Geoengineering, the deliberate modification of the climate system, is a proposed set of techniques to counter some of the effects of Anthropogenic Global Warming (AGW; Shepherd, 2009). Geoengineering includes Carbon Dioxide Removal (CDR) and Solar Radiation Management (SRM; Council, 2015). Global modelling studies of geoengineering have typically considered idealized scenarios, to understand the physical processes of interventions and their general impacts. These scenarios are not necessarily policy-relevant, and are often physically implausible (such as instantaneous quadrupling of CO2). The climatic and ecological impacts of politically-relevant and potentially plausible solutions have rarely been modeled and assessed. Nevertheless, commentators and policymakers often falsely assume that idealized or extreme scenarios are proposed as solutions to the AGW problem.
This paper discusses various scenarios, which appear to be broadly plausible from both a political and Earth-system standpoint. These fall into the following categories:
1) Well-designed intervention strategies, including combined approaches, intended to meet specific climate targets
2) Global emergency response strategies, in case of unexpected natural or social events
3) Regional intervention strategies (with potential global consequences)
4) Miscellaneous and long-term intervention strategies
We propose relevant, non-prioritized model experiments, corresponding to these scenarios. Some may be performed with existing setups of global climate models; others need to be first designed in detail. Developing and running these experiments, and assessing likely resulting impacts on society and ecosystems, would help to inform the public debate on the real-world feasibility of CDR and SRM geoengineering.