Popular environmentalism began in the 1960s and 1970s when marine biologist Rachel Carson (1907–1964) traced the movement of toxic pesticides (specifically, DDT) through the food chain in her classic book, Silent Spring (1962). Intellectually, this led to a rediscovery of ecologist and forester Aldo Leopold’s (1887–1948) land ethic, A Sand County Almanac (1949), and the thought of John Muir (1838–1914), founder of the Sierra Club.

Leopold had written: “That land is a community is the basic concept of ecology, but that land is to be loved and respected is an extension of ethics.” This moral tone set the basic philosophical orientation toward environmentalism as a moral/ethical matter. The Norwegian philosopher Arne Naess (1912–) was inspired by his encounter with the Himalayan Sherpas’ reverence for their great mountains when his guides would not take him to sacred places. Naess developed an important distinction between deep ecology and shallow ecology.