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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]

• BECCS technologies operated on waste feedstock present a negative carbon footprint. • Technology and market readiness levels quantify the risk for commercial exploitation. • Climate change impact is highly dependent on the choice of functional unit. • WtH 2 has higher emissions than WtE with CCS, but these are offset by higher credits. • Temporal and geographical aspects can change the ranking order of different technologies. A growing global population and rising living standards are producing ever greater quantities of waste, while at the same time driving ever-larger demand for energy, especially electricity, or new emerging markets, such as hydrogen in more industrialised countries. A key solution to these challenges of waste disposal, rising energy and hydrogen demand is BECCS (Bioenergy with Carbon Capture and Storage); the generation of bioenergy – in the form of electricity (WtE) or hydrogen (WtH 2), as well as heat – from the thermochemical processing of waste. The addition of carbon capture and storage (CCS) to WtE or WtH 2 has the potential to make waste a zero or even negative emissions energy source, thus contributing to the removal of greenhouse gases from the atmosphere. This work undertakes a pre-screening of different BECCS configurations based on state of the art technologies and then performed an assessment of representative cases in UK for WtE and WtH 2 , necessary to understand if novel waste thermal treatment processes may become potential alternatives or improvements to current WtE plants when retrofitted with CCS. A systematic and comprehensive examination of different key Life Cycle Assessment methodological aspects reveals the importance of the functional unit and allocation approach in determining the preferred pathway in a specific context. [ABSTRACT FROM AUTHOR]

Biomass can be converted into a range of different end-products; and when combined with carbon capture and storage (CCS), these processes can provide negative CO 2 emissions. Biomass conversion technologies differ in terms of costs, system efficiency and system value, e.g. services provided, market demand and product price. The aim of this study is to comparatively assess a combination of BECCS pathways to identify the applications which offer the most valuable outcome, i.e. maximum CO 2 removal at minimum cost, ensuring that resources of sustainable biomass are utilised efficiently. Three bioenergy conversion pathways are evaluated in this study: (i) pulverised biomass-fired power plants which generate electricity (BECCS), (ii) biomass-fuelled combined heat and power plants (BE-CHP-CCS) which provide both heat and electricity, and (iii) biomass-derived hydrogen production with CCS (BHCCS). The design and optimisation of the BECCS supply chain network is evaluated using the Modelling and Optimisation of Negative Emissions Technology framework for the UK (MONET-UK), which integrates biogeophysical constraints and a wide range of biomass feedstocks. The results show that indigenous sources of biomass in the UK can remove up to 56 Mt CO 2 /yr from the atmosphere without the need to import biomass. Regardless of the pathway, Bio-CCS deployment could materially contribute towards meeting a national CO 2 removal target and provide a substantial contribution to a national-scale energy system. Finally, it was more cost-effective to deploy all three technologies (BECCS, BE-CHP-CCS and BHCCS) in combination rather than individually. [Display omitted] • Indigenous sources of biomass in the UK could generate up to 56 MtCO2 of negative emissions per year. • All three pathways (electricity, heat, hydrogen) provides a substantial energy supply for the UK. • It is more cost-effective to deploy technologies in combination, BE-CHP-CCS with BECCS and BHCCS. • The cost-optimal combination of technologies is a function of the H 2 , electricity and heat price. • Capital cost savings (e.g. retrofit existing plants) and high capture rates enhance deployment. [ABSTRACT FROM AUTHOR]

The majority of global emissions scenarios compatible with holding global warming to less than 2 °C depend on the large-scale use of Greenhouse Gas Removal (GGR) technologies. Recent critiques have highlighted the concerns of building long-term climate policy on such speculative technological scenarios emerging from orthodox modelling approaches – including integrated assessment modelling prominently assessed by the IPCC. Through a stakeholder consultation process with the UK modelling and policy community, we critically examine the integration of GGR technologies into UK Net Zero scenarios and the decision-making philosophy underlying the use of orthodox modelling to inform UK climate policy. We identify a number of features of orthodox modelling approaches which are unable to manage the pervasive extent of deep uncertainty in possible UK climate and energy futures. We further argue that a more fundamental issue lies in the way that the models are used by UK climate policy makers: that the handling of uncertainties which pervade the integration of GGR into Net Zero policy are resulting in substantial distortions in net-zero policy design and associated decision-making. Drawing on the principles of decision-making under deep uncertainty techniques, exemplified by Robust Decision Making, we recommend an alternative approach that explicitly embraces uncertainty, multiple values and diversity among stakeholders and viewpoints, and in which modelling exists in an iterative exchange with policy development rather than separate from it. We advocate that such an approach would provide more relevant and robust information to near-term policymaking and enable an inclusive societal dialogue about the appropriate role of GGR within UK climate policy. • The deployment of greenhouse gas removal to address UK Net Zero is subject to deep uncertainty. • There is a need to develop greater stakeholder capacity as to the role of models in informing policy design. • Societal scenarios, extreme events and disruptions are underrepresented in the conventional Net Zero analyses. • Participatory processes would unpack uncertainty, aid transparency and promote deliberative decision-making. • Tools for decision-making under deep uncertainty could play a fundamental role in the deployment of negative emissions. [ABSTRACT FROM AUTHOR]

• Responsible incentivisation requires attention to situated stakeholder perspectives. • We develop four policy scenarios and subject them to deliberation in the UK and Sweden. • New incentives and enabling reforms to existing policy instruments are needed. • Mitigation deterrence must be considered in real world (not abstracted) contexts. • Multi-instrument approaches are needed to overcome single instrument deficiencies. Bioenergy with carbon capture and storage (BECCS) plays a central role in scenario pathways that limit global warming in line with the objectives of the Paris Agreement. Yet deliberate policy efforts to incentivise BECCS—whether through amending existing climate policies or introducing entirely new ones—remain rare. In this paper, we contend that BECCS must be incentivised responsibly, through policy-making processes which account for diverse and geographically varying societal values and interests. More specifically, we make the case for responsible incentivisation by undertaking a comparative analysis of stakeholder attitudes to four idealised policy scenarios for BECCS, including representatives of government, business, nongovernmental and academic communities, in the UK and Sweden. The scenarios were: business as usual; international policy reform; national BECCS policy; and national policy for negative emissions technologies. Based on our findings, we recommend that policymakers 1) recognise the need to develop new incentives and make enabling reforms to existing policy instruments; 2) consider the risk of mitigation deterrence in their real world (and not abstracted) contexts; 3) employ multi-instrument approaches to incentivisation that do not overly rely on carbon pricing or 4) force a choice between technology specific or technology neutral policies; and 5) attend to the diversity of stakeholder and wider public perspectives that will ultimately determine the success—or failure—of their policy designs. [ABSTRACT FROM AUTHOR]

Enhanced silicate weathering, the application of crushed calcium and magnesium-rich rocks to arable cropland, has been proposed as a potential negative emissions technology for the drawdown of atmospheric CO 2. Previous estimates have suggested that enhanced silicate weathering (EW) has the potential to remove significant quantities of CO 2 , as much as 6–30 Mt CO 2 yr−1 for the UK. However, if secondary carbonates are precipitated during the riverine transport of the products of EW, a portion of this CO 2 will be re-released, lowering the net carbon dioxide removal (CDR) potential of the mitigation strategy. Here, we assess the fluvial response to EW in the UK by calculating the expected riverine carbonate precipitation due to the dissolution of 10–50 t ha−1 yr−1 of silicate rock on available arable cropland in major UK catchments. Increases in calcite saturation due to the export of soluble cations sourced from EW from soil to rivers are simulated to cross thresholds for spontaneous carbonate precipitation in several major UK river catchments (e.g. the Great Ouse, Thames). Catchments most susceptible to potential secondary carbonate precipitation are those with a high ratio of cropland to water discharge. On average, carbonate precipitation for major UK catchments is expected to make EW 16% (10 t ha−1), 21% (20 t ha−1) or 27% (50 t ha−1) less effective at removing CO 2 than that predicted in the absence of such precipitation. Furthermore, when placing strict silica limitations on weathering reactions within soils, the CDR potential of EW is reduced considerably, to 0.23 Mt CO 2 yr−1. Although reducing the CDR potential of EW, we suggest that under rapid weathering conditions, carbonate precipitation in UK rivers will prevent pH increases over the safe level for freshwater ecosystems (pH > 9). Together, the simulations suggest that ambient hydrological conditions may make certain UK agricultural areas less effective for CDR by EW and call for methods to quantify secondary carbonate precipitation in response to EW treatments and to further investigate the role of silica saturation in suppressing weathering reactions. • EW in the UK will drive significant changes in riverine chemistry. • This change is dependent on % arable land, annual discharge, and river chemistry. • Secondary carbonates are predicted to precipitate in most UK catchments. • Carbonate precipitation may reduce the CO 2 sequestration potential of EW by 16%–27%. • Silica saturation limits may further reduce the transport of EW products in rivers. [ABSTRACT FROM AUTHOR]

The application of crushed silicate minerals to agricultural soils has been suggested as a route to enhance weathering rates and increase CO 2 drawdown. Laboratory studies have attempted to evaluate the potential of enhanced weathering as a CO 2 removal technique but do not simulate the geochemical complexity of soil environments, and studies in the field are limited in the nature of data they can collect. To overcome these limitations, this study uses an experimental set-up which fully encapsulates field conditions in a controlled setting using soil cores removed from UK cropland and treated with crushed basalt. Cores were exposed to natural weather conditions throughout a 14-month time series, and soil solution was sampled in 10–20 cm intervals in the core to provide insight into the fate of dissolution products with soil depth. This study assessed the rate and chemistry of basalt dissolution 8 months after addition at a high application rate (100 t basalt ha−1) using direct measurements from a UK soil. Assuming conclusions drawn from this study are representative of field-scale enhanced weathering, findings indicate that a set application of basalt to lime-rich, unirrigated UK soils releases alkalinity at a rate of 310 ± 30 eq ha−1 yr−1 and could remove 10.2 ± 0.8 kgCO 2 ha−1 yr−1. Accumulation of undissolved basalt may also lead to large and irreversible changes to soil compositions following repeated application. When considering variation in hydrology around the UK, we assess the drawdown potential of application of basalt to all UK arable land as 1.3 ± 0.1 MtCO 2 yr−1 which is equivalent to 3% of current UK agricultural CO 2 emissions. This is 5- to 25- fold slower than previous modelled assessments, likely due to complexities of soil systems and to water limitation on alkalinity release. Further research is needed to fully assess controls on the potential of enhanced weathering in the real-world environment, across a range of hydrological and soil environments, before the approach is substantively scaled-up for CO 2 removal. • Crushed basalt was applied to a UK agricultural soil in a 14-month soil core study. • Five years of basalt application over UK cropland could remove 1.3 ± 0.1 MtCO 2 yr−1. • Enhanced weathering removes CO 2 considerably slower than model predictions. • Low water flux limits drawdown from enhanced weathering in dry UK cropland. [ABSTRACT FROM AUTHOR]

• I develop a novel method for public appraisal of five policy relevant CDR methods. • The British public support the inclusion of CDR in UK climate policy. • 'Natural' CDR is preferred but likely a result of prevailing Romanticist thought. • 'Technological' CDR is less polarising and may be held back by the nature framing. • Highest support is from egalitarians, older people, men, and higher social grades. Efforts to deliver on net zero emissions targets are set to rely on carbon dioxide removal (CDR) methods. Democratic, trustworthy and socially intelligent research, development, demonstration and deployment of CDR methods in aid of net zero will be highly dependent on how different publics evaluate them, and ultimately which groups support or oppose them. This paper develops a novel, nationally representative method for the multi-criteria appraisal of five policy relevant CDR methods – plus an option not to pursue CDR at all – by members of the British public (n = 2,111). The results show that the public supports the inclusion of CDR in UK climate policy. CDR methods often characterised as 'natural' or 'nature-based' are appraised more highly than 'technological' ones, in the descending order: habitat restoration, afforestation, wood in construction, bioenergy with carbon capture and storage, and direct air carbon capture and storage. Yet, there is no significant disagreement in the appraisal of technological methods and they therefore may be less polarizing, suggesting that popular preconceptions of what is natural – and therefore more attractive – may be holding them back. CDR methods being mainly developed by public sector and non-governmental organisations are also appraised more highly than those being developed by private interests. Regional differences in option appraisal reveal where particular CDR methods are more or less likely to be supported or opposed; stressing the importance of matching physical requirements for CDR with appropriate social contexts. Demographic and socio-economic analyses show that people who appraise CDR methods most highly tend to be older respondents, male, or of a higher social grade. Finally, those with hierarchical worldviews and who voted 'leave' in the UK's referendum on EU membership are less supportive of CDR than those with egalitarian worldviews and who voted 'remain'. [ABSTRACT FROM AUTHOR]

Bioenergy with carbon capture and storage (BECCS) technology is expected to support net-zero targets by supplying low carbon energy while providing carbon dioxide removal (CDR). BECCS is estimated to deliver 20 to 70 MtCO 2 annual negative emissions by 2050 in the UK, despite there are currently no BECCS operating facility. This research is modelling and demonstrating the flexibility, scalability and attainable immediate application of BECCS. The CDR potential for two out of three BECCS pathways considered by the Intergovernmental Panel on Climate Change (IPCC) scenarios were quantified (i) modular-scale CHP process with post-combustion CCS utilising wheat straw and (ii) hydrogen production in a small-scale gasifier with pre-combustion CCS utilising locally sourced waste wood. Process modelling and lifecycle assessment were used, including a whole supply chain analysis. The investigated BECCS pathways could annually remove between −0.8 and −1.4 tCO 2 e t biomass −1 depending on operational decisions. Using all the available wheat straw and waste wood in the UK, a joint CDR capacity for both systems could reach about 23% of the UK's CDR minimum target set for BECCS. Policy frameworks prioritising carbon efficiencies can shape those operational decisions and strongly impact on the overall energy and CDR performance of a BECCS system, but not necessarily maximising the trade-offs between biomass use, energy performance and CDR. A combination of different BECCS pathways will be necessary to reach net-zero targets. Decentralised BECCS deployment could support flexible approaches allowing to maximise positive system trade-offs, enable regional biomass utilisation and provide local energy supply to remote areas. • There is a big gap between present BECCS deployment and CDR targets in the UK. • Trade-offs between biomass use, energy output and CDR were quantified. • Investigated BECCS pathways could deliver 23% of UK's CO 2 removal goal. • Operational decisions and policy play key role in CDR yield and sustainability. • Modular BECCS systems could provide flexibility and support regional development. [ABSTRACT FROM AUTHOR]

The Royal Society's landmark report on geoengineering is predicated on a particular account of the context and rationale for intentional manipulation of the climate system, and this ethical framework probably explains many of the Society's conclusions. Critical reflection on the report's values is useful for understanding disagreements within and about geoengineering policy, and also for identifying questions for early ethical analysis. Topics discussed include the moral hazard argument, governance, the ethical status of geoengineering under different rationales, the implications of understanding geoengineering as a con- sequence of wider moral failure, and ethical resistance to invasive interventions in environmental systems. [ABSTRACT FROM AUTHOR]