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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]

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]

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]

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]

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]

Terrestrial enhanced weathering (EW) through the application of Mg‐ or Ca‐rich rock dust to soil is a negative emission technology with the potential to address impacts of climate change. The effectiveness of EW was tested over 4 years by spreading ground basalt (50 t ha−1 year−1) on maize/soybean and miscanthus cropping systems in the Midwest US. The major elements of the carbon budget were quantified through measurements of eddy covariance, soil carbon flux, and biomass. The movement of Mg and Ca to deep soil, released by weathering, balanced by a corresponding alkalinity flux, was used to measure the drawdown of CO2, where the release of cations from basalt was measured as the ratio of rare earth elements to base cations in the applied rock dust and in the surface soil. Basalt application stimulated peak biomass and net primary production in both cropping systems and caused a small but significant stimulation of soil respiration. Net ecosystem carbon balance (NECB) was strongly negative for maize/soybean (−199 to −453 g C m−2 year−1) indicating this system was losing carbon to the atmosphere. Average EW (102 g C m−2 year−1) offset carbon loss in the maize/soybean by 23%–42%. NECB of miscanthus was positive (63–129 g C m−2 year−1), indicating carbon gain in the system, and EW greatly increased inorganic carbon storage by an additional 234 g C m−2 year−1. Our analysis indicates a co‐deployment of a perennial biofuel crop (miscanthus) with EW leads to major wins—increased harvested yields of 29%–42% with additional carbon dioxide removal (CDR) of 8.6 t CO2 ha−1 year−1. EW applied to maize/soybean drives a CDR of 3.7 t CO2 ha−1 year−1, which partially offsets well‐established carbon losses from soil from this crop rotation. EW applied in the US Midwest creates measurable improvements to the carbon budgets perennial bioenergy crops and conventional row crops. [ABSTRACT FROM AUTHOR]

The conservation, restoration, and improved management of terrestrial forests significantly contributes to mitigate climate change and its impacts, as well as providing numerous co‐benefits. The pressing need to reduce emissions and increase carbon removal from the atmosphere is now also leading to the development of natural climate solutions in the ocean. Interest in the carbon sequestration potential of underwater macroalgal forests is growing rapidly among policy, conservation, and corporate sectors. Yet, our understanding of whether carbon sequestration from macroalgal forests can lead to tangible climate change mitigation remains severely limited, hampering their inclusion in international policy or carbon finance frameworks. Here, we examine the results of over 180 publications to synthesise evidence regarding macroalgal forest carbon sequestration potential. We show that research efforts on macroalgae carbon sequestration are heavily skewed towards particulate organic carbon (POC) pathways (77% of data publications), and that carbon fixation is the most studied flux (55%). Fluxes leading directly to carbon sequestration (e.g. carbon export or burial in marine sediments) remain poorly resolved, likely hindering regional or country‐level assessments of carbon sequestration potential, which are only available from 17 of the 150 countries where macroalgal forests occur. To solve this issue, we present a framework to categorize coastlines according to their carbon sequestration potential. Finally, we review the multiple avenues through which this sequestration can translate into climate change mitigation capacity, which largely depends on whether management interventions can increase carbon removal above a natural baseline or avoid further carbon emissions. We find that conservation, restoration and afforestation interventions on macroalgal forests can potentially lead to carbon removal in the order of 10's of Tg C globally. Although this is lower than current estimates of natural sequestration value of all macroalgal habitats (61–268 Tg C year−1), it suggests that macroalgal forests could add to the total mitigation potential of coastal blue carbon ecosystems, and offer valuable mitigation opportunities in polar and temperate areas where blue carbon mitigation is currently low. Operationalizing that potential will necessitate the development of models that reliably estimate the proportion of production sequestered, improvements in macroalgae carbon fingerprinting techniques, and a rethinking of carbon accounting methodologies. The ocean provides major opportunities to mitigate and adapt to climate change, and the largest coastal vegetated habitat on Earth should not be ignored simply because it does not fit into existing frameworks. [ABSTRACT FROM AUTHOR]

Algal carbon‐to‐nitrogen (C:N) and carbon‐to‐phosphorus (C:P) ratios are fundamental for understanding many oceanic biogeochemical processes, such as nutrient flux and climate regulation. We synthesized literature data (444 species, >400 locations) and collected original samples from Tasmania, Australia (51 species, 10 locations) to update the global ratios of seaweed carbon‐to‐nitrogen (C:N) and carbon‐to‐phosphorus (C:P). The updated global mean molar ratio for seaweed C:N is 20 (ranging from 6 to 123) and for C:P is 801 (ranging from 76 to 4102). The C:N and C:P ratios were significantly influenced by seawater inorganic nutrient concentrations and seasonality. Additionally, C:N ratios varied by phyla. Brown seaweeds (Ochrophyta, Phaeophyceae) had the highest mean C:N of 27.5 (range: 7.6–122.5), followed by green seaweeds (Chlorophyta) of 17.8 (6.2–54.3) and red seaweeds (Rhodophyta) of 14.8 (5.6–77.6). We used the updated C:N and C:P values to compare seaweed tissue stoichiometry with the most recently reported values for plankton community stoichiometry. Our results show that seaweeds have on average 2.8 and 4.0 times higher C:N and C:P than phytoplankton, indicating seaweeds can assimilate more carbon in their biomass for a given amount of nutrient resource. The stoichiometric comparison presented herein is central to the discourse on ocean afforestation (the deliberate replacement of phytoplankton with seaweeds to enhance the ocean biological carbon sink) by contributing to the understanding of the impact of nutrient reallocation from phytoplankton to seaweeds under large‐scale seaweed cultivation. [ABSTRACT FROM AUTHOR]

Within the next decade, NASA plans to launch three new missions with imaging spectrometers for aquatic science and applications: Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) in 2024, Geostationary Littoral Imaging Radiometer (GLIMR) in 2026, and Surface Biology and Geology (SBG) in 2028. Taken together, these missions will evaluate long‐term trends in phytoplankton biomass linked to climate change, and provide new spectral capabilities to assess aquatic biogeochemistry, biophysics, and habitats. Hyperspectral measurements of ocean color, paired with advanced retrieval algorithms, can provide new information on phytoplankton community composition and water quality. We compare the mission architecture and sensor characteristics to identify the synergistic opportunities to merge algorithms, field data, and calibration and validation techniques. Each mission has unique temporal and spatial characteristics to monitor the aquatic transitions from watershed to open ocean ecosystems. SBG provides observations at high spatial scales to monitor emergent, floating, submerged, and benthic habitats from inland to coastal waters. With global daily coverage, PACE can track the fate of material as it meanders offshore and provides an enhanced context for phytoplankton diversity and global biogeochemical cycling. GLIMR is optimized to resolve temporal processes that give rise to aquatic rates and fluxes including phytoplankton growth rates, physiology, and episodic events such as storms. Applications with high spectral, spatial, and temporal resolution from these NASA missions include assessing carbon dynamics and biogeochemical cycling across the land‐ocean continuum, harmful algal blooms, and oil spills. Plain Language Summary: NASA plans to launch three new missions for monitoring aquatic ecosystems from space: PACE in 2024, Geostationary Littoral Imaging Radiometer in 2026, and SBG in 2028. Each mission monitors unique space and time scales from inland water quality to coastal seagrass habitats to upwelling zones supporting rich phytoplankton blooms. Having many more wavebands than historic sensors, these missions will allow us for the first time to monitor phytoplankton diversity from space and how different communities of these microscopic photosynthetic organisms produce oxygen, consume carbon dioxide, and serve as the base of the aquatic foodweb. Merging data from these three missions will allow us to better link processes across the continuum from inland lakes and rivers to the major ocean basins and assess hazards impacting coastal communities. Key Points: Upcoming ocean color satellites offer new opportunities to study processes across the continuum of inland‐coastal‐oceanic environmentsCommon working groups, algorithms, shared field and simulated data sets, calibration, validation, and atmospheric correction capabilitiesCombining unique spatial and temporal capabilities of each mission allows for new interdisciplinary applications [ABSTRACT FROM AUTHOR]

The article discusses the potential of enhanced weathering as a method for carbon dioxide removal (CDR) to mitigate climate change. The authors highlight the importance of the soil system in carbon sequestration, specifically the role of soil organic carbon (SOC) and soil inorganic carbon (SIC). They explore the concept of organo-mineral interactions and how they can promote soil carbon sequestration. The article also discusses the challenges and limitations of enhanced rock weathering as a CDR method, including the need for consistent weathering rates and further investigation into the interplay between plants, rock dust, and soil carbon. The authors emphasize the importance of field studies and process-based modeling to evaluate the efficacy of enhanced rock weathering and guide soil management practices. [Extracted from the article]

Enhanced rock weathering (ERW) on croplands has emerged as an economically and ecologically promising negative emissions technology. However, estimated total carbon sequestration potential from ERW on croplands and its potential sensitivity to climate conditions requires further understanding. Here we combine 1‐D reactive transport modeling with climate model experiments to simulate ERW on ∼1,000 agricultural sites globally. Applying a fixed rate of 10 tons of basalt dust per hectare on these sites sequesters 64 gigatons of CO2 over a 75‐year period; when extrapolated to all agricultural land, ERW sequesters 217 gigatons of CO2 over the same time interval. However, we find that a significant fraction of applied basalt does not weather even on a multidecadal timescale, indicating the need to optimize application strategies for cost effectiveness. We find that ERW becomes modestly more effective with global warming and predict that the payback period for a given ERW deployment is significantly shorter in hot and humid environments currently coinciding with relatively low per‐capita incomes. These results provide strong impetus for investment in agricultural reform in developing economies and highlight an additional potential co‐benefit of ERW. Plain Language Summary: Enhanced rock weathering (ERW) on croplands is a promising negative emissions concept that accelerates natural weathering by amending soils with crushed rock. Our simulations of ERW with a fixed rate of 10 tons of basalt dust per hectare on all global croplands suggest ERW can sequester >200 gigatons of CO2 over a 75‐year period. This suggests that cost and logistical concerns, rather than weathering potential, are likely to be the key limiting factors for large‐scale deployment of enhanced weathering. Notably, ERW is resilient to global climate change and becomes more effective with global warming. ERW is moreover far more efficient in hot and humid environments currently coinciding with relatively low per‐capita gross domestic product economies. Our study provides strong support for the assertion that ERW represents a resilient carbon capture strategy that is non‐competitive for arable land and can foster CO2 removal at the gigaton scale. Key Points: Enhanced rock weathering (ERW) with fixed annual application rates of 10 tons of basalt dust per hectare on 1,000 global cropland sites sequesters 64 gigatons of CO2 over 2006–2080Extrapolated to all croplands, ERW with a fixed application rate of 10 tons of basalt dust per hectare sequesters 215 gigatons of CO2 over 2006–2080ERW is resilient to global climate change but is much more efficient over hot and humid environments [ABSTRACT FROM AUTHOR]

Deliberations are underway to utilize increasingly radical technological options to help address climate change and stabilize the climatic system. Collectively, these options are often referred to as "climate geoengineering." Deployment of such options, however, can create wicked tradeoffs in governance and require adaptive forms of risk management. In this study, we utilize a large and novel set of qualitative expert interview data to more deeply and systematically explore the types of risk–risk tradeoffs that may emerge from the use of 20 different climate geoengineering options, 10 that focus on carbon dioxide or greenhouse gas removal, and 10 that focus on solar radiation management and reflecting sunlight. We specifically consider: What risks does the deployment of these options entail? What types of tradeoffs may emerge through their deployment? We apply a framework that clusters risk–risk tradeoffs into institutional and governance, technological and environmental, and behavioral and temporal dimensions. In doing so, we offer a more complete inventory of risk–risk tradeoffs than those currently available within the respective risk‐assessment, energy‐systems, and climate‐change literatures, and we also point the way toward future research gaps concerning policy, deployment, and risk management. [ABSTRACT FROM AUTHOR]

Climate change is a paradigmatic example of systemic risk. Recently, proposals for large‐scale interventions—carbon dioxide removal (CDR) and solar radiation management (SRM)—have started to redefine climate governance strategies. We describe how evolving modeling practices are trending toward optimized and "best‐case" projections—portraying deployment schemes that create both technically slanted and politically sanitized profiles of risk, as well as ideal objectives for CDR and SRM as mitigation‐enhancing, time‐buying mechanisms for carbon transitions or vulnerable populations. As promises, stylized and hopeful projections may selectively reinforce industry and political activities built around the inertia of the carbon economy. Some evidence suggests this is the emerging case for certain kinds of CDR, where the prospect of future carbon capture substitutes for present mitigation. Either of these implications are systemic: explorations of climatic futures may entrench certain carbon infrastructures. We point out efforts and recommendations to forestall this trend in the implementation of the Paris Agreement, by creating more stakeholder input and strengthening political realism in modeling and other assessments, as well as through policy guardrails. [ABSTRACT FROM AUTHOR]

Negative emissions (NE) are under discussion as elements of mitigation strategies aiming to achieve the climate targets of the Paris Agreement. However, biomass‐based NE technologies such as bioenergy with carbon capture and storage (BECCS) require vast land areas in order to meet the targets projected by climate economic optimization models, thereby competing with food production and ecosystem protection. Here we assess feasible NE contributions of alternative, more sustainable pyrogenic carbon capture and storage (PyCCS) based on land‐neutral biomass production using biochar‐mediated yield increases to maintain calorie production while realizing net CO2 extraction from the atmosphere. Simulations with a biosphere model indicate that such a land‐ and calorie‐neutral PyCCS approach could sequester 0.44–2.62 Gt CO2 yr−1 depending on the assumed biochar‐mediated yield increase achievable on (sub‐)tropical cropland (15%, 20% and 30%, respectively). Cumulatively, by the end of the century, 33–201 Gt CO2 could be sustainably supplied by such an approach, equaling 6%–35% of the NE demand projected for trajectories likely to limit climate warming to 2°C or lower. Furthermore, additional areas dedicated to BECCS in integrated assessment scenarios could instead be used to increase global calorie production (by 2%–16%), or spared for nature protection (up to ∼ 100 Mha). Thus, land‐ and calorie‐neutral PyCCS may, within limits, contribute to lessening the additional land use pressure of biomass‐based NE technologies. Plain Language Summary: We assessed a land‐ and calorie‐neutral approach to pyrogenic carbon capture and storage (LCN‐PyCCS) as a supply‐driven, bottom‐up approach to large‐scale carbon dioxide removal. LCN‐PyCCS relies on the process of biomass pyrolysis, where biomass carbon is transferred into the more stable biochar that can be used as soil amendment enhancing the soil properties and storing carbon in the soil. The approach is based on land‐neutral biomass production using biochar‐mediated yield increases to maintain calorie production while realizing net CO2 extraction from the atmosphere. In our analysis building on process‐based simulations of biomass growth we find a potential of 0.44–2.62 Gt CO2 yr−1 depending on the yield increase achievable. Furthermore, this approach could substitute negative emissions from other, less sustainable, biomass‐based negative emission technologies. Assuming that this could free biomass plantations, we evaluated the potential of alternative uses of this land, showing potential increased calorie production of 2%–16% or land sparing for nature protection of up to ∼100 Mha. Key Points: Land‐ and calorie‐neutral pyrogenic carbon capture and storage can provide negative emissions of 0.44–2.62 Gt CO2 yr−1 depending on yield increase achievedCumulated until 2100, this amounts to 6%–35% of the negative emission demand in integrated assessment scenarios of climate stabilizationLand not required compared to alternative deployment of bioenergy with carbon capture and storage could be used for increasing food production or nature restoration [ABSTRACT FROM AUTHOR]

Carbon sequestration is defined as the secure storage of carbon‐containing molecules for >100 years, and in the context of carbon dioxide removal for climate mitigation, the origin of this CO2 is from the atmosphere. On land, trees globally sequester substantial amounts of carbon in woody biomass, and an analogous role for seaweeds in ocean carbon sequestration has been suggested. The purposeful expansion of natural seaweed beds and aquaculture systems, including into the open ocean (ocean afforestation), has been proposed as a method of increasing carbon sequestration and use in carbon trading and offset schemes. However, to verify whether CO2 fixed by seaweeds through photosynthesis leads to carbon sequestration is extremely complex in the marine environment compared to terrestrial systems, because of the need to jointly consider: the comparatively rapid turnover of seaweed biomass, tracing the fate of carbon via particulate and dissolved organic carbon pathways in dynamic coastal waters, and the key role of atmosphere–ocean CO2 exchange. We propose a Forensic Carbon Accounting approach, in which a thorough analysis of carbon flows between the atmosphere and ocean, and into and out of seaweeds would be undertaken, for assessing the magnitude of CO2 removal and robust attribution of carbon sequestration to seaweeds. [ABSTRACT FROM AUTHOR]

Background: Consumption of platelets and coagulation factors during extracorporeal carbon dioxide removal (ECCO2R) increases bleeding complications and associated mortality. Regional infusion of lactic acid enhances ECCO2R by shifting the chemical equilibrium from bicarbonate to carbon dioxide. Our goal was to test if regional blood acidification during ECCO2R inhibits platelet function and coagulation. Methods: An ECCO2R system containing a hemofilter circulated blood at 0.25 L/min in eight healthy ewes (Ovis aries) for 36 h. Three of the sheep received ECCO2R with no recirculation compared to five sheep that received ECCO2R plus 12 h of regional blood acidification via the hemofilter, placed upstream from the oxygenator, into which 4.4 M lactic acid was infused. Blood gases, platelet count and function, thromboelastography, coagulation‐factor activity, and von Willebrand factor activity (vWF:Ag) were measured at baseline, at start of lactic acid infusion, and after 36 h of extracorporeal circulation. Results: Twelve hours of regional acid infusion significantly inhibited platelet aggregation response to adenosine diphosphate; vWF; and platelet expression of P‐selectin compared to control. It also significantly reduced consumption of fibrinogen and of coagulation factors V, VII, IX, compared to control. Conclusions: Regional acidification reduces platelet activation and vitamin‐K‐dependent coagulation‐factor consumption during ECCO2R. This is the first report of a simple method that may enhance effective anticoagulation for ECCO2R. [ABSTRACT FROM AUTHOR]

The North Atlantic Ocean is a key region for carbon sequestration by the biological carbon pump (BCP). The quantity of organic carbon exported from the surface, the region and depth at which it is remineralized, and the subsequent timescale of ventilation (return of the remineralized carbon back into contact with the atmosphere), control the magnitude of BCP sequestration. Carbon stored in the ocean for >100 years is assumed to be sequestered for climate‐relevant timescales. We apply Lagrangian tracking to an ocean circulation and marine biogeochemistry model to determine the fate of North Atlantic organic carbon export. Organic carbon assumed to undergo remineralization at each of three vertical horizons (500, 1,000, and 2,000 m) is tracked to determine how much remains out of contact with the atmosphere for 100 years. The fraction that remains below the mixed layer for 100 years is defined as the sequestration efficiency (SEff) of remineralized exported carbon. For exported carbon remineralized at the 500, 1,000 and 2,000 m horizons, the SEff is 28%, 66% and 94%, respectively. Calculating the amount of carbon sequestered using depths ≤1,000 m, and not accounting for downstream ventilation, overestimates 100‐year carbon sequestration by at least 39%. This work has implications for the accuracy of future carbon sequestration estimates, which may be overstated, and for carbon management strategies (e.g., oceanic carbon dioxide removal and Blue Carbon schemes) that require long‐term sequestration to be successful. Plain Language Summary: The North Atlantic Ocean is a key region for carbon uptake and organic carbon storage in the interior ocean for climate‐relevant timescales (>100 years). Sinking organic carbon that reaches the interior ocean is respired there to form dissolved inorganic carbon. The fate of this carbon, that is, whether it remains in the ocean interior or returns to the surface and is ventilated to the atmosphere, depends on its physical circulation pathways. To investigate the efficiency of carbon storage in the North Atlantic Ocean we released virtual particles at three different starting depths (500, 1,000 and 2,000 m) into a global ocean model and tracked the pathways they followed for 100 years. 66% of virtual particles released at 1,000 m depth remained out of contact with the atmosphere for 100 years. Combining this pathway analysis with observation‐ and model‐derived geographical fields of sinking carbon flux, we estimate that the 100‐year North Atlantic carbon storage may be overestimated by 39% at 1,000 m because of this ventilation to the atmosphere. These findings have important implications for accurately estimating future ocean carbon storage. In particular, for carbon management strategies that require long‐term sequestration to be successful (e.g., oceanic carbon dioxide removal and Blue Carbon schemes). Key Points: Lagrangian simulations show that North Atlantic Ocean sequestration efficiency of remineralized exported carbon (REC) varies strongly by regionOnly 66% of North Atlantic REC at 1,000 m will remain out of contact with the atmosphere for 100 yearsFixed sequestration horizons ≤1,000 m can significantly overestimate long‐term carbon sequestration [ABSTRACT FROM AUTHOR]

In order to achieve greenhouse gas neutrality, hydrogen generated from renewable sources will play an important role. Additionally, as underlined in the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), new technologies to remove greenhouse gases from the atmosphere are required on a large scale. A novel concept for hydrogen production with net negative emissions referred to as HyBECCS (Hydrogen Bioenergy with Carbon Capture and Storage) combines these two purposes in one technological approach. The HyBECCS concept combines biohydrogen production from biomass with the capture and storage of biogenic carbon dioxide. Various technology combinations of HyBECCS processes are possible, whose ecological effects and economic viability need to be analyzed in order to provide a basis for comparison and decision‐making. This paper presents fundamentals for the techno‐economic and environmental evaluation of HyBECCS approaches. Transferable frameworks on system boundaries as well as emission, cost, and revenue streams are defined and specifics for the application of existing assessment methods are elaborated. In addition, peculiarities concerning the HyBECCS approach with respect to political regulatory measures and interrelationships between economics and ecology are outlined. Based on these considerations, two key performance indicators (KPIs) are established, referred to as levelized cost of carbon‐negative hydrogen (LCCNH) and of negative emissions (LCNE). Both KPIs allow deciding whether a specific HyBECCS project is economically viable and allows its comparison with different hydrogen, energy provision, or negative emission technologies (NETs). Carbon‐negative hydrogen production referred to as HyBECCS (Hydrogen Bioenergy with Carbon Capture and Storage) combines hydrogen production from biomass with the capture and storage of biogenic carbon dioxide. Various technology combinations of HyBECCS processes are possible, whose ecological effects and economic viability need to be analysed. This paper presents fundamentals for the techno‐economic and environmental evaluation of HyBECCS approaches. Transferable frameworks on system boundaries as well as emission, cost and revenue streams are defined and specifics for the application of existing assessment methods are elaborated. [ABSTRACT FROM AUTHOR]

The work assesses the availability and localizations of different raw materials suitable for ocean alkalinity enhancement (OAE), like limestone, olivine, magnesite and brucite, since several billion tons of rocky materials are needed to achieve meaningful results for carbon sequestration through OAE. Resources of carbonates are immense and widespread around all continents. Availability of pure carbonates is still very large (outcrop area 4.1 million km2) and is not a constraint for the large‐scale development of OAE. Outcrops of pure carbonates within 10 km from the coastline and below bare ground or scrub/shrub, preferred for the logistics of exploitation, account for about 70,000 km2, and could provide about 5,000 Gt of limestone. These values increase by a factor of 3 and 8 within 50 and 100 km from the coastline, respectively. Potential resources of olivine, less easily identifiable from the geological data, are estimated in the order of a few hundred billion tons and could provide only a minor contribution to ocean‐based carbon removal strategies. A comparison with the current level of world extraction of mineral raw materials is also provided. The annual production of limestone, estimated to be more than 6.6 Gt from deposits scattered all around the world, is about 9% of the world production of mineral raw materials (around 44 Gt yr−1), and is of the same order of magnitude as coal (7.3 Gt yr−1). The annual productions of magnesite (29 Mt yr−1), olivine (8.4 Mt yr−1) and brucite (1.5 Mt yr−1) are two orders of magnitude lower. Plain Language Summary: The ongoing acidification of the oceans due to the increase of carbon dioxide (CO2) concentration in the atmosphere and the consequent increased uptake by the sea can be tackled by adding alkaline compounds under controlled conditions. Since this promotes a number of reactions in the carbonate system which ultimately results in a drawdown of atmospheric CO2, the enhancement of ocean alkalinity can also contribute to the global effort of limiting global warming, and it is widely studied in the literature among the CO2 removal technologies. A limiting factor can be the worldwide availability of alkaline materials to be used for such a scope. The paper shows that the global availability of pure carbonates is vast, although unevenly distributed, and it could largely satisfy the requirement for large‐scale development of ocean alkalinization. The required up‐scaling of limestone production compared to the current level is much lower than what would be needed for other raw materials that could be used, such as olivine, magnesite and brucite. Moreover, a large fraction of pure limestone resources that could be exploitable is located nearby the coastline, in areas without or with low vegetation cover, which favors the logistics related to the exploitation. Key Points: Pure carbonate potential resources are of several trillion tons and are not a constraint for the development of global‐scale ocean limingA large part of pure limestone resources is located nearby the coastline, in area with no to low vegetation cover, mainly in North Africa and IranThe global limestone yearly production is similar to that of coal, thus the needed upscale is far lower than for olivine, magnesite and brucite [ABSTRACT FROM AUTHOR]

An innovative strategy to control the metabolism of microorganisms is offered by bioelectrochemical systems in which a graphite‐based cathode can be used as electron donor or acceptor. An advanced microbial electrolysis cell is developed to combine CO2 removal from a synthetic biogas in a biocathode and the organic matter oxidation in a bioanode. A novel biogas upgrading approach is presented in which an electron recycle concept is obtained by the combination of CO2 reduction and oxidation. While the bioelectrochemical anodic chemical oxygen demand oxidation provides the electrons necessary for the cathodic CO2 reduction into methane and acetate, the acetate produced by acetogenic microorganisms migrates from the cathode to the anode being oxidized again by the bioanode. [ABSTRACT FROM AUTHOR]

Germany 2050: For the first time Germany reached a balance between its sources of anthropogenic CO2 to the atmosphere and newly created anthropogenic sinks. This backcasting study presents a fictional future in which this goal was achieved by avoiding (∼645 Mt CO2), reducing (∼50 Mt CO2) and removing (∼60 Mt CO2) carbon emissions. This meant substantial transformation of the energy system, increasing energy efficiency, sector coupling, and electrification, energy storage solutions including synthetic energy carriers, sector‐specific solutions for industry, transport, and agriculture, as well as natural‐sink enhancement and technological carbon dioxide options. All of the above was necessary to achieve a net‐zero CO2 system for Germany by 2050. Plain Language Summary: Here a net‐zero‐2050 Germany is envisioned by combining analysis from an energy‐system model with insights into approaches that allow for a higher carbon circularity in the German system, and first results from assessments of national carbon dioxide removal potentials. A back‐casting perspective is applied on how net‐zero Germany could look like in 2050. We are looking back from 2050, and analyzing how Germany for the first time reached a balance between its sources of CO2 to the atmosphere and the anthropogenic sinks created. This would consider full decarbonization in the entire energy sector and being entirely emission‐free by 2050 within three priorities identified as being the most useful strategies for achieving net‐zero: (a) Avoiding‐ (b) Reducing‐ (c) Removing emissions. This work is a collaboration of interdisciplinary scientists with the Net‐Zero‐2050 cluster of the Helmholtz Climate Initiative HI‐CAM. Key Points: The net‐zero system shows that for countries like Germany, avoiding CO2 emissions was the largest contribution to achieve net‐zero CO2With the three strategies of emissions avoidance, reduction, and removal, Germany has achieved its net‐zero CO2 goal for the first timeIn addition, to natural sink enhancement carbon dioxide removal (CDR) options, technological CDR measures combined with geological CO2 storage were necessary to reach net‐zero CO2 [ABSTRACT FROM AUTHOR]

The alkalinity concentration swing (ACS) is a new process for direct air capture of carbon dioxide driven by concentrating an alkaline solution that has been exposed to the atmosphere and loaded with dissolved inorganic carbon. Upon concentration, the partial pressure of CO2 increases, allowing for extraction and compression. Higher concentration factors result in proportionally higher outgassing pressure, and higher initial alkalinity concentrations at the same concentration factor outgas a higher concentration of CO2. Two desalination technologies, reverse osmosis and capacitive deionization, are examined as possible ACS implementations, and two corresponding energy models are evaluated. The ACS is compared to incumbent technologies and estimates for water, land, and energy requirements for capturing one million tonnes of CO2 per year are made. Estimates for the lower end of the energy range for both approaches compare favorably to other approaches, such as solid sorbent and calcining methods. [ABSTRACT FROM AUTHOR]

Enhanced weathering (EW) of alkaline minerals can potentially capture CO2 from the atmosphere at gigaton scale, but the reactor design presents great challenges. We model EW with fresh water in a counter‐current trickle flow packed bed batch of 1–10 mm calcite particles. Weathering kinetics are integrated with the mass transfer of CO2 incorporating transfer enhancement by chemical reaction. To avoid flooding, flow rates must be reduced as the particles shrink due to EW. The capture rate is mainly limited by slow transfer of CO2 from gas to liquid although slow dissolution of calcite can also play a role in certain circumstances. A bed height of at least 7–8 m is required to provide sufficient residence time. The results highlight the need to improve capture rate and reduce energy and water consumption, possibly through enriching the feed with CO2 and further chemical acceleration of the mass transfer. [ABSTRACT FROM AUTHOR]

Artificial carbon dioxide removal (CDR) from the atmosphere has been proposed as a measure for mitigating climate change and restoring the climate system to a target state after exceedance ("overshoot"). This research investigates to what extent overshoot and subsequent recovery of a given cumulative CO2 emissions level by CDR leaves a legacy in the marine environment using an Earth system model. We use RCP2.6 and its extension to year 2300 as the reference scenario and design a set of cumulative emissions and temperature overshoot scenarios based on other RCPs. Our results suggest that the overshoot and subsequent return to a reference cumulative emissions level would leave substantial impacts on the marine environment. Although the changes in sea surface temperature, pH, and dissolved oxygen are largely reversible, global mean values and spatial patterns of these variables differ significantly from those in the reference scenario when the reference cumulative emissions are attained. Plain Language Summary: Commitments by countries to reduce emissions of carbon dioxide (CO2) fall short of what is needed to limit global warming to below 2°C, a goal of the Paris Agreement, creating a risk that the 2°C limit may be exceeded. Restoring global temperature to a target level after exceedance ("overshoot") requires artificial carbon dioxide removal (CDR) from the atmosphere. Earlier studies showed that changes in surface air temperature can be reversed by CDR but climate variables that take longer to respond to changes in atmospheric CO2 are slower to reverse. In this research we investigate to what extent the impacts of overshoot on the marine environment can be reversed with CDR. We show that the ocean responds slowly to a decrease in atmospheric CO2 concentration by CDR, particularly for scenarios with large levels of overshoot. The overshoot results in substantial impacts on the marine environment for centuries with potentially detrimental effects for marine ecosystems. Key Points: Changes in sea surface temperature, pH, and dissolved oxygen concentration in overshoot scenarios are largely reversibleChanges in average ocean values of these variables are not reversible centuries after the overshoot is removedSpatial changes in these variables exhibit substantial differences between overshoot and nonovershoot scenarios in some regions [ABSTRACT FROM AUTHOR]

Extracorporeal carbon dioxide (CO2) removal (ECCO2R) facilitates the use of low tidal volumes during protective or ultraprotective mechanical ventilation when managing patients with acute respiratory distress syndrome (ARDS); however, the rate of ECCO2R required to avoid hypercapnia remains unclear. We calculated ECCO2R rate requirements to maintain arterial partial pressure of CO2 (PaCO2) at clinically desirable levels in mechanically ventilated ARDS patients using a six‐compartment mathematical model of CO2 and oxygen (O2) biochemistry and whole‐body transport with the inclusion of an ECCO2R device for extracorporeal veno‐venous removal of CO2. The model assumes steady state conditions. Model compartments were lung capillary blood, arterial blood, venous blood, post‐ECCO2R venous blood, interstitial fluid and tissue cells, with CO2 and O2 distribution within each compartment; biochemistry included equilibrium among bicarbonate and non‐bicarbonate buffers and CO2 and O2 binding to hemoglobin to elucidate Bohr and Haldane effects. O2 consumption and CO2 production rates were assumed proportional to predicted body weight (PBW) and adjusted to achieve reported arterial partial pressure of O2 and a PaCO2 level of 46 mmHg at a tidal volume of 7.6 mL/kg PBW in the absence of an ECCO2R device based on average data from LUNG SAFE. Model calculations showed that ECCO2R rates required to achieve mild permissive hypercapnia (PaCO2 of 46 mmHg) at a ventilation frequency or respiratory rate of 20.8/min during mechanical ventilation increased when tidal volumes decreased from 7.6 to 3 mL/kg PBW. Higher ECCO2R rates were required to achieve normocapnia (PaCO2 of 40 mmHg). Model calculations also showed that required ECCO2R rates were lower when ventilation frequencies were increased from 20.8/min to 26/min. The current mathematical model predicts that ECCO2R rates resulting in clinically desirable PaCO2 levels at tidal volumes of 5‐6 mL/kg PBW can likely be achieved in mechanically ventilated ARDS patients with current technologies; use of ultraprotective tidal volumes (3‐4 mL/kg PBW) may be challenging unless high mechanical ventilation frequencies are used. [ABSTRACT FROM AUTHOR]

Bioenergy is expected to have a prominent role in limiting global greenhouse emissions to meet the climate change target of the Paris Agreement. Many studies identify negative emissions from bioenergy generation with carbon capture and storage (BECCS) as its key contribution, but assume that no other CO2 removal technologies are available. We use a global integrated assessment model, TIAM‐UCL, to investigate the role of bioenergy within the global energy system when direct air capture and afforestation are available as cost‐competitive alternatives to BECCS. We find that the presence of other CO2 removal technologies does not reduce the pressure on biomass resources but changes the use of bioenergy for climate mitigation. While we confirm that when available BECCS offers cheaper decarbonization pathways, we also find that its use delays the phase‐out of unabated fossil fuels in industry and transport. Furthermore, it displaces renewable electricity generation, potentially increasing the likelihood of missing the Paris Agreement target. We found that the most cost‐effective solution is to invest in a basket of CO2 removal technologies. However, if these technologies rely on CCS, then urgent action is required to ramp up the necessary infrastructure. We conclude that a sustainable biomass supply is critical for decarbonizing the global energy system. Since only a few world regions carry the burden of producing the biomass resource and store CO2 in geological storage, adequate international collaboration, policies and standards will be needed to realize this resource while avoiding undesired land‐use change. [ABSTRACT FROM AUTHOR]

Although Indic perspectives toward nature are now well documented, climate engineering discussions seem to still lack the views from Indic or other non‐Western sources. In this article, I will apply some of the Hindu and Jain concepts such as karma, nonviolence (Ahiṃsā), humility (Vinaya), and renunciation (Saṃnyāsa) to analyze the two primary climate geoengineering strategies of solar radiation management (SRM) and carbon dioxide removal (CDR). I suggest that Indic philosophical and religious traditions such as Hinduism, Buddhism, and Jainism offer ethical concepts to call for humility in all acts of climate engineering leading to a favoring of CDR over SRM and a favoring of lifestyle changes (particularly vegetarianism) over both. I demonstrate these concepts by introducing the five great elements from the Hindu philosophy, two Hindu legends from Hindu mythology, the Indic ethical ideas of karma, renunciation, and humility, and the moral authority of Gandhi. [ABSTRACT FROM AUTHOR]

Societal Impact Statement: Human‐made climate change places the future of the planet in peril. Rapid greenhouse gas emissions over the past few decades already commit Earth to a warmer climate state and lock‐in future extinctions. I consider what steps might be taken to protect the climate and the future of the biosphere by drawing on our understanding of the Devonian rise of forests. At stake is nothing less than the future of humanity and the fate of species we are fortunate enough to share the planet with. Summary Drastic phase down of our carbon dioxide (CO2) emissions from burning fossil fuels within decades will likely be insufficient to avoid seeding catastrophic human‐caused climate change. We have to also start removing CO2 from the atmosphere, safely, affordably and within decades. Technological approaches for large‐scale carbon removal and storage hold great promise but are far from the gigaton‐scale required. Enhanced chemical weathering of crushed silicate rocks and afforestation are proposed CO2 removal approaches mimicking events during the Devonian rise of forests that triggered massive CO2 drawdown and the great late Palaeozoic cooling. Evidence from Earth's history suggests that if undertaken at scale, these strategies may represent key elements of a climate restoration plan but will still be far from sufficient. Climate protests by the world's youth are justified. They recognize the urgency of the situation and the intergenerational injustice of our time: current and future generations footing the immense economic and ecological bill for damaging carbon emissions they had no part in and which world leaders are failing to limit. [ABSTRACT FROM AUTHOR]

Models suggest that climate change mitigation now depends on negative emissions, i.e. the large‐scale removal of carbon dioxide from the atmosphere. This assumption has been criticised in the climate policy literature for being unfeasible and unjust. This article asks how critical scholars can make sense of, and contribute to these debates. It suggests that negative emissions can be conceived of as a spatiotemporal fix that promises to defer the devaluation of fixed capital. But the negative emissions example also challenges us to broaden our conception of how the socioecological contradictions of capitalism can be "fixed". I outline three ways in which it does this by highlighting the significance of a predominantly temporal fix, the role of hegemonic, sociopolitical interventions involving multiple actors, and the possibility of safeguarding existing production processes. I conclude that spatiotemporal fixes to climate change should be seen as part of a wider political economy of delay in devaluing carbon‐intensive accumulation processes. [ABSTRACT FROM AUTHOR]

Cryogenic carbon dioxide removal from natural gas requires accurate thermodynamic phase study of the natural gas mixture and individual components. Thermodynamic data generation of carbon dioxide‐methane mixture having 90 % carbon dioxide for cryogenic carbon dioxide capture from natural gas using Peng Robinson equation of state is discussed in this research work. Golden section search technique along with Eureqa optimizing tool is then used to optimize the pressure‐temperature conditions for the cryogenic carbon dioxide capture in the solid‐vapour two‐phase region. Cost optimization is done for the carbon dioxide capture system at atmospheric pressure and 20 bar. Temperature ranges for optimization were obtained from the predicted thermodynamic data for the mixture. The optimum temperatures obtained in this research work for the cryogenic carbon dioxide capture at atmospheric pressure and the 20 bar are −103.8 °C and −60.90 °C respectively. For atmospheric pressure at −103.8 °C the worth of methane, carbon dioxide, and energy is 114 $/h, 9 $/h, and 53 $/h respectively, while at 20 bar and −60.9 °C the worth of carbon dioxide, methane, and the energy are found to be 129 $/h, 46 $/h, 52 $/h, respectively. [ABSTRACT FROM AUTHOR]

Selective and simultaneous separation of H2S and CO2 from CH4 was accomplished in a hollow‐fiber membrane contactor (HFMC). The absorption of both H2S and CO2 using an aqueous solution of methyldiethanolamine (MDEA) was almost complete and acid gases were totally removed. Despite the large difference between H2S and CO2 concentrations, the rate of H2S absorption was not significantly influenced by CO2 absorption. The independent effect and interactions of several process variables on the separation performance of H2S and CO2 were investigated. The results indicated that the membrane contactor could be a highly efficient choice for removal of almost all H2S in the presence of a large CO2 content even at high gas/liquid flow ratio. The selectivity of H2S was about three times higher compared to the conventional absorption packed towers. Selective and simultaneous removal of H2S and CO2 from CH4 by hollow‐fiber hydrophobic membrane contactors is introduced. The removal performances of H2S and CO2 using an aqueous methyldiethanolamine solution were much higher than those reported for conventional packed towers. The membrane contactor is a highly efficient tool for removal of almost all H2S in the presence of a large CO2 content. [ABSTRACT FROM AUTHOR]

Abstract: Most climate mitigation scenarios involve negative emissions, especially those that aim to limit global temperature increase to 2°C or less. However, the carbon uptake potential in land‐based climate change mitigation efforts is highly uncertain. Here, we address this uncertainty by using two land‐based mitigation scenarios from two land‐use models (IMAGE and MAgPIE) as input to four dynamic global vegetation models (DGVMs; LPJ‐GUESS, ORCHIDEE, JULES, LPJmL). Each of the four combinations of land‐use models and mitigation scenarios aimed for a cumulative carbon uptake of ~130 GtC by the end of the century, achieved either via the cultivation of bioenergy crops combined with carbon capture and storage (BECCS) or avoided deforestation and afforestation (ADAFF). Results suggest large uncertainty in simulated future land demand and carbon uptake rates, depending on the assumptions related to land use and land management in the models. Total cumulative carbon uptake in the DGVMs is highly variable across mitigation scenarios, ranging between 19 and 130 GtC by year 2099. Only one out of the 16 combinations of mitigation scenarios and DGVMs achieves an equivalent or higher carbon uptake than achieved in the land‐use models. The large differences in carbon uptake between the DGVMs and their discrepancy against the carbon uptake in IMAGE and MAgPIE are mainly due to different model assumptions regarding bioenergy crop yields and due to the simulation of soil carbon response to land‐use change. Differences between land‐use models and DGVMs regarding forest biomass and the rate of forest regrowth also have an impact, albeit smaller, on the results. Given the low confidence in simulated carbon uptake for a given land‐based mitigation scenario, and that negative emissions simulated by the DGVMs are typically lower than assumed in scenarios consistent with the 2°C target, relying on negative emissions to mitigate climate change is a highly uncertain strategy. [ABSTRACT FROM AUTHOR]

Scenarios meeting the Paris Agreement's temperature targets envisage a major and imminent deployment of technologies to remove carbon dioxide from the atmosphere, of which there has been almost no practical implementation to date. Here we explore the political dimensions and policy implications of expectations for “negative emissions” in the European Union (EU), considering its largely successful leadership role in mitigation action and corresponding low‐carbon technology development and deployment. Carbon dioxide removal and especially Bio‐Energy with Carbon Capture and Storage present significant challenges to the EU's dominant climate policy paradigm and low‐carbon policy experience. Considering this challenge, we assess expectations for widespread implementation of carbon dioxide removal in the EU to be unrealistic, and explore possible pathways for its more limited introduction. This article is categorized under: Policy and Governance > Multilevel and Transnational Climate Change Governance The Carbon Economy and Climate Mitigation > Policies, Instruments, Lifestyles, Behavior [ABSTRACT FROM AUTHOR]

Abstract: To maintain the chance of keeping the average global temperature increase below 2°C and to limit long‐term climate change, removing carbon dioxide from the atmosphere (carbon dioxide removal, CDR) is becoming increasingly necessary. We analyze optimal and cost‐effective climate policies in the dynamic integrated assessment model (IAM) of climate and the economy (DICE2016R) and investigate (1) the utilization of (ocean) CDR under different climate objectives, (2) the sensitivity of policies with respect to carbon cycle feedbacks, and (3) how well carbon cycle feedbacks are captured in the carbon cycle models used in state‐of‐the‐art IAMs. Overall, the carbon cycle model in DICE2016R shows clear improvements compared to its predecessor, DICE2013R, capturing much better long‐term dynamics and also oceanic carbon outgassing due to excess oceanic storage of carbon from CDR. However, this comes at the cost of a (too) tight short‐term remaining emission budget, limiting the model suitability to analyze low‐emission scenarios accurately. With DICE2016R, the compliance with the 2°C goal is no longer feasible without negative emissions via CDR. Overall, the optimal amount of CDR has to take into account (1) the emission substitution effect and (2) compensation for carbon cycle feedbacks. [ABSTRACT FROM AUTHOR]

Abstract: To contribute to a quantitative comparison of climate engineering (CE) methods, we assess atmosphere‐, ocean‐, and land‐based CE measures with respect to Earth system effects consistently within one comprehensive model. We use the Max Planck Institute Earth System Model (MPI‐ESM) with prognostic carbon cycle to compare solar radiation management (SRM) by stratospheric sulfur injection and two carbon dioxide removal methods: afforestation and ocean alkalinization. The CE model experiments are designed to offset the effect of fossil‐fuel burning on global mean surface air temperature under the RCP8.5 scenario to follow or get closer to the RCP4.5 scenario. Our results show the importance of feedbacks in the CE effects. For example, as a response to SRM the land carbon uptake is enhanced by 92 Gt by the year 2100 compared to the reference RCP8.5 scenario due to reduced soil respiration thus reducing atmospheric CO2. Furthermore, we show that normalizations allow for a better comparability of different CE methods. For example, we find that due to compensating processes such as biogeophysical effects of afforestation more carbon needs to be removed from the atmosphere by afforestation than by alkalinization to reach the same global warming reduction. Overall, we illustrate how different CE methods affect the components of the Earth system; we identify challenges arising in a CE comparison, and thereby contribute to developing a framework for a comparative assessment of CE. [ABSTRACT FROM AUTHOR]

Bioreactor scale-up is a critical step in the production of therapeutic proteins such as monoclonal antibodies (MAbs). With the scale-up criterion such as similar power input per volume or O2 volumetric mass transfer coefficient ( [ABSTRACT FROM AUTHOR]

Biogas is a popular source of renewable energy. However, production and conversion of biogas at the same location can result in energy losses up to 60 %. This energy loss can be reduced by upgrading the biogas to biomethane for injection into an existing gas delivery network and other uses. In order to upgrade the raw biogas produced from agriculture and industrial plants unwanted and harmful gases like CO2 and H2S need to be removed. An innovative process for biogas conditioning using hollow fiber membrane contactors is presented. In comparison to membrane gas separation no elevated pressure is needed. [ABSTRACT FROM AUTHOR]

The energy efficiency of hydrogen recovery from mixtures of CO, HO, and H by a polymer electrolyte hydrogen pump (PEHP) has been evaluated. The PEHP pumps protons across the polymer electrolyte, producing >99.99% pure H and a concentrated CO stream. Single stage PEHP experiments recovered 65% of the hydrogen with an energy efficiency of 50%. The energy efficiency is limited by hydrogen mass transport across the porous gas diffusion electrode. The mass transport resistance for hydrogen increases as H is depleted from the CO/H mixture by the PEHP. Analysis shows that a multistage PEHP with fixed applied potential difference can recover >90% of the hydrogen with an energy efficiency of 75%, whereas a novel multistage PEHP design with a programmed voltage profile can achieve >90% energy efficiency with >98% hydrogen recovery. © 2010 American Institute of Chemical Engineers AIChE J, 2011 [ABSTRACT FROM AUTHOR]

The most common method of controlling acidemia during lung-protective ventilation is CO removal with an extracorporeal lung assist (ECLA) system. Another possibility to prevent acidemia is based on intravenous (i.v.) application of tris-hydroxymethyl-aminomethane (3 mol/L, THAM) buffer, which can bind hydrogen protons and which can be removed from the body via renal replacement therapy (RRT). We investigated whether RRT combined with predilutional (prefilter) THAM-application provides an alternative to ECLA for a rescue situation. For this, anesthetized pigs, 40 kg of body weight, six animals per group, underwent 5 h of acidemia (pH 7.19-7.24) induced by acid infusion and permissive hypercapnia (low tidal volume ventilation, PaCO 80-90 mm Hg). Isovolemic, high-volume hemofiltration (HVHF) was operated with predilutional THAM-infusion for treatment. To evaluate adverse effects of this approach, we set up further groups: HVHF with postdilutional (post-filter) THAM-application; i.v.-THAM without HVHF; normal pH homeostasis with HVHF. Acid-base parameters, hemodynamics, renal function, and lung morphology were investigated. HVHF with predilutional THAM-infusion of 8 mmol/kg/h allowed fast pH normalization, significant reduction in PaCO to 56 mm Hg and tolerable hemodynamics. HVHF alone or lower dose i.v. THAM (2 mmol/kg/h) failed to produce a comparable result. A postdilutional THAM infusion reduced hemodynamic tolerability and increased lung edema formation. HVHF in pigs with normal acid-base status resulted in a decreased base excess and urine acidification. In conclusion, predilutional THAM-application and HVHF corrected the acid-base disorder and improved pulmonary hemodynamics. Further studies are necessary to optimize the protocol including the dosage. [ABSTRACT FROM AUTHOR]

Bioreactor scale-up is a critical step in the production of therapeutic proteins such as monoclonal antibodies (MAbs). With the scale-up criterion such as similar power input per volume or O 2 volumetric mass transfer coefficient ( kLa), adequate oxygen supply and cell growth can be largely achieved. However, CO 2 stripping in the growth phase is often inadequate. This could cascade down to increased base addition and osmolality, as well as residual lactate increase and compromised production and product quality. Here we describe a practical approach in bioreactor scale-up and process transfer, where bioreactor information may be limited. We evaluated the sparger kLa and kLaCO2 (CO 2 volumetric mass transfer coefficient) from a range of bioreactor scales (3-2,000 L) with different spargers. Results demonstrated that kLa for oxygen is not an issue when scaling from small-scale to large-scale bioreactors at the same gas flow rate per reactor volume (vvm). Results also showed that sparging CO 2 stripping, kLaCO2, is dominated by the gas throughput. As a result, a combination of a minimum constant vvm air or N 2 flow with a similar specific power was used as the general scale-up criterion. An equation was developed to determine the minimum vvm required for removing CO 2 produced from cell respiration. We demonstrated the effectiveness of using such scale-up criterion with five MAb projects exhibiting different cell growth and metabolic characteristics, scaled from 3 to 2,000 L bioreactors across four sites. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1146-1159, 2017., (© 2017 American Institute of Chemical Engineers.)