Climate change is one of the defining challenges of our times and its implications for energy security are profound. Climate concerns, declining reserves of easily accessible oil and gas, and the rise of new energy consumers will drive transformative changes to global energy systems. While these issues prompt widespread economic, environmental, and security fears, they are also connected to positive changes that include democratization of access to modern energy in the developing world. Viewed on a global scale, the primary challenge is to manage the legitimate energy demands of 6.9 billion people within the context of ecological limits. In the light of these trends, the authors examine how the concept of energy security is, will, and ideally should be transformed in the light of scientific evidence that combustion of fossil fuels contributes to dangerous climatic change.