Climate change ‘greatly overestimated’? Oceans cooling Earth far more than we thought

 When it comes to climate change, a new study finds that our fear over the planet’s health may be “greatly overestimated.” For the first time, researchers have found oceans help cool global temperatures more than anyone previously thought.

Specifically, sulfur gas produced by marine life emits a second compound that significantly cools the planet. The discovery will help create more accurate climate models and provide another tool to slow global warming.

With almost three-fourths of Earth covered by oceans, the waters capture and redistribute the Sun’s heat. The latest study in Science Advances shows the process goes much deeper than that. The oceans also create sulfur gases that create particles to cool the Earth, such as brightening clouds that reflect heat.

The new compound released from sulfur gas is known as methanethiol. It has not been detected before because it is extremely hard to measure. Additionally, much research has been done on warmer oceans, while polar oceans are the emission hotspots. Microscopic plankton living on the seas’ surfaces emit a type of sulfur gas known as dimethyl sulphide. This gas is the one responsible for the stinky smell in shellfish.

Once sulfur gas reaches the atmosphere, it oxidizes and produces small particles called aerosols. These aerosols reflect solar radiation back into space, lowering the heat on Earth. 

Plankton also releases methanethiol. The authors quantified the amount of methanethiol released into clouds over the Southern Ocean and observed an even greater cooling effect. The cooling impact on the climate is bigger than expected and works the opposite of greenhouse gases such as carbon dioxide and methane, which absorb heat.

“This is the climatic element with the greatest cooling capacity, but also the least understood. 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,” says Dr. Charel Wohl, a researcher at the University of East Anglia’s Centre for Ocean and Atmospheric Sciences, in a media release. “Climate models have greatly overestimated the solar radiation actually reaching the Southern Ocean, largely because they are not capable of correctly simulating clouds. The work done here partially closes the longstanding knowledge gap between models and observations.”

The authors note that the new research helps create more accurate climate models, refining their understanding of the ocean’s role in cooling the planet. These models include those that predict what would happen to the Earth when the global temperature rises by 1.5 ºC or 2 ºC, with results influencing current climate change policies.

The researchers grouped up all measurements of methanethiol in seawater and added them to measurements made in the Southern Ocean and the Mediterranean coast. Using seawater temperature collected from satellite data, they then used statistics to calculate their results. Yearly, methanethiol increases marine sulfur emissions by 25%.

“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 Dr. Julián Villamayor, a researcher at the Blas Cabrera Institute of Physical Chemistry in Spain

The team also added marine methanethiol emissions to a climate model to measure their effects on the planet’s radiation. The impact is more visible in the Southern Hemisphere, where there are more oceans and fewer humans burning fossil fuels. While sulfur aerosols are important in cooling the planet, the authors note that human behavior will determine whether the planet continues to warm.

Paper Summary

Methodology

The research team embarked on a comprehensive study of methanethiol (MeSH), a little-known sulfur compound in the ocean. They collected seawater samples from diverse marine regions, including the Atlantic Ocean, Nordic Seas, Northeast Pacific, Southern Ocean, and Mediterranean Sea. By carefully measuring the concentrations of MeSH and dimethyl sulfide (DMS) in these samples, the researchers developed a sophisticated statistical model to predict MeSH concentrations.

This model took into account various environmental factors such as sea surface temperature, water depth, and chlorophyll concentration. After creating global maps of MeSH emissions, they used an advanced climate model called CAM-Chem to simulate how this compound interacts with the atmosphere.

Key Results

The study uncovered fascinating insights into ocean chemistry and climate regulation. Researchers discovered that MeSH, previously overlooked, is a significant player in the Earth’s climate system. This compound represents approximately 19% of ocean-emitted sulfur compounds, and when incorporated into climate models, it increases atmospheric sulfur by 34%.

The Southern Ocean emerged as a particularly important region for MeSH emissions, especially during summer months. The most groundbreaking finding was MeSH’s role in creating more reflective aerosols, which can help cool the planet by reflecting sunlight back into space.

Study Limitations

The team acknowledged the scarcity of historical data on MeSH concentrations, with most measurements taken during the summer months. Their global emissions estimates relied on statistical models, which inherently carry some uncertainty. The researchers also recognized potential variations in the chemical reaction rates and MeSH production by marine microorganisms. These limitations don’t invalidate the research but provide important context for understanding the study’s scope and potential areas for future investigation.

Discussion & Takeaways

The study challenges previous understanding of how oceans regulate climate. It reveals that MeSH is more than just a simple byproduct – it’s an important climate agent. The research suggests that ocean microorganisms produce a more complex array of sulfur compounds than scientists previously believed. By including MeSH in climate models, researchers might better explain existing discrepancies in Southern Ocean climate simulations.

The findings lend additional support to the long-standing CLAW hypothesis, which proposes that marine life plays a crucial role in climate regulation through the emission and transformation of volatile sulfur compounds.

Funding & Disclosures

This international research effort was supported by a diverse array of funding sources, including the European Research Council, Spanish Ministry of Science and Innovation, Argentine research institutions, the US National Science Foundation, Alfred Wegener Institute, French research programs, and the Indian Ministry of Earth Sciences. Despite the multiple funding sources, the researchers emphasized their commitment to scientific integrity by declaring no competing interests.

The study was a collaborative effort involving researchers from multiple international institutions, with a special acknowledgment to Ron Kiene, a pioneering researcher in marine sulfur compounds.