Ocean Acidification: The Silent Killer

More on water-related problems: here is a guest review article from Kenneth Xu, Founder and Executive President of the Student Environmental Education Coalition.

In a few decades, once-vibrant coral reef ecosystems will erode away. Along the coast, plankton and shellfish at the base of the food web will slowly dissolve into seawater. The herring, mackerel, and other commercially important fish that feed on them will struggle to survive. People in maritime industries and coastal economies will undoubtedly suffer from the far-reaching consequences of more acidic waters. No, this is not the same problem as global warming. This looming issue is known as ocean acidification, commonly referred to as “the other carbon dioxide problem” (The Economist 2010). By 2100, the average pH of seawater is expected to drop from 8.1 to 7.8-7.6, possibly tripling the ocean’s acidity (Mora et al. 2013). Because this change is scarcely noticed on land, many people are unaware of its significance and ramifications. Understanding the causes and effects of ocean acidification is crucial for governments to make informed decisions that will not only protect marine life but also future generations of people around the world.

The oceans cover 71% of Earth’s surface and serve as the world’s largest carbon sink, bearing the brunt of humanity’s abundant carbon dioxide emissions. Along with global warming and sea level rise, ocean acidification is a lesser-known but very troubling consequence of rising greenhouse gas levels. It is caused by the ocean’s increased uptake of carbon dioxide from the atmosphere, an action that slows down global warming but fundamentally alters marine chemistry in the process. When seawater (H2O) absorbs carbon dioxide (CO2) from the overlying air, it forms carbonic acid (H2CO3), which can then react with H2O to form a bicarbonate ion (HCO3) and a hydronium ion (H3O+). This increases the water’s hydrogen ion concentration and therefore raises seawater acidity, indicated by a lower pH.

The lowered pH of seawater leads to a myriad of ecological effects, some of which include more frequent toxic algal blooms (Tatters, Fu, and Hutchins 2012), poorly developed coral reefs (Manzello et al. 2008), dissolution of important calcifying plankton (Bednaršek et al. 2012), decreased calcification of mussels and oysters (Gazeau et al. 2007), lowered metabolic rates in predators like the Humboldt squid (Rui and Seibel 2008), reduced immune response of shellfish (Mackenzie et al. 2014), increased numbers of invasive species (Hall-Spencer and Allen 2015), and reduced growth and survival rates of many fish (Baumann, Talmage, and Gobler 2011). Clearly, many vital species will be endangered by more acidic conditions. In addition, as CO2 uptake increases, the ability of the ocean to absorb atmospheric CO2 decreases, which means that the pace of global warming will actually speed up as the ocean becomes more saturated with carbon (Schuster and Watson 2007).

Ocean acidification obviously poses a serious risk to marine ecosystems, but it also threatens the livelihood of people who rely on the ocean’s resources. Shellfish harvests will likely decline, coral reefs will no longer provide food or shoreline protection, and valuable top predators like tuna will be harmed by the disappearance of their food sources (Logan 2010). Commercial fisheries will then be devastated and food security will likely be jeopardized in maritime nations. Coastal economies in the U.S. such as Chesapeake Bay could effectively be bankrupted (National Resources Defense Council 2015). Not only will ocean acidification mount up serious socioeconomic costs in the U.S., but it will also unfairly hurt the developing countries and islands that have contributed the least to CO2 emissions. Ocean acidification is an imminent, fundamental change that most of humanity is unprepared to handle. Combined with other marine environmental problems such as ocean pollution, coastal eutrophication, and overfishing, the future of the ocean is troubling. In conjunction with global warming and other anthropogenic hazards, the future of the entire biosphere is grim.

Despite presenting serious economic repercussions in the near future, ocean acidification is woefully under-addressed in the media. Budget cuts for oceanography research seem to be as commonly mentioned in the news as actual discussion of marine environment issues themselves. There remains a wealth of knowledge to be gained from ocean acidification research, which is still only in its early stages. Even though ocean acidification is perhaps equally as significant as global warming, it commands far less attention. Thus, in order to fuel research on this topic, there must be increased public awareness and grassroots activity. Furthermore, policymakers need to adequately fund marine scientists to learn more about the changes in ocean chemistry that are currently occurring and the issues that ocean acidification will bring in the future, in addition to devising last-resort solutions like geoengineering.

Most importantly, governments need to take a preventative approach and focus on reducing anthropogenic greenhouse gas emissions to combat ocean acidification at its core. As stated by famed climate scientist Ken Caldeira, “It is within our technical and economic means…to largely eliminate carbon dioxide emissions from our economies by mid-century. It is thought that the cost of doing this — perhaps 2% of the worldwide economic production — would be small, yet at present it has proven difficult for societies to decide to undertake this conversion” (2012). People tend not to react until problems have already been exacerbated, so perhaps we should strive to break this pattern before the consequences of our wasteful habits become dire. Although the Paris Agreement of 2015 was a strong start, each and every one of us needs to build on this momentum to truly make progress in the fight against ocean acidification and climate change. The solution to this problem lies within the people’s hands, especially the next generation of scientists, politicians, and responsible citizens.


Baumann, Hannes, Stephanie C. Talmage, and Christopher J. Gobler. 2011. “Reduced Early Life Growth and Survival in a Fish in Direct Response to Increased Carbon Dioxide.” Nature Climate Change, 2011, 38-41. doi: 10.1038/nclimate1291.
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Mackenzie CL, Lynch SA, Culloty SC, and Malham SK. 2014. “Future Oceanic Warming and Acidification Alter Immune Response and Disease Status in a Commercial Shellfish Species, Mytilus edulis L.” Jiravanichpaisal P, ed. PLoS ONE. 2014;9(6):e99712. doi:10.1371/journal.pone.0099712.
Manzello DP, Kleypas JA, Budd DA, Eakin CM, Glynn PW, and Langdon C. 2008. “Poorly cemented coral reefs of the eastern tropical Pacific: Possible insights into reef development in a high-CO2 world.” Proceedings of the National Academy of Sciences of the United States of America. 2008;105(30):10450-10455. doi:10.1073/pnas.0712167105.
Mora, Camilo et al. 2013. “Biotic and Human Vulnerability to Projected Changes in Ocean Biogeochemistry over the 21st Century.” Ed. Georgina M. Mace. PLoS Biology 11.10 (2013): e1001682. doi:10.1371/journal.pbio.1001682.
“Ocean Acidification.” National Resources Defense Council. Accessed December 29, 2015. http://www.nrdc.org/oceans/acidification/files/ocean-acidification-eastcoast.pdf.
Rui, Rosa, and Seibel, Brad. 2008. “Synergistic Effects of Climate-related Variables Suggest Future Physiological Impairment in a Top Oceanic Predator.” Proceedings of the National Academy of Sciences of the United States of America. doi: 10.1073/pnas.0806886105.
Schuster, U., and A. J. Watson. 2007. “A variable and decreasing sink for atmospheric CO2 in the North Atlantic.” J. Geophys. Res., 112, C11006, doi:10.1029/2006JC003941.
Tatters AO, Fu F-X, Hutchins DA. 2012. “High CO2 and Silicate Limitation Synergistically Increase the Toxicity of Pseudo-nitzschia fraudulenta.” PLoS ONE 7(2): e32116. doi:10.1371/journal.pone.0032116.
“The Other Carbon-Dioxide Problem.” The Economist. July 3, 2010. Accessed December 29, 2015. http://www.economist.com/node/16479264.

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