Overlooked ocean gas emerges as powerful force against global warming

BARCELONA — Scientists have discovered that the oceans have been secretly helping cool our planet more than we thought through an overlooked sulfur gas produced by marine life. This finding could help explain why climate models have been struggling to accurately predict temperatures over the Southern Ocean, that vast expanse of water surrounding Antarctica.

For decades, scientists focused on another sulfur compound called dimethyl sulfide (DMS), known for creating the evocative smell of shellfish, as the ocean’s main cooling contributor. DMS gets released into the air from tiny marine organisms and helps form clouds that reflect sunlight back to space. However, this new research published in Science Advances reveals that its chemical cousin methanethiol (MeSH) has been working behind the scenes all along, playing a much bigger role in cooling than previously recognized.

“This is the climatic element with the greatest cooling capacity, but also the least understood,” says Dr. Charel Wohl of the University of East Anglia’s Centre for Ocean and Atmospheric Sciences, in a statement. Wohl spearheaded the research with colleagues at the Institute of Marine Sciences in Spain. “We knew methanethiol was coming out of the ocean, but we had no idea about how much and where. We also did not know it had such an impact on climate.”

Current climate models may need updating to account for this additional cooling effect, especially in the pristine waters of the Southern Ocean where human pollution has less influence. “Climate models have greatly overestimated the solar radiation actually reaching the Southern Ocean, largely because they are not capable of correctly simulating clouds,” explains Dr. Wohl. “The work done here partially closes the longstanding knowledge gap between models and observations.”

Researchers compiled the first global database of ocean MeSH measurements, gathering data from multiple research cruises spanning from the tropical Atlantic to the icy waters near Antarctica. The measurements covered an impressive range of conditions — from nearly freezing temperatures to warm tropical waters, and from areas with sparse marine life to highly productive regions teeming with microscopic organisms.

What they found was surprising: MeSH concentrations showed distinct patterns based on water temperature and location. In colder waters and open ocean areas, MeSH levels were proportionally higher compared to DMS. Meanwhile, in warmer waters and coastal areas, MeSH made up a smaller fraction of the total sulfur emissions.

“It may not seem like much, but methanethiol is more efficient at oxidizing and forming aerosols than dimethyl sulfide and, therefore, its climate impact is magnified,” says co-lead Dr. Julián Villamayor, a researcher at Blas Cabrera Institute of Physical Chemistry.

When the researchers input these new MeSH measurements into sophisticated climate models, they discovered that including MeSH emissions increased the cooling effect of marine sulfur compounds by 30-70% over the Southern Ocean. This enhancement was particularly strong during the Southern Hemisphere summer when marine life is most active and solar radiation is at its peak.

But MeSH doesn’t just add its own cooling effect, it actually makes DMS more effective too. The team found that MeSH acts like a chemical teammate, competing with DMS for reactive compounds in the atmosphere. This competition allows DMS to survive longer and travel farther, spreading its cooling influence over a wider area.

This tag-team effect between MeSH and DMS leads to more sulfate aerosols, tiny particles that help form clouds and reflect sunlight. The increased aerosol formation was most pronounced over the Southern Ocean, where globally, methanethiol increases known marine sulfur emissions by 25%. The impacts are most visible in the Southern Hemisphere, where there is more ocean and less human activity, and therefore the presence of sulfur from the burning of fossil fuels is lower.

These findings represent a major advance on a groundbreaking theory proposed 40 years ago about the ocean’s role in regulating Earth’s climate. As human-caused sulfur emissions continue to decline due to air quality regulations, understanding natural sulfur sources becomes increasingly important for predicting future climate changes.