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1 Introduction
Pages 23-44

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From page 23...
... , will be deployed to reduce atmospheric CO2 after fossil emissions have been reduced to near zero. However, this viewpoint does not consider the fact that decreasing fossil emissions once they reach low levels will likely be very expensive and therefore methods for reduced and negative emissions will likely be used in concert for centuries, even during a sustained period of net negative global emissions (see Box 1.1, Figure A)
From page 24...
... . Several global models predict that the terrestrial sink will eventually switch to a source under business-as-usual emissions due to warming-accelerated decomposition of organic matter in high-latitude soils, nutrient limitation of CO2 fertilization, and forest die-back from heat, drought, and insect pests (Joos et al., 2001; Prentice et al., 2001)
From page 25...
... The green and dark blue boxes show the predicted sizes of the "natural" land and ocean sinks, while the light blue boxes show the starting and ending atmospheric concentrations (the atmospheric concentration at the end of each period and the beginning of the next are mildly inconsistent because of small inconsistencies between the scenario and modeled predictions as described in the supplementary information of Jones et al., 2016)
From page 26...
... Similarly, over the 250-year period from 2050 to 2300 in Figure B, the large net ocean and land sink causes the atmospheric concentration to decline by 75 ppm, though net anthropogenic emissions are slightly positive. At the same time, reducing the average 2050-2100 fossil fuel and land-use emissions to the ~3.3 Gt/y CO2 in Figure B (less than 10 percent of today's emissions)
From page 27...
... Thus, like photovoltaics or hydraulic fracturing and horizontal drilling, the development of direct air capture will likely require long-term government investment in incentives. BACKGROUND ON THE CARBON CYCLE AND CARBON SINKS Isotopic evidence shows that the increase in atmospheric CO2 concentration from 280 parts per million (ppm)
From page 28...
... . The land and ocean carbon sinks are often referred to as "natural" sinks, though a more appro­ priate adjective is probably "inadvertent," because they are unintended ­ yproducts b of fossil fuel consumption and land use.
From page 29...
... It quantifies the input of CO2 to the atmosphere by emissions from human activities, the growth of CO2 in the atmosphere, and the resulting changes in land and ocean carbon fluxes in response to increasing atmospheric CO2 levels, climate change and climate variability, and other anthropogenic and natural changes.
From page 30...
... and in short-lived and rapidly decomposing tissues on land (such as most of the carbon in leaves and fine roots) are carbon sinks that rapidly reach equilibrium with the atmosphere.
From page 31...
... The persistent disequilibrium uptake by the land and ocean carbon sinks would allow for achievement of this reduction even with net positive anthropogenic emissions during the 50 ppm decline. Nonetheless, the strengths of the land and ocean sinks decline through time in Figure 1.4 because of the concerted effects of the rapid decline in the time-derivative of atmospheric CO2 during the middle part of the century (for the rapidly equilibrating pools)
From page 32...
... This report focuses on the vital and productive role that NETs could play to reduce climate change immediately and throughout this century. The critical quantity here is net anthropogenic emissions, that is, the sum of positive emissions from fossil fuels and land use and negative emissions from NETs.
From page 33...
... . Article 4 of the Paris agreement states that increases in atmospheric CO2 should cease "in the second half of the century," although preventing the increase of atmospheric CO2 does not require that anthropogenic emissions cease, only that they be less than or equal in strength to carbon sinks.
From page 34...
... . Net negative emissions in the second half of the century and beyond, achieved by the combined action of NETs, emissions reductions, and natural sinks, would allow atmospheric CO2 to temporarily overshoot levels consistent with 1.5°C or 2°C of warming at equilibrium, as in the time-series of atmospheric concentrations in RCP 2.6 (Figure 1.5; Fuss et al., 2014)
From page 35...
... Introduction FIGURE 1.5  Panel a depicts CO2 emission pathways until 2100, and panel b depicts the extent of net negative emissions and BECCS using RCP 2.6 in 2100.
From page 36...
... NEGATIVE EMISSIONS TECHNOLOGIES In response to item E of the Statement of Task, the committee focused on five major approaches (see Figure 1.6) : • Coastal blue carbon (Chapter 2)
From page 37...
... FIGURE 1.6  Negative emissions technologies considered in this report.
From page 38...
... Building on this report, the National Academies convened two committees, one to identify research needs for CO2 removal from the atmosphere and sequestration, and one to study utilization of concentrated carbon waste gas streams. The Committee on Developing a Research Agenda for Carbon Dioxide Removal and Reliable Sequestration assessed the benefits, risks, and "sustainable scale potential" for atmospheric CO2 removal and sequestration approaches and defined the essential components of an R&D program, including estimates of the program's cost and potential impact.
From page 39...
... . • Direct air capture and sequestration (Chapter 5)
From page 40...
... Given the relative nascency of coastal blue carbon, direct air capture, and carbon mineralization approaches in the literature, these approaches are described in much more technical and comprehensive detail in their respective chapters, with supplemental technical details for direct air capture and carbon mineralization included in Appendices D and E The committee's focus on sequestration in terrestrial and nearshore/coastal environments is not intended to undervalue the potential of technologies or practices for oceanic sequestration, but instead is a response to the Statement of Task.
From page 41...
... offers increased resiliency to managing the risks of surprises arising from nature and mitigation actions. Furthermore, the possibility of irreversible consequences of temporary warming is another reason to quickly develop NETs so that they can more quickly reduce net anthropogenic emissions.
From page 42...
... If the price of capture and sequestration is P $/t CO2, the economic discount rate is r, escape from reservoirs occurs at a constant rate per unit of carbon stored, and the average residence time of CO2 in a reservoir is T, then the +P !
From page 43...
... . Each chapter contains estimated costs of the research agenda and outlines implementation of the research agenda -- monitoring and verification, institutional structures, and research management.
From page 44...
... . Synthesis The research agendas proposed in Chapters 2-7 are combined in Chapter 8 into an integrated research proposal and a single list of research priorities.


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