Valuing the Ocean Carbon Sink in Light of National Climate Action Plans

formulate and implement national climate action (NCA) plans to direct their nationally determined contributions (NDCs) in reducing greenhouse gases (GHGs) and in particular carbon dioxide (CO2) emissions (UNFCCC, 2015). The NCA plans address CO2 management for all components of society, be it food, mobility, energy, or consumption. The extent to which NCA plans are in line with the overall targets will be assessed during global stocktakings, with the first one scheduled for 2023. Limiting global temperature increase by reducing GHG and CO2 emissions will depend crucially on natural, non-anthropogenic sink efficiency. The ocean currently removes 25%–30% of the CO2 emitted to the atmosphere by human activities (Friedlingstein et al., 2020), thereby providing, alongside other critical ecosystem services, an important societal wealth contribution via CO2 sequestration. From the above results, it is obvious that the ocean CO2 monitoring system must be able to determine the present and future CO2 uptake with sufficient accuracy. To justify the effort involved, it is also useful to determine the monetary value of the oceanic sink. This can be done in three ways: a cost-benefit analysis (CBA), a cost-effectiveness analysis (CEA), or a market-based CO2 pricing approach. CBA and CEA both use shadow prices in their calculations that measure the social costs of emitting a marginal tonne of carbon1, whereas market prices are used in national accounting to compute, for example, the gross domestic product. In CBA, shadow prices are derived from estimates of costs of climate change impacts. In CEA, shadow prices are derived under a given target, such as a temperature target as defined in the Paris Agreement. Put simply, CBA provides information on how much wealth is generated by the ocean in terms of reducing climate change, and CEA provides information on how much wealth is generated by reducing emissions abatement costs for the given target. The latter information is in most cases more reliable and can also be obtained with a market-based approach, given the regulatory framework and that a market is in place. Observed CO2 prices can also be used to assess the value of CO2 sinks, even though these sinks are not involved in trading. The market and the underlying regulatory framework are ideally designed to regulate anthropogenic activities, so given natural CO2 sequestration, targets like net-zero CO2 can be achieved. However, a weakening of natural sinks implies, in turn, that faster reductions and additional atmospheric CO2 removal will be required. Similarly, the market price would increase given that a weakening of CO2 sinks is expected to be considered in the underlying regulatory framework, defining the scarcity in a given CO2 market. Hence, highly reliable information about current and future ocean CO2 sinks provides value information for policymakers to properly align the regulatory framework, and for the business community to form realistic CO2 price expectations. Furthermore, CO2 sequestration by ocean sinks varies regionally—and 38% of the global ocean comprises territorial waters (Figure 1). Considering the regional variations in CO2 emissions and in sink activity implies that the CO2 wealth effects vary considerably for different countries (Bertram et al., 2021). Although regional differences in terrestrial CO2 sinks are considered in national emissions Valuing the Ocean Carbon Sink in Light of National Climate Action Plans

Signatory states to the Paris Agreement are required to formulate and implement national climate action (NCA) plans to direct their nationally determined contributions (NDCs) in reducing greenhouse gases (GHGs) and in particular carbon dioxide (CO 2 ) emissions (UNFCCC, 2015).The NCA plans address CO 2 management for all components of society, be it food, mobility, energy, or consumption.The extent to which NCA plans are in line with the overall targets will be assessed during global stocktakings, with the first one scheduled for 2023.Limiting global temperature increase by reducing GHG and CO 2 emissions will depend crucially on natural, non-anthropogenic sink efficiency.
The ocean currently removes 25%-30% of the CO 2 emitted to the atmosphere by human activities (Friedlingstein et al., 2020), thereby providing, alongside other critical ecosystem services, an important societal wealth contribution via CO 2 sequestration.
From the above results, it is obvious that the ocean CO 2 monitoring system must be able to determine the present and future CO 2 uptake with sufficient accuracy.To justify the effort involved, it is also useful to determine the monetary value of the oceanic sink.This can be done in three ways: a cost-benefit analysis (CBA), a cost-effectiveness analysis (CEA), or a market-based CO 2 pricing approach.
CBA and CEA both use shadow prices in their calculations that measure the social costs of emitting a marginal tonne of carbon 1 , whereas market prices are used in national accounting to compute, for example, the gross domestic product.In CBA, shadow prices are derived from estimates of costs of climate change impacts.In CEA, shadow prices are derived under a given target, such as a temperature target as defined in the Paris Agreement.Put simply, CBA provides information on how much wealth is generated by the ocean in terms of reducing climate change, and CEA provides information on how much wealth is generated by reducing emissions abatement costs for the given target.
The latter information is in most cases more reliable and can also be obtained with a market-based approach, given the regulatory framework and that a market is in place.
Observed CO 2 prices can also be used to assess the value of CO 2 sinks, even though these sinks are not involved in trading.The market and the underlying regulatory framework are ideally designed to regulate anthropogenic activities, so given natural CO 2 sequestration, targets like net-zero CO 2 can be achieved.However, a weakening of natural sinks implies, in turn, that faster reductions and additional atmospheric CO 2 removal will be required.
Similarly, the market price would increase given that a weakening of CO 2 sinks is expected to be considered in the underlying regulatory framework, defining the scarcity in a given CO 2 market.
Hence, highly reliable information about current and future ocean CO 2 sinks provides value information for policymakers to properly align the regulatory framework, and for the business community to form realistic CO 2 price expectations.Furthermore, CO 2 sequestration by ocean sinks varies regionally-and 38% of the global ocean comprises territorial waters (Figure 1).Considering the regional variations in CO 2 emissions and in sink activity implies that the CO 2 wealth effects vary considerably for different countries (Bertram et al., 2021).Although regional differences in   assessing CDR via ocean-based measurements, which will be part of future NDCs, requires accounting for the feedback of territorial ocean CO 2 uptake on global CO 2 uptake.
In general, the assessment of ocean CO 2 sequestration must be based on understanding the processes of and monitoring both fluxes and storage of CO 2 in the oceanfrom regional to global scales.The processes controlling CO 2 in the ocean are often separated into "solubility pump" (controlled by physics and biogeochemistry) and "biological pump" (controlled by biochemistry and biology) concepts.However, these two pumps are interlinked via underlying processes and may also counteract each other in the matter of net CO 2 uptake; for example, in highly productive upwelling regions, the CO 2 sink created by the biological pump may compensate for the outgassing of CO 2 driven by the solubility pump (Figure 2).Carbon assessments require determining the efficiency of both pumps and coordination of the underlying ocean observations that make use of multiple platforms (ships, underwater as well as surface autonomous vehicles, floats, moorings, and satellites) equipped with sensors and samplers employing a diverse pool of sensing technology (optical, particle probes, electrochemical) and operating at varying levels of technological readiness.
Data harmonization and quality control along with FAIR (Findable, Accessible, Interoperable and Reusable) access to data permit a wide spectrum of applications across disciplines and needs, and they must be ensured to enable integration of the various data streams into regional and global carbon products.Regional terrestrial CO 2 sinks are considered in national emissions Valuing the Ocean Carbon Sink in Light of National Climate Action Plans By Johannes Karstensen, Wilfried Rickels, Pierre Testor, and Maciej Telszewski 1 Marginal cost of the impacts caused by emitting one extra tonne of carbon dioxide at any point in time.inventories, regional ocean sink contributions are not yet included in the determination of international burden sharing regarding CO 2 emissions abatement.Thus, the current framework favors countries with large terrestrial CO 2 sinks to the disadvantage of countries with large territorial ocean sinks.However, costs of ocean CO 2 fluxes are highly interconnected: variability in the global ocean CO 2 uptake of atmospheric CO 2 will influence the CO 2 uptake in territorial waters.

FIGURE 2 .
FIGURE 2. Sketch of carbon fluxes for an arbitrary EEZ bounded by a seafloor (gray).
(and global) carbon data products with sufficient temporal and spatial resolutions are required for assigning values to Exclusive Economic Zone CO 2 sinks.Global coordination of observational efforts, science approaches, and coordination with global syntheses are performed under the auspices of the International Ocean Carbon Coordination Project (IOCCP).