Sulfur emissions from oceans affect our climate and vice versa (credit: Irina Markova on Shutterstock)
When talking about greenhouse gas emissions that contribute to climate change, the first gas that comes to mind is probably carbon dioxide (CO2). Greenhouse gases are gases that absorb heat radiated by the Earth’s surface. CO2 – which we emit into the atmosphere mainly by burning fossil fuels – is the most widely discussed greenhouse gas but the second most important one contributing to climate change. The first most important greenhouse gas is methane (further reading: Chapter 6 of “A Guide to a Healthier Planet”). Apart from CO2 and methane, also other gases exist that should not be underestimated. One of these gases is sulfur dioxide (SO2). An important difference is that SO2 emissions cause the opposite effect: they contribute to the cooling of our planet! This is because this gas reacts with other molecules in the stratosphere, forming tiny droplets that reflect incoming solar radiation into space, keeping the Earth’s surface cool.
The different layers of our planet’s atmosphere (credit: Macrovector on Shutterstock)
SO2 emissions naturally occur when volcanoes erupt. Also, our oceans are an important source, making up 80% of worldwide sulfur emissions. They contribute to these emissions through the so-called sulfur flux. The sulfur flux is the natural process in which sulfur that is stored in the ocean is exchanged with the air. This is possible because sulfur is released by many marine organisms, including phytoplankton and corals, in the form of a chemical compound (dimethylsulfoniopropionate, C5H10O2S, DMSP), which is turned into another chemical compound by microorganisms (dimethylsulfide, CH3SCH3, DMS). Some of these molecules are ventilated into the atmosphere, where they react with oxygen, resulting in SO2 emissions.
This sulfur flux is a natural process that is impacted by environmental circumstances. As environmental circumstances are changing due to climate change, this flux will change as well. Two changes that affect our oceans are rising temperatures and higher water acidity (further reading: “3 Tragic Consequences of Global Warming on Ocean Biodiversity”). This is how these changing environmental circumstances impact sulfur emissions: Rising temperatures
The first way sulfur emissions are affected by climate change is through rising temperatures. Rising temperatures can positively and negatively impact the growth of phytoplankton. An example of a positive impact on phytoplankton is that higher temperatures cause them to convert sunlight into energy at a faster rate, allowing them to grow faster. An example of a negative impact is that warmer water causes surface water to mix less well with deeper levels, causing fewer nutrients to be available to phytoplankton, causing them to grow slower (further reading: “World Changers: 4 Reasons Why Whales And Their Poop Are Important”).
As 25,000 different phytoplankton species are known and probably 100,000 different phytoplankton species exist, the effect of rising temperatures can differ between and within species. This is because not only environmental changes but also the phytoplankton’s sensitivity to temperature changes play a role in their changing numbers. As phytoplankton contribute to forming sulfur compounds that can be ventilated into the air, rising temperatures can change sulfur emissions of our oceans through changing phytoplankton communities. 
Different types of phytoplankton (credit: Ekky Ilham on Shutterstock)
Also, ocean warming causes coral reefs to bleach. Colors on reefs are a sign of vibrancy; the opposite – coral bleaching – is a sign of dying reefs. This is because the warmer water kills microorganisms that live on corals and provide color. These microorganisms live in a mutual relationship with corals, meaning they benefit from each other. When these microorganisms die, the corals are more likely to die as well. As the temperature range that is tolerated by corals is narrow, already small temperature changes have a devastating impact. As corals are also important sources of sulfur and the sulfur concentration on reefs is up to 2 times higher than in the rest of the ocean, dying coral reefs reduce the number of sulfur emissions and limit the cooling effect.
Acidification
The second way sulfur emissions are affected by climate change is through acidification. Acidification means that the acidity level of the ocean increases and the pH level decreases. This is caused by CO2 from the atmosphere being absorbed by the ocean and affects especially species that depend on carbonate, including corals. As mentioned before, corals release sulfur compounds, meaning that declining reefs due to acidification allow less sulfur emissions and result in a smaller cooling effect.
pH scale (credit: AlexVector on Shutterstock)
This effect is even more noticeable in the polar oceans, as cooler water can adsorb more CO2 than warmer water. Here, acidification can limit the growth of algae and sulfur production during the seasonal phytoplankton bloom. As some areas in the Arctic are impacted more than others, also regional factors seem to play a role in the amount of sulfur emissions.
Conclusion
So, climate change impacts natural sulfur emissions through higher ocean water temperatures and acidification. These changing environmental circumstances cause sulfur-producing organisms to die or to bloom, depending on several factors. When these changes positively affect marine organisms, this leads to more sulfur-producing organisms, eventually leading to more sulfur emissions and a larger cooling effect. When these changes negatively impact marine organisms, this leads to the opposite effect causing a smaller cooling effect and allowing global warming to progress.
How we can take action
Here are practical ideas of what you and I can do to limit ocean warming and acidification:
- Limiting CO2 emissions by using renewable energy instead of burning fossil fuels
- Reducing energy use (further reading: “How To Reduce The Impact Of Increasing Energy Prices” with over 100 ideas on how to reduce energy use in daily life)
- Carpooling instead of traveling in separate cars
- Traveling by train instead of car
- Booking a holiday nearby instead of flying to the other side of the globe
- Visiting a vegetarian restaurant instead of a steak house
About the author
Dr. Erlijn van Genuchten is a an internationally recognized environmental sustainability expert. She is a science communicator, helpings scientists in the fields of nature and sustainability increase the outreach of their results and allowing us all to put scientific insights into practice and contribute to a sustainable future. Erlijn has inspired thousands of people around the world — for example — by supporting the United Nations with her expertise, her book “A Guide to A Healthier Planet” published by Springer Nature, her YouTube channel Xplore Nature, and her posts on social media.
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With all this information and facts about the dire consequences of climate change and the ripple effect, then human beings have no choice but to restore the climate.
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Amazing and informative article, thank you! Let's join in taking care of our environment and emphasizing on taking steps to reduce climate change impacts
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This explanation is really informative. Relationship between climate change & natural sulfur emission is a commendable milestone. This a prodigious read!
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This is a very informative and comprehensive explanation of the complex relationship between climate change and natural sulfur emissions. Great read!
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I am intrigued by the coral reefs parts. Ocean warming has severe effects on coral reefs, making them more susceptible to disease. This process not only threatens the vibrant ecosystems that coral reefs support but also impacts the millions of species that depend on them for food and shelter. Addressing ocean warming is crucial to protecting these valuable and biodiverse marine habitats. We have to do something about it
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Amazing read on the impacts of natural sulfur emissions on the climate.