Ocean acidification is the gradual decrease in the pH level of Earth's oceans. From 1950 to 2020, the average pH of the ocean's surface dropped from about 8.15 to 8.05. Human activities that release carbon dioxide (CO₂) into the atmosphere are the main cause of ocean acidification. As of 2024, atmospheric CO₂ levels have exceeded 422 parts per million (ppm). When CO₂ from the air dissolves in ocean water, it forms 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, though seawater remains alkaline (with a pH higher than 8). Marine organisms that build shells and skeletons, such as mollusks and corals, are especially affected because they rely on calcium carbonate for their structures.
A change in pH by 0.1 means there is a 26% increase in hydrogen ion concentration in the oceans. The pH scale is logarithmic, meaning a change of one pH unit equals a tenfold change in hydrogen ion concentration. The pH of seawater and the amount of carbonate available vary depending on ocean depth and location. Colder and higher latitude waters can absorb more CO₂, which increases acidity and lowers pH and carbonate levels in these regions. Other factors that influence CO₂ exchange between the atmosphere and oceans include ocean currents, upwelling zones, proximity to large rivers, sea ice, and atmospheric interactions with nitrogen and sulfur from fossil fuels and agriculture.
A lower ocean pH can harm marine life. Scientists have observed reduced shell formation, weaker immune systems, and less energy for reproduction in some species. Ocean acidification can affect ecosystems that support food and livelihoods for many people. Around one billion people depend on fishing, tourism, and coastal management services provided by coral reefs. Continued acidification may disrupt ocean food chains.
The most effective solution to address ocean acidification is reducing carbon dioxide emissions, which is a key goal of climate change efforts. Removing CO₂ from the atmosphere could help reverse ocean acidification. Some ocean-based methods, such as increasing ocean alkalinity or using enhanced weathering, are being studied. However, these approaches are not yet widely tested and carry risks.
Ocean acidification has occurred in Earth's history before. Past events led to major changes in ocean ecosystems, which had long-term effects on Earth's carbon cycle and climate.
Cause
In 2021, the amount of carbon dioxide (CO₂) in the atmosphere was about 415 parts per million (ppm), which is about 50% more than before the industrial era. According to the National Oceanic and Atmospheric Administration in 2023, CO₂ levels have increased from approximately 280 ppm in the pre-industrial era to over 410 ppm today. This rise 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 increasing are unlike anything seen in the past 55 million years. The extra CO₂ in the atmosphere comes from human activities, including burning fossil fuels, industrial processes, and changes in land use. Fossil fuels are burned for energy, and this process releases CO₂ into the atmosphere as a byproduct. The ocean absorbs about a quarter of all human-caused CO₂ emissions. However, this 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 of this (120 gigatons) 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. Human-caused emissions between 1850 and 2021 totaled 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 the movement of carbon dioxide (CO₂) between the oceans, land, Earth’s crust, and the atmosphere. This cycle includes both organic materials, like cellulose, and inorganic materials, such as CO₂, carbonate ions, and bicarbonate ions, which are collectively called dissolved inorganic carbon (DIC). These inorganic compounds play a key role in ocean acidification, as they include various forms of dissolved CO₂ in Earth’s oceans.
When CO₂ dissolves in water, it forms a balance of chemical compounds: dissolved free CO₂ (CO₂(aq)), carbonic acid (H₂CO₃), bicarbonate (HCO₃⁻), and carbonate (CO₃²⁻). The amounts of these compounds depend on factors like seawater temperature, pressure, and salinity, as shown in a Bjerrum plot. These dissolved inorganic carbon forms move from the ocean’s surface to its deeper layers through a process called the solubility pump. The ability of an ocean area to absorb CO₂ from the atmosphere 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 the CO₂ released into the atmosphere. This has caused the ocean's pH (a measure of acidity) to decrease, as well as 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, such as corals and shellfish, to survive. This can harm coral reefs and the ecosystems that depend on them.
Ocean acidification is sometimes called the "evil twin of global warming" and "the other CO₂ problem." It happens alongside rising ocean temperatures and oxygen loss, forming what scientists call the "deadly trio" of climate change impacts on the ocean. These changes will most strongly affect coral reefs, shellfish, and the people who rely on these ecosystems for food and livelihood.
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, factors like photosynthesis, respiration, and upwelling (when deep water rises to the surface) influence how much CO₂ is exchanged between the ocean and air, and how pH changes. Ecosystem activity in freshwater sources that flow into coastal waters can also cause local changes in pH.
Freshwater bodies are also becoming more acidic, though this is less obvious and more complex to study.
Absorbing CO₂ from the atmosphere does not change the ocean's alkalinity, which is the ocean's ability to resist acidification. Adding more alkalinity to the ocean has been suggested as a way to help buffer against pH changes.
Changes in ocean chemistry can harm marine life and their habitats. A major effect of ocean acidification is on the ability of organisms to create shells made of calcium carbonate (CaCO₃), a process called calcification. Many marine organisms, such as coccolithophores, foraminifera, crustaceans, and mollusks, rely on this process. These calcium carbonate structures can dissolve unless the surrounding water has enough carbonate ions (CO₃²⁻) to keep them stable.
Most of the extra CO₂ absorbed by the ocean does not stay as dissolved CO₂. Instead, it breaks apart into bicarbonate ions and hydrogen ions. This increases hydrogen ions more than bicarbonate ions, creating an imbalance. To balance this, some carbonate ions in the ocean combine with hydrogen ions to form more bicarbonate, reducing the amount of carbonate ions available. This lowers the ocean's ability to support calcification.
These changes are shown in a graph called the Bjerrum plot.
Ocean acidification can also disrupt food chains because many marine animals depend on calcium carbonate-based organisms for food and habitat. This can harm fish populations and affect human communities that rely on fishing.
The saturation state (Ω) of seawater for calcium carbonate measures how likely it is for the mineral to form or dissolve. It is calculated by dividing the product of calcium and carbonate ion concentrations by the solubility product (Ksp) at equilibrium. In seawater, the depth where calcium carbonate begins to dissolve is called the saturation horizon. Above this depth, Ω is greater than 1, and calcium carbonate does not easily dissolve. Most calcifying organisms live in these waters. Below this depth, Ω is less than 1, and calcium carbonate dissolves. The carbonate compensation depth is where the amount of calcium carbonate dissolving equals the amount being supplied to the ocean floor. Ocean acidification lowers pH, reduces carbonate ion levels, and lowers Ω, increasing calcium carbonate dissolution.
Calcium carbonate exists in two main forms: aragonite and calcite. Aragonite dissolves more easily than calcite, so the depth where aragonite dissolves (aragonite saturation horizon) is closer to the surface than the calcite saturation horizon. This means organisms that produce aragonite may be more affected by ocean acidification than those that produce calcite. Ocean acidification lowers Ω for both forms, bringing their saturation horizons closer to the surface and reducing calcification in marine organisms.
In areas like the Pacific continental shelf near North America, from Vancouver to Northern California, water with low aragonite levels is rising to the surface. These shelves are important for marine life because many species live or reproduce there. Similar changes may be happening in other regions.
At ocean depths of thousands of meters, calcium carbonate shells begin to dissolve due to pressure and temperature. This depth is called the carbonate compensation depth. Ocean acidification increases this dissolution and shallows the carbonate compensation depth over decades to centuries. Areas where water sinks to deeper layers are affected first.
In the North Pacific and North Atlantic, the saturation states of calcium carbonate are decreasing, and the depths where calcium carbonate dissolves are becoming shallower. As CO₂ mixes into the open ocean, this causes carbonate compensation depths to move upward, allowing calcium carbonate to dissolve at shallower depths. In the North Pacific, these depths are shallowing by 1–2 meters per year.
Over the next few centuries, ocean acidification is expected to reduce the amount of calcium carbonate sediments buried in the ocean and may even cause existing sediments to dissolve.
Measured and estimated values
Between 1950 and 2020, the average pH level 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 world’s oceans 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, from 1995 to 2010, the acidity in the top 100 meters of the Pacific Ocean between Hawaii and Alaska increased by 6%.
The IPCC Sixth Assessment Report from 2021 stated that current ocean surface pH levels are the highest they have been in at least 26,000 years. The report also found that the pH level in the deeper parts of the ocean has decreased over the past 20 to 30 years everywhere in the global ocean. Additionally, the pH level in open ocean surface water has decreased by about 0.017 to 0.027 units each decade since the late 1980s.
The rate of pH decrease varies by region. This is because different factors, such as ocean currents and human-caused carbon dioxide emissions, influence acidification. For example, in the tropical Pacific, areas with strong upwelling of carbon dioxide-rich water saw a faster pH decrease of about -0.022 to -0.026 units per decade. In contrast, warm areas of the western tropical Pacific saw a slower pH decrease of about -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 carbon dioxide, which could slow the rate of pH change for a given increase in carbon dioxide. Differences in warming between ocean regions are a major reason for varying acidification rates.
Today’s ocean acidification rates are similar to a major climate event 56 million years ago, called the Paleocene–Eocene boundary. During this event, ocean temperatures rose by 5–6°C, and many deep-sea organisms went extinct. Currently, carbon is being added to the atmosphere and ocean about ten times faster than during that event.
Modern systems are being developed to monitor ocean chemistry and acidification in both open ocean and coastal areas.
Ocean acidification has occurred in Earth’s history before. It happened during the Capitanian mass extinction, the end-Permian extinction, the end-Triassic extinction, and the Cretaceous–Paleogene extinction.
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 gas hydrates from the ocean floor. High carbon dioxide levels reduced biodiversity. Lower calcium carbonate saturation, caused by the ocean absorbing carbon dioxide from volcanoes, is thought to have contributed to the extinction of many marine species during the end-Triassic event. This event is the best-known example of ocean acidification causing a marine mass extinction because (a) carbon isotope records show increased volcanic activity that reduced carbonate sedimentation and ocean saturation levels, and (b) the extinction specifically affected organisms with thick aragonitic skeletons, as predicted by experiments. Ocean acidification is also linked to the end-Permian and end-Cretaceous extinctions. Overall, ocean acidification and other climate stressors likely caused these past extinction events.
The most well-known example of ocean acidification is the Paleocene–Eocene Thermal Maximum (PETM), which happened about 56 million years ago. During this event, large amounts of carbon entered the ocean and atmosphere, causing carbonate sediments to dissolve across many ocean basins. Recent studies suggest the ocean’s pH dropped by 0.3 units during the PETM. However, some research suggests the rate of carbon release during the PETM was much slower than today’s human-caused emissions. More precise methods are needed to understand how much this pH change affected marine life.
Predicted future values
Ocean acidification is happening much faster now than it did in the past, according to scientific studies. This rapid change makes it difficult for ocean life to adjust slowly over time and stops natural processes that could help reduce the effects of acidification. Scientists predict that ocean pH levels may drop to the lowest they have been in 300 million years. The speed at which pH levels are changing is also greater than any recorded in the same time period. These changes are considered unique in Earth's history. If pH levels continue to fall, it could harm ocean ecosystems and the services they provide, such as food and clean water, as early as the year 2100.
How much ocean chemistry changes, including pH levels, will depend on how much nations reduce their greenhouse gas emissions. Scientists use models called Shared Socioeconomic Pathways (SSP) to predict future changes based on different global scenarios.
Under a scenario with very high emissions (SSP5-8.5), models suggest that ocean surface pH could drop by up to 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. Such a drop would increase hydrogen ion (H+) concentrations in the ocean by two to four times more than what has already occurred.
Impacts on oceanic calcifying organisms
Ocean acidification can have many effects on marine life. When the ocean becomes more acidic, it becomes harder for some animals to build and maintain their hard shells or skeletons. These animals, called calcifying species, include organisms like corals, oysters, shellfish, and tiny plankton such as coccolithophores and foraminifera. These organisms play important roles in ocean ecosystems, from the bottom of the food chain to the top.
Ocean acidification may cause some animals to use more energy to keep their shells strong, which can reduce their ability to grow or reproduce. For example, oysters like Magallana gigas may use more energy to maintain their shells, which affects their overall health. Under normal conditions, the ocean has enough carbonate ions to help these animals form their shells. However, as ocean pH decreases, the amount of carbonate ions also decreases, making it harder for animals to build and keep their shells.
Some studies show that certain species, like the sea star Pisaster ochraceus, may grow more quickly in more acidic waters. However, other species, such as corals, coccolithophores, and pteropods, may experience weaker shells or even the breakdown of their shells in more acidic conditions. These changes could affect how much carbon is stored in the ocean, which is important for regulating Earth’s climate.
Coccolithophores are tiny, single-celled algae that form hard shells. Changes in their calcification could affect the amount of sunlight reflected back into space, which influences Earth’s temperature. A study from 2008 found that over 224 years, the average size of coccolithophore shells increased by 40%, even though their species composition remained the same.
Warm water corals are declining due to ocean acidification, along with other factors like rising temperatures and pollution. Corals build their skeletons in internal compartments, and if the surrounding water has too little carbonate, they must work harder to maintain the right balance inside. This can slow their growth or stop it entirely. By 2050–2060, about 70% of North Atlantic cold-water corals may live in waters that are corrosive to their shells.
Experiments on the Great Barrier Reef showed that reducing seawater CO₂ levels (raising pH) increased coral calcification by 7%, while increasing CO₂ levels (lowering pH) decreased calcification by 34%. However, some corals may be more resilient than expected because they can regulate their internal environment, making heat stress a bigger threat than acidification.
In some areas, carbon dioxide bubbles up from the seafloor, changing the pH of nearby water. Studies of these areas show that different species respond in various ways. For example, in Papua New Guinea, lower pH near carbon dioxide seeps is linked to fewer coral species, but in Palau, coral diversity remains similar, though their shells erode more quickly.
In the Arctic, pteropods and brittle stars are especially vulnerable to acidification. Pteropods rely on carbonate ions to form their shells, but as acidification increases, these ions become less available, causing their shells to dissolve. Brittle stars also suffer, as their muscles weaken when they regenerate body parts. In experiments, brittle star larvae exposed to lower pH levels had survival rates below 0.1%. Some Arctic waters are already undersaturated with aragonite, making it harder for these animals to survive.
Other impacts on ecosystems
Ocean acidification can cause problems for marine life besides slowing or stopping the hardening of shells. These issues may happen indirectly by harming food sources or directly by affecting reproduction or body functions. For example, high levels of carbon dioxide in the ocean can increase acidity in the body fluids of some animals, a condition called hypercapnia. Scientists have found that increased acidity reduces the energy levels of jumbo squid and weakens the immune systems of blue mussels. Atlantic longfin squid eggs take longer to hatch in acidic water, and the squid’s statolith (a bone-like structure in their head) becomes smaller and misshapen in lower pH environments. However, research on these effects is still ongoing, and scientists do not yet fully understand how acidification impacts marine life or ecosystems.
Another way ocean acidification affects ecosystems is through changes in how sound travels in water. Acidification can make seawater more conductive to sound, allowing it to travel farther and increasing ocean noise. This can disrupt animals that rely on sound for communication or finding food.
Ocean acidification may also lead to more harmful algal blooms, which can produce dangerous toxins like domoic acid, brevetoxin, and saxitoxin. These toxins can build up in small fish and shellfish, increasing the risk of illnesses such as amnesic, neurotoxic, and paralytic shellfish poisoning in humans. While harmful algal blooms are dangerous, some photosynthetic plants, like seagrasses, may benefit from higher carbon dioxide levels. Studies show that as seagrasses grow more actively, nearby calcifying algae may increase their shell formation because the seagrasses absorb carbon dioxide and raise the local pH.
Ocean acidification can also harm marine fish larvae by affecting their sense of smell, which is important for their early development. Orange clownfish larvae live near ocean reefs surrounded by vegetative islands and use their sense of smell to find suitable habitats. They also use their sense of smell to recognize 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, which match predictions for ocean conditions in the year 2100 (pH 7.8 ± 0.05). At this lower pH, clownfish larvae reacted differently to environmental cues than those in normal water. At an even lower pH (7.6 ± 0.05), the larvae 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 very small.
European eel embryos, a species important for farming but critically endangered, are also affected by ocean acidification. Though most of their lives are spent in freshwater, they travel to the Sargasso Sea to reproduce. Here, they are exposed to acidification during a critical life stage. Fish embryos and larvae are more sensitive to pH changes than adults because their bodies are not fully developed to regulate pH. A 2021 study in the Sargasso Sea found that exposure to predicted future ocean conditions may harm the normal development of European eel embryos. Extreme acidification could reduce their survival and growth in hatcheries.
Research shows that ocean acidification combined with rising ocean temperatures has a greater harmful effect on marine life than either stressor alone. Warmer oceans and increased carbon dioxide levels also lead to more phytoplankton growth, which worsens ocean deoxygenation. Deoxygenation makes it harder for marine life to survive by separating ocean layers and reducing nutrients over time. Studies have confirmed that the combined effects of acidification, warming, and deoxygenation severely harm marine ecosystems. Experiments simulating these conditions found that the negative effects of warming outweigh any benefits from increased productivity of plants and animals due to higher carbon dioxide levels.
Impacts on the economy and societies
Ocean acidification slows down how quickly marine animals form their shells or skeletons. This makes coral reefs grow more slowly and become smaller, even though coral reefs support about 25% of all marine life. The effects of acidification are widespread, affecting fisheries, coastal areas, and even the deepest parts of the ocean. Acidification harms not only coral but also the many different types of marine life that depend on coral reefs for survival.
Ocean acidification can reduce the number of fish that people catch for food and income. It may also harm industries that rely on tourism near the ocean. Future acidification could negatively impact the lives of up to 470 to 870 million of the world’s poorest people, depending on how much greenhouse gases are released into the atmosphere.
About 1 billion people depend on fishing, tourism, and coastal management services provided by coral reefs. Continued acidification may harm ocean food chains that are important for future food supplies.
In the Arctic, acidification harms animals that form shells or skeletons, such as pteropods and brittle stars. These animals are the base of Arctic food webs, which are simple because there are few steps between small organisms and larger predators. Pteropods are an important food source for larger plankton, fish, seabirds, and whales. If pteropods and brittle stars disappear, it could harm the entire Arctic ecosystem and threaten fisheries.
The shellfish industry is an important part of the United Kingdom economy. In 2013, shellfish made up 37% of the total value of fish caught. England and Scotland catch the most shellfish, with about 66,000 tons and 61,000 tons caught each year. Wild-caught shellfish are worth about 203 million pounds annually. However, acidification is causing some shellfish to grow more slowly, leading to financial losses.
By 2100, ocean acidification could cause the United Kingdom to lose 14 to 28% of its shellfish production. This would result in losses of about 23 to 88 million pounds each year. The financial impact varies by region because different areas rely on different types of shellfish, which react differently to acidification. Solutions at local, national, or global levels may be needed to protect shellfish and the economy.
In the United States, ocean acidification harms many fish and shellfish that are important for commercial fishing. In 2007, fishing in the U.S. was worth $3.8 billion, and 73% of that value came from animals that form shells or skeletons and their predators. Acidification also harms other marine life, such as American lobsters, ocean quahogs, and scallops, by slowing their growth. This reduces the amount of shellfish available for sale and consumption.
Red king crab fisheries are also at risk because crabs form shells. Baby red king crabs exposed to higher acidification levels died completely after 95 days. In 2006, red king crabs made up 23% of the total amount of crab that could be legally caught. A drop in their population could seriously harm the crab fishing industry.
Possible responses
Reducing carbon dioxide emissions is the main way to stop ocean acidification. Some methods focus on removing CO2 from the air, like direct air capture and bioenergy with carbon capture and storage. These methods can also slow the speed of ocean acidification.
Other methods remove CO2 from the ocean, such as adding nutrients, using artificial water movement, farming seaweed, restoring ecosystems, increasing ocean alkalinity, using weathering, and electrochemical processes. These methods use the ocean to store CO2. They may help reduce CO2, but they can also affect marine life. Research on these methods has grown a lot since 2019.
Ocean-based methods could remove 1–100 gigatons of CO2 each year. Their costs range from $40 to $500 per ton of CO2. For example, enhanced weathering could remove 2–4 gigatons of CO2 yearly, costing between $50 and $200 per ton.
Some methods add alkalinity to the ocean, which helps balance pH changes and may protect nearby marine life. These include ocean alkalinity enhancement and electrochemical methods. Over time, the added alkalinity spreads to distant areas, which is why these are called local ocean acidification solutions. These methods can work on a large scale but are expensive, risky, and not yet fully developed.
Ocean alkalinity enhancement involves adding minerals like limestone or olivine to the ocean. This increases alkalinity, helping the ocean absorb more CO2. The process uses weathering of rocks to create bicarbonate, which can stay in the ocean for over 100 years or form calcium carbonate. If calcium carbonate is buried in the deep ocean, the carbon can be stored permanently.
Enhanced weathering is a type of ocean alkalinity enhancement. It increases alkalinity by spreading finely crushed rocks on land or in the ocean.
Adding alkalinity to the ocean also helps reduce acidification. However, scientists know little about how marine life reacts to added alkalinity, even from natural sources. For example, weathering some rocks might release harmful metals.
Ocean alkalinity enhancement is costly because of mining, crushing, and transporting materials. It costs between $20 and $50 per ton of CO2.
About 30% of CO2 emissions since the Industrial Revolution are stored as bicarbonate in the ocean.
Experiments use materials like limestone, olivine, and alkaline solutions. Another method uses electricity during desalination to capture CO2 from water.
Electrochemical methods, or electrolysis, can remove CO2 directly from seawater. These are also a type of ocean alkalinity enhancement. Some methods remove CO2 as gas or carbonate, while others increase alkalinity by forming metal hydroxides that absorb CO2. Hydrogen produced during this process can be used for energy or other purposes.
However, using electrolysis for carbon capture is expensive and uses a lot of energy. Research is still ongoing to understand its environmental effects. Problems include toxic chemicals in wastewater and lower levels of dissolved inorganic carbon in effluent, which may harm marine life.
Policies and goals
As more people learn about ocean acidification, new policies have been created to improve monitoring of this issue. In 2015, ocean scientist Jean-Pierre Gattuso said, "The ocean has been given little attention in past climate talks. Our study gives strong reasons for major changes at the UN climate conference in Paris."
International efforts, like the Wider Caribbean's Cartagena Convention (which started in 1986), can help regional governments support areas that are very vulnerable to ocean acidification. Many countries, such as those in the Pacific Islands, have developed policies like National Ocean Policies, National Action Plans, and Joint National Action Plans on Climate Change and Disaster Risk Reduction. These plans aim to help achieve Sustainable Development Goal 14 (SDG 14), which focuses on protecting the ocean. Ocean acidification is now being included in these 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. The OARS program works to improve science about ocean acidification, track changes in ocean chemistry, study how it affects marine life, and provide information to help leaders reduce and adapt to ocean acidification.
Ocean acidification is one of seven Global Climate Indicators. These indicators are used to describe changes in the climate without only focusing on rising temperatures. They cover important areas like temperature, the atmosphere, the ocean, 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 United Nations Framework Convention on Climate Change (UNFCCC). The European Commission's Copernicus Climate Change Service (C3S) also uses these indicators in its yearly report on the European climate.
In 2015, the United Nations adopted the 2030 Agenda and 17 Sustainable Development Goals (SDGs), including SDG 14, which focuses on protecting the ocean. SDG 14.3 specifically addresses ocean acidification. The goal is to "minimize and address the impacts of ocean acidification through better scientific cooperation." This goal has one indicator: "Average marine acidity (pH) measured at agreed-upon representative sampling stations."
The Intergovernmental Oceanographic Commission (IOC) of UNESCO is responsible for managing this indicator. IOC-UNESCO is in charge of creating the method to measure this indicator, collecting data each year, and reporting 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 the National Oceanic and Atmospheric Administration's (NOAA) "Ocean Acidification Program." In 2015, the Environmental Protection Agency (EPA) refused a request to regulate carbon dioxide under the Toxic Substances Control Act of 1976 to reduce ocean acidification. The EPA stated that ocean acidification risks are being "more efficiently and effectively addressed" through other actions, such as the Presidential Climate Action Plan, and that efforts are ongoing to reduce emissions, stop deforestation, and promote clean energy and energy efficiency.
History
Research about ocean acidification and efforts to inform people about this issue have continued for many years. Basic research began 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 knowledge was not widely recognized by most scientists. Throughout much of the 20th century, the focus was on the ocean’s ability to absorb carbon dioxide, which helped reduce the effects of climate change. The idea that absorbing too much carbon dioxide could cause problems developed slowly and was influenced by important events. The ocean’s ability to absorb heat and carbon dioxide remains a key way to slow climate change.
In the early 1970s, scientists worldwide began asking questions about the long-term effects of carbon dioxide from fossil fuels building up in the ocean. These questions led to debates about how this buildup might harm marine life. By the mid-1990s, scientists studying coral reefs were concerned about rising carbon dioxide levels and how they might change ocean pH and carbonate ion levels, which are important for coral health.
By the end of the 20th century, scientists better understood the balance between the ocean’s benefits, such as absorbing about 90% of Earth’s heat and 50% of fossil fuel carbon dioxide, and the harm this causes to marine life. In 2003, as plans were made for the "First Symposium on the Ocean in a High-CO₂ World" in Paris in 2004, many new studies about ocean acidification were published.
In 2009, members of the InterAcademy Panel urged world leaders to "Recognize that reducing carbon dioxide in the atmosphere is the only practical way to reduce ocean acidification." They also emphasized the need to "Encourage action to reduce stressors, such as overfishing and pollution, on marine ecosystems to help them better handle ocean acidification."
For example, a 2010 study found that between 1995 and 2010, the acidity in the top 100 meters of the Pacific Ocean from Hawaii to Alaska increased by 6%.
In July 2012, Jane Lubchenco, head of the U.S. National Oceanic and Atmospheric Administration, stated that surface ocean waters are changing faster than early predictions suggested. She said this is another reason to be seriously concerned about the amount of carbon dioxide currently in the atmosphere and the additional carbon dioxide humans continue to release.
A 2013 study found that ocean acidity is increasing 10 times faster than during any of Earth’s major historical changes.
The "Third Symposium on the Ocean in a High-CO₂ World" was held in Monterey, California, in 2012. A summary for decision-makers from the conference noted that "Ocean acidification research is growing rapidly."
In a report published in Science in 2015, 22 leading marine scientists said that carbon dioxide from burning fossil fuels is changing ocean chemistry faster than at any time since the Great Dying, Earth’s most severe known extinction event. They warned that the 2°C maximum temperature increase agreed on by governments is not enough to prevent serious harm to the world’s oceans.
A 2020 study found that ocean acidification not only harms marine life but also affects human health. It can lower food quality, worsen respiratory problems, and harm overall human health.