Jones, A.C. et al. Effects of hemispheric solar geoengineering on tropical cyclonic frequency. Nat. Common. 8, 1382 (2017). The combination of biomass energy with carbon capture and storage (BECCS), which can be used either for electricity generation or for the production of hydrogen or liquid fuels34, is widely accepted in integrated assessment model scenarios in order to provide sufficient CDR to keep delta bar T_ below 2oC18 ,19. The range of estimates of BECCS` maximum distance potential is broad, in part due to assumptions about land use competition with agriculture, economic incentives for comprehensive development and development, and other factors such as nature protection factors. The high-end estimates of BECCS in the literature include underlying assumptions, such as the use of forest and agricultural residues35, the transition to lower meat regimes and the diversion of more than half of the current use of nitrogen and phosphate fertilizers in the BECCS, resulting in an absorption of 10 Gt (CO2) per year by 205032,33 , estimates for 2100 are similar or even higher27.36. This would also depend on the development of bioenergy and co2 capture and storage (CCS) technologies to allow for a capacity of several orders of magnitude greater than current prototypes37,38,39. Excluding a linear evolution at 10 Gt (CO2) per year by 2050 and thereafter, this would imply a cumulative distance potential of 700 Gt (CO2), i.e.
greater than CDRref. Several factors may reduce this, but it could also rise below the high-end assumptions mentioned above. We highlight three steps in future reflections on climate geoengineering in the paris agreement. First, the early development of effective governance, including for research, could be designed to reduce the likelihood and magnitude of potential injustices (see Box 1) and allow proponents and critics of climate geoengineering technologies to raise their concerns. Second, further disciplinary and interdisciplinary research could help reduce major uncertainties about climate effects, side effects, costs, as well as the technical implementation and societal aspects of different techniques. Legitimization of this research would require cross-disciplinary processes involving scientific and political actors, civil society and the public, particularly in decision-making on potential large-scale research programmes. Such participation is a major challenge for effective governance. National and international efforts to promote the advice and coordination of future large-scale research could help reduce some of the risks of social policy, including the moral risk of diverting attention from or deterring climate protection.