There is a scale scientists use to measure liquids to determine how acidic or basic they are. The pH (the potential, or power, of hydrogen) scale runs from 0-14 with 7 being neutral, higher than 7 being alkaline and lower than 7 is acidic. Acidic and basic solutions occur in nature or can be manmade. For example, orange juice and vinegar are acidic, soaps, bleach, and toothpaste are basic. Distilled water is neutral with a pH of 7. In general, the more hydrogen ions in a liquid, the higher the acidity. As a basis of comparison, battery acid has a pH of 0 and liquid drain cleaner has a pH of 14. Traditionally, sea water has a pH of approximately 8.2 (slightly basic).

The ocean has always absorbed carbon dioxide from the atmosphere. Since the start of the industrial revolution, the burning of fossil fuels has released much greater quantities of CO2 and the ocean has absorbed at least 25% of it. Due to this extra carbon absorption, the ocean is 30% more acidic than it was just 200 years ago (about a 0.1pH drop in the last 200 years). And this change is happening faster than at any recorded moment in human history (10x faster than any other point in the last 300 million years). By 2100, the pH of the surface ocean could drop to under 7.8 (more than 150 percent compared to today).

Ocean systems are struggling to adapt to these rapid changes in pH. Small changes in pH can have big effects. For example, human blood has a pH between 7.35 and 7.45; a change of just .2 in pH can cause seizures, a coma, or death! It’s the same for creatures living in the ocean, small changes in pH can have big effects.

Ocean acidification, like climate change, is caused by excess CO2 in the Earth’s atmosphere. However, since its effects happen underwater, it is not nearly as obvious or as discussed.

Increased ocean acidity most directly affects animals with shells or skeletons made of calcium carbonate. Excess carbon causes the amount of carbonate ions in the water to decrease which means fewer are available to marine animals for shell or reef building.

Not only is the rate at which animals can build their shells slowing, but existing shells and skeletons are also weakened by the higher acidity – similar to the way acid rain falling on statues or limestone buildings causes corrosion. With a lower pH in ocean water, animals can struggle to create their shells and these same shells and skeletons can dissolve from the more acidic seawater. In more acidic waters, shells have been seen to have small holes or pits as they weaken from a lack of calcium carbonate. These animals must use more energy to constantly repair damage which also makes them more vulnerable to predators. In the end, this lessens how big and how strong these animals can grow.

A wide range of marine animals rely on calcium carbonate: hard corals, crustaceans (crabs, lobster, and shrimp), molluscs (clams, oysters, and mussels), sea urchins and sand dollars, sea snails, and even many small phytoplankton and zooplankton species. And it’s not just these animals that feel the effects, but all animals that eat these animals are also affected.

Problems and changes have already been seen:

  • Crustaceans are dying before they can reproduce and dungeness crabs have sensory organ damage due to their dissolving shells.
  • By the end of the century, mussels are expected to reduce shell size by 25% and oysters by 10%
  • The hard structure of Coral reefs is composed of calcium carbonate. With less carbonate ions available reefs become more brittle (making them weaker) and have difficulty reproducing. This not only affects the coral but makes it less effective as coastal protection from waves and storms.
  • Pteropods, about the size of a small pea, are tiny swimming sea snails and are a huge part of the marine food web (for example, they are a major food source of salmon and krill (which is a major food source of whales), etc.). Since they are snails, they have shells, and those shells are corroding with the increase in ocean acidification.
  • Fish are lucky to not need calcium carbonate, but they are affected by increased levels of acid – they have been shown to lose their sense of smell. And removing the excess acid from their bodies (through their gills, kidneys, and intestines) uses energy otherwise used for growth. This, coupled with the possibility of reduced food resources, could result in a 14-24% reduction in body size.
  • Oyster larvae need to rapidly build their shells in the first 48 hours but are struggling to do so. Oyster die offs of 70-80% have already been seen in the northwest US.

Watch this video for more information on ocean acidification.

Ocean acidification is a direct consequence of carbon dioxide released into the Earth’s atmosphere by humans. Since the start of the industrial revolution, humans have released 400 billion tons of carbon (in 1950 5 billion tons were generated, in 2017 it was 35 billion). CO2 levels are currently over 400ppm compared to 280ppm before the industrial revolution. The ocean absorbs more than 25% of all CO2 emissions, but this extra carbon takes a toll. As CO2 dissolves in seawater it forms carbonic acid and decreases the pH level of the ocean.

This acidification of the ocean paired with related marine stresses like temperature increase and deoxygenation (ocean dead zones) has a combined effect. With the number of stressors we are putting on our ocean it is not surprising that the ocean is suffering. Each stress causes its own problems and reduces the ocean’s ability to adapt. Cumulatively, the effects become more and more severe.

While ocean acidification is caused globally, local stresses can compound the problem. Runoff of excess fertilizer or waste water from land sources adds to the acidification problem in some regions.

It is nearly impossible to stop ocean acidification; but we can slow it down. Hopefully this will give our ocean, and its inhabitants, the chance to adapt to increased levels of acidity.


  • Spread Awareness: One of the most important things you can do is to tell your friends and family about ocean acidification. The size of this problem has only recently been discussed and addressed; many people are still unaware. Continue to educate yourself and talk about it with others!
  • Make Life Changes: Try to lower your carbon dioxide usage every day. Turn off lights, walk or ride a bike, use public transportation, check your tire pressure, slow down, reduce unnecessary trips, turn off the air conditioner, waste less, consume less! On a bigger scale, switch to clean energy sources (solar, wind, geothermal).
  • Be a Responsible Consumer: Demand that the businesses and organizations you patronize also lower their carbon footprint, reduce waste, and use clean energy sources. Consumers have a voice and should use it!
  • Show Your Support: Support conservation efforts that are strategically addressing ocean acidification. Support local, regional, and national initiatives and legislation that reduce carbon emissions and those that increase or protect sources of natural carbon capture (plants!).

Conservation Efforts

  • Seagrass Ecosystems: A recent study found that seagrass ecosystems can reduce local ocean acidity by up to 30% in the short term. Protecting these ecosystems, and restoring them in places where they have been destroyed can mitigate the negative effects of ocean acidification (as well as global warming and protecting biodiversity!).
  • Strategic Marine Protected Areas: Using ocean acidification research, marine protected areas can work together to select coral reefs with various ocean chemistry for protection. This increases the chance for corals to adapt to varying pH conditions in different geographical areas and potentially combat the effects of ocean acidification. Similarly, since seagrass ecosystems have been shown to reduce local acidity, strategically protecting areas with seagrass adjacent to coral reefs can provide a benefit to reefs.


  • Implementing national or global policies to stop or drastically reduce global carbon emissions is the most critical step towards reducing the effects of ocean acidification.
  • Local sources of carbon must be reduced (nutrient pollution), this will help with ocean acidification and improve coastal water quality!
  • Create carbon sinks, such as regrowing mangrove and seagrass ecosystems, as well as trees on land.
  • And protect existing sources of carbon capture (terrestrial and aquatic plant life).

Nearly every conservation organization is working to spread the word and encourage personal, community, national and global change to address the climate change crisis. We are ALL responsible for our contribution and for allowing governments and corporations to continue with the status quo.

Please learn more about what these organizations are doing to help and support their efforts.

Coral Gardeners
Inland Ocean Coalition

Seagrass Fights Against Acidification
In 2020, scientists in the Chesapeake Bay, US, made a fortunate discovery. The seagrass beds as they photosynthesize, were turning some of the carbon from the water into tiny crystals of calcium carbonate. These crystals were reducing the acidity of water, as much as 60 miles away by 0.6pH (four times what it otherwise would have been). These vital marine ecosystems are joining in the fight against ocean acidification!