The continuing inability of the world to effectively tackle rising greenhouse gas emissions and increasing evidence of the impacts of climate change is making geoengineering more attractive as a strategy for countering rising temperatures. A number of possible technologies have been touted as options for reflecting sunlight away from the earth’s surface. These include aerosol injection, marine cloud brightening, high-albedo crops and buildings, ocean mirrors, cloud thinning and space sunshades. Each of these techniques carries risks, not least because of the scale of the endeavour required and uncertainties concerning unintended consequences. The aim of this roundtable is to assess whether geoengineering could be a technically and politically viable component of a global strategy to combat climate change.