A taxonomy of negative emissions technologies (NETs). NETs are distinguished by approach to carbon capture, earth system and storage medium. Major implementation options are distinguished for each NET.

A taxonomy of negative emissions technologies (NETs). NETs are distinguished by approach to carbon capture, earth system and storage medium. Major implementation options are distinguished for each NET.

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With the Paris Agreement's ambition of limiting climate change to well below 2 °C, negative emission technologies (NETs) have moved into the limelight of discussions in climate science and policy. Despite several assessments, the current knowledge on NETs is still diffuse and incomplete, but also growing fast. Here, we synthesize a comprehensive bo...

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... BECCS is considered one of the most promising carbon removal technologies, however, lack of policy incentives is seen as the main barrier to prevent investments in BECCS (Fridahl and Lehtveer, 2018). The available technological options are still in the early stages of development (Minx et al., 2018) and the price of carbon allowances has been considerably lower than the cost of CCS . However, the prices have notably increased in Europe in 2020 and 2021 (Krukowska, 2021). ...
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The forest industry is a significant emitter of CO 2 and thus it needs to transform toward a more sustainable operation in order to contribute to tackling climate change. This paper looks at the progress, tools, possibilities, and barriers of Finnish and Swedish forest industries in achieving deep decarbonization. Finland and Sweden have set ambitious national targets to reach net negative greenhouse gas emissions. The role of the forest industry in reaching national targets in these countries remains unclear even if significant fossil CO 2 emission reduction and efficiency improvement has occurred. If the forest industries in these countries fulfill their planned future visions, their contribution to meeting the targets will be substantial. This study identified the largest CO 2 emitting sectors in the forest industry. They are for both countries, arranged by size, transport including non-road mobile machinery, on-site energy production, fossil fuel use in processes (lime kilns and dryers), and purchased electricity. Viable decarbonization measures exist for key fossil CO 2 emissions sources, but several technical, economic, and political barriers are hindering their implementation. Fuel switching from fossil energy sources to bio-based alternatives is the main tool in the decarbonization of the forest sector in both countries, but also electrification of e.g. transport, provides emission reduction opportunities. The forest industry has a high and sustainable potential to become carbon-negative by investing in bioenergy with carbon capture and storage (BECCS) but achieving net-zero emissions might not be realistic without changes in policies and suitable incentives.
... There are many solutions for CDR currently at hand -the so-called negative emissions technologies and practices-which hold the potential to remove CO 2 from the atmosphere [4][5][6][7]. On the one hand, nature-based solutions include planting trees (afforestation and reforestation) in which essentially the CO 2 is removed from the atmosphere and converted to biomass via photosynthesis [8,9]. ...
... In recent years, an extensive literature has explored the different CDR alternatives, providing helpful insights into their potential and costs and environmental and social impacts. To mention some prior studies, Minx et al. [5] and Fuss et al. [4] provided a thorough techno-economic assessment of several CDR alternatives. Other works investigated the CDR potentials and environmental impacts on the environment [29,30]; most of them focused only on BECCS [31][32][33][34][35] or DACCS [22,36,37], while other alternatives have received much less attention [9,11]. ...
... Nevertheless, all the activities across the BECCS value chains need to be assessed considering a comprehensive set of environmental effects to avoid burden shifting [31,32,73]. [5,125]. There are two main approaches: the use of biogenic materials in construction [126] and the CO 2 sequestration in minerals and alkaline materials [127]. ...
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Carbon dioxide removal (CDR) will be a key component of the climate change mitigation efforts to achieve the carbon-neutrality goals. Hence, a comprehensive assessment of the CDR potential at national and local levels is crucial to identify regional opportunities and deploy practical actions timely. This study focuses on the potential function of olive agroecosystems in delivering CDR in the European Mediterranean countries. Relying on a geospatial assessment of existing olive groves (and associated residual biomass) combined with statistical, process systems engineering, and life cycle emissions data, the CDR potential considering five promising actions linked with the olive agroecosystems was here estimated. These actions are i) conservation measures protecting tree carbon sequestration, ii) agricultural practices increasing soil carbon sequestration, iii) biochar production and utilization, iv) biomass conversion routes coupled with carbon capture and storage (CCS), and v) development of bio-based and CO2-based materials. Overall, the bottom-up assessment highlights the value of the olive groves, currently storing around 0.22 Gt CO2-eq in standing trees and potentially sequestering 0.03 Gt CO2-eq annually in soils. Moreover, exploiting the abundant biomass wastes in biorefineries coupled with CCS could deliver gigatonne-scale CDR while producing various value-added products, achieving above 0.01 Gt CO2-eq per year only using prunings for biochar or power, while other pathways show lower potential (e.g., 0.52 MtCO2eq yr⁻¹ for fermentation). These results may promote the large-scale deployment of CDR actions, stimulate new policy initiatives to exploit opportunities associated with the olive groves, and ultimately contribute to the transition toward the net-zero targets.
... Soil carbon sequestration in agroecosystems is a promising NET offering considerable mitigation potential (Bossio et al., 2020;Fuss et al., 2018) due to the important C-deficit of agricultural soils (Sanderman et al., 2017). Practices designed to increase soil organic carbon (SOC) are readily applicable at large scales by land managers because they do not require any new technological breakthrough (EASAC, 2018;Fuss et al., 2018;Minx et al., 2018). ...
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Atmospheric C sequestration in agricultural soils is viewed as one of the most promising negative emission technologies currently available. Nonetheless, it remains unclear how strongly soil organic carbon (SOC) stocks respond to agricultural practices, especially for subsoil. Here, we assess the SOC storage potential in croplands and how the presence of temporary grasslands (TG) in the crop rotation affects SOC stocks. We developed a new approach to correct for bias in bulk density (BD) induced by sampling conditions and land-use effects with a data-driven model to predict the BD of fine soil (<2 mm) for reference condition. Using 54 permanent grassland and cropland sites with various proportions of TG from a monitoring network in Switzerland, we showed that SOC stock differences down to 50-cm depth between cropland and permanent grasslands (maximum: 3.0 ± 0.8 kg C m⁻²) depend on the TG proportion in the crop rotation, regardless of clay content and pH. An increase of the TG proportion by 10% would induce a SOC gain of 0.40 ± 0.13 kg C m⁻². The responses of topsoil (0–20 cm) and subsoil (20–50 cm) SOC stocks to TG proportion were linear and equivalent. The effect of TG on SOC storage would have been underestimated by 58% without accounting for subsoil stocks response and by 16% without BD corrections. The conversion of all croplands to permanent grasslands in the study region would potentially store a quantity of SOC equivalent to the anthropogenic greenhouse gas emissions generated by the same region during one year. Although the potential of agricultural soils as negative emission technology is relatively modest compared to former expectations, the findings demonstrate the potential to manage SOC and its associated ecosystem services at large scales and down to deep soil layers.
... In marine environments, there is a strong overlap with ocean alkalinity enhancement (for consistency, this paper's case-study abbreviations use 'EWO' for 'enhanced weathering, ocean'), where miningsourced materials are added to oceans or on beaches, leaving the mechanical action of waves to (further) facilitate weathering processes [151][152][153][154][155][156]. Accordingly, we treat these approaches as a sub-set of enhanced weathering that differs primarily in locale. ...
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Large-scale and highly experimental interventions are being considered as strategies to address climate change. These include carbon dioxide removal approaches that are becoming a key pillar of post-Paris assessment and governance, as well as the more controversial suite of solar geoengineering methods. In this paper, we ask: Who defends and opposes these experiments, and why? After screening 44 early-stage experiments, we conduct a qualitative comparative analysis of 21 of them in five areas: ocean fertilization, marine cloud brightening, stratospheric aerosol injection, ice protection, and enhanced weathering. We develop a common framework of analysis, treating experiments as sites in which the risks and appropriate governance of early-stage science and technology are envisioned and disputed among scientists and other social groups. Our contribution is to map and explain the key issues of contention (why), actors (who), and tactics (how) that have shaped opposition across these linked fields of experimentation and technological development, from the 1990s till today. In doing so, we build upon and connect past studies on particular climate experiments and develop insights relevant to governance outlooks perceptions, discourses, and intents surrounding immature but potentially crucial climate technologies.
... Despite the lack of demonstrated scale [1], it has become increasingly clear that negative emissions technologies will be a necessary part of our climate change portfolio [2,3]. Negative emission technologies involve a range of ways of capturing and sequestering carbon, such as from the ambient air (e.g. ...
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This opinion aims to begin deliberation about investing in negative emissions technologies (NETs) by suggesting that the investment could be responsive to two particular values: need and efficiency—and that these values point us towards taking different actions. For negative emissions technologies, I suggest, we face a Need-Efficiency Tradeoff, i.e. a “NET effect”. This tradeoff also highlights several contrasts: responding to need focuses on regional and short-term moral considerations; responding to efficiency focuses on global and long-term moral considerations.
... Based on data from long-term field experiments, it has been estimated that pyrogenic organic matter is 1.6 times more stable than bulk organic matter (Lutfalla et al. 2017). Thus, application of biochar to soil may also contribute to climate change mitigation through long-term carbon storage in soil (Njenga et al. 2017;Minx et al. 2018). ...
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Despite efforts to increase agricultural production sustainably in sub-Saharan Africa, large gaps remain between actual and potential yield of food crops. Adding biochar to degraded cropland soils in the African tropics has significant potential to enhance crop productivity. Biochar-based farming can also mitigate climate change, through soil carbon storage. This study involved six smallholder farms at sites in eastern, central, and western Kenya that are characterized by different pedo-climatic conditions. We examined the response of non-fertilized and fertilized maize monoculture to three dosages of biochar that are realistic for domestic production by farmers at each of the sites over four growing seasons. Commonly available biomass wastes in each agro-ecosystem (coconut shells, coffee husks, maize cobs) were used as feedstock for biochar, which was applied at 1, 5, and 10 Mg ha ⁻¹ at the start of the experiment. Across seasons and fertilizer treatments, maize grain yield (dry matter) showed consistently positive responses, with an average increase of 1.0, 2.6, and 4.0 Mg ha ⁻¹ , respectively, above the control for the three biochar application rates. Absolute responses of maize grain yield to specific biochar doses were similar across the four investigated seasons and replicate farms within sites, and uncorrelated to yield levels in the control treatment. Here, we show for the first time that yield response to biochar decreased with increasing application rate, indicating that it may be better to spread a given amount of biochar over a large area rather than concentrating it to a smaller area, at least when biochar is applied along plant rows at rates ≥1 Mg ha ⁻¹ , as in our experiment. This study demonstrated that application of biochar, locally produced from available biomass residues, is a promising approach to enhance agricultural production and carbon storage on smallholder farms under a wide range of pedo-climatic conditions in Kenya.
... Until recently, coastal vegetation management has not been separately considered as a mitigation lever in IPCC climate assessments, being subsumed within afforestation and reforestation in Integrated Assessment Models (IPCC, 2018). It has also been omitted from several comparative assessments of negative emissions (e.g., Minx et al., 2018;GESAMP, 2019), or grouped with freshwater wetland and peatland restoration (McLaren, 2012;Royal Society Royal Academy of Engineering, 2018), or considered as a soil or land-based mitigation technique (Bossio et al., 2020;Roe et al., 2021). The IPCC AR6 cycle does, however, specifically discuss CBCEs in all three Working Group reports, with WG II coverage emphasizing their cobenefits (Parmesan et al., 2022) and vulnerability to climate change and direct anthropogenic impacts (Cooley et al., 2022). ...
Article
The Conversation, 29 July 2022 https://theconversation.com/climate-change-why-we-cant-rely-on-regrowing-coastal-habitats-to-offset-carbon-emissions-185726
... Until recently, coastal vegetation management has not been separately considered as a mitigation lever in IPCC climate assessments, being subsumed within afforestation and reforestation in Integrated Assessment Models (IPCC, 2018). It has also been omitted from several comparative assessments of negative emissions (e.g., Minx et al., 2018;GESAMP, 2019), or grouped with freshwater wetland and peatland restoration (McLaren, 2012;Royal Society Royal Academy of Engineering, 2018), or considered as a soil or land-based mitigation technique (Bossio et al., 2020;Roe et al., 2021). The IPCC AR6 cycle does, however, specifically discuss CBCEs in all three Working Group reports, with WG II coverage emphasizing their cobenefits (Parmesan et al., 2022) and vulnerability to climate change and direct anthropogenic impacts (Cooley et al., 2022). ...
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Mangrove forests, seagrass meadows and tidal saltmarshes are vegetated coastal ecosystems that accumulate and store large quantities of carbon in their sediments. Many recent studies and reviews have favorably identified the potential for such coastal “blue carbon” ecosystems to provide a natural climate solution in two ways: by conservation, reducing the greenhouse gas emissions arising from the loss and degradation of such habitats, and by restoration, to increase carbon dioxide drawdown and its long-term storage. The focus here is on the latter, assessing the feasibility of achieving quantified and secure carbon removal (negative emissions) through the restoration of coastal vegetation. Seven issues that affect the reliability of carbon accounting for this approach are considered: high variability in carbon burial rates; errors in determining carbon burial rates; lateral carbon transport; fluxes of methane and nitrous oxide; carbonate formation and dissolution; vulnerability to future climate change; and vulnerability to non-climatic factors. Information on restoration costs is also reviewed, with the conclusion that costs are highly uncertain, with lower-range estimates unrealistic for wider application. CO 2 removal using coastal blue carbon restoration therefore has questionable cost-effectiveness when considered only as a climate mitigation action, either for carbon-offsetting or for inclusion in Nationally Determined Contributions. Many important issues relating to the measurement of carbon fluxes and storage have yet to be resolved, affecting certification and resulting in potential over-crediting. The restoration of coastal blue carbon ecosystems is nevertheless highly advantageous for climate adaptation, coastal protection, food provision and biodiversity conservation. Such action can therefore be societally justified in very many circumstances, based on the multiple benefits that such habitats provide at the local scale.
... Until recently, coastal vegetation management has not been separately considered as a mitigation lever in IPCC climate assessments, being subsumed within afforestation and reforestation in Integrated Assessment Models (IPCC, 2018). It has also been omitted from several comparative assessments of negative emissions (e.g., Minx et al., 2018;GESAMP, 2019), or grouped with freshwater wetland and peatland restoration (McLaren, 2012;Royal Society Royal Academy of Engineering, 2018), or considered as a soil or land-based mitigation technique (Bossio et al., 2020;Roe et al., 2021). The IPCC AR6 cycle does, however, specifically discuss CBCEs in all three Working Group reports, with WG II coverage emphasizing their cobenefits (Parmesan et al., 2022) and vulnerability to climate change and direct anthropogenic impacts (Cooley et al., 2022). ...
Article
The Conversation, 29 July 2022 https://theconversation.com/pourquoi-on-ne-peut-pas-se-fier-a-la-restauration-des-habitats-cotiers-pour-ralentir-le-changement-climatique-187788
... For our data collection, we first listed the most well-known CDR activities (Table 1) drawing from the literature (Fawzy et al., 2020;Minx et al., 2018) following the IPCC's (2021) definition of CDR as the capture of CO2 from the atmosphere (e.g., directly from air, through photosynthesis, or through geochemistry) and the sequestration away from the atmosphere (e.g., to a geological, terrestrial, oceanic, or product reservoir). We extended the definition to include removal from the environment (e.g., seawater). ...
... Although their omittance could be the product of the database being incomplete, it may also reflect the relative infancy in their research and development . Their omittance may also reflect the notion that not all suggested CDR activities are necessarily good ideas, as some have unknown or high risks, sideeffects, or have implementation barriers Minx et al., 2018;Morrow et al., 2020;Williamson, 2016). A process to evaluate which CDR activity is not only promising but also fit-for-purpose, and where targeted research efforts would speed up the development of standards would support a more diverse representation of CDR activities. ...
... More standards are available for nature-based removal activities than engineeringbased ones ( Table 2). This observation may be explained by the longer history of methodologies developed for crediting afforestation and reforestation projects going back to the 1970s following ground-breaking work on REDD+ (Carton et al., 2020;Minx et al., 2018). Engineering-based and hybrid activities may not have as long of a history but, in the future, will likely exceed the number of possible nature-based activities. ...