Even as world religions, fundamentalist and otherwise, challenged global modernity on cultural or spiritual grounds, burgeoning environmental movements in the 1960s and later also did so with an eye to the human impact on the earth and its many living creatures, including ourselves. Among the distinctive features of the twentieth century, none has been more pronounced than humankind’s growing ability to alter the natural order and the mounting awareness of this phenomenon. When the wars, revolutions, and empires of this most recent century have faded from memory, environmental transformation and environmental consciousness may well seem to future generations the decisive feature of that century. Already, many scientists and other scholars have begun to refer to the current era, since at least the advent of the Industrial Revolution, as the Anthropocene, or the “age of man.” That informal term has called attention to the lasting impact of human activity on the planet.24 Species extinctions, increases of carbon dioxide in the atmosphere, the depletion of groundwater reserves, the enlargement of deserts, dead zones in the oceans, transformation of the landscape as wetlands shrink and urban centers grow—these and other environmental changes, all of them generated by human actions, will be apparent to our descendants thousands of years in the future, should they be around to reflect on them.