This article contrasts two fundamentally different understandings of economic growth and "development" that lead to diametrically opposed approaches to how to deal with global ecological deterioration. One is the currently hegemonic perspective of neoclassical economic theory, which has been used to advocate growth as a remedy for environmental problems. The other is the zero-sum perspective of world-system theory, which instead suggests that growth involves a displacement of ecological problems to peripheral sectors of the world-economy. The article begins by sketching the history of these two perspectives in recent decades and reflecting on the ideological and epistemological contexts of their appearance and different degrees of success. It then turns to the main task of critically scrutinizing some of the foundations of the neoclassical approach to environmental issues, arguing that its optimistic view of growth is based on faulty logic and a poor understanding of the global, physical realities within which money and the capitalist world-system operate.