At the edge of Arctic sea ice, where frigid pack ice gives way to open ocean, something unexpected was happening in the air above. On sunny days during a 2022 research expedition, scientists watched the number of microscopic particles capable of seeding clouds surge — not gradually, but dramatically, climbing as much as fiftyfold within a single day.
The measurements were real, not modeled. And until that expedition, researchers had no idea this process was unfolding at anywhere near this scale in the wild.
A particle explosion hiding in plain sight
During one event in the marginal ice zone — where melting sea ice meets open water — researchers watched cloud-condensation nuclei climb from roughly 50 to 1,500 particles per cubic centimeter. That fiftyfold surge happened within a single day. The trigger was sunlight reacting with a chemical mix released by the ocean, algae, and sea ice.
This wasn’t a fluke. The team recorded new particle formation on more than 80% of sunny days, suggesting the phenomenon is a routine feature of the Arctic environment rather than a rare anomaly.
The findings, published in Nature Geoscience and led by the University of Birmingham with collaborators in China and Spain, mark a significant milestone. They represent the first real-world validation of a particle-forming mechanism previously demonstrated only inside CERN’s CLOUD chamber — a tightly controlled lab setting. Seeing it happen in the wild, at this scale, is a different matter entirely.
What’s cooking in the Arctic air
Four ingredients drive the process: iodine compounds released from the ocean, sea ice, and coastal areas; dimethylsulfide, a sulfur compound produced by marine plants and algae; organic compounds from the ocean or nearby land; and sunlight, which chemically transforms the entire mixture and triggers rapid formation of new atmospheric particles.
The team also found something previously unobserved. They identified a new class of molecules called iodine-containing oxygenated organic molecules, or I-OOMs — compounds that appear to help newly formed particles grow large enough to actually influence cloud formation.
“We believe this is the first time such molecules have been observed,” said co-author Dr. James Brean of the University of Birmingham. Their existence points to entirely new pathways in iodine chemistry that atmospheric scientists are only beginning to map.
Why clouds matter so much in the Arctic
Clouds aren’t passive features of the sky. They act as a thermostat, regulating how much solar energy reaches the surface and how much escapes back into space — and in the Arctic, where the stakes are already high, their behavior is especially consequential.
The region has warmed more than three times faster than the global average over the past 40 years. That acceleration makes every feedback mechanism, including cloud cover, critically important to understand. More or thicker clouds during the warming season could cool the open ocean, yet simultaneously trap heat and speed up ice melt. The effect depends heavily on timing, thickness, and altitude.
Changes in cloud cover directly alter Earth’s radiation balance. How much sunlight is absorbed versus reflected shapes temperature trends across the entire planet, not just the Arctic. A natural process that seeds clouds at this scale — and that currently sits outside our models — is a meaningful blind spot.
A growing gap in our climate models
The newly documented mechanism is entirely absent from current climate models. Its effects on Arctic warming projections aren’t underestimated — they’re missing altogether.
The timing matters. As sea ice retreats, the marginal ice zone where this process is most active is expanding. A wider ice edge means a larger area where particle formation can occur, and the phenomenon may already be intensifying as the climate shifts. Our models have no way to reflect that.
Professor Zongbo Shi, the study’s corresponding author and a professor of atmospheric biogeochemistry at the University of Birmingham, put it plainly: understanding how natural emissions influence clouds is critical for predicting how the Arctic will change — and how those changes feed back into global climate.
The research team is now working to incorporate the mechanism into climate models to quantify its regional and global impact. The expedition was conducted aboard the Royal Research Ship Discovery around Greenland and the Davis Strait in spring and summer 2022, supported by the Natural Environment Research Council.
Once the process is built into models, scientists will have a clearer picture of how much this Arctic cloud factory is already shaping the climate — and how much more influential it may become as the ice continues to retreat.
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