Ocean acidification is the steady decrease in the pH level of Earth's oceans. From 1950 to 2020, the average pH of ocean surfaces 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 are over 422 parts per million (ppm). CO₂ from the air dissolves into the ocean, where it reacts 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, though seawater remains alkaline (pH above 8). Marine organisms that build shells and skeletons, such as mollusks and corals, are especially affected because they depend 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 ocean. The pH scale is logarithmic, so a one-unit change in pH equals a tenfold change in hydrogen ion concentration. Sea-surface pH and the availability of carbonate (a key component for shell-building) vary based on ocean depth and location. Colder and higher latitude waters absorb more CO₂, which can increase acidity and lower carbonate levels in these areas. Other factors that influence CO₂ exchange between the atmosphere and ocean include ocean currents, upwelling zones, proximity to large rivers, sea ice, and the release of nitrogen and sulfur from fossil fuels and agriculture.
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 disrupt ecosystems that support food and livelihoods for many people. Around one billion people rely on services from coral reefs, such as fishing, tourism, and coastal protection. Continued acidification may threaten ocean-based food chains.
The most effective solution to ocean acidification is reducing CO₂ emissions, a key goal of climate change efforts. Removing CO₂ from the atmosphere could also help reduce ocean acidification. Other methods, such as increasing ocean alkalinity or using enhanced weathering, are being studied but are not yet widely used due to technical challenges and risks.
Ocean acidification has occurred in Earth's history before. Past events led to major changes in ocean ecosystems, which had lasting effects on the global carbon cycle and climate.
Cause
In 2021, the amount of carbon dioxide (CO₂) in Earth's atmosphere was about 415 parts per million (ppm). This is about 50% higher than the levels before the industrial era. According to the National Oceanic and Atmospheric Administration in 2023, CO₂ levels have risen from about 280 ppm before the industrial era to over 410 ppm today. This increase is mainly because of 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. Fossil fuels, such as coal and oil, are burned for energy. When burned, CO₂ is released into the air as a byproduct. This contributes to the rising CO₂ levels in the atmosphere. 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) taken up by the ocean since 1960. Over time, the ocean has absorbed more CO₂ as human-caused emissions have increased. From 1850 to 2022, the ocean absorbed 26% of all human-caused CO₂ emissions. Total human-caused emissions from 1850 to 2021 were 670 ± 65 gigatons of carbon. These emissions were divided among the atmosphere (41%), the ocean (26%), and land (31%).
The carbon cycle describes the movement of carbon dioxide (CO₂) between the oceans, land, rocks, and atmosphere. This cycle includes both organic materials, such as cellulose, and inorganic materials, such as CO₂, carbonate ions, and bicarbonate ions, which are together called dissolved inorganic carbon (DIC). These inorganic materials are especially important in ocean acidification because they include forms of dissolved CO₂ in the ocean.
When CO₂ dissolves in water, it reacts to form a balance of different chemical forms: dissolved carbon dioxide (CO₂(aq)), carbonic acid (H₂CO₃), bicarbonate (HCO₃⁻), and carbonate (CO₃²⁻). The amounts of these forms depend on factors like water temperature, pressure, and salt content, 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 air is measured by the Revelle factor.
Main effects
The ocean's chemical balance 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 by humans. This has caused ocean pH levels, the amount of carbonate ions ([CO₃²⁻]), and the saturation state (Ω) of calcium carbonate minerals to decrease. 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 life.
Ocean acidification is sometimes called the "evil twin" of global warming and "the other CO₂ problem." Along with rising ocean temperatures and oxygen loss, these three factors form the "deadly trio" of challenges for the ocean. These changes will most strongly affect coral reefs, shelled marine organisms, and people who depend on these ecosystems.
When CO₂ dissolves in seawater, it increases the number of hydrogen ions (H⁺), which lowers the ocean's pH. This happens in shallow coastal and shelf areas, where factors like photosynthesis, respiration, and upwelling from deep water influence CO₂ exchange and pH changes. Ecosystem activity in freshwater sources that flow into coastal areas can also cause local pH changes.
Freshwater bodies are also becoming more acidic, though this is harder to notice. The absorption of CO₂ from the atmosphere does not change the ocean's alkalinity, which is the ability of water to resist acidification. Adding more alkalinity to the ocean has been suggested as a way to reduce the effects of acidification.
Changes in ocean chemistry can harm marine life and their habitats. One major effect is on the ability of organisms to produce 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 CaCO₃ structures can dissolve unless the surrounding water has enough carbonate ions (CO₃²⁻).
Most of the extra CO₂ absorbed by the ocean does not stay as dissolved CO₂. Instead, it breaks down into bicarbonate ions and hydrogen ions. The increase in hydrogen ions causes an imbalance, leading to more bicarbonate and fewer carbonate ions. To balance this, some carbonate ions in the ocean combine with hydrogen ions to form more bicarbonate, reducing the overall amount of carbonate ions. This makes it harder for marine organisms to build shells.
These changes are shown in the Bjerrum plot, which displays the levels of dissolved CO₂, bicarbonate, and carbonate ions. Disruption of the food chain can also occur because many marine animals depend on calcium carbonate-based organisms for food and habitat. This could reduce fish populations and harm human communities that rely on fishing.
The saturation state (Ω) of seawater for calcium carbonate measures how likely the mineral is 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 starts to dissolve is called the saturation horizon. Above this depth, Ω is greater than 1, and calcium carbonate remains stable. 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 carbonate ion levels and Ω, increasing calcium carbonate 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. Organisms that produce aragonite may be more affected by ocean acidification than those that produce calcite. As ocean acidification progresses, both saturation horizons move closer to the surface, reducing calcification in marine organisms.
Currently, areas near the Pacific continental shelf from Vancouver to Northern California have water with low aragonite levels. 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 high pressure and low temperatures. This depth is called the carbonate compensation depth. Ocean acidification will increase this dissolution and move the compensation depth upward over decades to centuries. Zones where deep water rises to the surface are affected first.
In the North Pacific and North Atlantic, the saturation state of calcium carbonate is decreasing, and the compensation depth is becoming shallower. As CO₂ mixes into deeper ocean layers, carbonate compensation depths are becoming shallower, causing more calcium carbonate to dissolve below these depths. In the North Pacific, the compensation depth is shallowing by 1–2 meters per year.
In the future, ocean acidification is expected to greatly reduce the burial of calcium 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 concentration 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, from 1995 to 2010, the acidity in the upper 100 meters of the Pacific Ocean, from Hawaii to Alaska, increased by 6%.
The IPCC Sixth Assessment Report (2021) stated that current ocean surface pH levels are the highest not seen in at least 26,000 years. The pH of the ocean’s interior has decreased in all parts of the global ocean over the last 20–30 years. The report also found that ocean surface pH has decreased by about 0.017 to 0.027 units per decade since the late 1980s.
The rate of pH change varies by region. In the tropical Pacific, areas with upwelling (when deep water rises to the surface) showed faster pH declines of –0.022 to –0.026 units per decade. This is likely due to increased upwelling of CO₂-rich deep water and human-caused CO₂ absorption. In contrast, some regions, like warm pools in the western tropical Pacific, experienced slower acidification, with pH declines of –0.010 to –0.013 units per decade.
Ocean acidification rates 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 warming between ocean regions are a major reason for varying acidification rates.
Current ocean acidification rates are similar to the Paleocene–Eocene Thermal Maximum (PETM), about 56 million years ago, when ocean temperatures rose by 5–6°C. During that event, deep-sea organisms faced major extinctions, while surface ecosystems were also affected. Today, the rate of carbon added to the atmosphere and ocean is about ten times faster than during the PETM.
Observational systems are now being developed to monitor seawater CO₂ chemistry and acidification in both open oceans and coastal areas.
Ocean acidification has occurred in Earth’s history, including during the Capitanian mass extinction, end-Permian extinction, end-Triassic extinction, and Cretaceous–Paleogene extinction event. Three of the five major mass extinctions in Earth’s history were linked to rapid increases in atmospheric CO₂, likely from volcanism or gas hydrate breakdown. High CO₂ levels reduced biodiversity, and lower calcium carbonate saturation (due to CO₂ absorption) may have caused extinctions during the end-Triassic event. This event is the best-supported example of ocean acidification causing a marine mass extinction, as evidence shows volcanic activity reduced carbonate sedimentation and marine life declined. Ocean acidification is also linked to the end-Permian and end-Cretaceous extinctions. Multiple climate stressors, including acidification, likely caused these past extinction events.
The PETM is the most well-known example of ocean acidification. During this event, large amounts of carbon entered the ocean and atmosphere, causing widespread dissolution of carbonate sediments. Studies suggest 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 studies are needed to fully understand how pH changes affected marine life during this event.
Predicted future values
Ocean acidification is happening much faster today than it did in the past. This rapid change makes it difficult for ocean life to adjust slowly over time, and it stops natural processes that usually help reduce acidification. Ocean pH levels are now expected to drop to their lowest point in the last 300 million years. The speed at which pH levels are changing is also considered the fastest ever recorded during that time. These changes are not seen in the geological history of Earth. Combined with other changes in ocean chemistry, this drop in pH could harm marine ecosystems and affect the benefits humans receive from the ocean, such as food and clean water, as early as the year 2100.
How much ocean chemistry, including pH, will change depends on how well nations work to reduce emissions. Scientists use Shared Socioeconomic Pathways (SSP) scenarios to predict future changes based on different global situations.
Under a scenario with very high emissions (SSP5-8.5), models predict 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, which means hydrogen ion (H+) levels would increase two to four times more than they have already.
Impacts on oceanic calcifying organisms
Ocean acidification can harm many sea creatures that build hard shells or skeletons. These organisms, such as corals, oysters, and sea stars, need carbonate ions to create their protective coverings. As ocean acidification increases, the availability of these ions decreases, making it harder for these creatures to form and maintain their shells. This can affect their survival and the health of ocean ecosystems.
Ocean acidification may cause some organisms to use more energy for shell-building, reducing resources for other important activities. For example, the oyster Magallana gigas has been shown to experience changes in metabolism and slower shell growth when ocean pH decreases.
Under normal conditions, the minerals calcite and aragonite are stable in ocean water because carbonate ions are more plentiful than needed. However, as ocean pH drops, carbonate ion levels fall, making it harder for organisms to form calcium carbonate structures. This can lead to weaker shells or even the breakdown of existing ones. Studies show that corals, sea snails, and certain plankton species experience reduced shell growth or increased breakdown when exposed to higher carbon dioxide levels. Even with conservation efforts, some shellfish populations may not recover.
Some organisms respond differently to acidification. For example, the coccolithophore, a type of plankton, may increase both shell-building and photosynthesis under higher carbon dioxide levels. However, other species show reduced growth or changes in how they use energy. The sea star Pisaster ochraceus has been observed to grow faster in more acidic waters.
Reduced shell-building due to acidification can weaken the ocean's ability to store carbon from the atmosphere, which is important for regulating Earth's climate. Acidification may also shrink phytoplankton in the Antarctic, reducing their ability to store carbon. Scientists are studying these effects using frameworks like the Adverse Outcome Pathway (AOP) to better understand the impacts.
Coccolithophores are single-celled algae that play a key role in ocean ecosystems. Changes in their shell-building could affect Earth's climate by altering cloud cover, which influences 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% during that time.
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 50%. Corals build their skeletons in internal compartments, and the balance of minerals in surrounding water affects this process. If the water has too little aragonite, corals must work harder to maintain their internal environment, slowing growth. By 2050–2060, about 70% of cold-water corals in the North Atlantic may live in water that is corrosive to their skeletons.
Ocean acidification primarily weakens the density of coral skeletons rather than their size. Some coral species could lose up to 20% of their skeleton density by the end of this century. An experiment on the Great Barrier Reef showed that reducing seawater carbon dioxide levels (raising pH) increased shell-building by 7%, while increasing carbon dioxide levels (lowering pH) reduced it by 34%.
However, some corals are more resilient than expected. A study in Queensland and Western Australia found that corals can regulate their internal chemistry to cope with pH changes, making heat-related stress a bigger threat than acidification.
In some areas, carbon dioxide bubbles from the ocean floor change local water chemistry. Studies near these "carbon dioxide seeps" show varied responses. In Papua New Guinea, lower pH from seeps has reduced coral diversity, but in Palau, coral diversity remains stable, though erosion of coral skeletons increases.
In the Arctic, pteropods (tiny sea snails) and brittle stars are critical to food webs but are harmed by acidification. Pteropods lose their shells as carbonate ions decrease, and brittle stars struggle to regrow body parts. Arctic waters are already undersaturated with aragonite, making these organisms vulnerable. Experiments show that brittle star larvae exposed to lower pH levels have very low survival rates.
Other impacts on ecosystems
Ocean acidification can cause problems for marine life beyond slowing or stopping the formation of hard structures like 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 lead to acidification of body fluids in some animals, a condition called hypercapnia. Studies show that increased acidity can lower the metabolic rates of jumbo squid and weaken the immune systems of blue mussels. Atlantic longfin squid eggs hatch more slowly in acidified water, and their statoliths (a part of the inner ear used for balance) are smaller and misshapen in lower pH conditions. However, research on these effects is still ongoing, and scientists have not yet fully understood how acidification impacts marine life or ecosystems.
Another way ocean acidification may 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 affects animals that rely on sound for communication or navigation, such as those that use echolocation.
Ocean acidification may also increase the frequency of harmful algal blooms. These blooms can produce toxins like domoic acid, brevetoxin, and saxitoxin, which can accumulate in small fish and shellfish. This may lead to more cases of amnesic, neurotoxic, and paralytic shellfish poisoning in humans. While harmful algal blooms can be dangerous, some beneficial photosynthetic organisms, such as seagrasses, may benefit from higher carbon dioxide levels. Research suggests that as seagrasses increase their photosynthesis, calcifying algae may also increase their calcification rates. This likely happens because the photosynthesis process reduces carbon dioxide and raises local water pH.
Ocean acidification can also affect marine fish larvae. It can harm their olfactory systems, which are important for early development. Orange clownfish larvae live on coral reefs surrounded by vegetative islands. They use their sense of smell to distinguish between reefs with and without these islands to 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 of 8.15 ± 0.07, similar to today’s ocean pH. Scientists tested the effects of lower pH levels, which match predictions for future carbon dioxide levels by 2100 (1,000 ppm, corresponding to a pH of 7.8 ± 0.05). The study found that larvae exposed to pH 7.8 ± 0.05 reacted differently to environmental cues compared to those in current pH levels. At pH 7.6 ± 0.05, larvae showed no reaction to cues. However, a 2022 review found that the effects of ocean acidification on fish behavior have decreased significantly over the past decade and are now minimal.
European eel embryos, a critically endangered species important to aquaculture, are also affected by ocean acidification. Although they spend most of their lives in freshwater, they travel to the Sargasso Sea to spawn and die. Here, they are exposed to acidification during a key life stage. Fish embryos and larvae are more sensitive to pH changes than adults because their pH-regulating organs are not fully developed. A 2021 study found that exposure to predicted end-of-century ocean conditions could harm the normal development of European eel embryos. Extreme acidification might also reduce their survival and development in hatcheries.
Research shows that the combined effects of ocean acidification and rising ocean temperatures are more harmful to marine life than either factor alone. Additionally, warmer ocean temperatures and increased phytoplankton productivity from higher carbon dioxide levels can worsen ocean deoxygenation. Deoxygenation increases ocean stratification, limits nutrients over time, and reduces biological gradients.
Studies have shown that the harmful effects of ocean acidification, warming, and deoxygenation together are greater than the effects of each individually. Experiments using mesocosms (controlled environments) that simulate these combined stressors found severe impacts on marine food webs. Thermal stress cancels out any increases in productivity from elevated carbon dioxide levels between primary producers and herbivores.
Impacts on the economy and societies
Ocean acidification slows down the process of calcification 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 harms coral reefs and the many different marine species that depend on them.
Ocean acidification can reduce commercial fisheries and the tourism industry that relies on coastal areas. Future acidification may harm ocean-related goods and services, possibly affecting the livelihoods of 470 to 870 million of the world’s poorest people, depending on future greenhouse gas emissions.
About 1 billion people rely completely or partially on fishing, tourism, and coastal management services provided by coral reefs. Continued ocean acidification may threaten ocean-based food chains.
In the Arctic, acidification harms calcifying organisms like pteropods and brittle stars, which form the base of Arctic food webs. These organisms are essential for many predators, such as fish, seabirds, and whales. If these organisms disappear, the Arctic food web could be seriously damaged, which might harm fisheries.
The shellfish industry is an important part of the United Kingdom economy. In 2013, shellfish made up 37% of the total value of landings. England and Scotland are the largest shellfish producers in the UK. Fishers in these regions catch about 66,000 and 61,000 tons of shellfish each year, worth 203 million pounds annually. However, ocean acidification is slowing the growth of many shellfish species, causing economic losses.
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 fishery output, totaling about 23 to 88 million pounds. Losses vary by region due to differences in shellfish species and their sensitivity to acidification. Solutions at the regional, national, or international level may be needed to protect shellfish resources and the economy.
In 2007, the value of fish caught in US commercial fisheries was $3.8 billion, with 73% of that value coming from calcifying species and their direct predators. Acidification harms other organisms as well. For example, slower growth in marine calcifiers like American lobsters, ocean quahogs, and scallops reduces the amount of shellfish meat available for sale and consumption. Red king crab fisheries are also at risk because crabs are calcifiers. Baby red king crabs exposed to higher acidification levels experienced 100% mortality after 95 days. In 2006, red king crabs made up 23% of the total guideline harvest levels. A decline in red crab populations could seriously harm the crab harvesting industry.
Possible responses
Reducing carbon dioxide emissions (climate change solutions) is the main way to fix the cause of ocean acidification. Some solutions focus on removing CO2 from the air, such as direct air capture (DAC) and bioenergy with carbon capture and storage (BECCS). These methods can also slow ocean acidification.
Other methods remove CO2 from the ocean, like adding nutrients, moving water up and down, growing seaweed, restoring ecosystems, increasing ocean alkalinity, speeding up rock weathering, and using electricity. These methods store CO2 in the ocean. They could help reduce CO2 but may harm marine life. Research on these methods has increased since 2019.
In total, 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 $50–$200 per ton.
Some methods add alkalinity to the ocean, which helps balance pH changes and may help marine life near the area where alkalinity is added. These methods include ocean alkalinity enhancement and electrochemical processes. Over time, the added alkalinity spreads to distant waters, which is why they are called "local ocean acidification mitigation." These methods can work on a large scale but are expensive, risky, and not yet widely used.
Ocean alkalinity enhancement (OAE) is a method that adds alkaline minerals to the ocean’s surface. This increases the ocean’s ability to absorb CO2. The process uses rocks like silicate, limestone, or quicklime to create bicarbonate (HCO3-), which can stay in the ocean for over 100 years or form calcium carbonate (CaCO3). When calcium carbonate is buried in the deep ocean, it holds carbon for a long time.
Enhanced weathering is a type of OAE. It increases alkalinity by spreading finely crushed rock particles, which can happen on land or in the ocean.
Adding alkalinity also helps reduce ocean acidification. However, little is known about how marine life reacts to added alkalinity, even from natural sources. For example, weathering some silicate rocks might release trace metals that could harm the environment.
Ocean alkalinity enhancement is costly and energy-intensive because it requires mining, crushing, and transporting materials. The cost is estimated at $20–$50 per ton of CO2 for adding alkaline minerals directly to the ocean.
About 30% of carbon emissions since the Industrial Revolution are stored as bicarbonate in the ocean.
Experiments use materials like limestone, brucite, olivine, and alkaline solutions. Another method uses electricity during desalination to capture CO2 from seawater.
Electrochemical methods, or electrolysis, can remove CO2 directly from seawater. These are also types of OAE. Some methods remove CO2 as gas or carbonate, while others increase seawater alkalinity by creating metal hydroxide residues that absorb CO2. Hydrogen produced during this process can be used for energy or other purposes.
However, using electrolysis for CO2 removal is expensive and uses a lot of energy. Research is ongoing to understand its environmental effects. Problems include toxic chemicals in wastewater and lower levels of dissolved inorganic carbon in treated water, which may 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 been overlooked in past climate discussions. His research provided strong reasons for changing how the United Nations handles ocean acidification during the Paris climate conference.
International efforts, such as the Wider Caribbean's Cartagena Convention (which started in 1986), may help regional governments support areas most affected by ocean acidification. Countries in the Pacific Islands and Territories have developed policies like National Ocean Policies, National Action Plans, and Joint National Action Plans on Climate Change and Disaster Risk Reduction to support Sustainable Development Goal 14. 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 and has been officially approved as part of the UN Decade of Ocean Science for Sustainable Development. OARS builds on GOA-ON's work and has these goals: to improve ocean acidification science, to increase observations of ocean chemistry changes, to study the effects on marine ecosystems locally and globally, and to provide information to help leaders reduce and adapt to ocean acidification.
Ocean acidification is one of seven Global Climate Indicators. These indicators are measurements that describe climate changes without focusing only on rising temperatures. They cover important areas like temperature, atmospheric composition, oceans, water, and the cryosphere (ice-covered regions). Scientists and communication experts, working with the Global Climate Observing System (GCOS), selected these indicators. They were approved by the World Meteorological Organization (WMO) and are used in the WMO's annual report on the global climate, which is sent to the United Nations Framework Convention on Climate Change (UNFCCC). The European Commission's Copernicus Climate Change Service (C3S) also uses these indicators in its "European State of the Climate" report.
In 2015, the United Nations adopted the 2030 Agenda and 17 Sustainable Development Goals (SDGs), including SDG 14, which focuses on the ocean. SDG 14 calls for conserving and using oceans and marine resources sustainably. Ocean acidification is directly addressed in Target 14.3, which aims to reduce its effects through better scientific cooperation. Target 14.3 has one indicator: "Average marine acidity (pH) measured at agreed-upon sampling stations."
The Intergovernmental Oceanographic Commission (IOC) of UNESCO is responsible for managing the SDG 14.3.1 indicator. This includes creating the method for measuring the 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 NOAA's "Ocean Acidification Program." In 2015, the Environmental Protection Agency (EPA) rejected 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 were being handled more effectively through domestic actions, such as the Presidential Climate Action Plan, and through international efforts to reduce emissions, deforestation, and promote clean energy.
History
Research on ocean acidification and efforts to raise awareness about this issue have continued for many years. The basic scientific work began with the development of the pH scale by Danish chemist Søren Peder Lauritz Sørensen in 1909. By the 1950s, scientists knew that the ocean plays a major role in absorbing carbon dioxide from fossil fuels, but this knowledge was not widely recognized by the broader scientific community. For much of the 20th century, the focus was on the ocean’s ability to take in carbon dioxide, which has helped reduce the effects of climate change. The idea that absorbing too much carbon dioxide could cause harm developed later, after key events. The ocean’s ability to absorb heat and carbon dioxide remains vital in slowing climate change.
In the early 1970s, scientists around the world began discussing the long-term effects of increasing carbon dioxide levels in the ocean, leading to debates. Researchers noted the buildup of carbon dioxide in both the atmosphere and the ocean and warned about possible effects on marine life. By the mid-1990s, scientists studying coral reefs were concerned about the rising levels of carbon dioxide and the changes in ocean pH and carbonate ions.
By the end of the 20th century, the balance between the ocean’s benefits—such as absorbing about 90% of the heat produced and about 50% of the carbon dioxide from fossil fuels—and the harm to marine life became clearer. In 2003, as plans were made for the "First Symposium on the Ocean in a High-CO₂ World" to be held in Paris in 2004, many new studies on 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 like overfishing and pollution on marine ecosystems to improve their ability to withstand ocean acidification."
For example, a 2010 study showed 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 ocean surface waters are changing faster than early predictions suggested. She said this is another reason to be seriously concerned about the amount of carbon dioxide in the atmosphere and the additional emissions we continue to produce.
A 2013 study found that ocean acidity is increasing at a rate 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 for policymakers from the conference noted that research on ocean acidification is growing quickly.
In a 2015 report published in Science, 22 leading marine scientists stated 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. The report highlighted that the 2°C maximum temperature increase agreed upon by governments is not enough to prevent serious harm to the world’s oceans.
A 2020 study argued that ocean acidification is not only harming marine life but also affecting human health. It can lower food quality, worsen respiratory problems, and negatively impact overall human health.