Scientists have long understood that, by absorbing carbon dioxide (CO2), the oceans of the world act as a large sink for carbon, reducing the amount of warming those emissions would otherwise cause. This CO2 absorption, however, presents other problems. As CO2 dissolves in the ocean, it reacts with seawater to form carbonic acid—the same acid that makes sodas and sparkling wines bubbly. Scientists have observed that, while the potential hydrogen (pH) of an ocean can be subject to natural variations, acidification can lower the pH of the water beyond those levels. These effects are still being studied and remain, in many ways, poorly understood. Ocean acidification (OA) is often called the “other CO2 problem,” because it receives far less attention than carbon emissions themselves. Whereas the magnitude of pH change from carbon emissions is predictable, the effects of increased acidity remain uncertain, and OA does not fit neatly within existing environmental laws. Carbon emissions occur all over the world, and many sources of OA are beyond the reach of U.S. environmental laws. Even within the United States, regulation of greenhouse gases (GHGs) remains controversial.
The term “ocean acidification” was only coined in 2003. Despite its short history, it quickly became the subject of increased interest when, in 2005, Washington—the country’s top provider of farmed oysters, clams, and mussels—saw its shellfish hatcheries experience large-scale die-offs of oyster larvae. While pathogens were initially thought to be responsible, scientists eventually concluded that the demise of oyster larvae was due to the low pH of the seawater. Because the seafood industry in Washington is worth an estimated $1.7 billion annually, a variety of stakeholders were motivated to study this issue, which has importance for other states and countries as well. For example, the National Oceanic and Atmospheric Administration has concluded that Alaska and its large fisheries also suffer from moderate to severe vulnerability to OA. Globally, the U.N. Convention on Biological Diversity has estimated that the total losses due to ocean acidification will be in the range of $1 trillion annually by 2100.
Before turning to the labyrinth of laws that address OA, a quick review of high school chemistry is worthwhile. The pH scale is a measurement of the concentration of H+ ions or the relative acidity of liquids, theoretically open-ended but usually ranging from 0 (very acidic) to 14 (very basic or alkaline). Like the Richter scale, the pH scale is logarithmic. For instance, a liquid with a pH of 1 (say, gastric acid) is 10 times more acidic than one with a pH of 2 (lemon juice or vinegar). In the ocean, equilibrium exists among CO2, bicarbonate (CHO3-) and carbonate (CO3-2). Oceans already contain carbonate, used by organisms for shells and structures. When CO2 dissolves in seawater, it forms carbonic acid, which breaks down and releases hydrogen ions, which then bind with carbonate. This shifts the equilibrium, resulting in an increase in bicarbonate ions and a decrease in carbonate ions, making the latter less available to calcifying organisms such as oysters and corals to build their shells and reefs. Despite the inherent variability in ocean pH (and other water bodies), scientists estimate that surface seawater acidity has increased by approximately 30 percent between 1750 and 1994, leading to a decrease in pH.
Global atmospheric carbon dioxide concentrations reached 413.32 parts per million (ppm) as of April 2019, and worldwide emissions are increasing by more than 2 ppm per year. NOAA Earth Sys. Research Lab., Glob. Monitoring Div., Trends in Atmospheric Carbon Dioxide, available at http://www.esrl.noaa.gov/gmd/ccgg/trends (last visited May 18, 2019). On November 23, 2018, the United States released a long-awaited report on climate change. That report noted that when carbon dioxide dissolves in seawater, it affects ocean chemistry in three ways: (1) it increases dissolved carbon dioxide and bicarbonate ions, used by algae and plants for photosynthesis, “potentially benefiting many of these species”; (2) it increases the concentration of hydrogen ions, lowering the pH and acidifying the seawater; and (3) it decreases the concentration of carbonate ions used by calcifying organisms. U.S. Global Change Research Program, Fourth National Climate Assessment, Vol. II, Chapter 9: Oceans and Marine Resources (Nov. 23, 2018), available at https://nca2018.globalchange.gov/chapter/9/. OA interacts with ocean warming and deoxygenation, as well as other factors such as nutrient inputs, to increase environmental stress on organisms. Id.
Some scientists contend that OA may have earlier and more noticeable effects along North America’s West Coast. This is because high latitude waters, like the California Current, may be the first to become undersaturated with respect to carbonate. While OA occurs in a mosaic pattern that varies with the trajectories of plumes of fossil-fuel emissions and varying mixing intensities among regions of the oceans, these higher-latitude waters tend to have lower carbonate ion concentrations because of factors like colder temperatures (which increase gas solubilities) and greater ocean mixing. Undersaturation of carbonate in seawater makes it more difficult for calcifying organisms to form and maintain calcite shells and structures, and even more difficult for organisms that form aragonite, another common but less stable form of calcium carbonate. At low carbonate concentrations, aragonite shells and other structures begin to dissolve. Not only that, markers of health such as metamorphosis, size, and survival rate are negatively affected.
Interestingly, some species may benefit from increased acidity, making responses to OA more varied than previously believed. Some photosynthetic algae and seagrasses may benefit from higher carbon dioxide conditions, which is consumed during photosynthesis (and, in turn, can help buffer areas from OA, acting to protect shell-forming species in a given area). While laboratory studies have shown impacts on fish and their prey, no studies have yet shown that acidification limits wild fish stock productivity.
Driggs A. & and Stratford B. G., American Bar Association, 5 August 2019. Article.