The long-standing concern of biologists and ecologists for the environment and their warnings that it was being seriously threatened by human production and consumption, were increasingly heeded by society in the late 1960s and the early 1970s. These signs of public interest stimulated economists to pay more attention to environmental problems. They observed that what had formerly been free goods such as clean air, clean surface water, unpolluted soil, silence and natural beauty, had become scarce. This problem of ‘new scarcity’ (Mishan 1967; Hueting 1970, 1980) was analysed by economists.