Given the current trajectory of global fossil-fuel use, the planet's temperature is likely to rise by 4-6 degrees Celsius above its pre-industrial level, an increase that would be catastrophic for food production, human health, and biodiversity; indeed, in many parts of the world, it would threaten communities' survival. Governments have already agreed to keep warming below 2º Celsius but have yet to take decisive action toward creating a low-carbon energy system.