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

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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Selected Potential Considerations with Respect to Marine Carbon Dioxide Removal

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

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Selected Potential Considerations with Respect to Marine Carbon Dioxide Removal

•

•

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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Selected Potential Considerations with Respect to Marine Carbon Dioxide Removal

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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Selected Potential Considerations with Respect to Marine Carbon Dioxide Removal

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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Selected Potential Considerations with Respect to Marine Carbon Dioxide Removal

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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