Carbon pollution isn't just causing our climate to warm — it's also increasing the acidity of our ocean. This has huge implications for ocean life and the people that depend on it. That's why we've created this official Ocean Decade Toolkit, providing key information and imagery to help improve understanding of the issue.

Climate change’s equally evil twin

Humans’ increased reliance on fossil fuels has caused a flood of carbon dioxide to enter the atmosphere — and the ocean absorbs about 30% of it.

It’s caused by the ocean absorbing CO2 from the atmosphere

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While ocean acidification is not a result of climate change, both stem from the same issue — humans pumping carbon dioxide into the air. According to the National Oceanic and Atmospheric Administration, the ocean absorbs around 30% of the carbon dioxide we release into the atmosphere. 

For millions of years, there was a constant exchange of carbon dioxide between the atmosphere and the ocean’s surface. However, over the past nearly 200 years since the industrial revolution, humans’ reliance on fossil fuels has exponentially increased the amount of CO2 in the atmosphere. In fact, according to the Woods Hole Oceanographic Institution, the current atmospheric concentration of carbon dioxide may be the highest it's been in the last 20 million years. This has put a strain on the ocean to absorb more CO2, thus becoming more acidic.

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As the ocean absorbs more CO2, it becomes more acidic, impacting the development of marine life and ecosystems.

It impacts tiny marine animals to entire ecosystems

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When carbon dioxide mixes with saltwater, it sets off a chemical reaction that decreases the ocean’s pH level, causing the water to increase in acidity. 

A byproduct of this reaction is carbonic acid, which breaks down to release hydrogen ions and bicarbonate ions into the water and removes carbonate ions from the water in the process. This reaction can wreak havoc on the life cycles of marine animals that rely on carbonate ions to grow shells and skeletons like corals, shellfish, coccolithophores, and pteropods (sea butterflies). 

The effects of ocean acidification are most prominent in shallower, near-shore environments where marine life is highly concentrated.

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Corals and coastal marine plants are some of the organisms most affected by ocean acidification.

It makes it harder for coral to grow and build reefs.

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The ocean acidification process removes carbon ions from seawater. This impacts coral reefs and other marine animals and plants, which rely on carbonate ions to grow. Coral polyps, for example, bond carbonate ions and calcium ions in the water to form a substance called calcium carbonate. They use this calcium carbonate to build their internal skeletons.

Because there are fewer carbonate ions in the water, ocean acidification slows the rate that coral reefs can generate calcium carbonate. This slows down the growth of reef systems.

Additionally, ocean acidification makes it that much harder to bounce back from other climate-related stressors, like coral bleaching.

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The process of ocean acidification removes valuable carbonate from the water, so animals that rely on calcium carbonate to build their skeletons and shells have fewer resources to use.

It makes it difficult for marine life to form shells and skeletons

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Calcium carbonate is a substance made when calcium ions and carbonate ions bond in seawater. Many ocean animals use calcium carbonate as a building block for skeletons and shells, including clams, mussels, crabs, phytoplankton, and coral. 

When the ocean absorbs carbon dioxide from the atmosphere, a chemical reaction happens that removes carbonate ions from the water. With fewer carbonate ions to bond, there’s less calcium carbonate to go around.

It’s not just affecting young animals that are forming shells and exoskeletons for the first time. Adult animals must expend more energy to combat the effects of ocean acidification, too. According to the Environmental Protection Agency (EPA), scientists have even found that, if the acidity of seawater is too high, some animals start to dissolve their own shells to counter the elevated acidity in their body fluids. 

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When ocean acidification-related issues affect animals at the bottom of the food web, it impacts other species in the food chain too.

It disrupts the marine food web

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As the EPA explains, “if acidification reduces the populations of small animals like clams, oysters, and sea urchins, the larger animals like fish that feed upon those could run short of food, and so on up the food chain.”

From plankton to whales, this can significantly affect the ocean food web. But it can also impact humans’ food sources and economies. 

Millions of people across the globe eat shellfish as a major source of protein. And in the U.S., the shellfish industry largely contributes to coastal economies, employing thousands of workers and bringing in millions of dollars in revenue every year. Scientists estimate that ocean acidification could cause the industry to lose more than $400 million per year by 2100.

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Acidification can make climate change worse by restricting the ocean’s ability to absorb CO2.

It affects the ocean’s ability to store carbon

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The ocean acidification process reduces the concentration of carbonate ions in seawater. Scientists have determined that the reduction in these ions lowers the ocean’s chemical capacity to take up further carbon dioxide.

If humans keep increasing the amount of carbon dioxide we pump into the atmosphere through the use of fossil fuels — and the ocean sequesters less of the carbon dioxide humans produce — it could quickly accelerate climate change.

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While ocean acidification is a global problem, certain areas of the ocean are more at risk than others.

It currently impacts colder regions more than warmer ones

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Carbon dioxide dissolves faster in colder water, which means that polar regions can take up more CO2 than tropical regions. Because of this, the waters around places like Alaska, Antarctica and Greenland are acidifying faster than warmer areas. In fact, in some warm areas, the ocean is actually releasing carbon dioxide into the atmosphere rather than absorbing it.

Communities in colder regions, like the U.S. Pacific Northwest, for example, rely on the shellfish industry to support thousands of jobs and bring in hundreds of millions of dollars each year. With acidification taking the most immediate effects on marine animals with shells, this could spell disaster in more ways than one for these regions.

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Download and use free photos and video from our Ocean Image Bank

The 7 things absolutely everyone should know about ocean acidification...

Ocean acidification is caused by the rise of carbon dioxide in the atmosphere, much of which is absorbed by the ocean. As such, one of the simplest yet most effective ways to slow ocean acidification is to reduce fossil fuel emissions. 

While climate-friendly legislation and fossil fuel regulations would go a long way to reduce CO2 emissions, individuals can also do their part by conserving electricity, driving and flying less, and using renewable energy sources.

Reduce our fossil fuel emissions

Marine plants like seagrass, kelp, and other algae are excellent at combating ocean acidification.

Seagrasses absorb carbon dioxide from the ocean during photosynthesis, which can raise the pH of surrounding seawater, making it less acidic. Scientists at the Monterey Bay Aquarium Research Institute have tested water around seagrass beds that have shown a pH close to pre-industrial levels.

Marine macroalgae (also called seaweed) can also help mitigate ocean acidification. Kelp is one such type of seaweed. While many creatures that live in kelp forests, like rockfish, Dungeness crab, abalone, and lobster, have been negatively affected by ocean acidification, the kelp itself has a high potential to sequester carbon and reduce acidification overall.

Microscopic algae, or phytoplankton, are considered the most productive organisms in the ocean. They take up carbon dioxide as they grow, and after working their way through the food chain, that carbon gets sequestered in the deep ocean. Cultivation of phytoplankton, which is currently being tested by scientists, could lead to a greater reduction in CO2.

Plant and restore carbon-capturing marine plants like seagrass and kelp

Over time, the ocean has sequestered significant amounts of carbon through the weathering of coastal rock formations. Waves and rain beating against rock has continuously washed alkaline molecules into the ocean. Alkaline molecules are higher on the pH scale, so they’re more basic and can neutralize acid. Researchers are now working on ways to speed up this natural process, storing carbon faster and, thus, reducing ocean acidification.

Direct ocean capture is another emerging solution. Like direct air capture with terrestrial plants, scientists can use electrochemistry to strip carbon dioxide from seawater and store it deep within layers of rock or use it to increase the alkalinity of rocks.

Additional long-term carbon storage techniques include making products from biomass, such as bioplastics and biochar, and sinking bundles of biomass into the deep sea.

Invest in new technologies like alkalinity enhancement and direct ocean capture

What can we do to solve ocean acidification?

The ocean is acidifying at a faster rate now than at any point in the past at least 66 million years. Some scientists estimate the ocean’s surface waters are 30% more acidic today than they were at the start of the Industrial Revolution. If we do not curb our carbon emissions, researchers project surface waters could be more than two times as acidic as they were at the end of the last century.

The ocean is expected to be 150% more acidic by the end of the century than it is now.

Pteropods, also known as “sea butterflies,” are tiny sea snails about the size of a pea. They play an important role in the ocean’s food web, but recently, they’ve been used to gain more insight into the future of the ocean. Scientists placed pteropod shells in seawater with pH and carbonate levels projected for the year 2100, and the shells dissolved within 45 days.

In the natural world, researchers have already found pteropod shell dissolution in the Southern Ocean around Antarctica and off the west coast of America. NOAA scientists have said that they didn’t expect to see pteropods so affected by ocean acidification for decades, indicating that the issue may be more severe than once thought.

The "sea butterfly” is an icon of ocean acidificaiton

You don’t need to know much more about ocean acidification…

…but we think you might like to.

Ocean Acidification | National Oceanographic and Atmospheric Administration (NOAA)
Understanding Ocean and Coastal Acidification: Teacher Resources | NOAA
Ocean Acidification | Woods Hole Oceanographic Institution
Impacts of Ocean Acidification on Marine Biodiversity | UN Environment Programme
Oceans and Atmosphere: Ocean Acidification | Scripps Institution of Oceanography

The Threat of Ocean Acidification | The Economist
Ocean Acidification’s Impact on Oysters and other Shellfish | NOAA & PBS Newshour
What is Ocean Acidification? With Jim Toomey | PEW Charitable Trusts
Demystifying Ocean Acidification | Khan Academy
Ocean Acidification Videos | NOAA National Marine Sanctuaries 

How does OA Work? | Scripps Institution of Oceanography
Acidification in our Ocean | NOAA Coral Reef Conservation Program 
Ocean Acidification Infographics | NOAA National Marine Sanctuaries
What is Ocean Acidification | OA Alliance
What is Ocean Acidification | Save Our Seas Foundation

Imagery provided by Ocean Image Bank photographers: Amanda Cotton, Cameron Venti, Grant Thomas, Kimberly Jeffries, Martin Colognoli, Matt Curnock, Nicolas Job, Nico Marin, Richard Vevers and Stefan Andrews, Thomas Horig and Toby Matthews
Imagery from Unsplash by Andy Castille, Chris Leboutillier, Clyde Thomas, EJ Strat, Ennis Price, Erik McLean, Henry Perks, Jeremy Bishop, Jong Marshes, Josephine Bredehoft, Milada Vigerova, Nilogy Palit and Tim Marshall. Thank you!

A toolkit to help raise awareness of ocean acidification — climate change's equally evil twin.