The discovery, from the University of East Anglia and the Did Someone Tell Al Gore? department, illustrates the vast complexity of Earth's atmosphere and its systems.
Oceans emit more sulfur and cool climate than previously thought.
Researchers have quantified for the first time global emissions of sulfur gas produced by marine life, finding that it is cooling the climate to a greater extent than previously thought, particularly in the Southern Ocean.
The research is published in the journal scientific progress, Show that the ocean not only captures and redistributes the sun's heat, but also produces gases that produce particles that have a direct impact on climate, such as through the brightening of clouds that reflect this heat.
It amplifies the impact of ocean sulfur on climate because it adds a new, previously unnoticed compound called methylmercaptan. Researchers have only recently detected the gas because it has been difficult to measure in the past and early work focused on warm oceans, while polar oceans are emission hotspots.
The research was led by a team of scientists from the Spanish Institute of Marine Sciences (ICM-CSIC) and the Institute of Physics and Chemistry of Bras Cabrera (IQF-CSIC). Among them is Dr. Charel Wohl, previously at ICM-CSIC and now at the University of East Anglia (UEA) in the UK.
Their findings represent a major advance in one of the most groundbreaking theories about the ocean's role in regulating Earth's climate, proposed 40 years ago.
This suggests that tiny plankton living on the surface of the ocean produce sulfur in the gas form known as dimethyl sulfide, which, once in the atmosphere, oxidizes and forms small particles called aerosols.
Aerosols reflect some of the sun's radiation back into space, reducing the amount of heat the Earth retains. When they participate in cloud formation, their cooling effect is amplified, to the opposite, but to the same extent, of well-known warming greenhouse gases such as carbon dioxide or methane.
The researchers believe this new work improves our understanding of how Earth's climate is regulated by adding a previously overlooked component and illustrates the critical importance of sulfur aerosols. They also highlighted the serious impact of human activity on the climate and that without action, the planet will continue to warm.
Dr Wall, one of the lead authors from the University of East Anglia's Center for Marine and Atmospheric Science, said: “This is the most cooling climate factor, but it is also the least understood. We know that methyl mercaptan is released from the ocean , but we don't know how much and where, and we don't know it has such a big impact on climate.
“Climate models significantly overestimate the solar radiation that actually reaches the Southern Ocean, largely because they fail to model clouds correctly. The work done here partially closes the long-standing knowledge gap between models and observations.
With this discovery, scientists can now more accurately represent the climate in models for predicting +1.5°C or +2°C warming, a significant contribution to policy development.
“So far, we thought that the ocean only releases sulfur into the atmosphere in the form of dimethyl sulfide, a plankton residue from which the smell of shellfish mainly comes,” said Dr. Martí Galí, researcher at ICM-CSIC explain.
Dr Wall added: “Today, thanks to developments in measurement technology, we know that plankton also emit methylmercaptan, and we have found a way to quantify where, when and how much this emission occurs on a global scale.
“Understanding the emissions of this compound will help us more accurately represent clouds over the Southern Ocean and more realistically calculate their cooling effects.”
The researchers gathered all available measurements of methyl mercaptan in seawater, added measurements they made in the Southern Ocean and along the Mediterranean coast, and statistically correlated them with seawater temperatures obtained from satellites.
This led them to conclude that methyl mercaptan would increase known ocean sulfur emissions by 25% per year on a global average.
“This may not seem like much, but methyl mercaptan is more effective at oxidizing and forming aerosols than dimethyl sulfide, so its impact on climate is amplified,” said IQF-CSIC researcher and co-leader Dr. Julián Villamayor.
The team also incorporated marine emissions of methyl mercaptan into state-of-the-art climate models to assess its impact on Earth's radiation balance.
Research shows the impact is more pronounced in the Southern Hemisphere, which has more oceans and less human activity and therefore produces lower levels of sulfur from burning fossil fuels.
This work was funded by organizations including the European Research Council and the Spanish Ministry of Science and Innovation.
“Ocean emissions of methyl mercaptan increase aerosol cooling in the Southern Ocean” by Charel Wohl, Julian Villamayor and Martí Galí et al. scientific progress November 27th.
Journal – Science Advances.
Paper: 10.1126/sciadv.adq2465
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