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Ocean Acidification
When discussing climate change, most people think about rising temperatures. However, increasing atmospheric carbon dioxide (CO2) affects Earth in another important way: it changes the chemistry of the oceans.
The world's oceans absorb approximately 25–30% of human-caused carbon dioxide emissions. This slows the rate of atmospheric warming, but it comes with an environmental cost. As carbon dioxide dissolves in seawater, it reacts with water molecules to form carbonic acid (H2CO3), increasing the concentration of hydrogen ions (H+) and lowering ocean pH. This process is known as ocean acidification.
What Is Ocean Acidification?
Ocean acidification is the gradual decrease in the pH of seawater caused primarily by the absorption of atmospheric carbon dioxide.
Since the beginning of the Industrial Revolution, average ocean pH has decreased by approximately 0.1 pH units, representing about a 30% increase in acidity. Scientists project that ocean acidity will continue to increase if atmospheric CO₂ concentrations continue to rise.
Because the pH scale is logarithmic, even seemingly small declines in pH represent substantial changes in ocean chemistry.
Why Ocean Acidification Matters
Many marine organisms use calcium carbonate (CaCO3) to build shells, skeletons, and other structures. Examples include:
- Corals
- Clams
- Oysters
- Mussels
- Pteropods ("sea butterflies")
- Some plankton
As ocean acidity increases, carbonate ions become less available. This makes it more difficult for organisms to build and maintain shells and skeletons. In severe cases, existing shells may begin to dissolve.
Effects on Coral Reefs
Coral reefs are among the ecosystems most vulnerable to ocean acidification. Corals build their skeletons from calcium carbonate. As carbonate availability declines, coral growth slows. If atmospheric CO₂ concentrations continue to increase, coral calcification rates may decrease substantially, making reefs more vulnerable to erosion, disease, bleaching, and storm damage. Because coral reefs provide habitat for thousands of species, impacts on corals can affect entire marine ecosystems.
Effects on Food Webs
Ocean acidification also affects species at the base of marine food webs. Small planktonic organisms can experience reduced growth, reproduction, and survival. Because many fish, marine mammals, and seabirds depend on these organisms as food sources, disruptions can cascade through entire ecosystems. Ocean acidification therefore has the potential to influence fisheries, biodiversity, and food security.
Ocean Acidification and Climate Change
Ocean acidification and climate change share the same primary cause: increasing atmospheric carbon dioxide.
However, they are different environmental problems:
| Climate Change | Ocean Acidification |
|---|---|
| Caused by greenhouse gases trapping heat in the atmosphere | Caused by carbon dioxide dissolving in seawater |
| Raises global temperatures | Lowers ocean pH |
| Alters weather, precipitation, and sea level | Alters marine chemistry |
| Affects both terrestrial and marine ecosystems | Primarily affects marine ecosystems |
Because both problems result from carbon dioxide emissions, reducing fossil fuel use can help address both climate change and ocean acidification.
Connection to California and San Diego
Ocean acidification is particularly important along the California coast. Seasonal upwelling brings cold, carbon-rich water to the surface, making coastal waters naturally more acidic than many other regions. Additional carbon dioxide from human activities further increases acidity, posing challenges for marine ecosystems and shellfish industries.
Researchers are monitoring ocean acidification along the Southern California coastline because of its potential impacts on kelp forests, fisheries, marine biodiversity, and coastal food webs.
Key Takeaways
- Ocean acidification is caused by the absorption of atmospheric carbon dioxide by seawater.
- Since the Industrial Revolution, ocean acidity has increased by approximately 30%.
- Acidification reduces the availability of calcium carbonate needed by many marine organisms.
- Corals, shellfish, plankton, and other calcifying organisms are particularly vulnerable.
- Ocean acidification is distinct from global warming but is caused by the same increase in atmospheric carbon dioxide.
- Reducing carbon dioxide emissions helps slow both climate change and ocean acidification
This page titled 9.6: Ocean Acidification- The Other Carbon Problem was last modified on Fri, 11 Sep 2026 23:33:11 GMT and is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by Erin Rempala.
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