# Selected Potential Considerations with Respect to Marine Carbon Dioxide Removal: In Brief

> Briefs, arguments, decisions, and more.

URL: https://www.frixlaw.com/law-library/documents/crs%3AR48159

## Record

- **Collection:** Congressional research report
- **Document type:** Reports
- **Published:** March 10, 2025
- **Citation:** R48159

## Text

Selected Potential Considerations with
Respect to Marine Carbon Dioxide Removal:
In Brief
Updated March 10, 2025

Congressional Research Service
https://crsreports.congress.gov
R48159

Selected Potential Considerations with Respect to Marine Carbon Dioxide Removal

Contents
Overview of Marine Carbon Dioxide Removal Approaches .................................................... 2
Biological Pathway Approaches ......................................................................................... 2
Chemical Pathway Approaches........................................................................................... 3
Considerations for Congress ..................................................................................................... 4
Permitting for Marine Carbon Dioxide Projects ................................................................. 4
Federal Research for Marine Carbon Dioxide Removal ..................................................... 6

Tables
Table 1. Selected Potential Co-benefits and Negative Impacts of Marine Carbon Dioxide
Removal Approaches.................................................................................................................. 10

Contacts
Author Information........................................................................................................................ 12

Selected Potential Considerations with Respect to Marine Carbon Dioxide Removal

T

he Intergovernmental Panel on Climate Change (IPCC) states in its Sixth Assessment
Report that “human activities, principally through emissions of greenhouse gases, have
unequivocally caused global warming.”1 The IPCC projects average global warming
“more likely than not” will continue to increase in the near term (through 2040) under the lowest
greenhouse gas (GHG) emission scenarios considered.2 Both the IPCC’s Sixth Assessment Report
and the U.S. Global Change Research Program’s Fifth National Climate Assessment state that
carbon dioxide removal (CDR) approaches, in addition to other efforts, are likely needed to
mitigate rising atmospheric carbon dioxide (CO2) and the associated impacts of climate change
(e.g., increasing average global temperature, rising sea levels, increasingly severe weather
events).3 According to experts, to be effective, CDR approaches must remove CO2 from the
atmosphere and durably store carbon for prolonged periods of time.4
The ocean is a major component of the global climate system, serving as a planetary reservoir of
heat, water, and carbon. The IPCC estimates that the ocean has taken up and stored between 18%
and 28% of anthropogenic CO2 emissions over the past 60 years.5 Scientists have investigated
how marine CDR (mCDR, also referred to as ocean or ocean-based CDR) approaches may
augment the ocean’s natural ability to absorb atmospheric CO2 and store carbon for extended
periods of time in coastal and ocean environments.6
Interest from various stakeholders in the use of mCDR to mitigate rising atmospheric CO2 levels
is growing. For example, the National Oceanic and Atmospheric Administration’s (NOAA’s)
Office of National Marine Sanctuaries reports that it has received an increased number of external
inquiries about mCDR deployment in national marine sanctuaries.7 To this end, in 2023, the
Biden Administration identified obtaining new information about the “safest and most effective
approaches” to mCDR as a high priority and established the Marine Carbon Dioxide Removal
Fast Track Action Committee (mCDR FTAC).8 The mCDR FTAC’s charter acknowledged the
“urgent need to resolve key knowledge gaps for different [mCDR] techniques.”9 In the 118th
1 For example, Intergovernmental Panel on Climate Change (IPCC), “Summary for Policymakers,” in Synthesis Report.

Contribution of Working Groups I, II, and III to the Sixth Assessment Report of the Intergovernmental Panel on
Climate Change, eds. Core Writing Team, Hoesung Lee, and José Romero, 2023, p. 4. Hereinafter IPCC, “Summary
for Policymakers.”
2 IPCC, “Summary for Policymakers,” p. 12.
3 Sarah Cooley et al., “Chapter 3: Oceans and Coastal Ecosystems and Their Services,” in Climate Change 2022:
Impacts, Adaptation and Vulnerability, eds. Hans-Otto Pörtner et al., 2022, p. 464; and Steven J. Davis et al., “Chapter
32: Mitigation,” in Fifth National Climate Assessment, eds. Allison R. Crimmins et al., 2023, p. 21.
4 For example, see Prati Rosen et al., Guidance for the Potential Application of Marine Carbon Dioxide Removal
(mCDR) in U.S. National Marine Sanctuaries, National Oceanic and Atmospheric Administration (NOAA), Office of
National Marine Sanctuaries, June 2023, p. 3 (hereinafter Rosen et al., Marine Carbon Dioxide Removal); and Jessica
N. Cross et al., Strategy for NOAA Carbon Dioxide Removal Research: A White Paper Documenting a Potential NOAA
CDR Science Strategy as an Element of NOAA’s Climate Interventions Portfolio, NOAA Special Report, May 2023, p.
22 (hereinafter Cross et al., Strategy for NOAA Carbon Dioxide Removal Research).
5 B. Fox-Kemper et al., “Chapter 5: Ocean, Cryosphere and Sea Level Change,” in Climate Change 2021: The Physical
Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on
Climate Change, eds. V. Masson-Delmotte et al., (Cambridge University Press, 2021), p. 1236.
6 For example, see National Academies of Sciences, Engineering, and Medicine (NASEM), A Research Strategy for
Ocean-Based Carbon Dioxide Removal and Sequestration (Washington, DC: The National Academies Press, 2022)
(hereinafter NASEM, Research Strategy for Ocean-Based Carbon Dioxide Removal and Sequestration).
7 Rozen et al., Marine Carbon Dioxide Removal (mCDR) in U.S. National Marine Sanctuaries, p. 1.
8 White House, “Marine Carbon Dioxide Removal: Potential Ways to Harness the Ocean to Mitigate Climate Change,”
October 6, 2023.
9 Charter of the Marine Carbon Dioxide Removal Fast Track Action Committee of the Subcommittee on Ocean Science
and Technology, National Science and Technology Council, September 2023, p. 2 (hereinafter mCDR FTAC Charter).
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Congress, congressional interest in mCDR primarily focused on advancing mCDR research,
development, and demonstration (RD&D).10 No legislation related to mCDR had been introduced
in the 119th Congress as of March 10, 2025.
The study of mCDR is a relatively new field. In light of growing interest in mCDR, this In Brief
provides an overview of different mCDR approaches and discusses some outstanding related
research questions. These questions may be informed by additional RD&D, including controlled
field experiments. Congress also may consider laws applicable to the various mCDR approaches
and the potential challenges, if any, researchers may encounter in conducting RD&D, including
field experiments in the U.S exclusive economic zone (EEZ).11

Overview of Marine Carbon Dioxide Removal Approaches
mCDR approaches generally are categorized into those that enhance or accelerate marine
biological pathways or chemical pathways.12

Biological Pathway Approaches
Approaches that manipulate marine biological pathways enhance the uptake of atmospheric CO2
by increasing the growth of marine plants (i.e., micro- and macroalgae). These mCDR biological
pathway approaches include the following:
•

•

Artificial Upwelling. This approach relies on a technological intervention to
transport cold, nutrient-rich ocean waters from the deep ocean to the surface.
Cold, nutrient-rich waters can stimulate primary producers (i.e., phytoplankton)
to take up CO2 via photosynthesis. Once dead, the primary producers may sink
into the ocean, transporting carbon out of the surface ocean. A small portion of
this carbon may be buried in ocean sediments for up to 100 years.13
Artificial Downwelling. This approach relies on a technological intervention to
transport relatively warm and CO2-rich surface waters, as well as the primary
producers (i.e., phytoplankton) living in the surface waters, to water depths
below the pycnocline (generally between 500 and 1,000 meters below the ocean
surface) for the purpose of storing downwelled CO2 in the deep ocean and
burying carbon associated with dead primary producers in ocean sediments for
up to 100 years.14

The charter determined that the mCDR FTAC “shall terminate no later than 14 months after the date of approval.” The
mCDR FTAC terminated on November 15, 2024.
10 For example, see S. 1576, H.R. 5457/S. 2812, H.R. 7054, H.R. 7797, and H.R. 10471/S. 5629.
11 For example, Clear Path, “Ocean CDR Permitting and Regulations 101,” https://clearpath.org/tech-101/ocean-cdrpermitting-and-regulations-101/. Hereinafter Clear Path, “Ocean CDR Permitting and Regulations 101.” The U.S.
exclusive economic zone is the ocean area located generally between 3 and 200 nautical miles from the shoreline
(White House, “Proclamation 5030: Exclusive Economic Zone of the United States of America,” 48 Federal Register
10605, March 10, 1983).
12 For example, Lennart T. Bach et al., “Implementation of Marine CO Removal for Climate Mitigation: The
2
Challenges of Additionality, Predictability, and Governability,” Elementa, vol. 12, no. (1), pp.1-16, see p. 2 (hereinafter
Bach et al., “Implementation of Marine CO2 Removal for Climate Mitigation”); and Rosen et al., Marine Carbon
Dioxide Removal, p. 3.
13 For example, Cross et al., Strategy for NOAA Carbon Dioxide Removal Research, p. 22; and NASEM, Research
Strategy for Ocean-Based Carbon Dioxide Removal and Sequestration, p. 111.
14 For example, S. Zhou and P.C. Flynn, “Geoengineering Downwelling Ocean Currents: A Cost Assessment,” Climate
(continued...)

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•

•

Macroalgal (Seaweed) Cultivation. This approach uses fast-growing marine
plants to take up CO2 via photosynthesis.15 In order for this to be a successful
mCDR technique, these plants cannot be harvested for food or other uses (e.g.,
fertilizers, feed and fuel for land activities), and, once dead, these plants must
sink and be buried in ocean sediments.16 Depending on the offshore environment,
such carbon may be stored in ocean sediments for decades to millennia.17
Ocean Fertilization. This approach adds micro- (iron) or macronutrients
(nitrogen or phosphorous) to the surface ocean. These nutrients can stimulate
primary producers (i.e., phytoplankton) to take up CO2 via photosynthesis. Once
dead, the primary producers may sink into the ocean, transporting carbon out of
the surface ocean. A small portion of this carbon may be buried in ocean
sediments for centuries to millennia.18

Chemical Pathway Approaches
Approaches that manipulate marine chemical pathways alter the natural air-sea gas exchange by
changing seawater alkalinity (i.e., the ocean’s ability to resist pH changes). These approaches aim
to change seawater alkalinity so the ocean can absorb more CO2.19 mCDR approaches that
augment marine chemical pathways include the following:
•

•

Direct Ocean Removal. This approach relies on technologies to remove and
capture CO2 directly from seawater by changing the pH of the treated water. The
treated (decarbonized) water is returned to the surface ocean, where it can absorb
more CO2.20
Ocean Alkalinity Enhancement (OAE). OAE alters seawater alkalinity either
by adding alkaline minerals to increase the ocean’s ability to absorb atmospheric
CO2 or by using electricity to split seawater into its acidic and basic
components.21 In the absence of processes that remove the added alkalinity, some
have proposed OAE can sequester CO2 on timescales of millennia or longer.22

Change, vol. 71, no. 1 (2005), pp. 203-220, see p. 204; Cross et al., Strategy for NOAA Carbon Dioxide Removal
Research, p. 22; and NASEM, Research Strategy for Ocean-Based Carbon Dioxide Removal and Sequestration, p.
111. The pycnocline is a layer in the ocean marking a sharp density (i.e., temperature and salinity) change.
15 For example, Cross et al., Strategy for NOAA Carbon Dioxide Removal Research, pp. 34-35; and NASEM, Research
Strategy for Ocean-Based Carbon Dioxide Removal and Sequestration, p. 3.
16 Seaweed harvested for food or fertilizer sequesters carbon on the order of months to a few years (i.e., shorter than the
timeframe required for carbon dioxide removal [CDR]) and allows sequestered carbon to be reemitted back to the
atmosphere. M. Troell et al., “Farming the Ocean—Seaweeds as a Quick Fix for the Climate?,” Reviews in Fisheries
Science and Aquaculture, vol. 31, no. 3 (2023), pp. 285-295.
17 For example, Cross et al., Strategy for NOAA Carbon Dioxide Removal Research, p. 35; and Rosen et al., Marine
Carbon Dioxide Removal, p. 4.
18 For example, NASEM, Research Strategy for Ocean-Based Carbon Dioxide Removal and Sequestration, p. 77. For
more information about ocean iron fertilization, see CRS Report R47172, Geoengineering: Ocean Iron Fertilization,
by Caitlin Keating-Bitonti.
19 Cross et al., Strategy for NOAA Carbon Dioxide Removal Research, p. 33; and Bach et al., “Implementation of
Marine CO2 Removal for Climate Mitigation,” p. 3.
20 For example, Cross et al., Strategy for NOAA Carbon Dioxide Removal Research, pp. 40-41.
21 U.S. Environmental Protection Agency (EPA), “About mCDR and mSRM,” https://www.epa.gov/ocean-dumping/
about-mcdr-and-msrm (hereinafter EPA, “About mCDR and mSRM”); NASEM, Research Strategy for Ocean-Based
Carbon Dioxide Removal and Sequestration, p. 3; and Cross et al., Strategy for NOAA Carbon Dioxide Removal
Research, p. 38.
22 NASEM, Research Strategy for Ocean-Based Carbon Dioxide Removal and Sequestration, p. 185.

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Considerations for Congress
Limited experimentation, including a lack of controlled field experiments,23 for many mCDR
approaches creates uncertainties regarding the efficacy, cost, potential co-benefits, and potential
negative impacts of full-scale deployment of mCDR approaches.24 On February 23, 2024, the
National Science Foundation (NSF), acting through the mCDR FTAC, sought input from all
interested stakeholders to inform the development of an implementation plan to advance mCDR
research.25 In its notice, NSF stated, “As of yet, however, no marine CDR methods are considered
ready for full-scale deployment or commercial application.”26 Some stakeholders contend that
small-scale proof-of-concept field testing is necessary to quantify CDR potential (i.e., efficacy) as
well as the potential co-benefits and negative impacts associated with different mCDR
approaches.27
Federal RD&D and federally funded research may elucidate whether mCDR approaches are
effective and at what scale. Some stakeholders may question the relative priority of mCDR
RD&D compared with other federal activities, such as existing programs that support more
technologically mature CDR options or GHG emissions reductions.28 Others may invoke a moral
hazard argument against CDR because they prefer policies and actions to reduce GHG emissions
prioritized over those aimed at removing emitted GHG from the atmosphere.29 If Congress is
interested in directing federal agencies to conduct and advance mCDR RD&D or to support
nonfederal RD&D, it could consider several policy approaches, including identifying a permitting
framework for mCDR RD&D in the U.S. EEZ.

Permitting for Marine Carbon Dioxide Projects
Some stakeholders contend that scaling and accelerating mCDR RD&D is unlikely to happen
without a regulatory framework that facilitates controlled field experiments.30 Either a field-based
demonstration or a fully deployed mCDR project likely would require compliance with certain
state, federal, and/or international regulations, depending on the mCDR approach and the
23 For example, according to NASEM, artificial downwelling has never been tested in the field as means of CDR.

NASEM, Research Strategy for Ocean-Based Carbon Dioxide Removal and Sequestration, p. 105.
24 For example, see National Science Foundation (NSF), “Marine Carbon Dioxide Removal Research Plan,” 89 Federal
Register 13755-13757, February 23, 2024 (hereinafter NSF, “Marine Carbon Dioxide Removal Research Plan”); Cross
et al., Strategy for NOAA Carbon Dioxide Removal Research, pp. 13 and 17; and EPA, “About mCDR and mSRM.”
25 NSF, “Marine Carbon Dioxide Removal Research Plan.” NSF sought feedback to advance a recommendation of the
Biden Administration’s Ocean Climate Action Plan (White House Ocean Policy Committee, Ocean Climate Action
Plan: A Report by the Ocean Policy Committee, March 2023, pp. 41-43).
26 NSF, “Marine Carbon Dioxide Removal Research Plan.”
27 For example, Hongjie Wang et al., “Simulated Impact of Ocean Alkalinity Enhancement on Atmospheric CO
2
Removal in the Bering Sea,” Earth’s Future, vol. 11, no. 1 (2022), pp. 1-17; and Clear Path, “Ocean CDR Permitting
and Regulations 101.”
28 For example, direct air capture (DAC) removes CO from the atmosphere and stores the carbon in a stable or long2
lived reservoir. For more information about DAC, see CRS In Focus IF11501, Carbon Capture Versus Direct Air
Capture, by Ashley J. Lawson. As another example, soil carbon sequestration approaches, including certain land-use
activities, involve removing CO2 from the atmosphere (primarily mediated by plants through photosynthesis) and
storing it in the soil carbon pool. For more information about soil carbon sequestration, see CRS In Focus IF11693,
Agricultural Soils and Climate Change Mitigation, by Megan Stubbs.
29 For example, Institute for Policy Integrity, Consensus on Carbon Dioxide Removal: A Large-Sample Expert
Elicitation on the Future of CDR, July 2024, p. 36.
30 Ocean Visions, “A Comprehensive Program to Prove or Disprove Marine Carbon Dioxide Removal Technologies by
2030,” p. 2. Hereinafter Ocean Visions, “A Comprehensive Program to Prove or Disprove Marine Carbon Dioxide
Removal Technologies by 2030.”

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project’s location. Proposals for mCDR projects within the U.S. EEZ could be subject existing
laws, such as the Marine Protection, Research, and Sanctuaries Act (MPRSA; P.L. 92-532); the
Coastal Zone Management Act (P.L. 109-58); Section 10 of the Rivers and Harbors Act of 1899
(33 U.S.C. §403); the Clean Water Act (33 U.S.C. §1251 et seq.); and the Magnuson-Stevens
Fishery Conservation and Management Act (MSA; 16 U.S.C. §1801 et seq.), among others. For
example, the MSA requires federal agencies to consult with NOAA on activities that may
adversely affect essential fish habitat.31 As another example, the MPRSA, also known as the
Ocean Dumping Act, regulates the transportation and “dumping” of any material—which may
include alkalinity enhancement materials—into ocean waters (see textbox, below).32
Congress has not authorized mCDR projects in law. Should Congress support testing of mCDR
projects, it could take different approaches. Congress could amend existing laws to specifically
address mCDR broadly (or selected mCDR approaches). Alternatively, Congress could consider
new legislation that provides a framework for mCDR projects deployed within the U.S. EEZ or
regulates the scale and siting of a project to limit the potential impact on waters adjacent to the
EEZ. For example, H.R. 5457/S. 2812 in the 118th Congress would have directed NSF, in
collaboration with other federal agencies, to “award funding for research into governance
frameworks for safe and sustainable experimentation” with mCDR.33
U.S. Environmental Protection Agency Permits for Ocean Alkalinity Enhancement
The U.S. Environmental Protection Agency (EPA) has clarified that marine carbon dioxide removal (mCDR)
activities, such as ocean alkalinity enhancement (OAE), may require a permit under either the Clean Water Act
(33 U.S.C. §1251 et seq.) or the Marine Protection, Research and Sanctuaries Act (MPRSA, also known as the
Ocean Dumping Act; P.L. 92-532). The applicability of these EPA-administered statutes depends on case-specific
aspects of the mCDR activity (e.g., the type and location).
In May 2024, EPA published a public notice of its tentative determinations to issue two research permits to
Woods Hole Oceanographic Institution (WHOI) pursuant to MPRSA for two sequential research projects (i.e.,
LOC-NESS Phase 1 and LOC-NESS Phase 2) to collect information on the feasibility, potential benefits, and
potential adverse impacts of a ship-based OAE project. The research study was proposed to take place at two
locations offshore of Massachusetts. In November 2024, WHOI researchers withdrew their permit application for
LOC-NESS Phase 1 and updated the application for LOC-NESS Phase 2. In January 2025, EPA updated its tentative
permit for LOC-NESS Phase 2. Under MPRSA, EPA may issue research permits for a period up to 18 months for
the transportation and disposition of materials into the ocean as part of a research study when it is determined
that the scientific merit of the proposed research study outweighs the potential environmental or other damage
that may result from the activities (33 U.S.C. §1412; 40 C.F.R. §220.3(e)). If EPA finalizes the permits for WHOI, it
would be EPA’s first use of such research permits for mCDR activities.
Sources: EPA, “Permitting for mCDR and mSRM,” https://www.epa.gov/ocean-dumping/permitting-mcdrand-msrm; EPA, “LOC-NESS Project Overview and Permitting Status,” https://www.epa.gov/ocean-dumping/
loc-ness-project-overview-and-permitting-status; and WHOI, “The LOC-NESS Project,”
https://locness.whoi.edu/.

31 16 U.S.C. §1855(b). The Magnuson-Stevens Fishery Conservation and Management Act, under 16 U.S.C. §1802(10)

defines essential fish habitat as “those waters and substrate necessary to fish for spawning, breeding, feeding or growth
to maturity.”
32 The Marine Protection, Research, and Sanctuaries Act (MPRSA; P.L. 92-532, 33 U.S.C. §§1401 et seq.) defines
dumping to mean the disposition of a “material,” which the statute defines broadly as “matter of any kind or
description,” with some specific exclusions. The MPRSA authorizes the U.S. Army Corps of Engineers to issue permits
under the MPRSA for dredged materials. EPA is the permitting authority for all other materials.
33 §905 of H.R. 5457/S. 2812.

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Federal Research for Marine Carbon Dioxide Removal
Several federal agencies have existing mandates, programs, and activities that intersect with
mCDR research. NOAA has acknowledged that it has “capabilities that can be applied to
understand and assess CDR.”34 For example, NOAA’s Ocean Acidification Program conducts and
funds research, monitoring, and other activities to develop mitigation strategies to address ocean
acidification, among other purposes.35 Some mCDR approaches, such as OAE, have the potential
to mitigate ocean acidification.36 The Department of Energy’s (DOE’s) Office of Fossil Energy
and Carbon Management (FECM) identified CDR as a priority area.37 For FY2025, DOE
requested $237.5 million for CDR activities.38 On June 6, 2024, DOE and NOAA signed a
memorandum of agreement to collaborate on mCDR RD&D.39
Within agencies, Congress may consider designating an existing program (or office) or creating a
new program to lead mCDR RD&D activities for the agency.40 For example, within DOE,
Congress could designate FECM, designate another office, or create a new office to lead mCDR
activities. Several Members introduced legislation in the 118th Congress that would have directed
certain agencies to establish mCDR RD&D programs (e.g., H.R. 5457/S. 2812, H.R. 7797) or
amend existing programs to include mCDR approaches as part of their RD&D programs (e.g., S.
1576). Additionally, H.R. 10471/S. 5629 in the 118th Congress would have established a research
and competitive grant program in NOAA to advance the science and understanding of mCDR. It
also would have established mCDR-related programs at NSF, the National Aeronautics and Space
Administration (NASA), and for the National Institute of Standards and Technology.
Congress also could designate a federal agency to coordinate federal mCDR RD&D activities or
establish an interagency working group (IWG) for this purpose. Some stakeholders have
proposed NOAA lead on federal mCDR research and coordination.41 In the 118th Congress, S.
2002 and H.R. 9212 would have established the Interagency Group on Large-Scale Carbon
Management in the National Science and Technology Council for the purpose of developing a
federal strategic plan for CDR RD&D and coordinating federal CDR activities.42 H.R. 10471/S.
5629 in the 118th Congress also proposed the creation of an interagency working group for mCDR
that would have been cochaired by NOAA and DOE. Alternatively, Congress could amend
34 Cross et al., Strategy for NOAA Carbon Dioxide Removal Research, p. 17.
35 NOAA requested $17.1 million for its Integrated Ocean Acidification line item for FY2025 (NOAA, FY2025

Congressional Budget Justification, p. OAR-58). In 2022, Congress passed the Coastal and Ocean Acidification
Research and Innovation Act of 2021 (P.L. 117-167, Division B, Title VI, Subtitle E), which amended Federal Ocean
Acidification Research and Monitoring Act of 2009 (FOARAM Act; P.L. 111-11). As amended, FOARAM Act
directed the Secretary of Commerce to establish an ocean acidification program (33 U.S.C. §3705). For more
information, see CRS Report R47300, Ocean Acidification: Frequently Asked Questions, by Caitlin Keating-Bitonti
and Eva Lipiec.
36 Cross et al., Strategy for NOAA Carbon Dioxide Removal Research, p. 39.
37 Department of Energy (DOE), Office of Fossil Energy and Carbon Management (FECM), “Mission,”
https://www.energy.gov/fecm/mission. For more information on FECM’s carbon dioxide removal activities, see CRS
In Focus IF11861, DOE’s Carbon Capture and Storage (CCS) and Carbon Removal Programs, by Ashley J. Lawson.
38 CDR funding would be drawn from DOE’s Office of Fossil Energy and Carbon Management ($130.2 million),
Office of Energy Efficiency and Renewable Energy ($13.3 million), and Office of Science ($94.0 million).
DOE, FY2025 Congressional Justification, vol. 2, March 2024, p. 241.
39 NOAA, “NOAA, DOE Sign Agreement to Advance Marine Carbon Dioxide Removal,” June 6, 2024,
https://www.noaa.gov/news-release/noaa-doe-sign-agreement-to-advance-marine-carbon-dioxide-removal.
40 For example, see Center for the Blue Economy, Turning the Tide, p. 39.
41 For example, see Center for the Blue Economy, Turning the Tide, p. 39.
42 The agencies responsible for focusing on mCDR activities under the Interagency Group would be NOAA, National
Aeronautics and Space Administration, Department of Defense, NSF, Department of the Interior, and EPA.

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existing laws to broaden the scope of an existing IWG, such as the IWG on Ocean Acidification,
to explicitly include mCDR research activities.43 In addition to reducing potential duplication
across federal agencies, improved federal coordination on mCDR activities could yield research
results that inform whether mCDR approaches are effective.44
The private sector may be reluctant to fund mCDR activities until the risks and benefits are better
understood. In the absence of private sector support, agencies such as DOE, NOAA, and NSF
have provided funding to support external and/or joint (federal and nonfederal) projects aimed at
advancing mCDR RD&D.45 In addition to H.R. 10471/S. 5629, some Members introduced other
legislation in the 118th Congress that would have directed certain federal agencies to provide
funding for nonfederal research. For example, Section 101 of H.R. 5457/S. 2812 would have
directed DOE’s FECM to provide competitive demonstration awards for mCDR projects within
the U.S. EEZ, and Section 903 would direct NSF, in collaboration with other federal agencies, to
provide funds for mCDR research. Some stakeholders contend that recipients of federal funding
should be required to abide by a code of conduct designed to ensure researchers avoid, minimize,
mitigate, and monitor the environmental impacts of mCDR activities,46 as with DOE’s
Responsible Carbon Management Initiative.47

What Is the Effectiveness of Marine Carbon Dioxide Removal?
Results of some laboratory and modeling studies indicate that mCDR may be effective at
absorbing atmospheric CO2 and storing it in the ocean for prolonged periods of time.48 Some
stakeholders contend that controlled field experiments are needed to determine whether mCDR
approaches can lead to a net increase in ocean carbon storage.49 A controlled field experiment
may include (1) quantifying the rate at which carbon is taken up by the ocean (i.e., sequestration
rate); (2) monitoring and verifying carbon sequestration; (3) determining the permanence of
carbon sequestration; and (4) monitoring ecological and environmental shifts to demonstrate that

43 33 U.S.C. §3703. See Interagency Working Group on Ocean Acidification, Strategic Plan for Federal Research and

Monitoring of Ocean Acidification, September 2023, p. 19.
44 For more information about existing interagency working groups and committees as well as federal coordination on
research related to coastal CDR and mCDR, see CRS Report R48148, Coastal Blue Carbon as a Carbon Dioxide
Removal Approach: Selected Issues for Congress, by Caitlin Keating-Bitonti and Eva Lipiec.
45 For example, NOAA, “Announcing $24.3M Investment Advancing Marine Carbon Dioxide Removal Research,”
September 7, 2023, https://oceanacidification.noaa.gov/fy23-nopp-mcdr-awards/; DOE, “DOE Announces $36 Million
to Advance Marine Carbon Dioxide Removal Techniques and Slash Harmful Greenhouse Gas Pollution,” October 26,
2023, https://www.energy.gov/articles/doe-announces-36-million-advance-marine-carbon-dioxide-removal-techniquesand-slash; DOE, “U.S. Department of Energy Announces $45 Million to Validate Marine Carbon Dioxide Removal
Techniques,” February 16, 2023, https://arpa-e.energy.gov/news-and-events/news-and-insights/us-department-energyannounces-45-million-validate-marine-carbon-dioxide-removal-techniques; and NSF, “mCDR 2023: Data
Requirements for Quantifying Natural Variability and the Background Ocean Carbon Sink in Marine Carbon Dioxide
Removal (mCDR) Models,” https://www.nsf.gov/awardsearch/showAward?AWD_ID=2333608.
46 Center for the Blue Economy, Turning the Tide, pp. 38-39.
47 The Responsible Carbon Management Initiative encourages developers to “pursue the highest levels of safety,
environmental stewardship, accountability, community engagement, and societal benefits in carbon management
projects.” DOE, “Notice of Intent and Request for Information Regarding Launching a Responsible Carbon
Management Initiative,” 88 Federal Register 54608, August 11, 2023.
48 For example, Bach et al., “Implementation of Marine CO Removal for Climate Mitigation, p. 4.
2
49 For example, Cross et al., Strategy for NOAA Carbon Dioxide Removal Research, pp. 38, 40, 67; NASEM, Research
Strategy for Ocean-Based Carbon Dioxide Removal and Sequestration, p. 239; Ocean Visions, “A Comprehensive
Program to Prove or Disprove Marine Carbon Dioxide Removal Technologies by 2030,” pp. 2-4.

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the approach is effective while minimizing impacts. This research may be challenging, because
“extremely precise measurements are required to detect a small [carbon] removal signal.”50
Several federal agencies have established programs to collect ocean data that may be applicable
to monitoring and verifying carbon removal (e.g., NOAA, NASA, U.S. Geological Survey).51 To
accelerate the development of “marine carbon sensor technologies operating across spatial and
temporal scales broad enough to sufficiently understand mCDR,” among other research
questions, the Advanced Research Projects Agency-Energy established the Sensing Exports of
Anthropogenic Carbon Through Ocean Observation (SEA-CO2) program.52 SEA-CO2 has
supported at least 11 projects.53 Congress may consider whether the current federal investment in
ocean monitoring and observational instruments is sufficient to provide accurate information
about the efficiency of mCDR.

What Is the Cost of Marine Carbon Dioxide Removal?
Experts have estimated the cost per ton of carbon removal ($/tCO2 removed) for future at-scale
deployment for the different mCDR approaches.54 Approaches proposed to have a low-tomoderate cost include macroalgal cultivation ($25-$125/tCO2 removed), ocean alkalinity
enhancement ($25-$160/tCO2 removed), and ocean fertilization ($50-$125/tCO2 removed).55
Artificial upwelling and downwelling are proposed to have a moderate cost ($100-$150/tCO2
removed), and direct ocean removal is proposed to have a high cost ($400-$600/tCO2 removed).56
Direct air capture CDR is estimated to cost $40-$1,000/tCO2 removed.57 Some stakeholders may
contend the cost for full-scale deployment of mCDR should be compared with the costs of a noaction alternative, such as the economic costs associated with climate-related risks and impacts.58
Some stakeholders have proposed goals for cost per ton of carbon removal for CDR. H.R. 7054,
introduced in the 118th Congress, would have directed DOE to determine if technologies to
remove CO2 directly from ambient air or seawater are economically feasible and provide a
roadmap for decreasing the cost per ton of carbon removal to no more than $150 by 2035, among
other research objectives.59 DOE’s Negative Carbon Shot aims to advance technologies that
reduce the cost of CDR approaches to less than $100/tCO2-equivalent removed.60

50 Cross et al., Strategy for NOAA Carbon Dioxide Removal Research, p. 20.
51 For an overview of federal programs engaged in ocean research, see CRS Report R47021, Federal Involvement in

Ocean-Based Research and Development, by Caitlin Keating-Bitonti.
52 The Advanced Research Projects Agency-Energy is a DOE office authorized by the America COMPETES Act (P.L.
110-69) to support transformational energy technology research projects. DOE, “Sensing Exports of Anthropogenic
Carbon through Ocean Observation,” https://arpa-e.energy.gov/technologies/programs/sea-co2.
53 DOE, “Sensing Exports of Anthropogenic Carbon through Ocean Observation.”
54 Cross et al., Strategy for NOAA Carbon Dioxide Removal Research, p. 22; and NASEM, p. 256.
55 Cross et al., Strategy for NOAA Carbon Dioxide Removal Research, p. 22.
56 Cross et al., Strategy for NOAA Carbon Dioxide Removal Research, p. 22.
57 Cross et al., Strategy for NOAA Carbon Dioxide Removal Research, p. 22.
58 For example, Climate Policy Initiative, “The Cost of Inaction,” https://www.climatepolicyinitiative.org/the-cost-ofinaction/.
59 §2(d)(1) of H.R. 7054 in the 118th Congress would have considered CDR “economically feasible if such removal can
be accomplished” under five different scenarios with specific timeframes with a cost per ton of carbon removal
($/tCO2) removed (e.g., not more than $750/tCO2 removed in FY2024-2025).
60 DOE, “Carbon Negative Shot,” https://www.energy.gov/fecm/carbon-negative-shot. For any quantity and type of
greenhouse gas (GHG), CO2 equivalent signifies the amount of CO2 which would have the equivalent global warming
impact based on the global warming potential of the GHG.

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Related to elements of cost, S. 5369 in the 118th Congress would have amended the Internal
Revenue Code of 1986 to establish a technology-neutral tax credit available to those investing in
U.S. next-generation CDR technologies (including “marine-based” CDR) among its proposed
provisions.

What Are Potential Co-benefits and Negative Impacts of Marine Carbon
Dioxide Removal?
Limited experimentation for many mCDR approaches provides uncertainties regarding the
potential ecological and environmental co-benefits and impacts associated with mCDR.61 For
example, over the past 30 years, at least 16 ocean fertilization experiments have taken place in the
open ocean.62 No field experiments have taken place for other mCDR approaches.63 Results from
these experiments led some stakeholders to assert that such efforts will have “unknown,
unpredictable, and potentially highly damaging impacts on the food web in marine ecosystems.” 64
The specific interactions and degree of impact of potential deleterious effects on the marine food
web and other ecological interactions remain unknown.
Some scientists, primarily through laboratory and modeling studies, have identified a range of
effects associated with mCDR approaches. Depending on the approach, these effects include
potential reduction in deep-sea oxygen levels,65 reduction in ocean acidification,66 and changes to
biochemical cycling with potential repercussions on marine ecosystems (Table 1). A study by
NOAA’s Office of National Marine Sanctuaries evaluated the level of risk associated with mCDR
approaches based on their level of potential negative environmental impacts. The study identified
ocean fertilization and OAE via accelerated weathering as having medium environmental risk. It
identified macroalgal cultivation, artificial upwelling and downwelling, and OAE via
electrochemical acid removal as having high environmental risk.67 Some bills introduced in the
118th Congress would have directed federal agencies to either conduct research examining the
potential impacts of mCDR or provide funding to nonfederal researches investigating these
impacts (e.g., H.R. 5457/S. 2812, S. 1576, H.R. 7797, and H.R. 10471/S. 5629).

61 In this context, environmental primarily refers to the physical and chemical (i.e., abiotic) environment and ecological

refers to biological interactions with the abiotic environment. A discussion of the social impacts and governance
challenges associated with mCDR are beyond the scope of this product. For an overview of social impacts and
governance challenges associated with mCDR, see NASEM, Research Strategy for Ocean-Based Carbon Dioxide
Removal and Sequestration.
62 Geoengineering Monitor, “Geoengineering Technology Briefing: Ocean Fertilization,” January 2021, p. 1,
https://www.geoengineeringmonitor.org/wp-content/uploads/2021/04/ocean-fertilization.pdf.
63 Geoengineering Monitor, “Geoengineering Technology Briefing: Ocean Fertilization,” p. 1.
64 Geoengineering Monitor, “Geoengineering Technology Briefing: Ocean Fertilization,” p. 2.
65 Anand Gnanadesikan et al., “Effects of Patchy Ocean Fertilization on Atmospheric Carbon Dioxide and Biological
Production,” Global Biogeochemical Cycles, vol. 17, no. 2 (2003), pp. 1-17.
66 For example, see ibid., pp. 37 and 39; and NASEM, Research Strategy for Ocean-Based Carbon Dioxide Removal
and Sequestration, pp. 6 and 200.
67 Rozen et al., Marine Carbon Dioxide Removal (mCDR) in U.S. National Marine Sanctuaries, pp. 6-10.

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Table 1. Selected Potential Co-benefits and Negative Impacts of Marine Carbon
Dioxide Removal Approaches
(listed in alphabetical order)
Approach
Artificial downwelling

Artificial upwelling

Potential Co-benefit(s)

Potential Negative Impact(s)

Increase ventilation of oxygen-poor
deepwater, countering hypoxiaa and
eutrophicationa

Alter food web interactions

Increase prey for fishes and higherorder consumers (e.g., marine
mammals) in the marine food web

In addition to the impacts listed above,

Reduce thermal stress in coral
ecosystems with cold upwelled
deepwater and abate coral bleaching

Alter atmospheric circulation and
precipitation patterns due to changes in
surface ocean temperatures

Alter physical oceanic processes, including
ocean circulation and density structure (i.e.,
stratification)

Increase surface temperature and
atmospheric CO2 to higher than pre-welling
conditions following the cessation of
artificial upwelling
Release deepwater CO2 to the atmosphere
prior to the onset of primary production
Direct ocean removalc

Captured CO2 can be turned into
commercial products
Captured CO2 can be used to
neutralize alkaline wastewater or
alkaline stormwater

Alter phytoplankton, invertebrate, and
vertebrate physiology, community
composition, and ecological interactions

Counter ocean acidificationd
Macroalgal (seaweed)
cultivation

Enhance closed-circuit finfish, shellfish,
and seaweed aquaculture, if cultivation
occurs near existing aquaculture
facilitiese
Counter ocean acidification (i.e., increase
pH by 0.01 unit per decade) in certain
geographic regionsd

Alter small-scale seawater processes,
including seawater exchange rates (i.e.,
between water masses) in a given area
Bury seafloor life with macroalgae
Cause deepwater hypoxiaa and eutrophicationa
Entangle marine animals
Increase seawater stagnation (i.e., inability
for seawater to mix with other water
masses)
Introduce disease, invasive species, and/or
parasites
Produce halocarbons by macroalgaef
Reduce light availability
Reduce nutrient availability
Reduce phytoplankton productivity with
potential impacts to higher-order consumers
throughout the water column

Ocean alkalinity
enhancement

Benefit calcifying organism (e.g.,
coccolithophores) if carbonate-derived
alkaline minerals are appliedg

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Selected Potential Considerations with Respect to Marine Carbon Dioxide Removal

Approach

Ocean fertilization

Potential Co-benefit(s)

Potential Negative Impact(s)

Benefit nitrogen-fixing organisms (e.g.,
cyanobacteria) if the mineral olivine is
applied

Alter natural chemical cycling and seawater
chemistry

Benefit organisms that grow silicate
structures (e.g., diatoms) if the mineral
olivine is applied

Alter phytoplankton, invertebrate, and
vertebrate physiology and potential
mortality

Counter ocean acidificationd

Increase turbidity and alter light availabilityh

Increase the sinking rate of feces of
organisms that ingest mineral particles,
thereby enhancing the export of carbon
to the deep ocean

Release trace metals, if alkaline minerals are
sourced from certain mines and industry

Counter ocean acidificationd
Increase prey for fishes and higherorder consumers (e.g., marine
mammals) in the marine food web
Enhance deep-sea biomass in certain
regions (due to increased supply of
organic matter on the seafloor)
Increase oxygen production in surface
waters temporarily

Alter food web interactions
Bury seafloor life due to increased rates of
particle deposition
Cause deepwater hypoxia or anoxiaa
Cause eutrophicationa
Cause nutrient robbingi
Cause deepwater ocean acidification (i.e.,
decrease pH by 0.1 unit) due to moving
atmospheric CO2 into the deep oceand
Cause toxic algal blooms
Enhance stratification due to the
phytoplankton bloom increasing seawater
temperature
Increase turbidity and alter light availability
during the resulting phytoplankton bloomh
Introduce toxic mine tailings to seawater if
iron filings are used
Produce GHGs (e.g., nitrous oxide,
methane)

Sources: Mustafa Babiker et al., “Cross-Sectoral Perspectives,” in Climate Change 2022: Mitigation of Climate
Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate
Change, eds. Priyadarshi R. Shukla et al. (Cambridge, UK: Cambridge University Press, 2022), pp. 1245-1354;
Lennart T. Bach et al., “Implementation of Marine CO2 Removal for Climate Mitigation: The Challenges of
Additionality, Predictability, and Governability,” Elementa, vol. 12, no. (1), pp. 1-16; Manon Berger et al., “Ocean
Dynamics and Biological Feedbacks Limit the Potential of Macroalgae Carbon Dioxide Removal,” Environmental
Research Letters, vol. 18, no. 2 (2023), 024039, pp. 1-13; Jessica N. Cross et al., Strategy for NOAA Carbon Dioxide
Removal Research: A White Paper Documenting a Potential NOAA CDR Science Strategy as an Element of NOAA’s
Climate Interventions Portfolio, NOAA Special Report, May 2023, pp. 1-81; National Academies of Sciences,
Engineering, and Medicine, A Research Strategy for Ocean-Based Carbon Dioxide Removal and Sequestration,
(Washington, DC: The National Academies Press, 2022); Prati Rosen et al., Guidance for the Potential Application of
Marine Carbon Dioxide Removal (mCDR) in U.S. National Marine Sanctuaries, National Oceanic and Atmospheric
Administration (NOAA), Office of National Marine Sanctuaries, June 2023; U.S. Environmental Protection
Agency, “About mCDR and mSRM,” https://www.epa.gov/ocean-dumping/about-mcdr-and-msrm; and Jiajun Wu,
David P. Keller, and Andreas Oschlies, “Carbon Dioxide Removal via Macroalgae Open-Ocean Mariculture And
Sinking: An Earth System Modeling Study,” Earth System Dynamics, vol. 14, no. 1 (2023), pp. 185-221.
Notes: CO2 = carbon dioxide; GHG = greenhouse gas; mCDR = marine carbon dioxide removal. The table
does not identify upstream or other lifecycle effects from the mCDR approach.
a. Hypoxia refers to water conditions that have dissolved oxygen levels below 2 milligrams per liter, and anoxia
refers to waters that are depleted of dissolved oxygen (NOAA, “Hypoxia,” https://oceanservice.noaa.gov/
hazards/hypoxia/).

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b.

c.

d.

e.

f.

g.
h.
i.

Some experts define eutrophication as “an increase in the rate of supply of organic matter to an ecosystem,”
which can promote the growth of algae through nutrient enrichment of coastal and marine systems.
Eutrophication may lead to hypoxia, fish kills, turbidity, and other consequences. For example, see Scott W.
Nixon, “Eutrophication and the Macroscope,” Hydrobiologia, vol. 629, no. 1 (2009), pp. 5-19.
In theory, the infrastructure for direct ocean capture can be deployed offshore to avoid competitive
nearshore use and also be powered by renewable energy sources. Some have proposed these two
deployment strategies as potential benefits of this mCDR approach.
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. One pH unit decrease equates to 10 times increase in
seawater acidity. For more information, see CRS Report R47300, Ocean Acidification: Frequently Asked
Questions, by Caitlin Keating-Bitonti and Eva Lipiec.
Some experts define closed (i.e., closed circuit or closed recirculating systems) aquaculture systems as those
where the water is reconditioned and recirculated to the culture unit(s) (e.g., tank or pond). For example,
see Thomas B. Lawson, “Aquaculture in Open Systems,” in Fundamentals of Aquaculture Engineering (Norwell,
MA: Kluwer Academic Publishers Group, 1995), p. 58.
Halocarbons are compounds that contain carbon, contain one or more halogens (e.g., fluorine, chlorine,
bromine), and may contain hydrogen. Their emissions are associated with stratospheric ozone depletion.
See O. Hodnebrog, K. Shine, and T. Wallington, “Halocarbons: What Are They and Why Are They
Important?,” EOS, vol. 101 (2020); and “H2,” in Bretherick’s Handbook of Reactive Chemical Hazards, ed. P. G.
Urben, 8th ed. (Cambridge, MA: Elsevier, 2017), pp. 1247-1260.
Enhanced calcification could have an increasing or decreasing effect on carbon removal.
Turbidity is a measure of the relative clarity of the water. Increased particles (e.g., sediment, phytoplankton)
in the water will increase the turbidity.
Nutrient robbing may occur when nutrients used by ocean fertilization biological production are not available
for biological production and CO2 uptake by surface ocean waters elsewhere.

Author Information
Caitlin Keating-Bitonti, Coordinator
Specialist Natural Resources Policy

Claire M. Jordan
Senior Research Librarian

Laura Gatz
Specialist in Environmental Policy

Anthony R. Marshak
Analyst in Natural Resources Policy

Disclaimer
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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/crs%3AR48159. Public record. Not legal advice.