Introduction to Geoengineering

Carbon dioxide (CO₂) concentrations in the atmosphere have been rising largely due to human activities, such as the combustion of fossil fuels for transportation and electrical power generation. For each of the last four decades, as atmospheric CO₂ concentrations have continued to increase, average global temperatures have been successively warmer than in any preceding decade.¹ To limit, or mitigate, the rise of global temperatures, government policy measures typically have focused on reducing the emissions of CO₂ and other greenhouse gases (GHGs) to the atmosphere or enhancing the sinks that accumulate and store these gases.²

In 2021, the U.S. government, in an international declaration, stated its aim to be "on a path to achieve net-zero emissions, economy wide, by no later than 2050."³ Certain climate change mitigation studies generally find that removing CO₂ from the atmosphere will be necessary to achieve net-zero global emissions over specified timeframes.⁴

Geoengineering is a field of study that involves large-scale technological interventions to manipulate the processes that affect Earth's climate, generally with an aim of countering climate change. Geoengineering is controversial and divides researchers. A complete examination of this controversy is outside the scope of this report. In short, critics of geoengineering assert that its use could result in unintended consequences and divert action from mitigation activities. These critics often call for either the establishment of an international framework on how to conduct geoengineering research or the implementation of strategies to reduce the sources of GHG emissions.⁵ Those in favor of implementing geoengineering technologies argue that urgent action is needed to reduce the potential effects of rising atmospheric CO₂ concentrations.⁶

Geoengineering techniques are categorized as either carbon dioxide removal (CDR) methods or solar radiation management (SRM) methods. CDR methods address the warming effects of GHG by removing CO₂ from the atmosphere. SRM methods address Earth's energy balance by increasing the reflectivity of the Earth's atmosphere or surface, thereby reducing the amount of solar energy (heat) absorbed by the land and the ocean.⁷ This report outlines CDR methods and focuses on one method in particular: ocean iron fertilization (OIF).

Terrestrial-based CDR methods include the following:

• Direct air capture uses technology to remove CO₂ from the atmosphere and then compresses it, aiming to permanently store the CO₂ underground.⁸
• Afforestation involves planting trees on land that has not recently been covered with forest, generally for the last decade or more, thereby increasing the amount of CO₂ removed via photosynthesis.⁹
• Enhanced weathering stimulates the natural geologic process of silicate rock weathering by scattering crushed silicate-rich rocks across land surfaces to invoke a chemical reaction that removes CO₂ from the atmosphere and stores it in soils.

Ocean-based CDR methods include the following:

• Ocean fertilization adds nutrients, such as iron, to the surface of the ocean to enhance CO₂ uptake by marine algae (phytoplankton) via photosynthesis.
• Ocean pumping brings deep ocean water, which is generally nutrient rich, to the surface to enhance CO₂ uptake by phytoplankton via photosynthesis.
• Enhanced ocean alkalinity increases the concentration of calcium, magnesium, or sodium ions in seawater, allowing these ions to chemically bind with CO₂ to form bicarbonate ions, which selected marine organisms subsequently use to build shells.
• Direct ocean capture uses technology for the removal of CO₂ from ocean water.¹⁰

Congressional interest in certain geoengineering techniques generally has grown over the past two decades. This report provides an overview of the ocean-based geoengineering technique of OIF, including the natural marine biological process that removes CO₂ from the atmosphere and how OIF could amplify this natural process. Because most OIF experiments have occurred in the open ocean (international waters), the report also outlines relevant international bodies and treaties. The report further discusses concerns over OIF's effectiveness as a CDR method and highlights issues Congress may consider, such as whether to authorize selected federal agencies to research the method more closely, focusing on learning more about potential environmental and ecological consequences.

Ocean Iron Fertilization

Ocean fertilization refers to the technique of adding iron or other nutrients to ocean areas with low biological productivity (i.e., low abundance of photosynthetic plankton, or phytoplankton). Ocean fertilization could enhance atmospheric CO₂ removal by increasing biological productivity, namely by stimulating the growth of phytoplankton, similar to afforestation on land. Ocean fertilization as a geoengineering technique is based on the concept that because phytoplankton capture atmospheric CO₂ and add photosynthetic carbon to their cells, stimulating the growth of phytoplankton could result in more atmospheric carbon captured and more photosynthetic carbon produced.¹¹ When phytoplankton die, their cells sink and may store atmospheric CO₂ in the deep ocean for hundreds to thousands of years.

Biological Pump

The biological pump, or biological carbon pump, is the natural process of cycling carbon through the ocean (Figure 1). Similar to plants on land, phytoplankton use energy from the sun and take up atmospheric CO₂ during photosynthesis to form organic carbon matter as part of their cells. Phytoplankton can either be consumed by larger organisms, such as zooplankton (e.g., krill), transferring carbon up the food chain, or it can die and sink to the deep ocean. In the deep ocean, the dead phytoplankton can be broken down by bacteria or can settle on the seafloor and be buried. If bacteria break down the organic carbon matter, the CO₂ is rereleased into the water and may remain in the water, isolated from the atmosphere, for years to decades. If buried, the organic carbon matter is stored in the ocean sediments for hundreds to thousands of years.¹² On average, studies show that approximately 10% of phytoplankton organic carbon matter settles from the sunlight zone to the dark zone; of that 10%, possibly less than 1% is buried in ocean sediments (Figure 1).¹³

The biological pump is an important component of the global carbon cycle, which works over geological timescales (millions of years) and keeps atmospheric CO₂ concentrations in equilibrium with concentrations in the ocean. Similar to forests on land, the biological pump is a carbon sink, naturally removing CO₂ from the atmosphere in the short term and supporting the stabilization of Earth's climate over hundreds to thousands of years.

Figure 1. Biological Pump Schematic

Source: 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), p. 78, at https://doi.org/10.17226/26278. Notes: The schematic does not show all of the pathways (e.g., bacterial respiration, oceanic upwelling) that can release carbon dioxide back into the water and the atmosphere. In the sunlight zone, carbon can be cycled back to the atmosphere on timescales of years to decades. In the dark zone, carbon can be cycled back to the atmosphere on 100-year timescales. Buried in the seafloor, carbon can be isolated from the atmosphere for thousands of years. Graphic created by CRS Visual Information Specialist Jamie Hutchinson.

Effects of Ocean Nutrients

The biological pump's strength—namely, how much carbon cycles through the ocean-atmosphere system—depends on the amount of nutrients in the ocean, among other factors.¹⁴ Nitrogen, phosphorus, silica, and iron are important nutrients for the growth of phytoplankton, and they can be rare in the open ocean environment. This report focuses on the addition of iron to the surface of the ocean; the scientific community has primarily focused on iron because only relatively small amounts (in mass and volume) of iron may be needed for ocean fertilization relative to the amounts of nitrogen, phosphorus, and silica required for this process.¹⁵

Iron is naturally delivered to the ocean primarily by coastal and riverine sources, wind carrying terrestrial dust, and volcanic ash.¹⁶ The farther from these sources, the scarcer iron becomes in the ocean's surface. Phytoplankton growth is limited by the availability of iron (and other nutrients). Thus, the growth of phytoplankton is strongest in coastal regions and weakens in the open ocean. Areas of the global ocean that have limited iron availability—conditions favorable for OIF experiments—are the equatorial Pacific, subarctic Pacific, and Southern Ocean.¹⁷ Field observations and laboratory experiments suggest that adding iron to parts of the ocean that are not iron limited probably would not stimulate phytoplankton growth to the same extent as would adding iron to iron-limited areas.¹⁸

Experiments

Between 1993 and 2009, researchers conducted 13 OIF experiments in the open ocean environment—1 in the Atlantic,¹⁹ 2 in the equatorial Pacific, 3 in the subarctic Pacific, and 7 in the Southern Ocean (Figure 2).²⁰ During these experiments, researchers added between 350 and 4,000 kilograms of iron to the ocean from a moving ship over an area of 25-300 square kilometers and observed the effects for periods between 10 and 40 days.²¹ Iron for OIF may be sourced from land-based mining or may be obtained as byproduct from the iron and steel industry.²²

Figure 2. Site Locations of Ocean Iron Fertilization Experiments, 1993-2009

Source: 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), p. 79, at https://doi.org/10.17226/26278. Notes: Approximate site locations for ocean iron fertilization (OIF) experiments (white crosses) and an iron and phosphorus fertilization experiment (green cross). Red crosses mark the site locations of natural OIF experiments and are not discussed in this report. Colors and contours correspond to annual nitrate concentrations (micromoles per liter, shown on the color bar on the right) of the top 10-20 meters of the surface of the ocean. Regions with relatively high nitrate concentrations (warm colors) tend to be scarce in iron.

According to researchers, the OIF experiments conducted in the equatorial Pacific and the Southern Ocean produced phytoplankton blooms (i.e., an increase in the total mass of phytoplankton in a given ocean area).²³ However, these experiments did not provide clear evidence that blooms increased rates of sinking carbon—a necessary step for OIF to serve as carbon removal.²⁴ Of the 13 experiments, 1 found that OIF increased carbon levels in the deep ocean.²⁵ The other 12 OIF experiments did not observe increased carbon levels in the deep ocean or were too short-lived to make measurements.²⁶ The short observation period of these experiments made it difficult to understand if phytoplankton growth was sustained and, if so, for how long. Some researchers contend that studies incompletely addressed the short- and long-term environmental and ecological consequences of OIF in the study region versus in adjacent regions.²⁷

International Guidelines for Ocean Fertilization

Most OIF experiments have occurred in the open ocean where iron is scarce, and beyond the exclusive economic zone (EEZ) of coastal nations.²⁸ These areas in the open ocean are subject to international agreements. Early OIF experiments were conducted largely without international oversight. No international body or agreement is specifically devoted to ocean fertilization. International bodies have produced nonbinding guidelines for future ocean fertilization experiments.²⁹

The London Convention and the London Protocol

The principal international instruments addressing the potential impacts of ocean fertilization on the marine environment are the 1972 Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter, known as the London Convention,³⁰ and the 1996 Protocol to the London Convention, known as the London Protocol.³¹ The United States is a party to the London Convention and is not a party to the London Protocol. Both the convention and the protocol provide sets of international standards that attempt to guide and limit ocean fertilization.

In 2008, the International Maritime Organization adopted a nonbinding resolution under the London Convention that allows for only ocean fertilization activities that fall within the scope of "legitimate scientific research."³² As a party to the London Convention, the United States supported this 2008 resolution. The U.S. Environmental Protection Agency (EPA) is responsible for implementing the convention's guidelines for the dumping of wastes and other matter at sea under the Marine Protection, Research and Sanctuaries Act (MPRSA; P.L. 92-532).³³

In 2013, the parties to the London Protocol agreed to amend the protocol to limit ocean fertilization for research purposes.³⁴ This amendment would become legally binding only if ratified by two-thirds of the parties to the protocol, and only those parties that ratified the amendment would be bound by it. There are 53 parties to the London Protocol, and, as of June 2022, the amendment has not been ratified. The United States is not a party to the protocol, so the amendment (if ratified) would not limit U.S. activities.

Convention on Biological Diversity

The objectives of the United Nations Convention on Biological Diversity (CBD) are to conserve and sustainably use the components of biodiversity, among others.³⁵ A decision under the CBD rejects OIF as a means for climate mitigation until scientists better understand the potential associated risks for the environment and biodiversity, including socioeconomic and cultural impacts.³⁶ In 2008, the CBD issued a statement requesting member states restrict ocean fertilization activities, with the exception of "small scale studies within coastal waters" for the purpose of specific scientific research.³⁷ The United States is not a Party to the CBD.³⁸

Antarctic Treaty System

The Antarctic Treaty System (ATS) established the legal framework for Antarctica and the surrounding Southern Ocean.³⁹ The ATS guarantees free access and research rights for the international community to undertake research activities that fall within its geographic scope.⁴⁰ The United States is a Party to the ATS. Parties to the treaty are to take certain actions prior to undertaking any activity in the region. For example, parties are to develop an environmental assessment, provide advance notice to other parties, share data with other parties, and prevent marine pollution.⁴¹ Ocean fertilization occurring in the Southern Ocean may be subject to attention by the Scientific Committee and Commission of the 1980 Convention on the Conservation of Antarctic Marine Living Resources under the ATS.⁴²

United Nations Framework Convention on Climate Change

The United Nations Framework Convention on Climate Change (UNFCCC) entered into force in 1994 with the aim of preventing "dangerous" human interference with the climate system.⁴³ Under the UNFCCC, the Kyoto Protocol calls for the promotion and implementation of climate technologies.⁴⁴ In terms of carbon credits, the Kyoto Protocol's Clean Development Mechanism does not recognize ocean fertilization as a way to create carbon credits for regulated international trade.⁴⁵ The United States is a Party to the UNFCC and is not a Party to the Kyoto Protocol.⁴⁶

Within the UNFCCC, the Paris Agreement calls for holding the average global temperature increase to "well below 2˚C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5˚C above pre-industrial levels."⁴⁷ The Paris Agreement does not mandate or authorize the use of geoengineering techniques. Some scientists believe a range of CDR methods must be implemented to achieve the Paris Agreement's objectives.⁴⁸ As part of the United States reentering the Paris Agreement, the National Climate Task Force established "a new target for the United States to achieve a 50-52 percent reduction from 2005 levels in economy-wide net greenhouse gas pollution in 2030" in its "Nationally Determined Contributions" (NDC) submission to the UNFCCC.⁴⁹ The U.S. NDC makes no reference to geoengineering techniques.

United Nations Convention on the Law of the Sea

The 1982 United Nations Convention on the Law of the Sea (UNCLOS) does not specifically address ocean-based geoengineering techniques, but several of its principles and concepts may apply to ocean fertilization activities.⁵⁰ The United States is not a Party to UNCLOS. The United States recognizes that the convention reflects customary international law and complies with many of its provisions.⁵¹

The United Nations and other international bodies generally categorize ocean fertilization experiments as marine scientific research. UNCLOS provides general principles for this category of research, including that research be conducted in compliance with the convention's international standards for the "protection and preservation of the marine environment."⁵²

Some environmental groups consider ocean fertilization a form of pollution and a potential threat to the marine ecosystem.⁵³ UNCLOS defines pollution of the marine environment as

the introduction by man, directly or indirectly, of substances or energy into the marine environment, including estuaries, which results or is likely to result in such deleterious effects as harm to living resources and marine life, hazards to human health, hindrance to marine activities, including fishing and other legitimate uses of the sea, impairment of quality for use of sea water and reduction of amenities.⁵⁴

Because UNCLOS does not describe a level of environmental harm and biological tolerance in its definition of pollution, it may not be possible to categorize all future ocean fertilization experiments as pollution.⁵⁵ Conversely, given that ocean fertilization adds nutrients to the surface of the ocean for the purpose of removing CO₂ from the atmosphere and sequestering it in the deep ocean, some may consider this technique to be protecting the marine environment from climate change impacts.⁵⁶

Issues for Congress

In recent appropriations, Congress has recommended and funded several direct air capture research activities—technologies that remove CO₂ from the atmosphere.⁵⁷ Instead of relying on technologies to remove carbon from the atmosphere, OIF would amplify the naturally occurring biological pump. Because OIF is stimulating a biological process, models suggest that its cost of deployment at scale could range from $30 to $300 per metric ton CO₂ (/t CO₂);⁵⁸ by contrast, direct air capture technologies are estimated at $100-$1,000/t CO₂.⁵⁹ However, some environmental nongovernmental organizations contend that OIF would be impractical and costly.⁶⁰

In a 2017 U.S. House Committee on Science, Space, and Technology hearing on geoengineering, a climate engineering witness discussed "at scale" deployment of ocean fertilization in a prepared statement. The witness noted that "ocean iron fertilization could increase marine phytoplankton, increasing CO₂ uptake through photosynthesis, some unknown fraction of which may ultimately be sequestered in the deep ocean by settling of biological detritus. At scale this approach would have significant implications for ocean ecosystems."⁶¹

Funding for Ocean Iron Fertilization Research⁶²

Some researchers in the U.S. scientific community estimate that as much as $2.5 billion is needed over the next decade to further study ocean-based geoengineering and how implementation of these techniques might impact the ocean.⁶³ A better understanding of the ocean uptake of atmospheric CO₂ and the impacts associated with OIF could elucidate the criteria for purposefully selecting sites for fertilization.

Congressional funding for ocean research technology and equipment already provides data products that could be useful for monitoring and verifying the effectiveness of ocean fertilization. For example, National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA) satellites that measure chlorophyll concentrations can estimate the size of phytoplankton blooms.⁶⁴ Researchers could use satellite observations to study the development and duration of blooms created via ocean fertilization.⁶⁵ Ocean-based research monitoring equipment (e.g., Argo profiling floats, autonomous surface vehicles, sediment traps) is suited to study the sinking from the surface to the deep ocean of atmospheric carbon incorporated into phytoplankton cells. Moreover, using federally supported ocean research technology and equipment to monitor ocean waters adjacent to a fertilized area could serve as a control and could allow for observations on the bloom's size, spatial extent, and impact on the physical and chemical properties of the ocean. For instance, Congress directed NOAA to expand coverage of the Biogeochemical Argo fleet in FY2022.⁶⁶ According to some stakeholders, an expanded Biogeochemical Argo fleet would allow for additional direct observations of biological productivity, oceanic uptake of atmospheric CO₂, and carbon export into the deep ocean.⁶⁷

In the Energy Act of 2020 (enacted as Division Z of the Consolidated Appropriations Act, 2021; P.L. 116-260), Congress directed the U.S. Department of Energy (DOE) to establish a research program for carbon removal options.⁶⁸ The law mentions several carbon removal options that may be included in the research program but does not explicitly mention ocean fertilization. Congress could consider giving DOE or other agencies additional guidance regarding federal research into OIF. Congress also could consider oversight action related to DOE's carbon removal research programs and the extent to which DOE is coordinating with other relevant agencies, such as NOAA.

Research of Ocean Iron Fertilization's Environmental and Ecological Impacts

Some groups contend that, under UNCLOS, ocean fertilization could be considered pollution of the marine environment due to the addition of nutrients to the ocean's surface.⁶⁹ Congress may consider authorizing research studies to quantify the environmental effects of OIF, if any. For example, some research indicates that ocean fertilization might result in oxygen loss in regions of the ocean.⁷⁰ Other studies suggest iron fertilization might increase atmospheric concentrations of nitrous oxide, which could counteract some of the climate benefits of OIF.⁷¹

Adverse impacts associated with ocean fertilization may include the growth of phytoplankton associated with harmful algal blooms,⁷² and acidification of the deep ocean, which could harm deep-sea corals.⁷³ U.S.-based proposals for ocean fertilization within the EEZ could be subject to authorities under federal laws, such as the Marine Protection, Research, and Sanctuaries Act (P.L. 92-532); Coastal Zone Management Act (P.L. 109-58); National Marine Sanctuaries Act (P.L. 106-513); and Magnuson-Stevens Fishery Conservation and Management Reauthorization Act of 2006 (MSA; P.L. 109-479), among others. For example, the MSA requires federal agencies to consult with NOAA on proposed, funded, authorized, or undertaken activities that may adversely affect the marine habitat.⁷⁴ In addition to evaluating whether ocean fertilization proposals might trigger a review under the MSA, Congress could consider stand-alone legislation that provides a framework for ocean fertilization activities taking place within the U.S. EEZ.

Another consideration could be to determine whether OIF is a form of transboundary pollution and how OIF might fit into existing international law. Although one nation might weigh the climate change mitigation aspects of OIF more favorably than the environmental costs, other nations may consider the addition of nutrients that spread into their EEZs to be pollution. In addition, a 2009 Royal Society report points to nutrient robbing, where nutrients in the area of fertilization reduce biological productivity in adjacent regions. Nutrient robbing could affect the marine food web, including fisheries.⁷⁵ If the nutrient-robbed area falls within another nation's EEZ, this could present potential geopolitical issues.⁷⁶ Congress may consider legislation that regulates the scale and siting of ocean fertilization activities to limit ocean fertilization's impacts on adjacent marine ecosystems, particularly those within a neighboring nation's EEZ.