As early as the 1970s, the concept of sustainability was used to describe an economy "in equilibrium with basic ecological support systems". Scientists in many fields have highlighted "The Limits to Growth", and economists have presented alternatives, for example a 'steady-state economy', to address concerns over the impacts of expanding human development on the planet. In 1987 the economist Edward Barbier published the study "The Concept of Sustainable Economic Development", where he recognised that goals of environmental conservation and economic development are not conflicting and can be reinforcing each other.