What Is Ocean Acidification?

Ocean acidification means the ongoing drop in the pH level of the Earth’s oceans, making them more acidic with time. This big environmental problem happens mostly because the ocean is soaking up extra carbon dioxide (CO2) from the air. Since the Industrial Revolution started over 200 years ago, human activity has raised atmospheric CO2 levels a lot, changing how the ocean’s chemistry works. Ocean acidification is more than just a small shift; it is a major change that affects sea life, marine ecosystems, and the people who rely on them.

What is ocean acidification?

In simple terms, ocean acidification is when the ocean’s pH value goes down, showing there’s a rise in acidity. Even though the word “acidification” might make you think of really strong acids, the ocean still stays on the basic (alkaline) side – it’s just less alkaline than before. Even a small change in pH can have large effects on the ocean’s chemistry and everything that lives there.

How does ocean acidity change?

Acidity in the ocean increases when CO2 from the air dissolves into seawater and reacts in a few steps. The ocean absorbs about 30% of human-made CO2 each year. After CO2 dissolves in the ocean, it forms carbonic acid. This weak acid breaks apart, creating hydrogen ions (H+) and bicarbonate ions. More hydrogen ions means a lower pH, making the water more acidic.

This also decreases how many carbonate ions (CO3^2-) are in the water. Many sea creatures, especially those with shells or skeletons made from calcium carbonate, depend on carbonate ions. With fewer carbonate ions available, it becomes much harder for them to form and keep their shells, risking their survival.

What does the pH scale show about ocean changes?

The pH scale runs from 0 (most acidic) to 14 (most basic); 7 is neutral. Each unit change on the scale is a tenfold change in acidity. For example, a pH of 6 is ten times more acidic than a pH of 7.

The ocean usually sits at about pH 8.1, a little on the basic side. Since the Industrial Revolution, though, this has dropped by about 0.1 pH units. That might seem small, but because of how the scale works, it actually means ocean water is around 30% more acidic than before. This change is happening much faster than anything seen in millions of years, and many scientists predict surface ocean pH could fall to around 7.8 by 2100. The last time the ocean’s pH was this low was the middle Miocene (14-17 million years ago), which was a time of high temperatures and extinctions.

What causes ocean acidification?

The main reason for ocean acidification is the rising amount of carbon dioxide in the atmosphere, mostly from human actions. After CO2 enters the sea, it triggers chemical reactions that change ocean water’s makeup.

How does carbon dioxide interact with seawater?

CO2 from the air doesn’t just sit in the water – it mixes and reacts. First, it joins with water to make carbonic acid. This acid quickly breaks down into hydrogen ions and bicarbonate ions. The growing number of hydrogen ions makes the water more acidic.

Extra hydrogen ions also bond with carbonate ions to form more bicarbonate. This means fewer carbonate ions are left for animals that need them to build shells. As a result, species that rely on these ions face big challenges to survive.

What role does burning fossil fuels play?

Most extra CO2 in the air, and much of the acidification problem, comes from burning fossil fuels like coal, oil, and gas. Since the Industrial Revolution, human energy needs have meant huge CO2 emissions. Cutting down forests also adds to the problem, since trees soak up CO2 and losing them puts more carbon in the air.

Scientists have clearly shown that more fossil fuel emissions mean more atmospheric CO2, which then leads to lower ocean pH. The ocean has taken in about one-third of all fossil fuel CO2 since industrial times, helping buffer climate change, but at the cost of stressing sea life and changing ocean chemistry.

How is ocean acidification measured?

Scientists use a range of tools and methods to keep track of changes in ocean acidity and understand its impacts. They measure pH with instruments, take samples, and use indirect methods to look at the past.

Which indicators measure acidification?

• pH: Shows how acidic or basic the water is.
• Dissolved inorganic carbon: Total CO2 in the water.
• Total alkalinity: Ability of water to neutralize acid.
• Calcium carbonate saturation: Indicates if it’s easy or hard for sea creatures to form shells.

Of these, the amount of carbonate ions is very important for shell-building organisms. If aragonite (a form of calcium carbonate) is undersaturated, shells can actually start to dissolve.

What tools and methods are used to track pH changes?

• Research cruises: Scientists collect water samples across oceans for lab analysis.
• Moorings and buoys: Long-term, on-site monitoring stations gather continuous data.
• Proxies: Chemical clues from ancient coral, ice cores, and seabed sediments tell us about pH levels in the past.

By studying these sources, researchers get a picture of both current and past acidification trends.

How has ocean pH changed over time?

Looking at both direct data and proxy records, before industrial times, surface seawater pH stayed between about 8.2 and 8.3 for a million years. Since then, pH has dropped to roughly 8.1, a 26% increase in acidity. For example, at a station near Hawaii, pH fell from 8.11 in 1985 to below 8.05 in 2021-a 15% jump in acidity for that period and roughly 40% higher acidity than before the industrial age.

The speed of acidification now is about 100 times faster than in the past tens of millions of years. Models predict a drop of 0.15 to 0.5 pH units by 2100, possibly resulting in 150% more acidity than pre-industrial times. This fast change gives ocean life little time to adjust.

What are the effects of ocean acidification on marine ecosystems?

When the ocean grows more acidic, it impacts all sea life, from tiny plankton to big fish and coral reefs.

How are shell-forming organisms affected?

The creatures most at risk are those that build shells, such as oysters, clams, mussels, sea urchins, corals, and some plankton. They need carbonate ions to form calcium carbonate shells. As carbonate ions become scarcer, they struggle to create and keep their shells, and this often means slower growth, weaker shells, or even shell dissolution.

For example, pteropods (“sea butterflies”) have shells that start to dissolve within 45 days in seawater that matches pH conditions expected for 2100. Problems like this are already seen in places like the Southern Ocean, threatening these species and the food webs they support.

What happens to coral reefs?

Coral reefs are also in danger. When ocean waters turn more acidic, corals have trouble building their skeletons. Existing reef structures can weaken and even break down. Australia’s Great Barrier Reef, for instance, saw a 14% drop in coral calcification since 1990.

This is especially troubling since coral reefs support about a quarter of all marine species and provide natural protection for coastlines.

How do fish and seaweeds react?

Other creatures, like fish, are affected too. For example, clownfish in acidic waters may not be able to sense predators as well or find safe habitats when young, making them more likely to die.

On the other hand, some algae and seaweeds could grow better with more CO2, using it for photosynthesis like plants on land. Researchers are exploring if growing seaweed could help, by soaking up CO2 in local areas and protecting nearby shellfish farms.

Are plankton and other small species in danger?

Yes. Many plankton build calcium carbonate shells and have problems in acidified waters, which may cause them to die in larger numbers. If plankton populations drop, it could cause a chain reaction throughout the ocean’s food web, since so many animals-right up to whales-depend on them for food.

How does ocean acidification affect people and communities?

Ocean acidification affects more than nature – it affects people, especially those who depend on the ocean for food, jobs, or culture.

Which areas are most at risk?

Cooler waters dissolve CO2 faster, so places like the Arctic, Antarctic, and U.S. Pacific Northwest are seeing impacts sooner. Many of these areas also have industries, like fishing, that rely on vulnerable shellfish.

How does acidification affect fisheries and economies?

Billions of people rely on seafood for protein, and many coastal jobs depend on healthy fisheries. The U.S. shellfish industry, for example, supports thousands of jobs and brings in millions every year. However, it’s estimated that ocean acidification could cost this industry over $400 million annually by 2100 if things don’t change.

• Reduced survival of oysters, clams, crabs, and others can lead to lower harvests.
• Less product means less income for fishers and higher prices for consumers.
• A study showed young Dungeness crabs in the Pacific Northwest already have damaged shells and sensory organs due to acidification.

What cultural effects are seen?

Indigenous and coastal communities often have a deep connection to the ocean. Sea animals play big roles in food traditions, ceremonies, and stories. If certain species decline, it can threaten these traditions, break ties between generations, and impact cultural identity.

Current research and monitoring efforts

To deal with ocean acidification, scientists do research in labs, collect data in the field, and monitor changes around the globe. The aim is to learn how acidification works, predict future effects, and find good ways to respond.

How do lab studies help?

In the lab, scientists can control CO2 and other conditions to see how different marine species respond to future ocean scenarios. For example, at Woods Hole Oceanographic Institution (WHOI), they grow shell-building species in tanks with current or higher CO2, to watch for signs of weaker shells or survival problems.

What about field experiments and natural variations?

Outside the lab, scientists use sensors in the ocean and set up monitoring stations, like Hawaii’s Aloha station, to see real-time changes. Some locations, like volcanic vents that leak natural CO2, show what high acidity does to ecosystems over time. These studies confirm lab results and help see how acidification interacts with other stressors like warmer water or low oxygen.

Which groups monitor ocean acidification?

• NOAA: Runs the Ocean Acidification Program and supports research on fisheries and reefs.
• WHOI: Conducts in-depth studies and shares data.
• Copernicus Marine Environment Monitoring Service (CMEMS): Offers global surface pH data.
• Other: Many universities and global organizations work together to share findings and push for action.

What are possible solutions to ocean acidification?

While there’s no quick fix, a mix of large and small actions can help slow or soften ocean acidification’s effects.

How can lowering CO2 emissions help?

• Switching to cleaner energy like wind and solar power
• Setting tougher emissions rules for factories and cars
• Protecting and replanting forests, since they absorb CO2
• Setting aside more land and sea areas (like the 30×30 pledge) for nature to heal itself

Each ton of CO2 not put in the air helps slow down ocean acidification and gives sea life more time to adapt.

Are there other ways to adapt or engineer solutions?

• Geoengineering: Ideas like capturing CO2 from the air or fertilizing the ocean are being studied, but could have big risks.
• Adaptation: Some hatcheries monitor local pH and close water intakes at bad times; researchers are breeding shellfish that can stand up better to acidity; growing seaweed near farms may help remove CO2 locally.

What can individuals and communities do?

• Cutting energy use and supporting green energy options
• Choosing sustainably caught seafood
• Joining or supporting ocean conservation groups
• Helping to educate others and push for strong local or national environmental policies
• Joining beach clean-ups and other community actions

The health of the oceans matters to everyone, and everyone has a part to play in protecting it.

What does the future look like for ocean acidification?

The future of ocean acidification depends on how quickly humanity cuts carbon emissions. Without big changes, major impacts are expected for marine life, food, and jobs.

What if emissions keep going up?

If emissions stay high, scientists predict ocean pH near the surface could fall to about 7.8 by 2100-making the ocean 150% more acidic than before factories and cars powered the modern world. Such a pH hasn’t been seen for 14-17 million years, and would be bad news for many sea creatures.

• Cold regions like the Arctic and Antarctic will see big effects quickly.
• Places where aragonite (important for many shell-makers) is no longer available will spread, making shell growth close to impossible for some species.
• Because it takes a long time for ocean CO2 to mix deeply, acidification will continue for generations, even if we take action soon.

How might sea life cope?

Some marine species might adjust over time, but most will struggle to keep up with such fast changes. When similar big changes happened in the past, it took millions of years for new species to fill the gaps.

• Shell-makers will spend much more energy just to form shells.
• Less energy is left for growing or reproducing, weakening their populations.
• Some algae or seaweeds could thrive, but many animals could decline or disappear if they can’t adapt.

Frequently asked questions about ocean acidification

Can ocean acidification be undone?

Technically, yes, but it would take thousands to millions of years for natural Earth processes to undo today’s acidification levels. Even if we stopped all CO2 emissions right now, the ocean would keep feeling the impact for centuries or more, as CO2 slowly cycles out. This is why prevention and cutting emissions now are so important.

Is ocean acidification linked to climate change?

Yes. Both come from burning fossil fuels and putting more CO2 in the air. Climate change is mostly about warmer global temperatures, while acidification deals with chemical changes in the ocean. Both problems share the same cause and fixing one helps the other.

How long will it take oceans to return to normal?

It will take thousands to tens of thousands of years for the ocean to balance out again. Past events show that Earth’s systems need a very long time to recover from CO2 spikes, and the present rate is much faster than anything before. For these reasons, acting now is the best option to minimize future damage.