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In the Sacramento–San Joaquin Delta (Delta), widespread drainage of historical wetlands has led to extensive subsidence and peat carbon losses, as well as high ongoing greenhouse gas (GHG) emissions. Large-scale wetland restoration and conversion to rice fields has the potential to mitigate these effects while conferring flood protection and creating habitat for wetland species. To explore the scale of these potential benefits, this study evaluated the effects of seven Delta-wide land-use scenarios on carbon stocks, land-surface elevation, GHG emissions, and habitat. Peat mapping and data from peat cores indicate that soil carbon stocks have decreased between the early 1800s and 2010s from 288 ± 15 to 145 ± 14 million metric tons (Mt) of carbon (C). If existing land uses continue, the Delta could lose an additional 8.3 Mt C during the coming 40 years, equal to average GHG emissions of 1.2 Mt CO2 equivalents (CO2e) yr-1. Future restoration and rice-farming scenarios indicate that wetland restoration could theoretically halt GHG emissions, converting the Delta from a large GHG source to a weak net source or sink. Across three future scenarios based on existing restoration targets, wetland creation and conversion to rice fields reduced GHG emissions by 0.39 to 0.67 Mt CO2e yr-1, with per-area benefits of 16 to 28 t CO2e per hectare (ha) yr-1. Differences among scenarios in extents of wetland types influenced their relative benefits for different management goals. Tidal restoration and conversion to rice fields enhanced habitat benefits and offered a source of agricultural income, but with reduced GHG mitigation compared with conversion to peat-building wetlands. This highlights the importance of clear objectives when developing land-use plans. A strategic land-management portfolio that includes rice fields and both impounded and tidal wetlands could be designed to provide GHG and subsidence mitigation while offering a diverse suite of benefits for ecosystems and people.

Carbon Dioxide Removals (CDR) and Carbon Capture and Storage (CCS) have received a lot of attention as a tool to mitigate climate change and reach climate neutrality. Bioenergy with Carbon Capture and Storage (BECCS) is seen as one of the more promising CDRs, and from 2026, the Danish utility Ørsted is establishing the first BECCS plants in Denmark. We present a case study of BECCS by installing CCS at a biomass‐fired CHP plant and the aim is to quantify the CDR potential and carbon dynamics of the BECCS system. Moreover, the study aims to quantify the emissions related to capturing and store CO2. The GHG emissions from CCS including heat, electricity, transport and storage are approximately 100 kgCO2/t stored CO2 and the carbon payback time of the BECCS system is 3–4 years relative to leaving the wood in the forest or at processing industries. The main driver of the payback time is the additional use of biomass to operate CCS which shifts the timing of CO2 emissions more towards the present. The additional biomass use also increases supply chain emissions, and on top of that, only 90% of the direct CO2 emissions from the CHP plant are captured. The study illustrates the importance of temporal scope in assessing the CDR potential of BECCS. With continuous use of biomass, GHG emissions are 207 kgCO2/t stored CO2 in year 1 and −742 kgCO2/t stored CO2 in year 99. This study reveals inconsistencies in the assessment of the CDR potential of BECCS in the literature. There is a considerable need for further research within this field to assess how BECCS can contribute to mitigating climate change and on the appropriate scale of BECCS deployment. [ABSTRACT FROM AUTHOR]

The international community is confronted with urgent questions relating to the protection of the marine environment, as well as climate change mitigation. In this vein, ocean interventions, such as ocean fertilisation and carbon capture and sequestration in sub-sea geological formations have gained popularity in order to accelerate the uptake of anthropogenic carbon dioxide. The interaction of such technologies with the ocean environment can potentially cause unintended effects beyond sequestration and storage of atmospheric carbon, hence clear regulations, adapting to emerging technologies and based on public international law, are indispensable and to be based on scientific evidence and research. [ABSTRACT FROM AUTHOR]

Enhanced silicate rock weathering (ERW) is an emerging strategy for carbon dioxide removal (CDR) from the atmosphere to mitigate anthropogenic climate change. ERW aims at promoting soil inorganic carbon sequestration by accelerating geochemical weathering processes. Theoretically, ERW may also impact soil organic carbon (SOC), the largest carbon pool in terrestrial ecosystems, but experimental evidence for this is largely lacking. Here, we conducted a 2‐year field experiment in tropical rubber plantations in the southeast of China to evaluate the effects of wollastonite powder additions (0, 0.25, and 0.5 kg m−2) on both soil organic and inorganic carbon at 0–10 cm depth. We found that ERW significantly increased the concentration of SOC and HCO3−, but the increases in SOC were four and eight times higher than that of HCO3− with low‐ and high‐level wollastonite applications. ERW had positive effects on the accrual of organic carbon in mineral‐associated organic matter (MAOM) and macroaggregate fractions, but not on particulate organic matter. Path analysis suggested that ERW increased MAOM mainly by increasing the release of Ca, Si, and Fe, and to a lesser extent by stimulating root growth and microbial‐derived carbon inputs. Our study indicates that ERW with wollastonite can promote SOC sequestration in stable MOAM in surface soils through both the soil mineral carbon pump and microbial carbon pump. These effects may have been larger than the inorganic CDR during our experiment. We argue it is essential to account for the responses of SOC in the assessments of CDR by ERW. [ABSTRACT FROM AUTHOR]

Background: Integrating trees into agricultural landscapes can provide climate mitigation and improves soil fertility, biodiversity habitat, water quality, water flow, and human health, but these benefits must be achieved without reducing agriculture yields. Prior estimates of carbon dioxide (CO2) removal potential from increasing tree cover in agriculture assumed a moderate level of woody biomass can be integrated without reducing agricultural production. Instead, we used a Delphi expert elicitation to estimate maximum tree covers for 53 regional cropping and grazing system categories while safeguarding agricultural yields. Comparing these values to baselines and applying spatially explicit tree carbon accumulation rates, we develop global maps of the additional CO2 removal potential of Tree Cover in Agriculture. We present here the first global spatially explicit datasets calibrated to regional grazing and croplands, estimating opportunities to increase tree cover without reducing yields, therefore avoiding a major cost barrier to restoration: the opportunity cost of CO2 removal at the expense of agriculture yields. Results: The global estimated maximum technical CO2 removal potential is split between croplands (1.86 PgCO2 yr− 1) and grazing lands (1.45 PgCO2 yr− 1), with large variances. Tropical/subtropical biomes account for 54% of cropland (2.82 MgCO2 ha− 1 yr− 1, SD = 0.45) and 73% of grazing land potential (1.54 MgCO2 ha− 1 yr− 1, SD = 0.47). Potentials seem to be driven by two characteristics: the opportunity for increase in tree cover and bioclimatic factors affecting CO2 removal rates. Conclusions: We find that increasing tree cover in 2.6 billion hectares of agricultural landscapes may remove up to 3.3 billion tons of CO2 per year – more than the global annual emissions from cars. These Natural Climate Solutions could achieve the Bonn Challenge and add 793 million trees to agricultural landscapes. This is significant for global climate mitigation efforts because it represents a large, relatively inexpensive, additional CO2 removal opportunity that works within agricultural landscapes and has low economic and social barriers to rapid global scaling. There is an urgent need for policy and incentive systems to encourage the adoption of these practices. [ABSTRACT FROM AUTHOR]

Understanding the behaviors of tropical cyclone (TC) intensity under the CO2 removal scenario is important for future climate adaptation and policy making. Based on the idealized CO2 ramp‐up (from 284.7 to 1,138.8 ppm) and symmetric ramp‐down experiments, our results suggest an asymmetric and irreversible response of TC potential intensity to CO2 reduction. Potential intensity shows an additional enhancement at the same CO2 level during the CO2 ramp‐down relative to the ramp‐up periods (though with regional differences), and does not completely return to the initial value even when CO2 recovers on multi‐decadal to centennial timescale. The enhanced potential intensity is dominated by the increased thermodynamic disequilibrium, which is mainly attributed to the weakened surface winds arising from the El Niño‐like warming pattern and inter‐hemispheric ocean temperature contrast. Our results highlight the potential risks of stronger storms on the socioeconomic development under the negative carbon emissions pathways. Plain Language Summary: Tropical cyclone (TC) is one of the most destructive natural disasters worldwide. Many studies pointed to the intensification of Tropical cyclones (TCs) in the warming future and thus it is important to limit the amplitude of global warming and mitigate the potential risks of enhanced TCs. This study examines whether TC potential intensity may return to its initial state with the CO2 removal method based on the idealized CO2 forcing experiments, in which CO2 increases from the preindustrial to quadruple level (284.7–1,138.8 ppm) and decreases symmetrically. Our results suggest an asymmetric and irreversible response of TC potential intensity to CO2 removal, with an additional enhancement at the same CO2 level during the CO2 ramp‐down relative to the ramp‐up periods. Moreover, potential intensity does not fully recover to the initial state even when CO2 is restored on multi‐decadal to centennial timescale. The increased potential intensity during the CO2 ramp‐down relative to the ramp‐up periods is dominated by the increased thermodynamic disequilibrium. This is further linked with the uneven sea surface temperature response and the resultant weakened surface wind speed. This study helps understand the response of TC activity under future mitigation pathways and highlights the potential risks of the enhanced storm intensity. Key Points: Asymmetric and irreversible response of tropical cyclone (TC) potential intensity under the symmetric CO2 rising and declining scenarioThe enhancement in TC potential intensity when CO2 recovers is dominated by the increased thermodynamic disequilibriumEl Niño‐like sea surface temperature pattern contributes to the weakened surface winds and thereby increased TC potential intensity [ABSTRACT FROM AUTHOR]

The global energy system is in transition. It is attempting to reach net‐zero greenhouse gas emissions by 2050. The systemic changes mean that the role of bioenergy will change. The potential of bioenergy to make a flexible contribution to the energy system is key for the achievement of global emission reduction ambitions and the functioning of the low‐carbon energy system and economy. As the volume of sustainably available biomass resources is limited, defining the contributions from bioenergy to a low‐carbon energy system and finding balances – and ideally synergies – between the different possible energy and climate system services that biomass can provide will be very important. The recognized system services include, among others, the flexible operation of bioenergy plants to integrate variable renewable energy sources and to provide negative carbon dioxide (CO2) emissions. Interest in flexible operation of bioenergy value chains, bioenergy with carbon capture and utilization as well as synergies with renewable hydrogen‐based value chains has increased recently. The objective of this paper is to present a holistic definition of flexible bioenergy as a system service based on the work conducted in International Energy Agency (IEA) Bioenergy Technology Collaboration Programme's Task 44 Flexible Bioenergy and System Integration, and to provide some practical examples. The paper also presents the different bioenergy system services and considers their definitions and interactions, as this is important in energy system design. The definition of flexible bioenergy shows that the flexibility provision from bioenergy goes far beyond the traditional definition of providing short‐term flexibility in the power sector. Indicators to demonstrate the value of services as well as further quantitative assessment of synergies and trade‐offs are needed to valorize the different services from bioenergy and create viable business cases. [ABSTRACT FROM AUTHOR]

Understanding the climate and carbon cycle response to negative CO2 emissions is important for developing climate mitigation strategies that aim to limit global warming to a specific threshold. In this study, using a coupled climate and carbon cycle model, a novel set of nine stylized simulations are conducted with cumulative emissions of 1,000 GtC, 2,000 GtC, and 5,000 GtC over 150, 250, and 500 years, followed by identical cumulative negative emissions so that the net cumulative emissions are zero. On millennial‐timescales, the climate system returns close to the preindustrial state, independent of the emission and removal pathways. However, the thermal and biogeochemical inertia of the ocean play an important role in determining the climate and carbon cycle response during the emission and removal phases. When zero net emissions are reached, surface air temperature is larger by 0–1°C than the preindustrial state, and the atmospheric CO2 concentration is less by 12–29 ppm. These changes increase with both the magnitude and duration of the emission and removal pulses. In contrast, hysteresis in the relationship between global mean surface temperature and cumulative carbon emissions increases with the magnitude but decreases with the duration of emission and removal pulses. Our study highlights the role of ocean inertia in the asymmetry in climate response to emissions and removals and indicates that an earlier emission reduction implying emission/removal pathways with smaller magnitudes and shorter durations for the positive and negative emission pulses would avoid larger climate and carbon cycle impacts on centennial‐timescales. Plain Language Summary: In this study, we examine the climate system response to a set of scenarios where emissions are followed by the removal of all carbon emitted into the atmosphere. We find that the climate system returns to preindustrial state on millennial timescales independent of emission and removal pathways. However, larger changes in the climate system at the end of removals (on centennial timescales) are simulated for a larger magnitude and longer duration of the emission and removal pulses. Since a delay in emission reduction implies a larger magnitude and longer duration for the emissions and consequently larger magnitude and longer duration for the removals to bring the climate state to preindustrial conditions, an earlier emission reduction would help to avoid large climate and carbon cycle impacts on centennial‐timescales. Key Points: The climate system response to net zero emissions is path independent on millennial timescalesOn centennial time scales, the climate system response to net zero emissions depends on the magnitude and duration of emission pulsesA larger magnitude and longer duration for the emission pulses lead to longer delays in climate response on centennial timescales [ABSTRACT FROM AUTHOR]

Limiting climate change to 1.5°C and achieving net-zero emissions would entail substantial carbon dioxide removal (CDR) from the atmosphere by the mid-century, but how much CDR is needed at country level over time is unclear. The purpose of this paper is to provide a detailed description of when and how much CDR is required at country level in order to achieve 1.5°C and how much CDR countries can carry out domestically. We allocate global CDR pathways among 170 countries according to 6 equity principles and assess these allocations with respect to countries biophysical and geophysical capacity to deploy CDR. Allocating global CDR to countries based on these principles suggests that CDR will, on average, represent ∼4% of nations total emissions in 2030, rising to ∼17% in 2040. Moreover, equitable allocations of CDR, in many cases, exceed implied land and carbon storage capacities. We estimate ∼15% of countries (25) would have insufficient land to contribute an equitable share of global CDR, and ∼40% of countries (71) would have insufficient geological storage capacity. Unless more diverse CDR technologies are developed, the mismatch between CDR liabilities and land-based CDR capacities will lead to global demand for six GtCO2 carbon credits from 2020 to 2050. This demonstrates an imperative demand for international carbon trading of CDR.

Abstract Background Integrating trees into agricultural landscapes can provide climate mitigation and improves soil fertility, biodiversity habitat, water quality, water flow, and human health, but these benefits must be achieved without reducing agriculture yields. Prior estimates of carbon dioxide (CO2) removal potential from increasing tree cover in agriculture assumed a moderate level of woody biomass can be integrated without reducing agricultural production. Instead, we used a Delphi expert elicitation to estimate maximum tree covers for 53 regional cropping and grazing system categories while safeguarding agricultural yields. Comparing these values to baselines and applying spatially explicit tree carbon accumulation rates, we develop global maps of the additional CO2 removal potential of Tree Cover in Agriculture. We present here the first global spatially explicit datasets calibrated to regional grazing and croplands, estimating opportunities to increase tree cover without reducing yields, therefore avoiding a major cost barrier to restoration: the opportunity cost of CO2 removal at the expense of agriculture yields. Results The global estimated maximum technical CO2 removal potential is split between croplands (1.86 PgCO2 yr− 1) and grazing lands (1.45 PgCO2 yr− 1), with large variances. Tropical/subtropical biomes account for 54% of cropland (2.82 MgCO2 ha− 1 yr− 1, SD = 0.45) and 73% of grazing land potential (1.54 MgCO2 ha− 1 yr− 1, SD = 0.47). Potentials seem to be driven by two characteristics: the opportunity for increase in tree cover and bioclimatic factors affecting CO2 removal rates. Conclusions We find that increasing tree cover in 2.6 billion hectares of agricultural landscapes may remove up to 3.3 billion tons of CO2 per year – more than the global annual emissions from cars. These Natural Climate Solutions could achieve the Bonn Challenge and add 793 million trees to agricultural landscapes. This is significant for global climate mitigation efforts because it represents a large, relatively inexpensive, additional CO2 removal opportunity that works within agricultural landscapes and has low economic and social barriers to rapid global scaling. There is an urgent need for policy and incentive systems to encourage the adoption of these practices.

Abstract As a highly developed region, Guangdong province has substantial industrial emissions. Its subtropical monsoon climate, characterized by abundant hydrothermal conditions, contributes to a substantial biomass potential. The adoption of potential biomass-based carbon dioxide removal (CDR) technologies, such as biochar, presents an opportunity to mitigate emissions and work towards carbon neutrality in the future. However, the current state of the land carbon balance and the CDR potential of biochar in Guangdong province remains unclear. We first calculated the land carbon balance based on inventory data. Then we estimated the CDR potential of biochar derived from agricultural residues, forestry residues, and bioenergy crops cultivated on marginal lands in Guangdong province using life cycle analysis (LCA). Results show that Guangdong province has not yet achieved carbon neutrality, with a net emission (carbon emissions remaining after offsetting by carbon sinks) of 925.63 Tg CO2e (CO2 equivalent, 1Tg = 106 t) in 2021. Emissions from energy consumption account for the highest proportion, contributing 83.8% of total emissions. In the highest biomass utilization scenario, the maximum CDR potential of biochar derived from all biomass types reaches 84.30 Tg CO2e yr-1, which could offset 9.11% of net carbon emissions in Guangdong province. Our findings provide crucial guidance for setting emission reduction targets and implementing effective mitigation strategies in Guangdong province under temperature warming. Graphical Abstract

Abstract Background Achieving a net zero greenhouse gas United States (US) economy is likely to require both deep sectoral mitigation and additional carbon dioxide removals to offset hard-to-abate emissions. Enhancing the terrestrial carbon sink, through practices such as the adoption of no-till and cover cropping agricultural management, could provide a portion of these required offsets. Changing domestic agricultural practices to optimize carbon content, however, might reduce or shift US agricultural commodity outputs and exports, with potential implications on respective global markets and land use patterns. Here, we use an integrated energy-economy-land-climate model to comprehensively assess the global land, trade, and emissions impacts of an adoption of domestic no-till farming and cover cropping practices based on carbon pricing. Results We find that the adoption of these practices varies depending on which aspects of terrestrial carbon are valued. Valuation of all terrestrial carbon resulted in afforestation at the expense of domestic agricultural production. In contrast, a policy valuing soil carbon in agricultural systems specifically indicates strong adoption of no-till and cover cropping for key crops. Conclusions We conclude that under targeted terrestrial carbon incentives, adoption of no-till and cover cropping practices in the US could increase the terrestrial carbon sink with limited effects on crop availability for food and fodder markets. Future work should consider integrated assessment modeling of non-CO2 greenhouse gas impacts, above ground carbon storage changes, and capital and operating cost considerations.

Abstract This article conducts a qualitative governance analysis of the European Commission’s 2022 proposal for a certification framework for carbon removals (CRCF). It highlights potential challenges and legal implications—with a specific focus on carbon farming. While the European Union (EU) acknowledges carbon farming as an important strategy to offset residual emissions, such carbon removal activities are prone to reversals and models often overestimate their sequestration potential. The CRCF aims to account for these issues, but the analysis shows that the proposal may, in part, undermine international climate and biodiversity goals set by the Paris Agreement and the Convention on Biological Diversity. Key concerns include its failure to consider the normative hierarchy between emission reductions and removals mandated by EU and international law, the introduction of a temporary removal crediting system, the extensive delegation of powers to the Commission, the possibility that it may incentivise shifting effects, and its lack of alignment with other EU environmental policies. Additionally, the CRCF’s failure to restrict the use of carbon credits after certification increases the risk of double claiming of removal activities—and the proposal may open the door for to future integration of carbon removals into the EU’s emission trading scheme, which should be avoided for various reasons. As an alternative, member states should consider targeted subsidy schemes and regulatory instruments to navigate these challenges in carbon farming effectively.

Direct Air Capture (DAC) offers a promising pathway for combating climate change by removing carbon dioxide (CO2) directly from the atmosphere. Here, we discuss Heirloom's approach to DAC, which uses naturally occurring minerals, namely, calcium carbonate (CaCO3), in a cyclic process that leverages warehouse automation systems previously developed for large warehouses. The integration of DAC with warehouse automation systems unlocks a degree of manufacturability, scalability, operational efficiency, and financial viability. For successful scaling, DAC technologies and project developers must think through key scalability constraints, including modularity, constructability, supply chains, and leveraging existing infrastructure. [ABSTRACT FROM AUTHOR]

As a highly developed region, Guangdong province has substantial industrial emissions. Its subtropical monsoon climate, characterized by abundant hydrothermal conditions, contributes to a substantial biomass potential. The adoption of potential biomass-based carbon dioxide removal (CDR) technologies, such as biochar, presents an opportunity to mitigate emissions and work towards carbon neutrality in the future. However, the current state of the land carbon balance and the CDR potential of biochar in Guangdong province remains unclear. We first calculated the land carbon balance based on inventory data. Then we estimated the CDR potential of biochar derived from agricultural residues, forestry residues, and bioenergy crops cultivated on marginal lands in Guangdong province using life cycle analysis (LCA). Results show that Guangdong province has not yet achieved carbon neutrality, with a net emission (carbon emissions remaining after offsetting by carbon sinks) of 925.63 Tg CO2e (CO2 equivalent, 1Tg = 106 t) in 2021. Emissions from energy consumption account for the highest proportion, contributing 83.8% of total emissions. In the highest biomass utilization scenario, the maximum CDR potential of biochar derived from all biomass types reaches 84.30 Tg CO2e yr-1, which could offset 9.11% of net carbon emissions in Guangdong province. Our findings provide crucial guidance for setting emission reduction targets and implementing effective mitigation strategies in Guangdong province under temperature warming. Highlights: • Guangdong province has not yet achieved carbon neutrality within its land boundary, requiring the removal of at least 925.63 Tg of CO2 to achieve it. • The implementation of biochar could offset 9.11% of net CO2 emissions in Guangdong province. • Energy consumption contributes the most significant share of carbon emissions in Guangdong province, amounting to 83.8% of the total emissions. • The significant biomass resources from residues and bioenergy crops play a critical role in carbon removal through biomass-based CDR technologies in Northern Guangdong. [ABSTRACT FROM AUTHOR]

Background: Achieving a net zero greenhouse gas United States (US) economy is likely to require both deep sectoral mitigation and additional carbon dioxide removals to offset hard-to-abate emissions. Enhancing the terrestrial carbon sink, through practices such as the adoption of no-till and cover cropping agricultural management, could provide a portion of these required offsets. Changing domestic agricultural practices to optimize carbon content, however, might reduce or shift US agricultural commodity outputs and exports, with potential implications on respective global markets and land use patterns. Here, we use an integrated energy-economy-land-climate model to comprehensively assess the global land, trade, and emissions impacts of an adoption of domestic no-till farming and cover cropping practices based on carbon pricing. Results: We find that the adoption of these practices varies depending on which aspects of terrestrial carbon are valued. Valuation of all terrestrial carbon resulted in afforestation at the expense of domestic agricultural production. In contrast, a policy valuing soil carbon in agricultural systems specifically indicates strong adoption of no-till and cover cropping for key crops. Conclusions: We conclude that under targeted terrestrial carbon incentives, adoption of no-till and cover cropping practices in the US could increase the terrestrial carbon sink with limited effects on crop availability for food and fodder markets. Future work should consider integrated assessment modeling of non-CO2 greenhouse gas impacts, above ground carbon storage changes, and capital and operating cost considerations. [ABSTRACT FROM AUTHOR]

Artificial CO 2 removal from the atmosphere (also referred to as negative CO 2 emissions) has been proposed as a potential means to counteract anthropogenic climate change. Here we use an Earth system model to examine the response of ocean acidification to idealized atmospheric CO 2 removal scenarios. In our simulations, atmospheric CO 2 is assumed to increase at a rate of 1% per year to four times its pre-industrial value and then decreases to the pre-industrial level at a rate of 0.5%, 1%, 2% per year, respectively. Our results show that the annual mean state of surface ocean carbonate chemistry fields including hydrogen ion concentration ([H+]), pH and aragonite saturation state respond quickly to removal of atmospheric CO 2. However, the change of seasonal cycle in carbonate chemistry lags behind the decline in atmospheric CO 2. When CO 2 returns to the pre-industrial level, over some parts of the ocean, relative to the pre-industrial state, the seasonal amplitude of carbonate chemistry fields is substantially larger. Simulation results also show that changes in deep ocean carbonate chemistry substantially lag behind atmospheric CO 2 change. When CO 2 returns to its pre-industrial value, the whole-ocean acidity measured by [H+] is 15%-18% larger than the pre-industrial level, depending on the rate of CO 2 decrease. Our study demonstrates that even if atmospheric CO 2 can be lowered in the future as a result of net negative CO 2 emissions, the recovery of some aspects of ocean acidification would take decades to centuries, which would have important implications for the resilience of marine ecosystems. [ABSTRACT FROM AUTHOR]

Carbon dioxide removal (CDR) technologies, such as direct air carbon capture and storage (DACCS), will be critical in limiting the rise of the average global temperature over the next century. Scaling up DACCS technologies requires the support of a complex array of policies and infrastructure across multiple overlapping policy areas, such as climate, energy, technology innovation and resource management. While the literature on DACCS and other CDR technologies acknowledges the path-dependent nature of policy development, it has tended to focus on abstract policy prescriptions that are not rooted in the specific political, social and physical (infrastructural) context of the implementing state. To address this gap, this paper provides a country-level study of the emerging DACCS policy regime in Canada. Drawing on the existing literature that identifies idealized (acontextual) policy objectives that support DACCS development and effective regulation, we identify the actionable policy objectives across six issue domains: general climate mitigation strategies; energy and resource constraints; carbon storage and transport regulation and infrastructure; financing scale-up and supporting innovation; removal and capture technology availability and regulation; and addressing social acceptability and public interest. Using a database of Canadian climate policies (n = 457), we identify policies within the Canadian (federal and provincial) policy environment that map to the idealized policy objectives within each of these domains. This exercise allows us to analyze how key policy objectives for DACCS development are represented within the Canadian system, and enables us to identify potential niches, and landscape influences within the system, as well as gaps and potential barriers to the system transition process. This paper contributes to our understanding of national DACCS policy development by providing a framework for identifying components of the DAC system and linking those components to desired policy outcomes and may provide a basis for future cross-country comparisons of national-level DACCS policy. [ABSTRACT FROM AUTHOR]

Climate stabilization is crucial for restabilizing the Earth system but should not undermine biosphere integrity, a second pillar of Earth system functioning. This is of particular concern if it is to be achieved through biomass-based negative emission (NE) technologies that compete for land with food production and ecosystem protection. We assess the NE contribution of land- and calorie-neutral pyrogenic carbon capture and storage (LCN-PyCCS) facilitated by biochar-based fertilization, which sequesters carbon and reduces land demand by increasing crop yields. Applying the global biosphere model LPJmL with an enhanced representation of fast-growing species for PyCCS feedstock production, we calculated a land-neutral global NE potential of 0.20–1.10 GtCO2 year−1 assuming 74% of the biochar carbon remaining in the soil after 100 years (for + 10% yield increase; no potential for + 5%; 0.61–1.88 GtCO2 year−1 for + 15%). The potential is primarily driven by the achievable yield increase and the management intensity of the biomass producing systems. NE production is estimated to be enhanced by + 200–270% if management intensity increases from a marginal to a moderate level. Furthermore, our results show sensitivity to process-specific biochar yields and carbon contents, producing a difference of + 40–75% between conservative assumptions and an optimized setting. Despite these challenges for making world-wide assumptions on LCN-PyCCS systems in modeling, our findings point to discrepancies between the large NE volumes calculated in demand-driven and economically optimized mitigation scenarios and the potentials from analyses focusing on supply-driven approaches that meet environmental and socioeconomic preconditions as delivered by LCN-PyCCS. [ABSTRACT FROM AUTHOR]

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Antarctic Bottom Water (AABW) transports surface nutrients deep into the ocean, sequestering them for centuries. Enhancing its biological carbon fixation could augment carbon sinks and reduce atmospheric CO2. Yet, it is uncertain if AABW receives enough light for significant photosynthesis before subducting. Using Lagrangian particle tracking in an ocean sea‐ice model, we found: (a) 70% (66%–73%, depending on euphotic zone (Zeu) criteria) nutrient rich circumpolar deep water never enters the Zeu before becoming AABW. This percentage varies from 70% to 91%, depending on the mixed layer (ML) parameterization adjustments; (b) The remaining particles in the euphotic zone have 39 (34–49, depending on Zeu criteria) days average residence time. The time is not sensitive to ML parameterization strength but turning it off doubles the time; and (c) AABW is mainly exposed to enough light on the Antarctic continental shelf during spring and summer. We conclude that the potential of biotic carbon sequestration in AABW is highly limited by light energy. Plain Language Summary: Antarctic Bottom Water (AABW) originates primarily from nutrient‐rich deep waters upwelled around Antarctica. AABW spends a relatively brief time at the sea surface, thus being exposed to comparatively little light energy and leaving a considerable amount of nutrients unused by photosynthetic carbon fixation. If more of these nutrients were utilized through photosynthesis, for example, stimulated by ocean iron fertilization, more atmospheric CO2 could be sequestered in the oceans. Understanding how long AABW stays in the euphotic zone is therefore critical to assess the potential for biologically based CO2 sequestration in the Southern Ocean. To constrain this residence time, we released virtual particles in a high‐resolution ocean model and tracked their trajectories through the Southern Ocean. We found that more than half of the particles are never exposed to sufficient light to enable carbon fixation while the remaining particles are only exposed to relevant light energy for less than 2 months in spring and summer near Antarctica. Our results indicate that the capacity for increasing atmospheric CO2 sequestration in the Southern Ocean near Antarctica is limited by sunlight. Key Points: 30% (27%–34%) of circumpolar deep water (CDW) transforming into Antarctic Bottom Water (AABW) enters the euphotic zone (Zeu), with uncertainty in parentheses based on adjusted Zeu thresholds4.1% (2.8%–6.2%) of the seawater that upwells as CDW and transforms into AABW has ≥4 consecutive weeks in the euphotic zoneThe euphotic zone residence occurred predominantly in spring and summer near Antarctica, with an average duration of 39 (34–49) days [ABSTRACT FROM AUTHOR]

In addition to radical reduction of greenhouse gas emissions, large-scale removal of anthropogenic CO2 will be required to mitigate the impacts of global warming. However, many greenhouse gas removal (GGR) methods remain at a nascent stage of development. A case study was carried out on the application of the collective intelligence (CI) model to the UK GGR sector and the need to scale up and accelerate development in an economically, socially and environmentally sustainable way. Through systems mapping, thematic analysis, workshops and semi-structured interviews, a rich dataset was formed on the existing level of and potential for CI within the UK GGR ecosystem. It was found that implementing CI thinking could address the need for increasing the visibility of the system and its workings to participants and the public. This would contribute to the formation of coherent, shared vision for the role of GGR in the UK's net zero strategy. It is proposed that these risks could be mitigated by creating a publicly accessible 'commons' to visualise the UK GGR ecosystem process, dynamics, components, and goals, allowing innovation policy to be more responsive to innovator and net zero policy needs. Increasing ecosystem awareness could lay the foundations for sharing of information, promotion of a more collective culture, and increased transparency and accountability, all of which are critical building blocks in establishing a robust GGR sector for the future. [ABSTRACT FROM AUTHOR]

Limiting the rise in global temperature to 1.5 °C will rely, in part, on technologies to remove CO2 from the atmosphere. However, many carbon dioxide removal (CDR) technologies are in the early stages of development, and there is limited data to inform predictions of their future adoption. Here, we present an approach to model adoption of early-stage technologies such as CDR and apply it to direct air carbon capture and storage (DACCS). Our approach combines empirical data on historical technology analogs and early adoption indicators to model a range of feasible growth pathways. We use these pathways as inputs to an integrated assessment model (the Global Change Analysis Model, GCAM) and evaluate their effects under an emissions policy to limit end-of-century temperature change to 1.5 °C. Adoption varies widely across analogs, which share different strategic similarities with DACCS. If DACCS growth mirrors high-growth analogs (e.g., solar photovoltaics), it can reach up to 4.9 GtCO2 removal by midcentury, compared to as low as 0.2 GtCO2 for low-growth analogs (e.g., natural gas pipelines). For these slower growing analogs, unabated fossil fuel generation in 2050 is reduced by 44% compared to high-growth analogs, with implications for energy investments and stranded assets. Residual emissions at the end of the century are also substantially lower (by up to 43% and 34% in transportation and industry) under lower DACCS scenarios. The large variation in growth rates observed for different analogs can also point to policy takeaways for enabling DACCS. [ABSTRACT FROM AUTHOR]

Understanding the response of the Earth system to varying concentrations of carbon dioxide (CO2) is critical for projecting possible future climate change and for providing insight into mitigation and adaptation strategies in the near future. In this study, we generate a dataset by conducting an experiment involving carbon dioxide removal (CDR)—a potential way to suppress global warming—using the Chinese Academy of Sciences Earth System Model version 2.0 (CAS-ESM2.0). A preliminary evaluation is provided. The model is integrated from 200–340 years as a 1% yr−1 CO2 concentration increase experiment, and then to ~478 years as a carbon dioxide removal experiment until CO2 returns to its original value. Finally, another 80 years is integrated in which CO2 is kept constant. Changes in the 2-m temperature, precipitation, sea surface temperature, ocean temperature, Atlantic meridional overturning circulation (AMOC), and sea surface height are all analyzed. In the ramp-up period, the global mean 2-m temperature and precipitation both increase while the AMOC weakens. Values of all the above variables change in the opposite direction in the ramp-down period, with a delayed peak relative to the CO2 peak. After CO2 returns to its original value, the global mean 2-m temperature is still ~1 K higher than in the original state, and precipitation is ~0.07 mm d−1 higher. At the end of the simulation, there is a ~0.5°C increase in ocean temperature and a 1 Sv weakening of the AMOC. Our model simulation produces similar results to those of comparable experiments previously reported in the literature. [ABSTRACT FROM AUTHOR]

This article conducts a qualitative governance analysis of the European Commission's 2022 proposal for a certification framework for carbon removals (CRCF). It highlights potential challenges and legal implications—with a specific focus on carbon farming. While the European Union (EU) acknowledges carbon farming as an important strategy to offset residual emissions, such carbon removal activities are prone to reversals and models often overestimate their sequestration potential. The CRCF aims to account for these issues, but the analysis shows that the proposal may, in part, undermine international climate and biodiversity goals set by the Paris Agreement and the Convention on Biological Diversity. Key concerns include its failure to consider the normative hierarchy between emission reductions and removals mandated by EU and international law, the introduction of a temporary removal crediting system, the extensive delegation of powers to the Commission, the possibility that it may incentivise shifting effects, and its lack of alignment with other EU environmental policies. Additionally, the CRCF's failure to restrict the use of carbon credits after certification increases the risk of double claiming of removal activities—and the proposal may open the door for to future integration of carbon removals into the EU's emission trading scheme, which should be avoided for various reasons. As an alternative, member states should consider targeted subsidy schemes and regulatory instruments to navigate these challenges in carbon farming effectively. [ABSTRACT FROM AUTHOR]

According to most climate mitigation scenario assessments, limiting global warming to 1.5–2°C in the long run will not be possible without the extensive deployment of carbon dioxide removal (CDR) from the atmosphere. CDR is required for drawing down and achieving net-zero CO2 emissions by mid-century. Thereafter, CO2 removals will likely need to exceed residual CO2 emissions, resulting in net negative emissions. A policy framework based on 'carbon removal obligations' (CROs) has been proposed to respond to concerns about the financial and fiscal viability, the lack of incentives for CDR uptake, as well as the physical and technological risks associated with any climate mitigation scenario that relies on large scale CDR. Here we propose an updated and improved CRO policy framework, consisting of two core elements: the 'principal CRO mechanism' obliges emitters of a tonne of CO2 to remove a tonne of CO2 at the time of maturity of the CRO. On top of this obligation, CRO holders need to pay a fee for the temporary storage of CO2 in the atmosphere. This 'CRO pricing instrument' is used by regulators to steer the carbon emissions and removals pathways independently. Our update suggests that markets for CDR under the CRO framework should operate independently from markets for emission reductions. We propose a blueprint for legal implementation where CROs are integrated akin to private financial borrowing and debt mechanisms. By aligning CROs with established financial systems, we leverage familiar institutional roles, seamlessly integrating climate mitigation into the core economy. The proposal applies the polluter pays principle to the costs of carbon removal from the atmosphere, whilst providing legal guarantees that the removals will materialize. By placing climate change mitigation pricing levers in the hands of the traditional managers of financial stability, that is, central banks, better account is taken of the externality of carbon emissions as part of core economic and financial management, with the corollary that climate change mitigation response management is better integrated into the economic mainstream. Establishing a standard for the creation of removal units by CDR projects facilitates a more efficient market by reducing transaction costs and enhancing price discovery. Early action by government to put in place legislative measures indicating the direction of policy, and a timetable for introducing CROs, would enhance private sector confidence and engagement in the CDR project sector. [ABSTRACT FROM AUTHOR]

This document is a retraction notice for an article titled "Promise and performance of agricultural nutrient management policy: Lessons from the Baltic Sea." The article was published in the journal Ambio in 2022. The retraction notice states that the article has been retracted and provides a link to the retraction notice on the Frontiers in Marine Science website. The summary does not provide any information about the content of the retracted article or the reasons for its retraction. [Extracted from the article]

The removal of atmospheric carbon dioxide (CO2) is now essential to meet net zero goals and limit the impacts of climate change. Enhanced weathering is a method of sequestering CO2 that involves the distribution of finely ground silicate rocks over agricultural land. The weathering of these silicate rocks releases cations into solution which can balance dissolved inorganic carbon, effectively removing CO2 from the atmosphere. Despite being a promising method of carbon dioxide removal (CDR), enhanced weathering has been limited by uncertainty surrounding the measurement of CO2 sequestration. This study compares current measurement approaches that focus on quantifying inorganic carbon and cations within the soil and leachate. Cation-based calculations of CDR were compared to inorganic carbon-based calculations of CDR and soil results were compared to leachate results. The recovery rate of cations in the soil fraction was also tested. Three different ground silicate minerals/rocks – basalt, olivine and wollastonite, were mixed with two different soils and were allowed to weather over 16 weeks in 320 pots with and without plants under different watering regimes and the application of an acidifying fertiliser. Soil and leachate samples were analysed for cations by ICP-OES and inorganic carbon by direct CO2 analysis after acidification and total alkalinity titration (in leachate only). The results indicate that the soil retains most enhanced weathering products through the cation exchange reactions. CDR estimated by cations is often greater than CDR estimated by inorganic carbon. Measurement approaches to estimate cations are susceptible to incomplete or improper accounting through the under-extraction of cations stored within the soil-exchangeable pool, the activity of non-carbonic acids and CO2 outgassing. Inorganic carbon-based measurements, including direct inorganic carbon and total alkalinity analysis, are also complicated by the potential for CO2 loss through carbonate precipitation and re-equilibration. Therefore, inorganic carbon-based approaches and cation-based approaches should be reconciled to validate the estimation of CDR. The inorganic carbon-based estimation of CDR in leachate should equal the cation-based estimation of CDR in leachate—which will be achieved after quantification or estimation of the natural mechanisms that affect each approach. These findings will support the development of accurate measurement processes for enhanced weathering.

Abstract Carbon Dioxide Removals (CDR) and Carbon Capture and Storage (CCS) have received a lot of attention as a tool to mitigate climate change and reach climate neutrality. Bioenergy with Carbon Capture and Storage (BECCS) is seen as one of the more promising CDRs, and from 2026, the Danish utility Ørsted is establishing the first BECCS plants in Denmark. We present a case study of BECCS by installing CCS at a biomass‐fired CHP plant and the aim is to quantify the CDR potential and carbon dynamics of the BECCS system. Moreover, the study aims to quantify the emissions related to capturing and store CO2. The GHG emissions from CCS including heat, electricity, transport and storage are approximately 100 kgCO2/t stored CO2 and the carbon payback time of the BECCS system is 3–4 years relative to leaving the wood in the forest or at processing industries. The main driver of the payback time is the additional use of biomass to operate CCS which shifts the timing of CO2 emissions more towards the present. The additional biomass use also increases supply chain emissions, and on top of that, only 90% of the direct CO2 emissions from the CHP plant are captured. The study illustrates the importance of temporal scope in assessing the CDR potential of BECCS. With continuous use of biomass, GHG emissions are 207 kgCO2/t stored CO2 in year 1 and −742 kgCO2/t stored CO2 in year 99. This study reveals inconsistencies in the assessment of the CDR potential of BECCS in the literature. There is a considerable need for further research within this field to assess how BECCS can contribute to mitigating climate change and on the appropriate scale of BECCS deployment.

Summary: Direct air capture (DAC) is a promising carbon dioxide removal technology, but its effectiveness hinges on access to cheap, low-carbon energy. Here, we present a spatial techno-economic and environmental assessment of the coupling of solid sorbent DAC with different energy sources. We found that the most cost- and energy-efficient option is to couple DAC with thermal power plants, e.g., nuclear and natural gas combined cycle with carbon capture. These two options have a gross levelized cost of DAC (LCODgross) starting at $246–$503 and $314–$557 per tCO2, respectively, for different regions. For renewable energy and energy storage options, regions with good solar irradiation can achieve low LCODgross, at $319 per tCO2 when utilizing concentrated solar power, whereas regions with low solar irradiation are unsuitable for this option due to the high cost and large land requirement. Achieving an LCODgross of ≤$200 per tCO2 would require significant improvements in the current technology. Science for society: Cost-effective transition pathways to keep global temperature rise below 2°C require billions of tons of CO2 removal from the atmosphere annually. Direct air capture (DAC) offers advantages like permanent storage of CO2 with low land use but it is energy-intensive. Thus, sustainable and cost-effective large-scale DAC deployment needs optimal site identification for cheap, low-carbon energy and regional co-benefit maximization. This study presents a global assessment of DAC energy supply options, including conventional and renewable energy sources, considering region-specific factors. Our analysis identifies the most suitable energy supply options for different regions, assessed based on techno-economic and environmental performance and potential co-benefits. The results help provide a foundation of evidence that will be essential for developing business models, strategies, and policies for the sustainable and cost-effective large-scale deployment of DAC systems.

Abstract Understanding the behaviors of tropical cyclone (TC) intensity under the CO2 removal scenario is important for future climate adaptation and policy making. Based on the idealized CO2 ramp‐up (from 284.7 to 1,138.8 ppm) and symmetric ramp‐down experiments, our results suggest an asymmetric and irreversible response of TC potential intensity to CO2 reduction. Potential intensity shows an additional enhancement at the same CO2 level during the CO2 ramp‐down relative to the ramp‐up periods (though with regional differences), and does not completely return to the initial value even when CO2 recovers on multi‐decadal to centennial timescale. The enhanced potential intensity is dominated by the increased thermodynamic disequilibrium, which is mainly attributed to the weakened surface winds arising from the El Niño‐like warming pattern and inter‐hemispheric ocean temperature contrast. Our results highlight the potential risks of stronger storms on the socioeconomic development under the negative carbon emissions pathways.

Abstract Understanding the climate and carbon cycle response to negative CO2 emissions is important for developing climate mitigation strategies that aim to limit global warming to a specific threshold. In this study, using a coupled climate and carbon cycle model, a novel set of nine stylized simulations are conducted with cumulative emissions of 1,000 GtC, 2,000 GtC, and 5,000 GtC over 150, 250, and 500 years, followed by identical cumulative negative emissions so that the net cumulative emissions are zero. On millennial‐timescales, the climate system returns close to the preindustrial state, independent of the emission and removal pathways. However, the thermal and biogeochemical inertia of the ocean play an important role in determining the climate and carbon cycle response during the emission and removal phases. When zero net emissions are reached, surface air temperature is larger by 0–1°C than the preindustrial state, and the atmospheric CO2 concentration is less by 12–29 ppm. These changes increase with both the magnitude and duration of the emission and removal pulses. In contrast, hysteresis in the relationship between global mean surface temperature and cumulative carbon emissions increases with the magnitude but decreases with the duration of emission and removal pulses. Our study highlights the role of ocean inertia in the asymmetry in climate response to emissions and removals and indicates that an earlier emission reduction implying emission/removal pathways with smaller magnitudes and shorter durations for the positive and negative emission pulses would avoid larger climate and carbon cycle impacts on centennial‐timescales.

Summary: The role of negative emissions technologies (NETs) in climate change mitigation remains contentious. Although numerous studies indicate significant carbon dioxide removal (CDR) requirements for Paris Agreement mitigation goals to be achieved, others point out challenges and risks associated with high CDR strategies. Using a multiscale modeling approach, we explore NETs’ potential for a single country, the United Kingdom (UK). Here, we report that the UK has cost-effective potential to remove 79 MtCO2 per year by 2050, rising to 126–134 MtCO2 per year with well-integrated NETs in industrial clusters. Results highlight that biomass gasification for hydrogen generation with CCS is emerging as a key NET, despite biomass availability being a limiting factor. Moreover, solid DACCS systems utilizing industrial waste heat integration offer a solution to offsetting increases in demand from transportation and industrial sectors. These results emphasize the importance of a multiscale whole-systems assessment for integrating NETs into industrial strategies. Science for society: Understanding how to effectively mitigate climate change is crucial for the well-being of our planet and future generations. Negative emissions technologies (NETs) that take CO2 out of the air are a vital component in this effort, but their effectiveness is still being debated. Our study examines NETs’ potential in the UK, providing valuable insights for policymakers, industry leaders, and the public. We find that the UK could remove up to 126–134 million tonnes by 2050 if NETs are well integrated into industrial clusters where there is high waste heat potential. Key technologies include biomass gasification for hydrogen generation with carbon capture and storage (CCS) and direct air carbon capture and storage (DACCS) systems using industrial waste heat. These findings highlight the importance of integrating NETs into industrial strategies to meet climate goals effectively while addressing the increasing demand in the transportation and industrial sectors.

Several billion metric tons per year of durable carbon dioxide removal (CDR) will be needed by mid-century to prevent catastrophic climate warming, and many new approaches must be rapidly scaled to ensure this target is met. Geologically permanent sequestration of carbon dioxide (CO2) in carbonate minerals-carbon mineralization-requires two moles of alkalinity and one mole of a CO2-reactive metal such as calcium or magnesium per mole of CO2 captured. Chemical weathering of geological materials can supply both ingredients, but weathering reactions must be accelerated to achieve targets for durable CDR. Here, a scalable CDR and mineralization process is reported in which water electrolysis is used to produce sulfuric acid for accelerated weathering, while a base is used to permanently sequester CO2 from air into carbonate minerals. The process can be integrated into existing extractive processes by reacting produced sulfuric acid with critical element feedstocks that neutralize acidity (e.g., rock phosphorus or ultramafic rock mine tailings), with calcium- and magnesium-bearing sulfate wastes electrolytically upcycled. The highest reported efficiency of electrolytic sulfuric acid production is achieved by maintaining catholyte feed conditions that minimize Faradaic losses by hydroxide permeation of the membrane-separated electrochemical cell. The industrial implementation of this process provides a pathway to gigaton-scale CO2 removal and sequestration during the production of critical elements needed for decarbonizing global energy infrastructure and feeding the world.

We explore the response of the Earth’s coupled climate and carbon system to an idealized sequential addition and removal of CO2 to the atmosphere, following a symmetric and continuous emissions pathway, in contrast to the discontinuous emissions pathways that have largely informed our understanding of the climate response to net zero and net negative emissions to date. We find, using both an Earth system model and an ensemble of simple climate model realizations, that warming during the emissions reduction and negative emissions phases is defined by a combination of a proportionality of warming to cumulative emissions characterized by the transient climate response to emissions (TCRE), and a deviation from that proportionality that is governed by the zero emissions commitment (ZEC). About half of the ZEC is realized before reaching zero emissions, and the ZEC thus also controls the timing between peak cumulative CO2 emissions and peak temperature, such that peak temperature may occur before peak cumulative emissions if ZEC is negative, underscoring the importance of ZEC in climate policies aimed to limit peak warming. Thus we argue that ZEC is better defined as the committed warming relative to the expected TCRE proportionality, rather than as the additional committed warming that will occur after reaching net zero CO2 emissions. Once established, the combined TCRE and ZEC relationship holds almost to complete removal of prior cumulative CO2 emissions. As cumulative CO2 emissions approach zero through negative CO2 emissions, CO2 concentrations drop below preindustrial values, while residual long-term climate change continues, governed by multicentennial dynamical processes.

The net-zero greenhouse gas (GHG) emissions concept is emerging as a fundamental principle for initiatives to address climate change ranging from global to corporate scale. Offsetting emissions using carbon credits features in many sub-global net-zero and carbon-neutrality claims and pledges. Assertions that the use of emission reduction credits (ERCs) is insufficient in the context of offsetting emissions for such claims at sub-global scales are gaining acceptance. Conversely, we show that regardless of whether offsetting is based on the use of ERCs or carbon removal credits (CRCs), the impact on the net transfer of GHG to the atmosphere is the same. Therefore, both ERCs and CRCs are adequate for offsetting with the purpose of achieving net-zero emissions or carbon neutrality. We show that assertions that the use of ERCs is insufficient for offsetting for these purposes are based on an incorrect setting of assessment boundaries and related misconceptions. The results presented in this paper have fundamental implications for what kind of GHG mitigation action beyond entities’ own value chains may be considered adequate in relation to entities’ claims concerning making no contribution to the net accumulation of GHG in the atmosphere, i.e. net-zero and carbon-neutrality claims.

Carbon dioxide removal (CDR) is a necessary complement to emissions reductions to achieve a state of global net zero emissions and stabilise future warming. Despite its utility, CDR remains poorly understood. Due to a range of constraints, CDR is a fundamentally finite resource, which we currently do not have enough of to achieve and go beyond global net zero. This has wide-ranging but underexplored implications for the technical and economic feasibility of our collective net zero transition. At the same time, both the opportunity and obligation to undertake CDR are not equally distributed amongst actors and geographies. As a result, there are ongoing questions as to how we can increase the supply of quality CDR whilst at the same time ensure equitable distribution of that same CDR, both within and between countries and non-state actors. To explore these phenomena, we introduce and define the concept of a Carbon Removal Budget (CRB), illustrate how it can apply to different contexts and scales, and distinguish it from the related but distinct concept of the carbon budget. We further estimate the global CRB, review its constraints and quality considerations and outline potential utilisation pathways and principles. We then examine the potential application of the CRB as a tool on which both public and private decision-makers can use to assess the feasibility of their nationally determined contributions and/or net-zero transition plans. In this manner, we illustrate how CRB forecasts can be used today to help build the net zero future of tomorrow.

One branch of the responsible innovation literature involves the direction of innovation: if the public or decision-makers can or should direct innovation, how should innovation be directed? This paper explicates a case study where directionality – the plurality of plausible values for innovation – is directly implicated. In this case, a key technology may require a strategy for innovation, but there are contrasting normative reasons to drive that innovation in different ways, reflecting two distinct moral values, ‘effectiveness’ and responsiveness to ‘need’. In this case, carbon dioxide removal, these values may well conflict. Strategically deploying carbon dioxide removal in a cost-effective manner would tend to support siting it in regions where there are significant oil and gas operations. In contrast, strategically deploying carbon dioxide removal in response to need would tend to support siting it in regions where expected demand for the technology is required for development.

AbstractTo achieve net-zero emissions by mid-century, the removal of carbon dioxide from the atmosphere through negative emission technologies (NETs) will play an integral part. With renewable energy technologies (RETs), there has already been the introduction and expansion of a clean technology that faced similar obstacles as NETs—high up-front costs, limited competitiveness, and low public perception. This article compares NET policy proposals with the lessons learned from RET support. For NETs, the use of R&D support for innovation is unequivocal due to its nascency, yet the demand-pull instrument differs whether NETs are used as an alternative mitigation strategy, as a bridging technology or as a last resort. As an alternative mitigation method, a market-based approach by integrating NETs into emission trading systems is applicable because the use of NETs has no additional environmental benefit compared to abatement. Using NETs as a bridging technology requires restricting the demand for NETs to control the volume, and possibly type of NETs. This can be achieved via mandates or auctions. As a last resort, the removal via NETs requires heavy state involvement as emission removal constitutes a pure public good. This warrants public procurement or even state-led NET operation.

Biomanufacturing has the potential to reduce demand for petrochemicals and mitigate climate change. Recent studies have also suggested that some of these products can be net carbon negative, effectively removing CO2 from the atmosphere and locking it up in products. This review explores the magnitude of carbon removal achievable through biomanufacturing and discusses the likely fate of carbon in a range of target molecules. Solvents, cleaning agents, or food and pharmaceutical additives will likely re-release their carbon as CO2 at the end of their functional lives, while carbon incorporated into non-compostable polymers can result in long-term sequestration. Future research can maximize its impact by focusing on reducing emissions, achieving performance advantages, and enabling a more circular carbon economy.

Institutional theory, behavioral science, sociology and even political science all emphasize the importance of actors in achieving social change. Despite this salience, the actors involved in researching, promoting, or deploying negative emissions and solar geoengineering technologies remain underexplored within the literature. In this study, based on a rigorous sample of semi-structured expert interviews (N = 125), we empirically explore the types of actors and groups associated with both negative emissions and solar geoengineering research and deployment. We investigate emergent knowledge networks and patterns of involvement across space and scale. We examine actors in terms of their support of, opposition to, or ambiguity regarding both types of climate interventions. We reveal incipient and perhaps unforeseen collections of actors; determine which sorts of actors are associated with different technology pathways to comprehend the locations of actor groups and potential patterns of elitism; and assess relative degrees of social acceptance, legitimacy, and governance. [ABSTRACT FROM AUTHOR]

The Paris Agreement plans for "net‐zero" carbon dioxide (CO2) emissions during the second half of the 21st century. However, reducing emissions from some sectors is challenging, and "net‐zero" permits carbon dioxide removal (CDR) activities. One CDR scheme is ocean alkalinity enhancement (OAE), which proposes dissolving basic minerals into seawater to increase its buffering capacity for CO2. While modeling studies have often investigated OAE at basin or global scale, some proposals focus on readily accessible coastal shelves, with TA added through the dissolution of seafloor olivine sands. Critically, by settling and dissolving sands on shallow seafloors, this retains the added TA in near‐surface waters in direct contact with atmospheric CO2. To investigate this, we add dissolved TA at a rate of ∼29 Teq y−1 to the global shelves (<100m) of an Earth system model (UKESM1) running a high emissions scenario. As UKESM1 is fully coupled, wider effects of OAE‐mediated increase in ocean CO2 uptake –e.g. atmospheric xCO2, air temperature and marine pH– are fully quantified. Applying OAE from 2020 to 2100 decreases atmospheric xCO2 ∼10 ppm, and increases air‐to‐sea CO2 uptake ∼8%. In‐line with other studies, CO2 uptake per unit of TA added occurs at a rate of ∼0.8 mol C (mol TA)−1. Significantly for monitoring, advection of added TA results in ∼50% of CO2 uptake occurring remotely from OAE operations, and the model also exhibits noticeable land carbon reservoir changes. While practical uncertainties and model representation caveats remain, this analysis estimates the effectiveness of this specific OAE scheme to assist with net‐zero planning. Plain Language Summary: The Paris Agreement aims to limit climate warming below 2.0°C by achieving net‐zero carbon dioxide (CO2) emissions during the 21st century. As they are difficult to abate for some sectors of activity, carbon dioxide removal schemes will be needed to offset residual emissions. One scheme, ocean alkalinity enhancement (OAE), proposes elevating the ocean's storage capacity for CO2 by increasing its alkalinity by adding basic minerals as solutions or particulates. The latter require time to dissolve but risk sinking away from the ocean's surface where they absorb CO2. Coastal OAE proposes adding particulate minerals on the shallow continental shelves, where dissolution products will remain within the upper water column. Here we investigate coastal OAE by adding alkalinity to the ocean of a state‐of‐the‐art Earth system model to quantify enhanced CO2 uptake, where this occurs, its efficiency, and its impacts on atmospheric CO2 concentration and climate. Overall, coastal OAE increased CO2 uptake, and did so with an efficiency of almost 0.8 mol carbon per equivalent alkalinity. Significantly, almost 50% of the additional CO2 uptake took place away from OAE operations, while a noticeable fraction of ocean uptake was balanced by land losses, both factors indicating challenges for monitoring the effectiveness of real‐world deployment. Key Points: Coastal ocean alkalinity enhancement investigated using state‐of‐the‐art Earth system model under high emissions scenarioAlkalinity addition of ∼29 Teq y−1 during 2020–2100 increases ocean CO2 uptake 8% and decreases atmospheric CO2 by 10 ppmAlmost 50% of extra CO2 uptake is remote from ocean alkalinity enhancement operations with implications for measurement, reporting and verification [ABSTRACT FROM AUTHOR]

In recent years, research on carbon dioxide removal (CDR) has significantly increased. Numerous studies have analyzed demonstration projects, outlined scenarios, modeled pathways, or focused on CDR's national or international governance. However, regional case studies investigating the dynamics that may facilitate or impede the broader adoption of CDR methods in spatially explicit settings are critically absent. Understanding implementation contexts on the ground is vital, and comparing them across different removal methods is essential for effectively scaling up CDR. This paper aims to address this research gap by comparatively examining the development of biomass-based CDR in three regions of Germany. Taking an exploratory approach, we conducted surveys in these regions to gain insight into stakeholder perceptions of the following six CDR methods: forest management, agriculture and soil carbon, long-lasting building materials, rewetting of peatlands and paludiculture, biochar, and bioenergy with carbon capture and storage. In this article, we present the results of the stakeholder survey, which offers multiple perspectives that can shape future studies of regional implementation and yield policy-relevant guidance. Although our research primarily focuses on the regional level in Germany, it sheds light on various conflicts, uncertainties, and potentials that are likely to be relevant for the rollout of CDR in other countries. By examining these aspects, we contribute to the broader discourse on CDR and its potential implementation. [ABSTRACT FROM AUTHOR]

This article examines how carbon dioxide (CO2) removal credits can be integrated into the European Union (EU) Emissions Trading System (ETS), focusing on questions of permanence and climate liability. It identifies challenges within the integration process and analyzes approaches from practice and literature to cultivate learning. These approaches apply different strategies to address the issue of permanence, including temporary credit issuance, granting credits once a certain number of carbon tonne-years have been accumulated, or issuing credits at the beginning of the project period and relying on liability instead. Drawing from the findings of this research, the article presents legal considerations that may inform a proposal for an EU legislative act on the integration of carbon removal credits into the EU ETS. It suggests that only credits issued for permanent CO2 removal should be integrated to ensure the environmental integrity of the system. Furthermore, the liability of the project operator should transfer to the Member State under certain conditions to make liability risks more predictable. [ABSTRACT FROM AUTHOR]

Macroalgae cultivation is receiving growing attention as a potential carbon dioxide removal (CDR) strategy. Macroalgae biomass harvesting and/or intentional sinking have been the main focus of research efforts. A significant amount of biomass is naturally lost through erosion and breakage of cultivated or naturally growing seaweed, but the contribution of the resulting particulates to carbon sequestration is relatively unexplored. Here, we use a fully coupled kelpbiogeochemistry model forced by idealized parameters in a closed system to estimate the potential of macroalgal-derived particulate organic carbon (POC) sinking as a CDR pathway. Our model indicates that at a kelp density of 1.1 fronds m−3, macroalgal POC sinking can export 7.4 times more carbon to the deep sea (depths > 500m) and remove 5.2 times more carbon from the atmosphere (equivalent to an additional 336.0 gC m−2 yr−1 ) compared to the natural biological pump without kelp in our idealized closed system. The results suggest that CDR associated with POC sinking should be explored as a possible benefit of seaweed farming and point to the need for further study on organic carbon partitioning and its bioavailability to quantify the effectiveness and impacts of macroalgal cultivation as a CDR strategy. [ABSTRACT FROM AUTHOR]

Limiting global warming to 2 °C requires urgent action on land-based mitigation. This study evaluates the biogeochemical and biogeophysical implications of two alternative land-based mitigation scenarios that aim to achieve the same radiative forcing. One scenario is primarily driven by bioenergy expansion (SSP226Lu-BIOCROP), while the other involves re/afforestation (SSP126Lu-REFOREST). We find that overall, SSP126Lu-REFOREST is a more efficient strategy for removing CO2 from the atmosphere by 2100, resulting in a net carbon sink of 242 ~ 483 PgC with smaller uncertainties compared to SSP226Lu-BIOCROP, which exhibits a wider range of -78 ~ 621 PgC. However, SSP126Lu-REFOREST leads to a relatively warmer planetary climate than SSP226Lu-BIOCROP, and this relative warming can be intensified in certain re/afforested regions where local climates are not favorable for tree growth. Despite the cooling effect on a global scale, SSP226Lu-BIOCROP reshuffles regional warming hotspots, amplifying summer temperatures in vulnerable tropical regions such as Central Africa and Southeast Asia. Our findings highlight the need for strategic land use planning to identify suitable regions for re/afforestation and bioenergy expansion, thereby improving the likelihood of achieving the intended climate mitigation outcomes. [ABSTRACT FROM AUTHOR]