Ocean acidification is the gradual decrease in the pH level of Earth's oceans. From 1950 to 2020, the average pH of the ocean surface dropped from about 8.15 to 8.05. Human activities, such as burning fossil fuels, release large amounts of carbon dioxide (CO₂) into the atmosphere. This CO₂ is absorbed by the oceans, where it reacts with water to form carbonic acid (H₂CO₃). This acid breaks down into bicarbonate ions (HCO₃⁻) and hydrogen ions (H⁺). The increase in hydrogen ions lowers the ocean's pH, making it more acidic. However, the ocean remains alkaline, with a pH above 8. Organisms like mollusks and corals are especially affected because they need calcium carbonate to form their shells and skeletons.
A change in pH by 0.1 means there is a 26% increase in hydrogen ions in the ocean. The pH scale is logarithmic, so a change of 1 unit equals a tenfold change in hydrogen ion concentration. Ocean pH and carbonate levels vary based on depth and location. Colder and higher latitude waters absorb more CO₂, which can increase acidity and lower carbonate levels in those areas. Other factors that influence ocean acidification include ocean currents, upwelling zones, proximity to large rivers, sea ice, and the exchange of nitrogen and sulfur from human activities like burning fossil fuels and agriculture.
Lower ocean pH can harm marine life. Scientists have seen reduced shell growth, weaker immune systems, and less energy for reproduction in some species. Coral reefs, which support food and livelihoods for about one billion people, are especially at risk. Ocean acidification may disrupt ocean food chains and affect ecosystems that provide resources for humans.
The main solution to ocean acidification is reducing CO₂ emissions, which is a key goal of climate change efforts. Removing CO₂ from the atmosphere could also help reverse acidification. Some ocean-based methods, like increasing ocean alkalinity or using enhanced weathering, are being studied, but these approaches are not yet fully developed and carry risks.
Ocean acidification has occurred in Earth's history before. Past events caused major ecological changes that affected the global carbon cycle and climate for a long time.
Cause
In 2021, the amount of carbon dioxide (CO₂) in Earth's atmosphere reached about 415 parts per million (ppm). This is about 50% higher than the levels before the industrial era, which were around 280 ppm. According to the National Oceanic and Atmospheric Administration in 2023, CO₂ levels have risen from about 280 ppm in the pre-industrial era to over 410 ppm today. This increase is mainly due to human activities, such as burning fossil fuels and cutting down forests. The current high levels of CO₂ and how fast they are rising are the highest in the past 55 million years. The main sources of this extra CO₂ are human-caused, including emissions from burning fossil fuels, industrial processes, and changes in land use. When fossil fuels are burned for energy, CO₂ is released into the atmosphere as a byproduct. This contributes to the growing amount of CO₂ in the air. The ocean absorbs about a quarter of all human-caused CO₂ emissions. However, the extra CO₂ in the ocean changes the chemical balance of seawater, making it more acidic and reducing the availability of carbonate minerals that many marine organisms use to build their shells and skeletons.
Since 1850, the ocean has absorbed up to 175 ± 35 gigatons of carbon, with more than two-thirds (120 gigatons) of this amount taken up by the global ocean since 1960. Over time, the ocean's ability to absorb CO₂ has increased along with the rise in human-caused emissions. From 1850 to 2022, the ocean absorbed 26% of all human-caused CO₂ emissions. Total human-caused emissions during this period (1850–2021) were 670 ± 65 gigatons of carbon, with 41% remaining in the atmosphere, 26% absorbed by the ocean, and 31% taken up by land.
The carbon cycle describes how carbon dioxide moves between the oceans, land, atmosphere, and Earth's crust. This cycle includes both organic compounds, such as cellulose, and inorganic compounds, such as CO₂, carbonate ions, and bicarbonate ions, which are grouped as dissolved inorganic carbon (DIC). These inorganic compounds are especially important in ocean acidification because they include many forms of dissolved CO₂ in the ocean. When CO₂ dissolves in water, it forms a balance of chemical species: dissolved CO₂, carbonic acid, bicarbonate, and carbonate. The proportion of these species depends on factors like seawater temperature, pressure, and salinity, as shown in a Bjerrum plot. These dissolved inorganic carbon forms are moved from the ocean's surface to its deeper layers through the ocean's solubility pump. The ability of an ocean area to absorb atmospheric CO₂ is measured by the Revelle factor.
Main effects
The ocean's chemistry is changing because it absorbs human-caused carbon dioxide (CO₂). Over the past 270 years, the ocean has taken in about 30% of all human-made CO₂ emissions. This has caused the ocean's pH to decrease, along with the levels of carbonate ions ([CO₃²⁻]) and the saturation states (Ω) of calcium carbonate minerals. This process, called "ocean acidification," makes it harder for marine organisms that build shells or skeletons to form these structures, which can harm coral reefs and other marine ecosystems.
Ocean acidification is sometimes called the "evil twin of global warming" and "the other CO₂ problem." It happens at the same time as rising ocean temperatures and oxygen loss, creating what scientists call the "deadly trio" of challenges for the ocean. These changes will most strongly affect coral reefs, shelled marine organisms, and the people who rely on these ecosystems.
When CO₂ dissolves in seawater, it increases the number of hydrogen ions (H⁺) in the ocean, which lowers the pH. This chemical reaction is described as:
In shallow coastal and shelf areas, several factors influence how much CO₂ is exchanged between the air and ocean, and how pH changes. These include biological processes like photosynthesis and respiration, as well as water upwelling. Ecosystem activity in freshwater sources that flow into coastal waters can also cause large, but local, changes in pH.
Freshwater bodies are also becoming more acidic, though this is a more complex and less obvious process.
The ocean's ability to absorb CO₂ does not change its alkalinity. Alkalinity is the ability of water to resist becoming more acidic. Scientists have proposed increasing the ocean's alkalinity as a way to help buffer against pH changes.
Changes in ocean chemistry can affect marine life directly and indirectly. One major impact is on the ability of organisms to produce shells made of calcium carbonate (CaCO₃), a process called calcification. This is essential for many marine species, such as coccolithophores, foraminifera, crustaceans, and mollusks. These organisms form CaCO₃ structures, which are vulnerable to dissolving if the surrounding seawater lacks enough carbonate ions (CO₃²⁻).
Most of the extra CO₂ that enters the ocean does not stay as dissolved CO₂. Instead, it breaks down into more bicarbonate ions and free hydrogen ions. The increase in hydrogen ions is greater than the increase in bicarbonate, creating an imbalance in the chemical reaction:
To balance this, some carbonate ions in the ocean combine with hydrogen ions to form more bicarbonate. This reduces the concentration of carbonate ions, which are needed for marine organisms to build shells. This change is shown in the Bjerrum plot.
Disruptions to the food chain may occur because many marine species depend on calcium carbonate-based organisms at the bottom of the food chain for food and habitat. This could harm fish populations and affect human livelihoods.
The saturation state (Ω) of seawater for a mineral measures how likely the mineral is to form or dissolve. For calcium carbonate, Ω is calculated by dividing the product of the concentrations of calcium (Ca²⁺) and carbonate ions (CO₃²⁻) by the solubility product (Ksp) at equilibrium. In seawater, the boundary where calcium carbonate dissolves is called the saturation horizon. Above this depth, Ω is greater than 1, and calcium carbonate does not dissolve easily. Most calcifying organisms live in these waters. Below the saturation horizon, Ω is less than 1, and calcium carbonate dissolves. The depth where carbonate dissolution balances the supply of carbonate to the seafloor is called the carbonate compensation depth. Higher CO₂ levels and lower ocean pH reduce carbonate ion concentrations and the saturation state of calcium carbonate, increasing its dissolution.
Calcium carbonate exists in two common forms: aragonite and calcite. Aragonite dissolves more easily than calcite, so the aragonite saturation horizon is closer to the ocean surface than the calcite saturation horizon. This means organisms that build aragonite shells may be more affected by ocean acidification than those that build calcite shells. Ocean acidification lowers the saturation states of both forms, moving their saturation horizons closer to the surface. This reduces calcification in marine organisms because the ability to form calcium carbonate is directly linked to its saturation state.
Large areas of water with low aragonite levels are already rising near the Pacific continental shelf off the coast of North America, from Vancouver to Northern California. These shelves are important for marine life, as many species live or reproduce there. Similar changes may be happening in other regions.
At depths of thousands of meters, calcium carbonate shells begin to dissolve due to pressure and temperature changes. This depth is called the carbonate compensation depth. Ocean acidification will increase this dissolution and bring the carbonate compensation depth closer to the surface over decades to centuries. Areas where water sinks (downwelling) are affected first.
In the North Pacific and North Atlantic, saturation states are decreasing, and the depth where calcium carbonate dissolves is becoming shallower. Ocean acidification is spreading in the open ocean as CO₂ moves to deeper layers through ocean mixing. This causes the carbonate compensation depth to become shallower, meaning calcium carbonate dissolves below these depths. In the North Pacific, the carbonate compensation depth is shallowing by 1–2 meters per year.
In the future, ocean acidification is expected to significantly reduce the burial of carbonate sediments for several centuries. It may also cause existing carbonate sediments to dissolve.
Measured and estimated values
Between 1950 and 2020, the average pH of the ocean surface is estimated to have decreased from about 8.15 to 8.05. This means the amount of hydrogen ions in the ocean has increased by about 26%. The pH scale is logarithmic, so a change of one unit equals a tenfold change in hydrogen ion concentration. For example, between 1995 and 2010, the upper 100 meters of the Pacific Ocean from Hawaii to Alaska became 6% more acidic.
The IPCC Sixth Assessment Report from 2021 stated that current ocean surface pH levels are the highest in at least 26,000 years. Since the late 1980s, the pH of the ocean interior has decreased in all areas of the global ocean. The report also noted that the pH of open ocean surface water has dropped by about 0.017 to 0.027 units per decade.
The rate of pH decline varies by region. This is because of complex interactions between different natural and human-caused factors. In the tropical Pacific, central and eastern upwelling zones experienced a faster pH decline of -0.022 to -0.026 units per decade. This is likely due to increased upwelling of CO₂-rich water from below the surface and human-caused CO₂ absorption. In contrast, warm pools in the western tropical Pacific saw a slower pH decline of -0.010 to -0.013 units per decade.
The speed of ocean acidification may depend on how quickly the ocean surface warms. Warmer water absorbs less CO₂, which could slow pH changes for a given increase in CO₂. Differences in ocean warming between regions are a major reason for varying acidification rates.
Current acidification rates are similar to a past event called the Paleocene–Eocene Thermal Maximum (PETM), about 56 million years ago. During this time, ocean temperatures rose by 5–6°C, and many deep-sea organisms went extinct. Today, the rate of carbon entering the atmosphere and ocean is about ten times faster than during the PETM.
Monitoring systems are now being developed to track seawater CO₂ levels and acidification in the open ocean and coastal areas.
Ocean acidification has occurred in Earth’s history. It happened during the Capitanian mass extinction, the end-Permian extinction, the end-Triassic extinction, and the Cretaceous–Palaeogene extinction event.
Three of the five major mass extinctions in Earth’s history were linked to rapid increases in atmospheric carbon dioxide, likely caused by volcanic activity or the release of methane from ocean sediments. High CO₂ levels affected biodiversity. During the end-Triassic extinction, reduced calcium carbonate saturation—due to CO₂ absorption—may have contributed to the extinction of marine life. This event is the best example of an extinction caused by ocean acidification because evidence shows volcanic activity reduced carbonate sedimentation and ocean pH, and the extinction matched these changes in the geological record. Ocean acidification is also linked to the end-Permian and end-Cretaceous extinctions. Multiple climate stressors, including acidification, likely caused these events.
The most well-known example of ocean acidification is the PETM, which occurred about 56 million years ago. Large amounts of carbon entered the ocean and atmosphere, dissolving carbonate sediments in many areas. Studies suggest ocean pH dropped by 0.3 units during the PETM. However, some research indicates the rate of carbon release during the PETM was slower than today’s human-caused emissions. More advanced methods are needed to better understand how pH changes affected marine life during this event.
Predicted future values
Ocean acidification is changing much faster now than it did in the past. This rapid change makes it hard for ocean life to adapt slowly, and it stops natural climate processes from helping reduce acidification. Ocean acidification is expected to reach pH levels lower than any time in the past 300 million years. The speed at which ocean pH is changing is also unusual compared to the past 300 million years. These changes are considered different from any seen in Earth’s history. Along with other changes in ocean chemistry, this drop in pH could harm ocean ecosystems and the services they provide, such as food and resources, as early as 2100.
How much ocean chemistry changes depends on how well countries reduce greenhouse gas emissions. Scientists use different future scenarios, called Shared Socioeconomic Pathways (SSP), to predict changes.
Under a scenario with very high emissions (SSP5-8.5), models predict that ocean pH could decrease by as much as 0.44 units by the end of this century compared to the late 1800s. This would bring pH levels as low as about 7.7. This would mean H+ levels would be two to four times higher than they are now.
Impacts on oceanic calcifying organisms
Ocean acidification is making it harder for many marine organisms to form shells or hard structures. These organisms, called calcifiers, need carbonate ions to build their exoskeletons. Examples include corals, shellfish, and tiny plankton like coccolithophores and foraminifera. These species play important roles in ocean food chains, from plants that make their own food to animals that eat others.
As ocean acidification increases, the amount of carbonate ions in seawater decreases. This makes it harder for organisms to build and maintain their shells. Studies show that corals, coccolithophores, and other calcifying species experience slower shell growth or increased shell breakdown when exposed to higher levels of carbon dioxide. Even with conservation efforts, some shellfish populations may not recover.
Under normal conditions, the minerals calcite and aragonite are stable in ocean water because carbonate ions are plentiful. However, as ocean pH decreases, carbonate ions become less available. This causes calcium carbonate structures to weaken or dissolve. Some species, like the sea star Pisaster ochraceus, may grow faster in more acidic water, but many others face challenges.
Ocean acidification can also affect how carbon is stored in the ocean. Weaker shells and slower growth in calcifying organisms may reduce the ocean's ability to move carbon from the atmosphere to the deep ocean. This process, called the "biological pump," is important for regulating Earth's climate.
Coccolithophores are single-celled algae that form calcium carbonate shells. Changes in their calcification could impact Earth's climate by altering cloud cover, which affects how much sunlight is reflected back into space. A study from 2008 found that while the types of coccolithophores in the North Atlantic remained the same over 224 years, their shell size increased by 40%.
Warm water corals are declining rapidly due to ocean warming, acidification, pollution, and human activities. Over the past 30–50 years, coral cover has dropped by about 50%. Corals build their skeletons in internal chambers using calcium carbonate from seawater. If seawater becomes too acidic, corals must work harder to maintain the right chemical balance, slowing their growth. By 2050–2060, about 70% of cold-water corals in the North Atlantic may live in waters that are corrosive to their shells.
Experiments on the Great Barrier Reef showed that reducing seawater carbon dioxide levels (increasing pH) led to a 7% rise in shell growth. However, increasing carbon dioxide levels (lowering pH) reduced shell growth by 34%. Some studies suggest corals may be more resilient to acidification than expected, as they can regulate internal chemical balances. This means that rising ocean temperatures, which cause coral bleaching, may be a bigger threat to reefs than acidification.
In some areas, carbon dioxide bubbles up from the ocean floor, lowering local seawater pH. Studies of these areas, called carbon dioxide seeps, show varied responses among marine life. In Papua New Guinea, lower pH near seeps has reduced coral diversity, but in Palau, coral diversity remains stable, though shell erosion increases.
In the Arctic, acidification harms pteropods and brittle stars, which are key parts of the food web. Pteropods rely on aragonite to build their shells, but acidification has reduced the availability of carbonate ions, causing their shells to dissolve. Brittle stars lose muscle mass when regrowing limbs in acidic water. Experiments show that Arctic conditions could cause brittle star eggs to die within days, and larvae survival drops to less than 0.1% when exposed to slightly lower pH levels.
Other impacts on ecosystems
Ocean acidification can harm marine life in many ways. It can slow or stop the process of calcification, which is how some animals build hard shells or skeletons. It can also harm animals indirectly by reducing their food sources or directly by affecting their ability to reproduce or function properly. For example, high levels of carbon dioxide in the ocean can make body fluids more acidic, a condition called hypercapnia. This has been shown to lower the metabolic rates of jumbo squid and weaken the immune systems of blue mussels. In acidified water, Atlantic longfin squid eggs hatch more slowly, and their statoliths (a part of the inner ear used for balance) are smaller and misshapen. However, research on these effects is still ongoing, and scientists have not yet fully understood how ocean acidification impacts marine life or ecosystems.
Another way ocean acidification can harm ecosystems is through changes in how sound travels in water. Acidification can alter the acoustic properties of seawater, allowing sound to travel farther and increasing ocean noise. This can disrupt animals that rely on sound for communication or to find prey.
Ocean acidification may also increase harmful algal blooms, which can produce toxins like domoic acid, brevetoxin, and saxitoxin. These toxins can accumulate in small fish and shellfish, leading to types of shellfish poisoning in humans. While harmful algal blooms are dangerous, some plants like seagrasses may benefit from higher carbon dioxide levels. Studies show that seagrasses increase their photosynthesis when carbon dioxide levels rise, which can raise local water pH and support calcifying algae.
Ocean acidification can also affect marine fish larvae by altering their sense of smell, which is important for their early development. For example, orange clownfish larvae live near coral reefs surrounded by vegetative islands. They use their sense of smell to distinguish between these reefs and others without vegetation, helping them find suitable habitats. They also use their sense of smell to identify their parents and avoid inbreeding.
In an experiment, clownfish were kept in seawater with a pH similar to today’s oceans (pH 8.15 ± 0.07). Scientists then tested the effects of lower pH levels predicted for the year 2100 (pH 7.8 ± 0.05) and even lower levels (pH 7.6 ± 0.05). At pH 7.8, clownfish larvae reacted differently to environmental cues compared to those in current ocean conditions. At pH 7.6, they had no reaction to any cues. However, a 2022 study found that the effects of ocean acidification on fish behavior have decreased significantly over the past decade and are now minimal.
European eel embryos, which are critically endangered but important for aquaculture, are also affected by ocean acidification. These eels spend most of their lives in freshwater but travel to the Sargasso Sea to spawn. In this area, acidification affects their development during a critical life stage. Fish embryos and larvae are more sensitive to pH changes than adults because their organs for regulating pH are not fully developed. A 2021 study found that exposure to predicted future ocean conditions may harm the normal development of European eel embryos in the Sargasso Sea. Extreme acidification could also reduce their survival and development in hatcheries.
Research shows that ocean acidification combined with rising ocean temperatures has a greater negative impact on marine life than either factor alone. Warmer ocean temperatures and increased carbon dioxide levels also contribute to ocean deoxygenation, which reduces oxygen availability in the water. This limits nutrient supply and weakens biological processes in the ocean.
Studies combining data from many experiments have shown that the harmful effects of ocean acidification, warming, and deoxygenation are significant. Experiments simulating these conditions in controlled environments found that the combined stressors severely disrupt marine food webs. For example, heat stress can cancel out any increases in productivity from higher carbon dioxide levels, harming the balance between producers and herbivores.
Impacts on the economy and societies
Ocean acidification slows the process of building shells or skeletons in saltwater, which causes coral reefs to grow more slowly and become smaller. Coral reefs support about 25% of marine life. The effects of acidification are widespread, affecting fisheries, coastal areas, and even the deepest parts of the ocean. Acidification not only harms coral but also the many different types of marine life that depend on coral reefs for survival.
Acidification can reduce the number of fish that people catch for food and income and harm industries that rely on coastal tourism. Future ocean acidification may harm services provided by the ocean, such as fishing and tourism, which could affect the livelihoods of between 470 million and 870 million of the world's poorest people, depending on how much greenhouse gases are released into the atmosphere.
About 1 billion people rely completely or partly on fishing, tourism, and coastal management services provided by coral reefs. Continued ocean acidification may threaten future ocean food chains.
In the Arctic, acidification harms small sea creatures that build shells or skeletons, such as pteropods and brittle stars. These creatures are the base of Arctic food webs, which are simple, meaning there are few steps from small organisms to larger predators. Pteropods are an important food source for many larger animals, including fish, seabirds, and whales. If these creatures disappear, it could seriously harm the entire Arctic ecosystem and the fisheries that depend on it.
The shellfish industry is an important part of the United Kingdom economy. In 2013, shellfish made up 37% of all fish caught by value. England and Scotland are the largest shellfish producers in the UK. Fishers in these areas catch about 66,000 metric tons and 61,000 metric tons of shellfish each year. Wild-caught shellfish are worth about 203 million pounds annually. However, ocean acidification is slowing the growth of many shellfish species, which is causing major economic losses in the UK.
It is predicted that by 2100, ocean acidification could cause economic losses in the UK shellfish industry. These losses could range from 14% to 28% of total fishery output, which would be about 23 million to 88 million pounds. Financial losses vary by region because of differences in the types of shellfish caught and how sensitive different species are to acidification. Solutions at the local, national, or international level may be needed to protect UK shellfish resources and reduce economic impacts.
In 2007, the value of fish caught in US commercial fisheries was $3.8 billion, and 73% of that came from animals that build shells or skeletons and their direct predators. Other marine animals are also harmed by acidification. For example, slower growth in shellfish like American lobsters, ocean quahogs, and scallops means less shellfish meat is available for sale and consumption. Red king crab fisheries are also at risk because crabs build shells. Baby red king crabs exposed to higher acid levels died completely after 95 days. In 2006, red king crabs made up 23% of the total amount of crab allowed to be caught. A serious drop in red king crab numbers would harm the crab fishing industry.
Possible responses
Reducing carbon dioxide emissions is the main way to solve the problem of ocean acidification. Some methods to reduce emissions focus on removing carbon dioxide from the air, such as direct air capture and bioenergy with carbon capture and storage. These methods can also slow the speed of ocean acidification.
Other methods remove carbon dioxide from the ocean, like adding nutrients to the ocean, using artificial water movement, growing seaweed, restoring ecosystems, increasing ocean alkalinity, using weathering processes, and using chemical methods. These methods use the ocean to take in carbon dioxide from the air and store it in the ocean. These methods could help reduce emissions but might harm marine life. Research on these methods has increased since 2019.
In total, ocean-based methods could remove 1–100 gigatons of carbon dioxide each year. Their costs range from US$40–500 per ton of carbon dioxide. For example, enhanced weathering could remove 2–4 gigatons of carbon dioxide each year. This method costs US$50–200 per ton of carbon dioxide.
Some methods add substances to the ocean that help balance its pH, which can protect marine life near where the substances are added. These methods include increasing ocean alkalinity and using chemical processes. However, the added substances will spread over time, so these methods are called "local ocean acidification mitigation." These methods could work on a large scale and be efficient, but they are expensive, have risks, and are not yet widely used.
Ocean alkalinity enhancement is a method that involves adding minerals to the ocean to increase its alkalinity. This helps the ocean absorb more carbon dioxide. The process uses rocks like silicate, limestone, and quicklime to create more bicarbonate, which holds carbon for a long time or forms calcium carbonate. When calcium carbonate is buried in the deep ocean, it can store carbon forever if silicate rocks are used.
Enhanced weathering is one way to increase ocean alkalinity. It involves spreading crushed rock particles on land or in the ocean, which eventually affects the ocean.
Adding alkalinity to the ocean also helps reduce acidification. However, scientists are still learning how marine life reacts to added alkalinity, even from natural sources. For example, weathering some rocks might release harmful metals into the water.
Ocean alkalinity enhancement requires a lot of energy and money because it involves mining, crushing, and transporting materials. The cost is estimated at US$20–50 per ton of carbon dioxide for adding minerals directly to the ocean.
About 30% of carbon emissions since the Industrial Revolution are stored in the ocean as bicarbonate.
Experiments use materials like limestone, brucite, olivine, and alkaline solutions. Another method uses electricity during desalination to capture carbon dioxide from seawater.
Electrochemical methods, or electrolysis, can remove carbon dioxide directly from seawater. These methods are also a type of ocean alkalinity enhancement. Some methods remove carbon dioxide as gas or carbonate, while others increase ocean alkalinity by creating substances that absorb carbon dioxide. The hydrogen produced during this process can be used for energy or other products.
However, using electrolysis for carbon capture is expensive and uses a lot of energy. Research is still being done to understand how this process affects the environment. Problems include harmful chemicals in wastewater and lower levels of dissolved carbon in water, which could harm marine life.
Policies and goals
As more people learn about ocean acidification, governments have created policies to improve monitoring of this issue. In 2015, ocean scientist Jean-Pierre Gattuso noted that the ocean had not been given enough attention in past climate discussions. His research showed the need for major changes in climate talks, such as the 2015 UN conference in Paris.
International programs, like the Wider Caribbean's Cartagena Convention (which started in 1986), can help regional governments support areas at risk from ocean acidification. Many countries, such as those in the Pacific Islands, have developed policies like National Ocean Policies and National Adaptation Plans to support Sustainable Development Goal 14. These policies now include ocean acidification as part of their plans.
The UN Ocean Decade has a program called "Ocean acidification research for sustainability" (OARS). This program was created by the Global Ocean Acidification Observing Network (GOA-ON) and its partners. It is officially part of the UN Decade of Ocean Science for Sustainable Development. OARS aims to improve scientific understanding of ocean acidification, track changes in ocean chemistry, study its effects on marine life, and provide information to help leaders reduce its impacts.
Ocean acidification is one of seven Global Climate Indicators. These indicators measure changes in the climate without focusing only on temperature. They cover areas like temperature, ocean health, and ice. Scientists and experts selected these indicators through the Global Climate Observing System (GCOS). The World Meteorological Organization (WMO) approved them. These indicators are used in the WMO's yearly report on the global climate, which is shared with the UN climate meetings. The European Commission also uses these indicators in its annual "European State of the Climate" report.
In 2015, the United Nations introduced the 2030 Agenda, which includes 17 Sustainable Development Goals (SDGs). SDG 14 focuses on protecting oceans and marine resources. It includes a target, SDG 14.3, which aims to reduce the effects of ocean acidification through better scientific collaboration. This target uses one indicator: the average ocean acidity (pH) measured at specific locations.
The Intergovernmental Oceanographic Commission (IOC) of UNESCO is responsible for tracking this indicator. It develops methods to measure ocean acidity, collects data yearly, and reports progress to the United Nations.
In the United States, the Federal Ocean Acidification Research And Monitoring Act of 2009 helps coordinate government efforts, such as NOAA's "Ocean Acidification Program." In 2015, the Environmental Protection Agency (EPA) refused to regulate carbon dioxide under the Toxic Substances Control Act to address ocean acidification. The EPA stated that other actions, like the Presidential Climate Action Plan, were already helping reduce emissions and deforestation while promoting clean energy.
History
Research on ocean acidification and efforts to inform people about the issue have continued for many years. The basic scientific work started when the pH scale was created by Danish chemist Søren Peder Lauritz Sørensen in 1909. By the 1950s, scientists knew the ocean played a major role in absorbing carbon dioxide from fossil fuels, but this was not widely understood by most scientists. For much of the 20th century, the focus was on the ocean’s ability to absorb CO₂, which helped reduce the effects of climate change. The idea that absorbing too much CO₂ could cause problems developed slowly and was influenced by key events. The ocean’s ability to absorb heat and CO₂ remains important in slowing climate change.
In the early 1970s, scientists began discussing the long-term effects of CO₂ from fossil fuels building up in the ocean. These discussions raised concerns about how this might harm marine life. By the mid-1990s, scientists studying coral reefs were worried about how rising CO₂ levels could change ocean pH and affect carbonate ions.
By the end of the 20th century, scientists better understood the balance between the ocean’s benefits, such as absorbing 90% of Earth’s heat and 50% of fossil fuel CO₂, and the harm it causes to marine life. In 2003, plans were made for the "First Symposium on the Ocean in a High-CO₂ World" in Paris in 2004, as new research on ocean acidification was being published.
In 2009, the InterAcademy Panel urged world leaders to reduce CO₂ emissions to address ocean acidification. The group also encouraged actions to reduce other threats, like overfishing and pollution, to help marine ecosystems survive.
For example, research in 2010 showed that between 1995 and 2010, the upper 100 meters of the Pacific Ocean from Hawaii to Alaska became 6% more acidic.
In 2012, Jane Lubchenco, head of the U.S. National Oceanic and Atmospheric Administration, stated that ocean surface waters are changing faster than expected. She warned that the high levels of CO₂ in the atmosphere are a serious problem.
A 2013 study found that ocean acidity is increasing 10 times faster than during any major extinction event in Earth’s history.
The "Third Symposium on the Ocean in a High-CO₂ World" was held in Monterey, California, in 2012. A summary from the conference said that research on ocean acidification is growing quickly.
In 2015, a report in Science by 22 marine scientists stated that CO₂ from burning fossil fuels is changing ocean chemistry faster than at any time since the Great Dying, Earth’s worst known extinction event. The report said that the goal of limiting global warming to 2°C is not enough to avoid major harm to the oceans.
A 2020 study showed that ocean acidification harms marine life and also affects human health. It can lower food quality, worsen breathing problems, and harm overall health.