'Opening up' geoengineering appraisal: Multi-Criteria Mapping of options for tackling climate change

Concerted efforts have begun to appraise deliberate, large-scale interventions in the Earth's climate system known as 'geoengineering' in order to provide critical decision support to policy makers around the world. To date geoengineering appraisals have employed narrowly framed inputs (such as context, options, methods and criteria) and 'closed' output reflexivity often amounting to unitary and prescriptive policy recommendations. For the first time, in this paper we begin to address these limitations by 'opening up' appraisal inputs and outputs to a wider diversity of framings, knowledges and future pathways. We use a Multi-Criteria Mapping methodology to appraise carbon and solar geoengineering proposals alongside a range of other options for responding to climate change with a select but diverse group of experts and stakeholders. Overall option rankings are found to vary considerably between participant perspectives and criteria. Despite these differences, the ranks of geoengineering proposals are most often lower than options for mitigating climate change (including voluntary behaviour change and low carbon technologies). The performance of all options is beset by uncertainty, albeit to differing degrees, and it can often be seen that better performing options are outperformed under their pessimistic scores by poorer performing options under their optimistic scores. Several findings contrast with those of other published appraisals. In particular, where stratospheric aerosol injection has previously outperformed other geoengineering options, when assessed against a broader diversity of criteria (spanning all the identified criteria groups) and other options for responding to climate change it performs relatively poorly. We end by briefly exploring the implications of our analysis for geoengineering technologies, their governance, and appraisal.