Negative Emissions Technologies and Reliable Sequestration A Research Agenda (2019) / Chapter Skim
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The focus of climate mitigation is to reduce energy sector emissions by 80-100 percent, requiring massive deploy ent of low-carbon technologies between now and 2050. Progress toward m these targets could be made by deploying negative emissions technologies (NETs)
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MITIGATION IN A NET ZERO EMISSIONS SYSTEM Studies using integrated assessment models that link greenhouse gas emissions, the economy, and climate conclude that the reductions in net anthropogenic emissions required to meet even the 2°C target will be difficult and expensive to achieve, even with foreseeable technological breakthroughs. In its Fifth Assessment Report (2014)
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One option for zero net aviation emissions FIGURE S.1. Scenario of the role of negative emissions technologies in reaching net zero emissions. NOTE: For any concentration and type of greenhouse gas (e.g.
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• Terrestrial carbon removal and sequestration (Chapter 3) -- Land use and management practices such as afforestation/reforestation, changes in forest management, or changes in agricultural practices that enhance soil carbon storage ("agricultural soils")
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Policymakers should consider the broadest possible portfolio of technologies to find the most inexpensive and least disruptive solutions, including those with positive, nearzero, and negative emissions. CARBON REMOVAL POTENTIAL AND NEED The committee identified the potential rates of CO2 removal and sequestration that could be achieved safely and economically, given our current knowledge and level of technological development.
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Current Technology and L = 0 - 20 Understanding and at M =20 -100 <$100/t CO2 H = >100 (Gt/y CO2) US Global Coastal blue L 0.02 0.13a • Available land given coastal carbon development and land use • Understanding of future rates with sea level rise and coastal management Terrestrial L 0.15 1 • Available land given needs for carbon food and fiber production and for removal and biodiversity sequestration: • Inability to fully implement forestry afforestation/ management practices reforestation Terrestrial L 0.1 1.5 • Demand for wood limits feasible carbon reduction in harvest rate, though removal and some forest management activities sequestration: would not impact fiber supplies forest • Inability to fully implement forestry management management practices Terrestrial L to M 0.25 3 • Limited per-hectare rates of carbon carbon uptake by existing agricultural removal and practices sequestration: • Inability to fully implement soil agricultural conservation practices practices to enhance soil carbon storage 6
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Others, such as several types of enhanced carbon mineralization, are at the early stages of exploration by academic researchers and have never been tried in the field. In general, the cost estimates for technologies that have not been demonstrated are more speculative than those for technologies that have been deployed at scale.
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The analysis in Table S.1 leads to the committee's most important conclusions about the readiness of NETs: Conclusion 2: Four negative emissions technologies are ready for large-scale deployment: afforestation/reforestation, changes in forest management, uptake and storage by agricultural soils, and bioenergy with carbon capture and storage (BECCS)
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Conclusion 4: If the goals for climate and economic growth are to be achieved, negative emissions technologies will likely need to play a large role in mitigating climate change by removing ~10 Gt/y CO2 globally by midcen tury and ~20 Gt/y CO2 globally by the century's end. FACTORS AFFECTING SCALE UP The committee considered a range of factors that will affect the scale-up of NETs.
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Energy Requirements Direct air capture and some carbon mineralization options require a large energy input per ton of CO2 captured, which increases costs. Direct air capture systems require between 5 and 10 GJ to capture a ton of atmospheric CO2.
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For example, historical adoption rates of agricultural soil conservation and forestry management practices that would save farmers and forest landowners money have been surprisingly low, as have dietary changes, such as reduced meat consumption, that would increase health while freeing agricultural land for forestry NETs and BECCS. These behaviors could limit deployment of NETs, as could public resistance to new local infrastructure, but they are not well represented in integrated assessment models.
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In contrast, BECCS, direct air capture, and carbon mineralization have comparatively minor issues of permanence. CO2 that is geologically sequestered can leak from saline aquifers but at rates low and straightforward enough to remediate.
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One way to maintain public confidence during rapid deployment of NETs is to invest in a substantial effort to educate the public during the research and development stage. Insufficient Scientific/Technical Understanding Significant scientific gaps remain for all NETs, but especially for carbon mineralization and coastal blue carbon.
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Conclusion 6: Direct air capture and carbon mineralization have high po tential capacity for removing carbon, but direct air capture is currently limited by high cost and carbon mineralization by a lack of fundamental understanding. Conclusion 7: Although their potential for removing carbon is lower than other negative emissions technologies, coastal blue carbon approaches war rant continued exploration and support.
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Coastal National Coastal Wetland Data Center, 2M 20 including data on all restoration and carbon removal projects. Carbon-rich NET demonstration projects 10M 20 and field experiment network Coastal blue carbon project deployment.
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N E G AT I V E E M I S S I O N S T E C H N O LO G I E S A N D R E L I A B L E S E Q U E S T R AT I O N TABLE S.2 Continued Research Cost Duration NET Title $/y Years Preservation of harvested wood 2.4M 3 Research on greenhouse gases and social 1M 3 impacts of reducing traditional uses of Forest biomass for fuel Management Social sciences research on improving 1M 3 landowner responses to incentives and equity among landowner classes National agricultural soils monitoring 5M Ongoing system Experimental network improving 6-9M ≥12 agricultural soil carbon processes. Data-model platform for predicting and 5M 5 Agricultural quantifying agricultural soil carbon removal Soils and storage Scaling up agricultural soils sequestration 2M 3 activities High carbon input crop phenotypes 40-50M 20 Soil carbon dynamics at depth 3-4M 5 Agricultural Biochar studies 3M 5-10 Soils, BECCS Agricultural Reactive mineral additions to soils 3M 10 Soils, Carbon Mineralization BECCS Biomass-to-fuel with biochar 40-103M 10 16
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National air capture test center support of 15-20M 10 demonstrations continued 17
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carbon removal pilot 3.5M 10 studies Carbon Medium-scale in-situ field experiment in 10M 10 Mineralization peridotite rock Development of a resource database for 2M 5 carbon mineralization Studying the environmental impact of 10M 10 mineral addition to terrestrial, coastal and marine environments Examining the social and environmental 5M 10 impact of an expanded extraction industry for the purpose of CO2 removal 18
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Reducing seismic risk 50M 10 Increasing the efficiency and accuracy of site 45M 10 characterization and selection Improving monitoring and lowering costs for 50M 10 Geologic monitoring and verification Sequestration: Saline Aquifer Improving secondary trapping prediction and 25M 10 Storage methods to accelerate secondary trapping Improving simulation models for performance 10M 10 prediction and confirmation. Assessing and managing risk in compromised 20M 10 storage systems.
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Inexpensive direct air capture or carbon mineralization could allow for some continued use of fossil fuels without impacting climate. Recent regulatory proposals to freeze lightduty fuel economy standards over the 2021-2025 period and changes to the Clean Power Plan may further the need for NETs.
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Several Gt/y CO2 of negative emissions at less than $20/t CO2 are already available. Nonetheless, existing options (coastal blue carbon, afforestation/reforestation, forest management, agricultural soils and BECCS)
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