Humanity now faces a dangerous dilemma: on one hand leading scientists predict that if we continue to burn coal, gas and oil the environmental consequences are likely to be catastrophic (e.g. Hansen et al., 2013); on the other hand many economists argue that if we stop using fossil fuels our industrial civilization will run out of energy and collapse (e.g. Canes, 2015). Although renewable technologies are beginning to compete with fossil fuels in the production of electricity, electricity is only 20% of energy use (IEA, 2014). In other areas—e.g. most heating, industrial production and transport—renewable alternatives are either non-existent or not yet cost-competitive.