Progress report Climate change: Climate engineering through stratospheric aerosol injection Mike Hulme University of East Anglia, UK Abstract In this progress report on climate change, I examine the growing literature dealing with the proposal to engineer global climate through the deliberate injection of aerosols into the stratosphere. This is just one of a wide range of technology proposals to geoengineer the climate, but one in particular which has gained the attention of Earth System science researchers and which is attracting wider public debate. I review the current status of this technology by exploring a number of different dimensions of the proposal: its history and philosophical and ethical implications; how it is framed in public discourse and perceived by citizens; its economic, political and governance characteristics; and how the proposed technology is being researched through numerical modelling and field experimentation. Unlike many other geoengineering interventions, stratospheric aerosol injection has no additional societal co-benefits: its sole raison d’etre would be to offset planetary heating caused by rising concentrations of greenhouse gases. The deployment of such a technology would have profound implications for the view humans have of themselves in relation to the non-human world. Keywords climate change, geoengineering, public engagement, science governance, solar radiation management, strato- spheric aerosol injection I Introduction This is the second of three progress reports I am writing for Progress in Physical Geography covering the broad theme of (anthropogenic) climate change. Two years ago I reviewed the growing scholarly literature examining (criti- cally or otherwise) the knowledge-making prac- tices of the IPCC (Hulme and Mahony, 2010). Here, I turn my attention to another feature of cli- mate change discourse which has gained salience in certain scientific, political and social settings in recent years, namely the prospect of control- ling the Earth’s heat balance through deliberate injection of aerosols into the stratosphere. This is not a review of the much wider field of deliberate engineering of the Earth’s climate (sometimes referred to as ‘geoengineering’, although this term is rather imprecise). This topic would be too broad for a short progress report and a good introduction exists in the form of the Royal Society’s (2009) report on geoengi- neering (see also popular books such as Corresponding author: Mike Hulme, University of East Anglia, Science, Society and Sustainability (3S) Group, School of Environmental Sciences, Norwich NR4 7TJ, UK Email: m.hulme@uea.ac.uk Progress in Physical Geography 36(5) 694–705 ª The Author(s) 2012 Reprints and permission: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0309133312456414 ppg.sagepub.com