming or pollution could quietly reshape cloud cover and planetary heat balance.
- Scientists are now racing to quantify how sensitive cloud formation is to shifts in plankton productivity, asking whether ocean ecosystem changes are already altering atmospheric patterns in ways current instruments have yet to detect.
- The finding repositions marine biological health from an environmental concern into a direct variable in climate prediction, demanding that ocean ecology and atmospheric physics be modeled as a single, entangled system.
Deep in the world's oceans, microscopic plankton have been shaping the clouds above them in ways science is only now beginning to measure. A new study from CERN's CLOUD experiment has identified the mechanism: as plankton die and decompose, their emissions transform into methanesulfonic acid, a compound that seeds the aerosol particles around which water vapor condenses into clouds across vast stretches of open sea.
The mystery had persisted for decades. Over the open ocean, far from land-based sources of dust and pollution, clouds still formed reliably — yet the origin of their microscopic seeds remained unclear. The CLOUD experiment, housed at CERN in Switzerland, was built to recreate atmospheric conditions in a controlled chamber and test how chemical compounds behave under real-world atmospheric pressures. What researchers found was unambiguous: methanesulfonic acid doesn't merely contribute to particle formation — it actively drives it, far more efficiently than existing models had assumed.
The implications reach well beyond atmospheric chemistry. Clouds are critical regulators of planetary temperature, reflecting sunlight and trapping heat in proportions that shape regional and global climate. If plankton emissions are a primary source of cloud-seeding particles over the ocean, then the health of marine ecosystems becomes directly tied to cloud behavior — and, by extension, to climate stability. A flourishing plankton bloom seeds more clouds; a declining one seeds fewer, potentially shifting radiation patterns in ways that feed back into the very warming stressing those ecosystems.
Climate models have long struggled most with cloud behavior over oceans, where predictions carry the greatest uncertainty. This discovery offers a biological key to that problem — but it also opens new questions. How quickly does cloud formation respond to changes in plankton populations? Are shifts in ocean biology already quietly rewriting cloud patterns? The CLOUD experiment has answered one foundational question, and in doing so, has made the ocean's invisible life a central variable in understanding Earth's atmospheric future.
Deep beneath the surface of the world's oceans, microscopic plankton are quietly shaping the clouds that drift above them. A new study from CERN's CLOUD experiment has revealed the mechanism behind this hidden influence: when plankton die and decompose, they release emissions that transform into methanesulfonic acid—a compound that acts as a seed for cloud formation across vast stretches of open ocean.
For decades, scientists understood that clouds require tiny particles to form, but the origin of those particles over the sea remained partly mysterious. Land-based sources like dust and pollution could explain cloud seeding near coasts, but over the open ocean, where such particles are scarce, clouds still formed reliably. The missing piece was biological. The CLOUD experiment, a collaboration housed at CERN in Switzerland, was designed to recreate atmospheric conditions in a controlled chamber and test how different chemical compounds behave when exposed to the conditions found in Earth's upper atmosphere.
What researchers discovered was that methanesulfonic acid—produced when plankton emissions break down in the air—plays a far more significant role in particle nucleation and growth than previously thought. This wasn't a minor contributor to the process. The compound actively drives the formation of aerosol particles, the microscopic seeds around which water vapor condenses to form visible clouds. The implications ripple outward: if plankton emissions are a major source of these particles, then the health and productivity of ocean ecosystems directly influences cloud cover and, by extension, the planet's radiation balance and climate patterns.
The CLOUD experiment provided the first direct experimental evidence linking marine biological activity to atmospheric particle formation. Researchers exposed air samples to the chemical signatures of plankton emissions and watched as methanesulfonic acid molecules collided, clustered, and grew into particles large enough to seed clouds. The process was measurable, reproducible, and far more efficient than models had previously suggested. This wasn't theoretical speculation—it was chemistry happening in real time, under conditions that matched the real atmosphere.
The significance of this finding extends beyond pure atmospheric science. Climate models have long struggled with cloud behavior, particularly over oceans, where predictions remain among the most uncertain aspects of future climate projections. Clouds reflect sunlight back to space and trap heat radiating from Earth's surface, making them critical regulators of planetary temperature. If scientists can now account for how plankton emissions seed clouds, they can build more accurate models of how cloud cover might change as ocean ecosystems shift in response to warming, pollution, and other stressors.
The research also highlights an interconnection often overlooked in climate discussions: the ocean's biological productivity is not separate from atmospheric chemistry and cloud physics. When plankton blooms flourish, they emit more of the compounds that seed clouds. When plankton populations decline, fewer particles form, potentially altering cloud patterns. This feedback loop means that changes to marine life—whether from overfishing, nutrient depletion, or warming waters—could have atmospheric consequences that ripple across weather and climate systems.
For now, the CLOUD experiment has answered one long-standing question about where marine aerosol particles come from. But the discovery opens new questions: How sensitive is cloud formation to changes in plankton emissions? Could shifts in ocean biology already be altering cloud patterns in ways we haven't yet detected? As climate science becomes increasingly focused on understanding feedback loops and tipping points, the role of plankton in seeding clouds over the oceans has moved from a minor detail to a central piece of the puzzle.
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The CLOUD experiment revealed that methanesulfonic acid plays a far more significant role in particle nucleation than previously thought— CERN research findings
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So plankton are making clouds now? How does that actually work?
Not making them exactly, but seeding them. When plankton die, they release compounds that break down into methanesulfonic acid. That acid forms tiny particles in the air, and water vapor condenses around those particles to create visible clouds.
And this was unknown before?
Not entirely unknown, but vastly underestimated. Scientists knew clouds needed particles to form, but they didn't realize plankton emissions were such a major source of those particles over open ocean.
Why does it matter if we understand this now?
Because clouds control how much sunlight reaches Earth and how much heat escapes back to space. If we don't understand what controls cloud cover, we can't predict how climate will actually change.
So if plankton populations drop, do we get fewer clouds?
Potentially, yes. Fewer plankton means fewer emissions, fewer particles, possibly fewer clouds. That's a feedback loop we need to account for in climate models.
Is this happening now, or is it just theoretical?
It's happening now. The CERN experiment proved the chemistry works under real atmospheric conditions. The question now is how much it's already affecting cloud patterns and how sensitive the system is to changes in ocean life.