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1 Introduction
Pages 19-38

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From page 19...
... An overall climate change response strategy will include climate mitigation approaches to reduce CO2 and other GHG emissions. Carbon dioxide removal (CDR)
From page 20...
... SOURCE: GML, NOAA, 2021. FIGURE 1.2  Reconstruction over time of the industrial period of human carbon emissions to the atmosphere from fossil fuel use and land-use change (positive fluxes)
From page 21...
... . While this report concentrates on removal of excess atmospheric CO2, comprehensive climate mitigation strategies incorporate approaches to reduce human emissions of all GHGs and may even explore deliberate removal of gas beyond CO2 such as methane.
From page 22...
... 1.2 CLIMATE MITIGATION, DECARBONIZATION, AND CARBON DIOXIDE REMOVAL Without deliberate action to reduce human CO2 emissions, continued rapid CO2 accumulation in the atmosphere increases the expected magnitude of climate change and ocean acidification (UNEP, 2017; IPCC, 2021)
From page 23...
... The reliance on, or even need for, CDR approaches varies considerably depending on the climate and socioeconomic scenarios and integrated assessment models used to evaluate human emissions and barriers to decarbonization. However, some form of CDR is common in climate/socioeconomic scenarios that attempt to limit global warming to well below 2°C, preferably to 1.5°C, compared to preindustrial levels in line with the international Paris Agreement (Figure 1.4; Allen et al., 2018; Fuhrman et al., 2019; Canadell et al., 2021; IPCC, 2021)
From page 24...
... . It is important, however, to keep in mind that these CDR estimates reflect model estimates using only a subset of possible approaches, typically landbased afforestation/reforestation and bioenergy with carbon capture and sequestration, and adding CDR approaches with different land, resource, energy, and cost constraints can result in a different estimates of total CDR, emissions abatement, and residual human CO2 emissions for the same climate target (e.g., recent studies adding direct air capture CDR, Fuhrman et al., 2020)
From page 25...
... At present, industrial-scale CDR approaches are even smaller scale than pilot and demonstration plants; for example, a new direct air capture facility in Iceland would, at fully planned capacity, remove 4 kt CO2/yr (Gertner, 2021)
From page 26...
... Further, some electrochemical CDR approaches produce hydrogen gas as a byproduct, and assuming that the initial electrical energy source for the CDR comes from low-CO2 sources, the hydrogen gas could be used as a clean fuel (or temporary energy storage) to reduce overall costs and carbon intensity of the CDR approach or other industrial activity.
From page 27...
... Detection and attribution of large-scale changes in ocean carbon storage due to ocean CDR approaches will have similar challenges. For comparison the cumulative ocean uptake of anthropogenic CO2 from 1850 to 2019 is estimated to be about 591 Gt CO2 or equivalently 161 Gt C (Friedlingstein et al., 2020)
From page 28...
... Ocean carbon storage is also sensitive to the fraction of sinking organic matter that reaches the deep sea prior to being respired (often termed the remineralization length scale) and to the extent of biological nutrient utilization in high-latitude surface ocean, especially in the Southern Ocean.
From page 29...
... , at least so far, there is only weak evidence of detectable changes in the global-scale ocean biological pump affecting net ocean carbon storage due to climate change or ocean acidification on a large scale and low confidence in our understanding of the magnitude and sign of ocean biological feedbacks to CO2 storage and climate; the ocean uptake in anthropogenic CO2 is attributed almost wholly to physicochemical processes and trends in human CO2 emissions. However, given the large carbon fluxes associated with the biological carbon pump, with 5–12 Gt C/ yr leaving the surface ocean annually (Siegel et al., 2014)
From page 30...
... 1.5 OCEAN-BASED CARBON DIOXIDE REMOVAL The objective of any CDR approach is to remove excess CO2 from the atmosphere and store or sequester this carbon in some other reservoir away from the atmosphere for some time period, typically decades or longer. For ocean CDR, the removal from the atmosphere is indirect via an enhancement of the downward air–sea flux of CO2 from the atmosphere to the surface ocean.
From page 31...
... Ocean CDR approaches must also be assessed against the consequences of no action. Without substantial decarbonization, emissions abatement, and potential options such as CDR, atmospheric CO2 growth will continue unabated with associated rising impacts from climate change and ocean acidification.
From page 32...
... The NRC (2015a) CDR report advised that "if carbon dioxide removal technologies are to be viable, it is critical now to embark on a research program to lower the technical barriers to efficacy and affordability while remaining open to new ideas, approaches, and synergies." In 2019, the National Academies published a report that advances this goal, Negative Emissions Technologies and Reliable Sequestration: A Research Agenda (NASEM, 2019)
From page 33...
... The scientific confidence regard ing the viability of different CDR approaches may change with time as further research expands scientific understanding, requiring flexibility in the design of any research program and periodic review of priorities as the science evolves. FIGURE 1.9 Potential learning curves over time for ocean CDR approaches.
From page 34...
... As part of ClimateWorks Ocean CDR Portfolio, this task included examination of six groups of ocean-based CDR approaches, to identify key scientific and technological questions, including questions surrounding governance and societal dimensions that could increase the viability of responsible use of the ocean as a mechanism for carbon removal from Earth's atmosphere. BOX 1.3 Statement of Task With the goal of reducing atmospheric carbon dioxide, an ad hoc committee will conduct a study exclusively focused on carbon dioxide removal (CDR)
From page 35...
... As such, nutrient fertilization essentially locally enhances the natural ocean biological carbon pump using energy from the sun, and in case of iron, relatively small amounts of iron are needed. • Artificial upwelling and downwelling (Chapter 4)
From page 36...
... 36 A RESEARCH STRATEGY FOR OCEAN-BASED CARBON DIOXIDE REMOVAL AND SEQUESTRATION FIGURE 1.10  Ocean-based CDR approaches considered in this study.
From page 37...
... were invited to present to the committee to assist the committee in better understanding stakeholder interest and exploring the current state of knowledge, potential, and limitations of ocean-CDR approaches. Workshop and meeting programs were developed to encourage discussion from diverse perspectives on ocean CDR feasibility and included presentations, made publically available, as well as moderated panel discussions incorporating questions from the committee and the online audience.
From page 38...
... What are the energy, resource, infrastructure, land, and ocean-space requirements for the CDR approach? Governance and social dimensions: What is the governance landscape for research on and possible future deployment of the CDR approach?


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