Scenarios are among the most visible and widely used products of the IPCC. Many kinds of scenarios are used in climate research, but emissions scenarios and the socio-economic assumptions that underpin them have a distinct status because the IPCC orchestrated their development. They have evolved from assessment cycle to assessment cycle and serve as ‘boundary objects’ across Working Groups and as instruments of policy relevance. The field of Integrated Assessment Modelling has emerged to produce these scenarios, thereby taking centre stage within the IPCC assessment process. Because these scenarios harmonise assumptions about the future across disciplines, they are essential tools for the IPCC’s production of a shared assessment of climate research and for ensuring the policy relevance of this assessment. Yet, the reliance on a relatively small set of complex models to generate scenarios spurs concerns about transparency, black-boxed assumptions, and the power of IAMs to define the ‘possibility space’.

NETs range from afforestation to bioenergy with carbon capture and storage. They are seen by many as instrumental in achieving the mitigation objectives of the Paris Agreement. However, uncertainty remains regarding the technical, economic, and political feasibility of the large-scale deployment of NETs. The focus in this chapter is on whether a state may lawfully presume, for instance in the course of determining its long-term low-greenhouse-gas-emission development pathway under Article 4(19) of the Paris Agreement, that a future large-scale deployment of NETs will be realized. Gareth Davies maintains that that makes perfect sense, not least because conventional mitigation methods are in the same boat (of uncertainty), and that in other respects as well conventional methods are on a continuum with NETs. By contrast, Duncan McLaren and Wil Burns argue that any heavy reliance now on a presumed large-scale availability of NETs in the future would be irresponsible, unethical, and unlawful.

NETs range from afforestation to bioenergy with carbon capture and storage. They are seen by many as instrumental in achieving the mitigation objectives of the Paris Agreement. However, uncertainty remains regarding the technical, economic, and political feasibility of the large-scale deployment of NETs. The focus in this chapter is on whether a state may lawfully presume, for instance in the course of determining its long-term low-greenhouse-gas-emission development pathway under Article 4(19) of the Paris Agreement, that a future large-scale deployment of NETs will be realized. Gareth Davies maintains that that makes perfect sense, not least because conventional mitigation methods are in the same boat (of uncertainty), and that in other respects as well conventional methods are on a continuum with NETs. By contrast, Duncan McLaren and Wil Burns argue that any heavy reliance now on a presumed large-scale availability of NETs in the future would be irresponsible, unethical, and unlawful.