The talk explores: the dependencies of human well-being on environmental conditions and processes; the causes and consequences of environmental disruptions in less developed, rapidly developing, and industrialized economies; the central role of civilization's energy sources in generating many of the most dangerous and intractable environmental problems at all levels of economic development; the reasons for considering disruption of global climate as ultimately the most challenging of these problems; what we ought to be doing about this challenge; and why we are not doing it.