Aldo Leopold's Sand County Almanac was first published in 1948 as a witness to what he saw as the anthropocentrism (human being centredness) of much ethical thinking.
In it he writes that "all ethics so far revolved around a central premise: that the individual is a member of a community of interdependent parts. . . . The land ethic simply enlarges the boundaries of the community to include soils, waters, plants, and animals, or collectively: the land. . . . In short, a land ethic changes the role of Homo Sapiens from conqueror of the land-community to plain member and citizen of it. It implies respect for his fellow members, and also respect for the community."
Human beings, so he argues, are part of one interdependent whole, not merely atomised pleasure seekers or preference maximisers. So he is seen as one of the fathers of Deep Ecology.
He went on to push for the development of an "ecological conscience." He writes:"obligations have no meaning without conscience, and the problem we face is the extension of the social conscience from people to the land. No important change in ethics was ever accomplished without an internal change in our mental emphasis, loyalties, affections, and convictions."
We needed to commit, argued Leopold, to an attitude of mind which sees nature not as a resource, but as a thing of beauty and wonder having intrinsic not instrumental value.
Leopold's own description for this new way of thinking is a "land ethic." It is the principle that "a thing is right when it tends to preserve the integrity, stability, and beauty of the biotic community. It is wrong if it tends otherwise." Here Leopold gave content to what goodness consists in - the values of stability and integrity of the biosphere - the interdependent relationships all living things have to one another.
We may not yet fully understand the nature and complexity of this relationship, just as we don't yet fully understand every possible implication of global warming on the ocean currents or the creation of dead zones in the ocean. Yet "if the land mechanism as a whole is good, then every part is good, whether we understand it or not..to keep every cog and wheel is the first precaution of intelligent tinkering" (Round River 1993: 145-6).
So he began a process of rethinking what it means to be human, of the moral relevance of the environment as something with intrinsic goodness, and of an ethics of responsible stewardship rather than selfish exploitation in the pursuit of profit.
Click here for a longer essay by an American academic explaining the significance of Aldo Leopold for environmental ethics.