Ocean Acidification:
November 3, 2022
Frequently Asked Questions
Caitlin Keating-Bitonti
The ocean absorbs carbon dioxide (CO2) from the atmosphere. Chemical reactions between CO2
Analyst in Natural
and water can change the pH of seawater (pH is a measure of water’s acidity or basicity). The
Resources Policy
current shift in the chemistry of seawater is toward a lower pH, commonly referred to as ocean

acidification (OA). Scientific consensus is that rising CO2 concentrations in the atmosphere will
Eva Lipiec
continue to contribute to OA globally, primarily affecting the ocean’s surface waters.
Analyst in Natural
Resources Policy
Some U.S. regions are experiencing impacts from OA (e.g., coastal waters of Oregon), and

scientists expect that nearly all U.S. coastlines and open ocean waters will experience impacts of
OA by 2100. OA also has negatively affected some marine organisms, such as reef-building

corals and shellfish, and may affect others in the future. These impacts have had consequences
for U.S. fisheries and aquaculture. Future OA’s economic impacts may include higher risks of storm damage to coastal
communities and loss of tourism revenue from OA-caused degradation of coral reefs.
Congress has authorized federal agencies, such as the National Oceanic and Atmospheric Administration (NOAA) and the
Environmental Protection Agency, to support activities that aim to adapt to and mitigate OA impacts. In 2009, Congress
passed the Federal Ocean Acidification Research and Monitoring Act (FOARAM; 33 U.S.C. §§3701 et seq.), which, among
other things, established the federal Interagency Working Group on Ocean Acidification (IWGOA) to coordinate OA
activities across the federal government. IWGOA’s work includes studying OA’s potential impact on marine species and
ecosystems as well as identifying adaptation and mitigation strategies.
Congress continues to show interest in OA. In 2022, Congress enacted the Coastal and Ocean Acidification Research and
Innovation Act of 2021 (P.L. 117-167, Title VI, Subtitle E), which amended FOARAM. The amendments added acidification
of coastal waters as a concern to be addressed; established an advisory board to the IWGOA; emphasized research on OA
adaptation and mitigation strategies, the compounding effects of OA with other environmental stressors, and the
socioeconomic impacts of OA; and authorized appropriations for NOAA and the National Science Foundation to conduct OA
activities.
Also in 2022, Congress provided funding to NOAA for OA activities in the Consolidated Appropriations Act, 2022 (P.L.
117-103). During the 117th Congress, Members have introduced and considered other bills related to OA, some of which
focused on examining and addressing the impacts of OA, among other activities. Proposed FY2023 appropriations bills
would provide NOAA with increased funding compared with FY2022 levels and additional OA-related directives.
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Ocean Acidification: Frequently Asked Questions

What Is Ocean Acidification?
Atmospheric gases, such as carbon dioxide (CO2), continuously diffuse into the surface of the
ocean.1 Dissolved gases in the surface of the ocean are in near equilibrium with gases in the
atmosphere. Thus, as more CO2 is emitted into the atmosphere, the surface of the ocean takes up
more CO2. The increased uptake of atmospheric CO2 by the ocean alters the chemistry of
seawater by decreasing its pH in a process referred to as ocean acidification, or OA (Figure 1).2
Figure 1. Pacific Atmospheric and Seawater Carbon Dioxide Concentrations and
Seawater pH

Source: National Oceanic and Atmospheric Administration (NOAA), “Hawaii Carbon Dioxide Time-Series,” at
https://www.pmel.noaa.gov/co2/file/Hawaii+Carbon+Dioxide+Time-Series.
Notes: Figure shows the relationship between atmospheric carbon dioxide (CO2) concentrations (red points
and line) and dissolved CO2 concentrations of seawater in surface ocean (green points and line), as well as the
relationship between increasing dissolved CO2 concentrations in surface ocean (green points and line) and
decreasing seawater pH (blue points and line). Atmospheric CO2 measurements were made at Mauna Loa
Baseline Observatory (refer to Station Mauna Loa on the insert map), which has been continuously monitoring
and col ecting data related to atmospheric change since the 1950s (NOAA, “Mauna Loa Baseline Observatory,”
at https://gml.noaa.gov/obop/mlo/). Dissolved CO2 and pH measurements were made at Station ALOHA, a circle

1 The surface mixed layer depth of the ocean varies seasonally and geographically but generally is between 0 and 200
meters beneath the surface of the ocean.
2 Rising carbon dioxide (CO2) emissions are the root cause for current surface ocean acidification (OA). In the ocean
interior, bacteria break down organic matter during cellular respiration, which adds CO2 to seawater (see “What
Factors Influence Ocean Acidification?”). Woods Hole Oceanographic Institution, “Ocean Acidification,” at
https://www.whoi.edu/know-your-ocean/ocean-topics/how-the-ocean-works/ocean-chemistry/ocean-acidification/; and
National Oceanic and Atmospheric Administration (NOAA), “Ocean Acidification,” at https://www.noaa.gov/
education/resource-collections/ocean-coasts/ocean-acidification.
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of a 6-mile radius in the Pacific Ocean north of Hawaii (refer to Station ALOHA on the insert map), which has
been col ecting oceanographic data since 1988 (Station ALOHA, at https://aco-ssds.soest.hawaii.edu/ALOHA/).
OA alters seawater chemistry following a series of chemical reactions. When atmospheric CO2
dissolves into water (H2O), it forms carbonic acid (H2CO3). Some of the carbonic acid breaks up
in ocean water, producing free hydrogen ions (H+). As the number of free hydrogen ions
increases, the pH of the ocean decreases and the water becomes more acidic. The prevailing
global average pH (a measure of hydrogen ion concentration) of water near the ocean surface is
around 8.1, with regional variations.3
How Might Ocean Acidification Change over the
21st Century?
Over the past two centuries, the average pH of water near the ocean surface has decreased by
almost 0.1 unit.4 That change represents a 26% increase in the concentration of free hydrogen
ions dissolved in seawater, because the pH scale is logarithmic (i.e., water with a pH of 8.0 is 10
times less acidic than water with a pH of 7.0 and 100 times less acidic than water with a pH of
6.0).
Modeling studies project that OA will continue over the 21st century, but the rate of OA likely will
depend on the rate of atmospheric CO2 emissions.5 Under the Intergovernmental Panel on
Climate Change’s scenario involving a doubling of the concentration of atmospheric CO2 by
2050 with no additional climate change policies, models project that average surface ocean pH
may decrease by 0.4 units by the year 2100 (Figure 2).6 However, using a scenario in which CO2
emissions reach net zero by 2050 or shortly thereafter, models project that average surface ocean
pH may decrease by less than 0.1 unit by 2050 and may rise slightly in the second half of the 21st
century (Figure 2).7 Figure 2 also shows the projected pathway of ocean surface pH for other
CO2 emissions scenarios in modeling studies.8

3 The pH scale is an inverse logarithmic representation of hydrogen ion (H+) concentration, indicating the activity of
hydrogen ions (or their equivalent) in the solution. A pH of less than 7.0 is considered acidic, a pH greater than 7.0 is
considered basic, and a pH level of 7.0 is defined as neutral.
4 James Orr et al., “Anthropogenic Ocean Acidification over the Twenty-First Century and Its Impact on Calcifying
Organisms,” Nature, vol. 437 (2005); and NOAA, “Ocean Acidification,” at https://www.noaa.gov/education/resource-
collections/ocean-coasts/ocean-acidification.
5 IPCC, AR6 Physical Science Basis, Chapter 5, p. 720.
6 Ibid., p. 714.
7 Net-zero emissions means that some greenhouse gases (GHGs) are emitted, but these emissions are offset by
removing an equivalent amount of GHGs from the atmosphere and storing it permanently in soil, plants, or materials.
Achieving net-zero emissions may be considered more feasible than releasing no GHGs to the atmosphere (i.e., zero
emissions).
8 IPCC, AR6 Physical Science Basis, Chapter 5, p. 720.
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Ocean Acidification: Frequently Asked Questions

Figure 2. Scenario Projections of Global Ocean Surface pH

Source: CRS with information from Intergovernmental Panel on Climate Change, “Summary for Policymakers,”
in Changing Climate 2021: The Physical Science Basis, eds. Valerie Masson-Delmotte et al., 2021, p. SMP-22.
Notes: CO2 = carbon dioxide; GHG = greenhouse gas. Models project decreasing ocean surface pH through
the 21st century for scenarios with intermediate to very high GHG emissions (yellow, red, and maroon lines) and
decreasing pH until around 2070, but that rises slightly after 2070 for scenarios with very low to low GHG
emissions (light and dark blue lines). The light blue line holds global warming to about 1.5 degrees Celsius (°C),
in line with the goals of the Paris Agreement; the dark blue line holds global warming to beneath 2°C.
Model projections of average global OA changes, such as the projections shown in Figure 2, are
driven primarily by atmospheric CO2 simulations.9 In general, the global trend would reflect
surface pH decline with increasing atmospheric CO2 concentrations. Regional seawater properties
may influence the surface pH value, resulting in geographic variations in OA.10 See “What
Factors Influence Ocean Acidification?” for a further discussion on the factors that may amplify
regional variations in seawater pH.
What Factors Influence Ocean Acidification?
Not all ocean and coastal regions experience OA in the same way. Increased CO2 concentrations
in the atmosphere contribute to OA, but other factors also influence coastal and ocean
acidification. Rates of acidification can vary geographically for numerous reasons, including
temperature, ocean circulation, biological activity, coastal upwelling, freshwater input, and
nutrient runoff, among other influences.11
 Temperature. Gases, such as CO2, are more soluble in colder water than in
warmer water. Thus, marine waters near the poles have a much greater capacity
to absorb atmospheric CO2 than do ocean waters in the tropics. As a
consequence, polar regions tend to experience greater regional changes due to
OA.12
 Ocean Circulation. Dissolved CO2 is transported from the ocean surface into
deeper ocean water at high latitudes, because cold polar surface waters have a
higher density than warm tropical waters. The cold polar surface waters sink to
depth (i.e., vertical ocean mixing), and both observations and modeling studies

9 IPCC, AR6 Physical Science Basis, Chapter 5, p. 719.
10 Ibid.
11 Josep G. Canadell et al., “Chapter 5: Global Carbon and Other Biogeochemical Cycles and Feedbacks,” in Changing
Climate 2021: The Physical Science Basis, Intergovernmental Panel on Climate Change (IPCC), eds. Valerie Masson-
Delmotte et al., 2021, p. 720 (hereinafter referred to as IPCC, AR6 Physical Science Basis).
12 IPCC, AR6 Physical Science Basis, Chapter 5, p. 677.
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show that the vertical ocean mixing contributes to acidification of the deeper
ocean.13 For example, OA below 2,000 meters has been detected in polar regions
in both the North Atlantic and the Southern Ocean.14
 Biological Activity. The breakdown of organic carbon in the ocean interior by
bacteria, via a biological process known as cellular respiration, adds CO2 to
seawater. Deep ocean water is enriched in CO2 due to cellular respiration, in
addition to the capacity of colder water in the deep ocean to absorb CO2.
Phytoplankton near the ocean surface and marine plants (i.e., kelp, seaweed,
seagrass) take up CO2 during photosynthesis, which may offset some effects of
OA.
 Coastal Upwelling. Coastal upwelling is a process by which coastal winds push
warm surface waters offshore, causing cold deep water to rise to the surface.
Upwelled ocean waters have high CO2 concentrations, because deep ocean
waters carry dissolved CO2 from two sources: (1) atmospheric CO2 from when
cold polar waters were last at the surface of the ocean and (2) CO2 respired by
bacteria during the decomposition of organic carbon in the ocean interior.15
 Freshwater Input. Riverine influx associated with high-intensity precipitation
events or glacial melt can yield large freshwater inputs that contribute dissolved
inorganic carbon, organic carbon, and nutrients to coastal waters. These
contributions can alter the chemistry of waters located at the mouths of large
rivers or the toes of glaciers. In addition, rainwater is naturally acidic, due to CO2
and other atmospheric gases, such as nitrogen dioxide.16
 Nutrient Runoff. Riverine inputs with high nutrient loads (often nitrogen and
phosphorous associated with farming practices) can lead to excessive plant and
algae growth in coastal settings, a process known as eutrophication.17 The
resulting decomposition of algae and plants in coastal waters produces increased
amounts of CO2 in the water column, which can lead to a lowering of seawater
pH.18
How Does Ocean Acidification Impact Marine Life?
The influence of OA on marine life is complicated. A pH of less than the global average of 8.1
may cause some organisms to expend more energy, but organisms may be able to adapt in
complex and species-specific ways to OA. OA may affect more marine species when
compounded by the effects of climate change, including warming seawater temperatures and
deoxygenation (loss of oxygen).19 In particular, OA poses physiological stress to invertebrate

13 IPCC, AR6 Physical Science Basis, Chapter 5, p. 717.
14 Ibid.
15 U.S. Global Change Research Program (USGCRP), “Chapter 13: Ocean Acidification and Other Ocean Changes,”
in Climate Science Special Report: Fourth National Climate Assessment, vol. I, eds. Donald J. Wuebbles et al., 2017, p.
373 (hereinafter referred to as USGCRP, NCA4 vol. I). For a discussion on coastal upwelling, see CRS Report R47021,
Federal Involvement in Ocean-Based Research and Development, by Caitlin Keating-Bitonti.
16 Rainwater is naturally acidic at a pH of around 5.6.
17 U.S. Environmental Protection Agency (EPA), “The Sources and Solutions: Agriculture,” at https://www.epa.gov/
nutrientpollution/sources-and-solutions-agriculture.
18 NOAA, “What Is Eutrophication?,” at https://oceanservice.noaa.gov/facts/eutrophication.html.
19 IPCC, AR6 Physical Science Basis, p. 721.
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organisms that build their hard parts (i.e., shells, skeletons, reef structures) with carbonate
minerals.20
Marine Invertebrates
For many marine invertebrate organisms, the abundance and availability of carbonate ions (CO 2-
3 )
in seawater are critical for survival. Most marine invertebrates have biochemical mechanisms to
regulate internal pH and are able, within limits, to grow their hard parts even when water external
to their internal environment is acidic. At current average ocean pH levels (about 8.1), ocean
waters near the surface have ample carbonate ions to support shell formation and coral reef
growth. However, as more CO2 dissolves into the ocean, the abundance and availability of
carbonate ions decline due to chemical reactions.21 A reduction in the availability of carbonate
ions in the ocean makes it physiologically challenging for shell-forming marine organisms to
grow shells, especially those in early stages of their life cycle (i.e., larval and juvenile stages). If
the availability of carbonate ions becomes too low (i.e., undersaturated) in seawater, then shells
made with carbonate minerals tend to dissolve.
The following sections expound on current or potential impacts of OA on invertebrate species,
including corals, oysters, lobsters, and crabs.
Corals
OA reduces corals’ ability to build and maintain reefs, the majority of which are located in
tropical and subtropical shallow waters. Most corals are colonial organisms, comprising hundreds
to hundreds of thousands of individual animals, called polyps.22 Some polyps secrete carbonate
skeletons that can grow into very large reef structures, called coral reefs. Modeling studies
employing an emissions scenario in which very little climate change mitigation is undertaken this
century project 2100 seawater pH conditions that are less favorable to the growth of coral reefs
(refer to the maroon line in Figure 2).23
Coral reefs are biodiverse, productive ecosystems that can provide socioeconomic benefits to
coastal communities. For example, studies show that reefs provide protection against waves
comparable to that provided by artificial structures such as breakwaters.24 Coral reef recreation
and tourism generate an estimated $192 million per year for Puerto Rico and $96 million per year
for the U.S. Virgin Islands.25 Coral reefs contribute an estimated $477 million to Hawaii’s
economy every year.26 In addition to potential impacts on tourism, declines in coral reef cover

20 Carbonate minerals include aragonite, calcite, and high-magnesium calcite.
21 As more CO
1-
2-
2 dissolves into the ocean, bicarbonate ions (HCO3 ) form at the expense of carbonate ions (CO3 ),
which is described by the following reaction: CO
2-
1-
2 + CO3 + H2O = 2HCO3 .
22 NOAA, “What Are Corals?,” at https://oceanservice.noaa.gov/education/tutorial_corals/coral01_intro.html.
23 USGCRP, “Chapter 27: Hawai’i and U.S.-Affiliated Pacific Islands,” in Impacts, Risks, and Adaptation in the United
States: Fourth National Climate Assessment, vol. II, eds. David R. Reidmiller et al., 2018, p. 1264 (hereinafter referred
to as USGCRP, NCA4 vol. II); and K.L. Ricke et al., “Risks to Coral Reefs from Ocean Carbonate Chemistry Changes
in Recent Earth System Model Projections,” Environmental Research Letters, vol. 8 (2013), p. 5.
24 Filippo Ferrario et al., “The Effectiveness of Coral Reefs for Coastal Hazard Risk Reduction and Adaptation,”
Nature Communications, vol. 5 (2014); and U.S. National Park Service, “Breakwaters, Headlands, Sills, and Reefs,” at
https://www.nps.gov/articles/breakwaters-headlands-sills-and-reefs.htm.
25 USGCRP, NCA4 vol. II, Chapter 20, p. 829.
26 USGCRP, NCA4 vol. II, Chapter 27, p. 1245.
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may reduce fisheries’ maximum catch potential in the exclusive economic zones of most central
and western Pacific islands and in the Caribbean region.27
Shellfish
OA’s effects on certain shellfish has impacted shellfish fishery revenues and may continue to do
so should OA expand to new regions and greater water depths.28 Of particular relevance to
shellfish hatcheries, relatively acidic ocean conditions caused by OA may impair the ability of
larval shellfish to build shells. For example, in the mid-2000s, oyster growers from Washington to
California experienced financial hardships from widespread death of larval shellfish (seed) at
hatcheries.29 In 2008, scientists from the National Oceanic and Atmospheric Administration
(NOAA) and various universities linked the oyster seed losses to OA; in turn, oyster hatcheries
shifted their operations to adapt to the OA conditions (see “What Is the Federal Government
Doing About Ocean Acidification?”).30 An additional consideration regarding OA’s impact on
oysters is the potential reduction in shell thickness and hardness, which could devalue oysters
commercially because a sought-after characteristic of oysters on the half shell is a shell that is
easily shucked and does not break or chip.31
OA also may affect other economically valuable shellfish, including the American lobster and
Dungeness crab. In 2019, the most recent year reported by NOAA Fisheries, the American lobster
found along the coast of New England was the highest-valued shellfish species in North
America.32 The Gulf of Maine, an area with record high stock abundance of American lobster,33
has experienced changing oceanographic conditions.34 Ocean warming has influenced lobster
fisheries in the region,35 and some research studies project the Gulf of Maine will experience OA
conditions by 2050.36 In the laboratory, researchers have shown that OA impacts both juvenile
and adult lobsters by causing erratic heart rates and fewer infection-fighting blood cells; should
these laboratory conditions occur in nature, they may impact lobsters’ survival.37 On the U.S.

27 USGCRP, NCA4 vol. II, Chapter 27, p. 1264; and USGCRP, NCA4 vol. II, Chapter 20, p. 853.
28 Sarah Cooley and Scott Doney, “Anticipating Ocean Acidification’s Economic Consequences for Commercial
Fisheries,” Environmental Research Letters, vol. 4 (2009).
29 Ryan Kelly, “Narratives Can Motivate Environmental Action: The Whiskey Creek Ocean Acidification Story,”
Ambio, vol. 43 (2014), pp. 592-599.
30 Ibid. and NOAA, “Improving an Ocean Acidification Observation System in Support of Pacific Coast Shellfish
Growers,” at https://ioos.noaa.gov/project/turning-headlights-high/.
31 Catherine Liberti et al., “The Impact of Oyster Aquaculture on the Estuarine Carbonate System,” Elementa: Science
of the Anthropocene, vol. 10 (2022).
32 NOAA Fisheries reported a total commercial catch of 132.6 million pounds of American lobster, yielding nearly
$910 million dollars, in 2021 (NOAA Fisheries, “Landings,” at https://www.fisheries.noaa.gov/foss/f?p=
215:200:14333709901427:Mail:NO, hereinafter referred to as NOAA Fisheries, Landings Database). NOAA Fisheries,
“U.S. Fisheries by the Numbers,” at https://www.fishwatch.gov/sustainable-seafood/by-the-numbers.
33 NOAA, “American Lobster,” at https://www.fisheries.noaa.gov/species/american-lobster.
34 Samantha Siedlecki et al., “Projecting Ocean Acidification Impacts for the Gulf of Maine into 2050: New Tools and
Expectations,” Elementa: Science of the Anthropocene, vol. 9 (2021).
35 Katherine Mills et al., “Fisheries Management in a Changing Climate: Lessons from the 2012 Ocean Heat Wave in
the Northwest Atlantic,” Oceanography, vol. 26 (2013), pp. 191-195.
36 Samantha Siedlecki et al., “Projecting Ocean Acidification Impacts for the Gulf of Maine into 2050: New Tools and
Expectations,” Elementa: Science of the Anthropocene, vol. 9 (2021).
37 Amalia Harrington and Heather Hamlin, “Ocean Acidification Alters Thermal Cardiac Performance, Hemocyte
Abundance, and Hemolymph Chemistry in Subadult American Lobsters Homarus americanus H. Milne Edwards, 1837
(Decapoda: Malcostraca: Nephropidae),” Journal of Crustacean Biology, vol. 39, no. 4 (2019), pp. 468-476.
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West Coast, Dungeness crabs are a valuable shellfish.38 Dungeness crabs have shown no change
in natural population dynamics due to changing oceanographic conditions. Laboratory
experiments have found decreased survival rates in Dungeness crabs hatched in waters with a pH
of 7.5 (a level that has been observed in upwelled waters along the Washington coast) compared
with those hatched in laboratory waters with a global average pH of 8.1.39
Marine Vertebrates
Whereas invertebrate organisms primarily build their hard parts with carbonate minerals,
vertebrate bones, including those of fish, are composed of a phosphate mineral. OA does not
affect the chemical structure of phosphate. Some studies, however, show that the durability and
robustness of some fish bones and shark teeth increase under OA conditions.40 Other studies have
claimed that OA can alter the behaviors of certain fish species, but the research methodology
behind these studies is debated.41
How Might U.S. Regions Be Affected by Ocean
Acidification?
Some U.S. regions have experienced measurable impacts from OA. Scientists expect that nearly
all U.S. coastlines will experience the impacts of OA by 2100.42 As shown in Figure 2, models
project a decrease in global ocean surface pH ranging from about 0.05 to 0.10 units by 2050. As
discussed above, regional seawater properties may affect the surface pH value, resulting in
geographic variations of OA.
Pacific waters along the West Coast of the United States are influenced by coastal upwelling.
Observations and models project the California Current System may experience an expansion and
intensification of low-pH water due to upwelling.43 OA has impacted some oyster hatcheries
along the West Coast. In particular, in 2007, the Oregon-based Whiskey Creek Shellfish Hatchery
was unable to provide shellfish growers with late-stage oyster larvae because the low-pH
seawater corroded the shells of early stage larvae.44 Waters circulating around Alaska’s Pacific

38 NOAA Fisheries reported a total commercial catch of 64.2 million pounds of Dungeness crab in 2021, yielding a
total revenue of $311.9 million for the Pacific Coast. Of this total, the total catch for Alaska was 9.0 million pounds,
with a revenue of $37.8 million. NOAA Fisheries, Landings Database.
39 Nina Bednarŝek et al., “Exoskeleton Dissolution with Mechanoreceptor Damage in Larval Dungeness Crab Related
to Severity of Present-Day Ocean Acidification Vertical Gradients,” Science of the Total Environment, vol. 716 (2020);
and NOAA, “Dungeness Crab Larvae Already Showing Effects of Coastal Acidification,” January 23, 2020, at
https://research.noaa.gov/article/ArtMID/587/ArticleID/2581.
40 Jonathan Leung et al., “Shark Teeth Can Resist Ocean Acidification,” Global Change Biology, vol. 28, no. 7 (2022);
Valentina Di Santo, “Ocean Acidification and Warming Affect Skeletal Mineralization in a Marine Fish,” Proceedings
of the Royal Society B: Biological Sciences, vol. 268 (2019); and Alice Mirasole et al., “Evidences On Alterations in
Skeleton Composition and Mineralization in a Site-Attached Fish Under Naturally Acidified Conditions in a Shallow
CO2 Vent,” Science of the Total Environment, vol. 761 (2021).
41 See Martin Enserink, “Sea of Doubts,” Science (2021), at https://www.science.org/content/article/does-ocean-
acidification-alter-fish-behavior-fraud-allegations-create-sea-doubt.
42 USGCRP, NCA4 vol. I; and USGCRP, NCA4 vol. II.
43 See the previous question for more information about coastal upwelling. IPCC, AR6 Physical Science Basis, Chapter
5, p. 721.
44 NOAA, “Improving an Ocean Acidification Observation System in Support of Pacific Coast Shellfish Growers,” at
https://ioos.noaa.gov/project/turning-headlights-high/; and R. Kelly, “Narratives Can Motivate Environmental Action:
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coastline also are derived from upwelled cold waters and may be impacted by OA.45 Moreover,
glacial runoff may further amplify OA along the Alaskan coast (e.g., Gulf of Alaska).46
U.S. coastal regions near agricultural watersheds and urbanized estuaries may be susceptible to
OA due to eutrophication.47 For example, the Mississippi River delivers riverine inputs of
nutrients (nitrogen and phosphorus) to the Gulf of Mexico, contributing to eutrophication of
coastal waters and a decrease in pH.48 Similarly, runoff into the Chesapeake Bay is contributing to
eutrophication and a decrease in pH in the Bay’s waters.49 In addition, coastal waters of the East
Coast and the mid-Atlantic are influenced by freshwater inputs from riverine and estuarine
sources, which may contribute to OA.50
Tropical oceans are expected to experience the greatest change in seawater chemistry associated
with rising atmospheric CO2 concentrations.51 The seawater pH off the Hawaiian Island of Oahu
has declined from an annual average of about 8.11 to 8.07 (roughly an 8.7% increase in acidity),
according to 34 years of ocean data collection at Station ALOHA (Figure 1).52 Although oceanic
pH varies geographically, scientists consider the conditions at Station ALOHA to be broadly
representative of those across the western and central Pacific Ocean.53 The tropical and
subtropical Pacific Ocean also is projected to experience the highest levels of thermal stress,
which could exacerbate the effects of increasing OA.54
Has Ocean Acidification Happened in the Past?
OA has occurred in the past when geologic events (e.g., volcanic eruptions) emitted large
quantities of CO2 and other gases to the atmosphere. The fossil record suggests that some mass
extinction events of marine organisms that have occurred in geologic history may have been
related to changes in ocean pH. For example, approximately 56 million years ago, a large pulse of
methane locked in ocean sediments was released into the ocean-atmosphere system over a 3,000-
20,000 year period.55 Methane released into the ocean-atmosphere undergoes a chemical reaction
to become CO2 within about 10 years. Chemical analyses of marine sediments suggest this

The Whiskey Creek Ocean Acidification Story,” Ambio, vol. 43 (2014).
45 Jeremy Mathis, “Ocean Acidification Risk Assessment for Alaska’s Fishery Sector,” Progress in Oceanography, vol.
136 (2015).
46 Ibid; IPCC, AR6 Physical Science Basis, Chapter 5, p. 720.
47 NOAA, “What Is Eutrophication?,” at https://oceanservice.noaa.gov/facts/eutrophication.html.
48 IPCC, AR6 Physical Science Basis, Chapter 5, p. 721.
49 NOAA, “OPA Projects in the Southeast U.S.,” at https://oceanacidification.noaa.gov/CurrentProjects/
Southeast.aspx#.
50 USGCRP, NCA4 vol. I, Chapter 13, p. 373.
51 OA generally occurs in shallow ocean waters in tropical regions because there is little to no vertical ocean mixing to
transport the atmospheric CO2 absorbed by the surface ocean into the deep ocean.
52 Data collection and observations began at the Station ALOHA in October 1988.
53 John Marra and Michael Kruk, “State of Environmental Conditions in Hawaii and the U.S. Affiliated Pacific Islands
und a Changing Climate: 2017,” NOAA National Centers for Environmental Information, 2017, p. 74, at
https://coralreefwatch.noaa.gov/satellite/publications/state_of_the_environment_2017_hawaii-usapi_noaa-nesdis-
ncei_oct2017.pdf
54 Ibid.
55 Miriam Katz et al., “Uncorking the Bottle: What Triggered the Paleocene/Eocene Thermal Maximum Methane
Release?,” Paleoceanography, vol. 16 (2001); James Zachos et al., “Rapid Acidification of the Ocean During the
Paleocene-Eocene Thermal Maximum,” Science, vol. 308 (2005); and IPCC, AR6 Physical Science Basis, Chapter 5, p.
714.
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methane release was associated with a global surface ocean pH decline ranging from 0.15 to 0.30
units. However, this change in pH occurred more slowly than the current rate of OA and
continued over a long time interval.56
What Actions or Interventions Might Limit or
Reduce Ocean Acidification?
Some stakeholders may be interested in limiting or reducing OA and its impacts. Mitigating OA
involves decreasing the availability of CO2 in the ocean by removing it from either the
atmosphere or the ocean. The ocean’s rate of uptake of atmospheric CO2 would start to decrease
if the concentration of atmospheric CO2 decreased.
Some shellfish industries have implemented approaches to mitigate CO2 concentrations in the
water. Some shellfish farmers on the Pacific and Atlantic coasts of the United States grow marine
plants (e.g., kelp, seaweed, seagrass) as a nature-based approach to offset the effects of OA.57
Researchers also are exploring an approach that involves placing bags of oyster shells near oyster
farms to improve the health of the living oysters.58 These researchers are testing the hypothesis
that, over time, the shells in the bags will dissolve and provide a natural buffer to OA. The
placement of oyster shells, or pulverized silicate or carbonate rocks, in seawater can alter the
water chemistry by fixing the CO2 dissolved in the seawater to the added material (i.e., shell,
pulverized rock or mineral). This approach for removing dissolved CO2 from the water is known
as ocean alkalinity enhancement or enhanced weathering.59
What Is the Federal Government Doing About
Ocean Acidification?
Congress has shown interest in OA and its impacts over the past few decades and has directed
federal agencies to take certain actions to address OA. Congress passed the Federal Ocean
Acidification Research and Monitoring Act of 2009 (FOARAM; P.L. 111-11) and amended the
act in 2022 (amendments described under “What Are Recent Congressional Actions Addressing
Ocean Acidification?”).60 As amended, FOARAM

56 IPCC, AR6 Physical Science Basis, Chapter 5, p. 714.
57 Marine plants remove CO
2 from the surface waters of the ocean via photosynthesis. See, for example, World
Wildlife Foundation, “Exploring the Benefits of Kelp Farming in Maine,” 2021, at https://www.worldwildlife.org/
magazine/issues/winter-2021/articles/exploring-the-benefits-of-kelp-farming-in-maine; and Marketplace, “Could Kelp
Help Mitigate Ocean Acidification?,” February 22, 2018, at https://www.marketplace.org/2018/02/22/could-kelp-help-
oyster-industry-mitigate-effects-ocean-acidification/.
58 NOAA, “Researchers Explore Using Empty Oyster Shells to Decrease Acidic Seawater,” October 13, 2017, at
https://seagrant.noaa.gov/News/Article/ArtMID/1660/ArticleID/1661/Researchers-Explore-Using-Empty-Oyster-
Shells-to-Decrease-Acidic-Seawater.
59 National Academies of Sciences, Engineering, and Medicine, A Research Strategy for Ocean-Based Carbon Dioxide
Removal and Sequestration (Washington, DC: National Academies Press, 2022), p. 181. For more information on
ocean-based CO2 removal technologies, see CRS Report R47172, Geoengineering: Ocean Iron Fertilization, by Caitlin
Keating-Bitonti.
60 33 U.S.C. §§3701 et seq. See “What Are Recent Congressional Actions Addressing Ocean Acidification” for
information on the amendments.
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 Established and assigned responsibilities to the federal Interagency Working
Group on Ocean Acidification (IWGOA) and a nonfederal advisory board
 Directed the Secretary of Commerce to establish an OA program within NOAA
and defined the program’s activities61
 Instructed the National Science Foundation (NSF) to continue its OA research
activities, supporting competitive proposals for OA research, observation, and
monitoring
 Charged the National Aeronautics and Space Administration with ensuring space-
based monitoring of OA and its impacts
 Authorized appropriations for NOAA and NSF to carry out these activities from
FY2023 through FY202762
The IWGOA released a strategic federal research and monitoring plan in 2014.63 In that plan, the
working group listed seven thematic areas of federal research and monitoring activities.64
1. Research to understand responses to OA
2. Monitoring of ocean chemistry and biological impacts
3. Modeling to predict changes in the ocean carbon cycle and impacts on marine
ecosystems and organisms
4. Technology development and standardization of measurements
5. Assessment of socioeconomic impacts and development of strategies to conserve
marine organisms and ecosystems
6. Education, outreach, and engagement strategy on OA
7. Data management and integration
Federal agencies, such as NOAA and the Environmental Protection Agency, also support
activities to adapt to and mitigate OA impacts.65 For example, following the significant drop in
oyster production levels at the Whiskey Creek Shellfish Hatchery in 2007, NOAA deployed a
network of sensors off the Northwest Pacific Coast to act as an early warning system for shellfish

61 Under statute, the federal Interagency Working Group on Ocean Acidification (IWGOA) is chaired by a
representative from NOAA and includes representatives from the National Science Foundation; National Atmospheric
and Space Administration; Smithsonian Institution; National Institute of Standards and Technology (NIST) of the
Department of Commerce; EPA; Bureau of Indian Affairs (BIA), Bureau of Ocean Energy Management, National Park
Service, U.S. Fish and Wildlife Service, and U.S. Geological Survey of the Department of the Interior; U.S.
Department of Agriculture; Department of State; Department of Energy; Department of the Navy; and other agencies as
appropriate.
62 The Federal Ocean Acidification Research and Monitoring Act of 2009 (FOARAM; P.L. 111-11), as amended, does
not provide an authorization of appropriations for the National Aeronautics and Space Administration.
63 IWGOA was charged with developing a strategic research and monitoring plan to guide federal research on OA and
overseeing the plan’s implementation (33 U.S.C. §§3703(a)(2)). IWGOA is to submit an updated plan to Congress at
least once every five years (33 U.S.C. §§3703(c)(3)). According to NOAA, a revised plan is forthcoming (email
correspondence with NOAA Office of Legislative and Intergovernmental Affairs, August 17, 2022).
64 IWGOA, Strategic Plan for Federal Research and Monitoring of Ocean Acidification, March 2014, at
https://oceanacidification.noaa.gov/Portals/42/Images/IWGOA Strategic Plan.pdf.
65 For example, see NOAA Ocean Acidification Program, “Adaptation Strategies,” at
https://oceanacidification.noaa.gov/WhatWeDo/EducationOutreach/SOARCEWebinars/TabId/3463/PID/16157/evl/0/
CategoryID/207/CategoryName/adaptation-strategies/Default.aspx; and EPA, “What EPA Is Doing to Address Ocean
and Coastal Acidification,” at https://www.epa.gov/ocean-acidification/what-epa-doing-address-ocean-and-coastal-
acidification.
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hatcheries.66 The early warning system would alert hatchery managers when upwelling produced
relatively colder and lower pH seawater; managers could then time when coastal waters were
pumped into the hatchery’s oyster larvae tanks to avoid harming the hatcheries. Such early
warning systems can help buffer the shellfish industry against OA; larvae grown at the hatchery
are sold to commercial shellfish growers. The 2022 FOARAM amendments further emphasized
mitigating OA’s impacts on marine ecosystems.67
The IWGOA’s 2016 report on implementation of the strategic plan identified multiple OA-related
activities across most of the IWGOA agencies.68 Of the seven thematic areas outlined in the 2014
strategic plan, most OA activities reported in 2016 were related to (1) research to understand
responses to OA and (2) monitoring of ocean chemistry and biological impacts.69 As of 2016 (the
latest update on implementation of the strategic plan), strategic plan actions remaining to be
addressed were (7) data management and integration.70
The IWGOA’s summary report for FY2016 and FY2017 (the most recent available), identified
funding levels by agency and research and monitoring activities by geographic area, with a focus
on locations of interest to the United States (Figure 3).71 In FY2017, total federal funding for OA
activities, including activities with a primary or secondary focus on OA, was approximately $45.7
million. Over the FY2012-FY2017 period, NSF and NOAA reported the highest amount of OA
activity funding in FY2017, with totals of $24.3 million and $19.3 million, respectively.72

66 NOAA, “Improving an Ocean Acidification Observation System in Support of Pacific Coast Shellfish Growers,” at
https://ioos.noaa.gov/project/turning-headlights-high/; and R. Kelly, “Narratives Can Motivate Environmental Action:
The Whiskey Creek Ocean Acidification Story,” Ambio, vol. 43 (2014).
67 P.L. 117-167, §10642(a)(4).
68 According to the report, the Smithsonian Institution and the Department of Energy’s Pacific Northwest National
Laboratory were not members of IWGOA in 2014, so their activities were not included in the 2016 implementation
plan. In addition, the U.S. Navy did not contribute to the document because its work on OA is “limited.” BIA’s
activities also were not included in the 2016 implementation plan; NIST’s activities were included (National Science
and Technology Council [NSTC] Subcommittee on Ocean Science and Technology, Implementation of the Strategic
Plan for Federal Research and Monitoring of Ocean Acidification, December 2016, p. 33, at
https://oceanacidification.noaa.gov/sites/oap-redesign/Documents/IWGOA/
OA%20Implementation%20Plan%20FINAL.pdf [hereinafter referred to as NSTC, Implementation Report, December
2016]).
69 NSTC, Implementation Report, December 2016, p. 3.
70 Ibid.
71 IWGOA, Fifth Report on Federally Funded Ocean Acidification Research and Monitoring Activities: Fiscal Years
2016 and 2017, January 28, 2020, p. 29, at https://oceanacidification.noaa.gov/Portals/42/
Federal%20OA%20report%20FY%2016%2017%20%20January%202020.pdf (hereinafter referred to as IWGOA,
Fifth Report, January 2020). IWGOA is to submit updated reports on implementation and funding to Congress every
two years (33 U.S.C. §§3703(c)(2)). According to NOAA, revised reports are forthcoming (email correspondence with
NOAA Office of Legislative and Intergovernmental Affairs, August 17, 2022).
72 IWGOA, Fifth Report, January 2020, p. 29.
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Figure 3. Trends in Federal Funding of Ocean Acidification Research and Monitoring
Activities, FY2012–FY2017

Source: CRS, using Interagency Working Group on Ocean Acidification (IWGOA), Third Report on Federally
Funded Ocean Acidification Research and Monitoring Activities, April 23, 2015, pp. 20 and 25-26, at
https://oceanacidification.noaa.gov/Portals/42/Images/
IWGOA%203rd%20Report%20on%20Federal%20Funding%202015%20FINAL%20REVISED.pdf; IWGOA, Fourth
Report on Federally Funded Ocean Acidification Research and Monitoring Activities, December 20, 2016, pp. 43, 48, and
50, at https://oceanacidification.noaa.gov/sites/oap-redesign/Documents/IWGOA/
Fourth%20Report%20on%20OA%20Research%20Monitoring%20FY%2014-15.pdf; and IWGOA, Fifth Report on
Federally Funded Ocean Acidification Research and Monitoring Activities: Fiscal Years 2016 and 2017, January 28, 2020,
p. 29, at https://oceanacidification.noaa.gov/Portals/42/
Federal%20OA%20report%20FY%2016%2017%20%20January%202020.pdf.
Notes: Fiscal year total funding for ocean acidification research and monitoring for all IWGOA member
agencies (Bureau of Ocean Energy Management, Environmental Protection Agency, Department of State,
National Aeronautics and Space Administration, National Oceanic and Atmospheric Administration [NOAA],
National Science Foundation [NSF], and U.S. Geological Survey; solid black line) and for the two agencies with
the most funding, NSF (dashed red line) and NOAA (dashed blue line). The IWGOA’s (fifth) summary report for
FY2016 and FY2017 provides the most recent publicly available funding levels and notes that the NSF
contributions are underreported. For example, ship support for NSF research activities is provided by NSF-
funded University National Oceanographic Laboratory System and is a major expense for OA activities; this
expense was not included in data used by CRS to create this figure.
What Are Recent Congressional Actions Addressing
Ocean Acidification?
In 2022, Congress enacted the Coastal and Ocean Acidification Research and Innovation Act of
2021 (P.L. 117-167, Title VI, Subtitle E), which amended FOARAM. The amendments included
 The addition of a coastal acidification definition and broadening of agency
activities to consider coastal acidification73
 The establishment of an advisory board to IWGOA

73 FOARAM only defined ocean acidification. The Coastal and Ocean Acidification Research and Innovation Act of
2021 (P.L. 117-167) amended the ocean acidification definition in FOARAM and defined coastal acidification as “the
decrease in pH and changes in the water chemistry of coastal oceans, estuaries, and Great Lakes from atmospheric
pollutions, freshwater inputs, and excess nutrient run-off from land.”
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 A greater research focus on OA adaptation and mitigation strategies, on how OA
may interact with other environmental stressors, and on the socioeconomic
impacts of OA
 Authorization of appropriations for FY2023 through FY2027
In FY2022, Congress appropriated $16 million to NOAA for the Integrated Ocean Acidification
Program.74 Language accompanying the FY2022 appropriations act directed the program to
prioritize efforts on “understanding, monitoring, and mitigating coastal ocean acidification,
especially where it impacts fisheries and aquaculture”; to provide grants to nonfederal partners to
operate “regional-scale research and education centers to address the impacts” of OA; and to
establish a prize competition to “stimulate innovation” to advance understanding, research, or
monitoring of OA and its impacts or to develop management or adaptation options for responding
to OA.75
Other bills regarding OA have been introduced in the 117th Congress. Some would direct the
Secretary of Commerce or NOAA to work with the National Academies of Sciences,
Engineering, and Medicine to examine the impact of OA and other environmental stressors on
estuarine environments.76 Another bill would direct NOAA to support state and local OA
vulnerability assessments and strategic research planning related to OA and its impacts on coastal
communities, among other OA activities.77 Some bills would include OA and its impacts as part
of broader climate change impacts or physical risks to be addressed in certain ways.78 In addition,
proposed language to accompany House and Senate appropriations acts for FY2023 would
increase funding for NOAA’s Integrated Ocean Acidification Program.79 The House committee
report would support a prize competition to stimulate OA-related innovation,80 and the Senate

74 “Explanatory Statement Submitted by Ms. DeLauro, Chair of the House Committee on Appropriations, Regarding
the House Amendment to the Senate Amendment to H.R. 2471, Consolidated Appropriations Act, 2022,”
Congressional Record, vol. 168, No. 42 - Book III (March 9, 2022), p. H1778 (hereinafter referred to as explanatory
statement accompanying P.L. 117-103).
75 U.S. Congress, House Committee on Appropriations, Commerce, Justice, Science, and Related Agencies
Appropriations Bill, 2022, Report Together with Minority Views to Accompany H.R. 4505, 117th Cong., 1st sess., July
19, 2021, H.Rept. 117-97, p. 43. The explanatory statement accompanying the 2022 Consolidated Appropriations Act
states that the “agreement adopts House language regarding the Integrated Ocean Acidification Program” (explanatory
statement accompanying P.L. 117-103, p. H1779).
A prize competition to stimulate innovation in understanding and addressing OA was proposed in other legislation,
such as H.R. 3764, Section 1011, and H.R. 6061.
76 For example, H.R. 2533 (passed the House May 18, 2021) and H.R. 3764, Section 1406 (ordered to be reported by
the House Committee on Natural Resources).
77 For example, H.R. 3764, Section 1001 (ordered to be reported by the House Committee on Natural Resources).
78 For example, H.R. 1187 (passed the House June 16, 2021), H.R. 2570 (reported by the House Committee on
Financial Services), H.R. 2780 (ordered to be reported by the House Committee on Natural Resources), H.R. 2872
(ordered to be reported by the House Committee on Natural Resources), and S. 1217 (Senate Committee on Banking,
Housing, and Urban Affairs hearings held).
79 U.S. Congress, House Committee on Appropriations, Commerce, Justice, Science, and Related Agencies
Appropriations Bill, 2023, Report Together with Minority Views to Accompany H.R. 8256, 117th Cong., 2nd sess., June
30, 2022, H.Rept. 117-395, p. 43 (hereinafter referred to as H.Rept. 117-395); and draft Explanatory Statement for
Commerce, Justice, Science, and Related Agencies Appropriations Bill, 2023, as posted on the Senate Committee on
Appropriations website, July 28, 2022, at https://www.appropriations.senate.gov/news/majority/breaking-chairman-
leahy-releases-fiscal-year-2023-senate-appropriations-bills (hereinafter referred to as draft Senate Explanatory
Statement, 2023).
80 H.Rept. 117-395.
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draft explanatory statement would direct NOAA to work with nonfederal entities on research to
complete FOARAM-mandated federal vulnerability assessments.81

Author Information

Caitlin Keating-Bitonti
Eva Lipiec
Analyst in Natural Resources Policy
Analyst in Natural Resources Policy

Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan
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under the direction of Congress. Information in a CRS Report should not be relied upon for purposes other
than public understanding of information that has been provided by CRS to Members of Congress in
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81 Draft Senate Explanatory Statement, 2023.
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