Changeability is an inherent component of climate on all time scales of variation. The importance of this changeability for people has largely been experienced through its influence on food production. For almost all of human history the harvesting of food has been the single most crucial determinant of well-being and socio-cultural development. It is even possible to speculate that the ecological dominance of the human species owes a great deal to its capability to survive and adapt to the swings of the climatic pendulum. The vital harvest surplus on which so much depended has always been largely determined by the vagaries of temperature and rainfall. Today, despite technological advancement - perhaps even more so because of it - humans remain highly susceptible to the jolts of a climatic system the functioning of which is only imperfectly understood. The lessons of history, however, demonstrate that climatic variability is ignored only at the cost of compromising the well-being of ourselves or our children, an unsustainable situation that runs counter to any principles of intergenerational equity.