Scientists discover a natural Arctic cloud factory missing from climate models

The findings, published August 5 in Nature Geoscience, come from an international team led by the University of Birmingham with collaborators in China and Spain. The researchers provide the first real-world evidence that a powerful particle-forming process occurs where Arctic sea ice meets open ocean. In this zone, marine life and sunlight help produce a chemical mixture that can seed the atmosphere with particles capable of influencing clouds.

Cloud-Forming Particles Surge Near Arctic Ice

The process involves naturally occurring iodine, sulfur, and organic compounds that are released into the air and contribute to the formation of new atmospheric particles. Near the edge of the sea ice, researchers observed the number of particles capable of forming cloud droplets increase fifty-fold within a single day.

As the Arctic atmosphere warms, more sea ice melts. That retreat exposes a larger area of the biologically productive ice edge, where particle formation can occur. Those additional particles may alter cloud cover, which in turn affects the Earth's radiation balance by changing how much energy is absorbed or reflected.

The research was supported by the Natural Environment Research Council (NERC). Scientists collected their measurements during an expedition aboard the Royal Research Ship Discovery around Greenland and the Davis Strait in spring and summer 2022.

Co-author Dr. James Brean, Assistant Professor in Atmospheric Science at the University of Birmingham, said: "Our findings provide the first real-world validation of a recently identified atmospheric chemistry mechanism involving iodine oxoacids and sulfuric acid. Until now, this process had only been demonstrated in laboratory experiments at the CLOUD chamber at CERN."

Newly Identified Molecules Help Particles Grow

The team also detected a previously unknown class of atmospheric compounds called iodine-containing oxygenated organic molecules (I-OOMs). These compounds appear to help newly created particles grow until they are large enough to affect cloud formation.

Dr. James Brean added: "These newly identified compounds help small particles grow into larger particles that can seed clouds -- we believe this is the first time such molecules have been observed and implies important new pathways for iodine chemistry."

The researchers found evidence of new particle formation on more than 80% of sunny days, suggesting the phenomenon is common in this part of the Arctic. The process begins with compounds released into the atmosphere that are then chemically transformed by sunlight. The ingredients include:

• Iodine compounds released from the ocean, sea ice, and coastal areas.
• Dimethylsulfide, from marine plants and algae.
• Organic compounds released naturally from the ocean or land.

Arctic Clouds Could Affect Regional Warming

Corresponding author Zongbo Shi, Professor of Atmospheric Biogeochemistry at the University of Birmingham, who led the study, said: "Our discovery is important because these new particles can influence clouds, which play a critical role in determining how much heat is retained or reflected. More clouds or thicker clouds in the warming season could potentially accelerate ice melt while cooling down the open ocean.

"The Arctic has warmed more than three times faster than the global average over the past 40 years, making it one of the most sensitive regions on Earth to climate change. Understanding how natural emissions influences clouds is critical for predicting climate changes in this region. Our discovery will help climate models to improve understanding of how climate change is affecting the Arctic and how the region itself influences global climate."

The largest changes were measured in the marginal ice zone, a narrow region where melting sea ice meets open water and marine algae are especially productive. During one event in this area, the concentration of cloud-seeding particles climbed from about 50 to 1,500 per cubic centimeter.

A Missing Process in Climate Models

As Arctic sea ice continues to retreat, the marginal ice zone is becoming wider. That could increase the area where this newly documented particle-forming process takes place.

Current climate models do not include the mechanism, which means its potential effects on Arctic climate are not yet represented in projections. The researchers are now working to incorporate the process into climate models so its influence on the region can be better understood.