Carbon Dioxide Removal (CDR) technologies may be needed to meet climate change targets.Currently full understanding of public attitudes towards such approaches is lacking. Here we report a mixed-methods study on public perceptions of CDR in the US and UK, focusing on bioenergy with carbon capture and storage, direct air capture and terrestrial enhanced rock weathering. A discourse of climate urgency had a substantial impact on perceptions, with CDR seen as offering too slow a response to the climate crisis. CDR also fails to reflect long-term hopes for a sustainable world, being interpreted as not addressing the root causes of climate change. A social license to operate may therefore depend upon resolving these temporal dilemmas regarding both the short and long-term implications of technology development. While research under well-controlled conditions is likely to be acceptable, at-scale deployment without corresponding efforts to reduce emissions may represent a red line for many people.The Paris Agreement on climate change stipulates the requirement to pursue efforts to limit the average global temperature increase to 1.5°C 1 , and several countries have committed to goals of net carbon neutrality by 2050. However, residual emissions from difficult-to-decarbonise sectors such as aviation and agriculture mean that this will be challenging to meet through emissions reduction alone. In order to achieve net zero across an economy as a whole there might be a need to simultaneously remove an equivalent amount of CO2 from the atmosphere using Carbon Dioxide Removal (CDR) 2 .CDR comprises a range of different proposals, from those widely practiced such as afforestation, to those still at concept stage. "o e of the e e , e gi ee ed app oa hes su h as Bioenergy with Carbon Capture and Storage (BECCS), Direct Air Capture (DAC) and Enhanced Rock Weathering (ERW) might have the potential for long-term sequestration of large quantities of CO2 3 . Of these, BECCS is the best understood and has the highest Technology Readiness Level, but there is considerable uncertainty over sequestration potential and cost for all three (see ref. 4 for a review).Public attitudes and risk perceptions are important for novel technologies, as illustrated by controversies over genetic modification, fracking for shale gas, and early Carbon Capture and Storage (CCS) [5][6][7] . For novel CDR, as e e gi g te h ologies, u de sta di g itize ie s th ough upst ea e gage e t a fa ilitate o e ethical and effective technology development 8 . Going beyond techno-scientific assessments, the actual scalable potential of CDR will depend on socio-political factors, including public perceptions (and their influence on political mandates), uptake by relevant market actors, and successful development of a social license to operate 2,9 . While public attitudes will not be the only factor driving development and deployment of CDR at scale, the current limited evidence on them represents an important gap in our understanding of the real-world potential of CDR 10 ....

The topic of Greenhouse Gas Removal (GGR) for climate geoengineering is becoming increasingly salient following the IPCC's 5th Assessment Report and the Paris Agreement. GGR is thought of as a separate category to mitigation techniques such as low-carbon supply or demand reduction, yet multiple social, ethical and acceptability concerns cut across categories. We propose moving beyond classifying climate strategies as a set of discrete categories (which may implicitly homogenize diverse technologies), toward a prioritization of questions of scale of both technology and decision-making in the examination of social and ethical risks. This is not just a theoretical issue: important questions for policy, governance and finance are raised, for instance over the future inclusion of GGR in carbon markets. We argue that the conclusions drawn about how best to categorize, govern and incentivize any strategy will depend on the framing used, because different framings could lead to very different policy recommendations being drawn. Because of this, a robust approach to developing, governing and financing GGR should pay attention first to urgent concerns regarding democracy, justice and acceptability.

This paper explores policies for Negative Emissions Technologies (NETs), in an attempt to move beyond the supply-side focus of the majority of NETs research, as well as the current dominance of carbon pricing as the main NETs policy proposal. The paper identifies a number of existing policies from four key areasenergy/transport, agriculture, subsoil , and oceans-which will have an impact on three NETs: Bioenergy with Carbon Capture and Storage (BECCS), Direct Air Capture (DAC), and terrestrial Enhanced Rock Weathering (ERW). We propose that non-climate co-benefits may be valuable in terms of the policy 'demand pull' for NETs; in particular, we find that ERW may provide multiple co-benefits which can be mandated through existing policy structures. However, interaction with numerous policy areas may also create barriers, particularly where there is tension between the priorities of different government departments. On the basis of existing and analogous policies from a range of geographical contexts and scales, this paper proposes four options for NETs policy that could be reasonably implemented in the near-term. We also argue that ERW demonstrates the importance of scale and framing, because the policy environment depends on whether it is framed as a soil amendment at local scales or as a climate stabilisation technique at international scale. Key policy insights • Co-benefits may assist the 'demand pull' for novel technologies by providing multiple policy angles for incentivisation rather than relying on a 'fix-all' policy such as a high carbon price. • DAC with storage might be overly reliant on a high carbon price, because it only provides one core benefit-that of atmospheric carbon reduction. • ERW may provide multiple co-benefits which can be mandated through existing policy structures, but should focus on using waste rock rather than mining virgin material. • We propose four near-term options for NETs policy: funding for small-scale BECCS demonstration and an international biomass certification mechanism; small-scale loans for ERW on farms and promotion of locally-sourced rock residues; amendment of fertiliser subsidy schemes to include silicate rock; and a clearer framework for licensing subsoil access for CO2 storage.

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