Understanding Ocean Acidification

Ocean acidification is a global threat to the world’s oceans, estuaries, and waterways. It is often called “climate change’s evil twin” and is projected to grow as carbon dioxide continues to be emitted into the atmosphere at record-high levels.

Like a sponge, our oceans are absorbing increasing amounts of carbon dioxide from the atmosphere. This exchange helps regulate the planet’s atmospheric carbon dioxide concentrations, but comes at a cost for the oceans and sea life, particularly shellfish such as commercially valuable oysters and clams. Ocean acidification is best known for its osteoporosis-like effects on shellfish, which makes building and maintaining shells difficult for these creatures. Acidification also affects other species vital to the marine ecosystem, including reef-building corals and pteropods (tiny snails eaten by numerous species such as fish and whales). 

Yes. Over the past 200 years, the world’s oceans have absorbed more than 150 billion metric tons of carbon dioxide emitted from human activities. That’s a worldwide average of 15 pounds per person per week, enough to fill a train long enough to encircle the equator 13 times every year. Ocean carbon dioxide concentrations are now higher than at any time during the past 800,000 years, and the current rate of increase is likely unprecedented.

The atmospheric concentration of carbon dioxide has increased because of the burning of fossil fuels such as coal, gas, and oil along with land use change (for instance, conversion of natural forest into crop production). The oceans have absorbed roughly one-third of all carbon dioxide emissions related to human activities since the 1700s. Estimates of future carbon dioxide levels, based on business-as-usual emission scenarios, indicate that by the end of this century the surface waters of the ocean could be nearly 150 percent more acidic, resulting in a pH that the oceans haven’t experienced for more than 20 million years.

The consequences of disrupting what has been a relatively stable ocean environment for tens of millions of years are beginning to show. Ocean acidification is literally causing a sea change that is threatening the fundamental chemical balance of ocean and coastal waters from pole to pole. For good reason, ocean acidification is sometimes called “osteoporosis of the sea.” Ocean acidification can create conditions that eat away at the minerals used by oysters, clams, lobsters, shrimp, coral reefs, and other marine life to build their shells and skeletons.

Human health is also a concern. In the laboratory, many harmful algal species produce more toxins and bloom faster in acidified waters. A similar response in the wild could harm people eating contaminated shellfish and sicken fish and marine mammals. And while ocean acidification won’t make seawater dangerous for swimming, it will upset the balance among the multitudes of microscopic life found in every drop of seawater. Such changes can affect seafood supplies and the ocean’s ability to store pollutants, including future carbon emissions.

The Pacific Northwest, Long Island Sound, Narragansett Bay, Chesapeake Bay, Gulf of Mexico, and areas off Maine and Massachusetts were revealed as hot spots in a 2015 study showing the vulnerability of the $1 billion U.S. shellfish industry to ocean acidification. Also at risk are Alaska’s fisheries, which account for nearly 60 percent of U.S. commercial fish catch and support more than 100,000 jobs.

Elsewhere in the world, ocean acidification is weakening coral structures in the Caribbean and in cold-water reefs in waters off of Scotland and Norway. It is also a concern for the Great Barrier Reef, where living corals have declined by half over the past three decades, reducing habitat for fish and the resilience of the entire reef system. Native fisheries in Patagonian waters may also be threatened, and dramatic change is apparent in the Antarctic, where the frigid waters can hold so much carbon dioxide that shelled creatures dissolve in the corrosive conditions, affecting food sources for fish, birds, and marine mammals.

Today, more than a billion people worldwide rely on food from the ocean as their primary source of protein. Approximately 20 percent of the world’s population derives at least one-fifth of its animal protein intake from fish. Many jobs and economies in the United States and around the world depend on the fish and shellfish that live in the ocean. Decreasing harvests could especially hurt the poorest people and the least developed nations that have the fewest agricultural alternatives. These challenges may influence migration to more urban regions, which may lead to further social disruption and even conflict.

Ocean acidification is expected to have negative overall effects on many marine species. This could alter marine food chains and food supply to humans. Acidification could also decrease storm protection from reefs, tourism opportunities, and other benefits that are difficult to value.

Smart investments in monitoring and observing are critical to hedging the risks. We can‘t manage what we don’t measure, and observations are vital to providing the environmental intelligence that underpins sound approaches to countering acidification.

There is urgency to making such investments. NOAA’s around-the-clock monitoring of global atmospheric carbon dioxide indicates that the rate of increase has never been higher than during the past 3 years, accelerating the ocean acidification process. This is why, in the most ambitious step the United States has ever taken to address climate change, President Obama called for 1,000 U.S. power plants to reduce emissions by 32 percent by 2030, as compared with 2005 levels. This reduction equals the annual output of 150 million cars, or two-thirds of all U.S. passenger vehicles.

To prevent ocean acidification from being a game-changer, robust forecasting capabilities and public–private partnerships are needed to interpret the global picture as well as the regional and community conditions. For this reason, NOAA co-leads the pioneering, 66-nation Global Ocean Acidification Observing Network, which monitors the progression of acidification and identifies areas of highest risk.

To forecast ocean and coastal conditions and understand implications all along the food chain, observations are essential. In the mid-2000s, ocean acidification nearly collapsed the $117 million West Coast shellfish industry. That’s when the NOAA Ocean Acidification Program and U.S. Integrated Observing System (IOOS) stepped in. Coastal partners used the fuller offshore picture provided by NOAA and real-time data from IOOS buoys to develop an early warning system. This warning system signals the approach of acidified seawater, enabling hatchery managers to schedule production when water quality is right or to modify seawater intake to mitigate the effects of acidified waters. In 2014, a NOAA-led study showed that acidified water was emerging off the coasts of Alaska’s already most vulnerable communities, allowing scientific insight to be factored into adaptation and mitigation strategies. In Maine, a broad coalition is considering monitoring local drivers such as industrial, agricultural, and urban runoff to understand how they might be contributing to the problem.

NOAA’s mission is to understand changes in the world’s oceans, share that knowledge, and conserve coastal and marine ecosystems. Our Ocean Acidification Program plays an important role in promoting ocean acidification education, engaging in public outreach activities related to ocean acidification and its impacts, and working with ocean science partners and other agencies on ocean acidification activities. The program also provides grants for critical research projects that will explore the effects of ocean acidification on marine organisms, ecosystems, and economies. Learn more.