Deliberate large-scale interventions in the Earth's climate system—known collectively as ‘geoengineering’—have been proposed in order to moderate anthropogenic climate change. Amidst a backdrop of many ways of framing the supposed normative rationales for or against their use, geoengineering proposals are undergoing serious consideration. To support decision makers in the multitude of governance considerations a growing number of appraisals are being conducted to evaluate their pros and cons. Appraisals of geoengineering are critically reviewed here for the first time using a systematic literature search and screen strategy. Substantial variability between different appraisals' outputs originates from usually hidden framing effects relating to contextual and methodological choices. Geoengineering has largely been appraised in contextual isolation, ignoring the wider portfolio of options for tackling climate change—spanning mitigation and adaptation—and creating an artificial choice between geoengineering proposals. Most existing appraisal methods do not adequately respond to the post-normal scientific context in which geoengineering resides and show a strong emphasis on closed and exclusive ‘expert-analytic’ techniques. These and other framing effects invariably focus—or close down—upon particular sets of problem definition, values, assumptions, and courses of action. This produces a limited range of decision options which seem preferable given those framing effects that are privileged, and could ultimately contribute to the closing down of governance commitments. Emergent closure around particular geoengineering proposals is identified and argued to be premature given the need for more anticipatory, responsible, and reflexive forms of governing what is an ‘upstream’ domain of scientific and technological development. WIREs Clim Change 2012, 3:597–615. doi: 10.1002/wcc.197
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