This article examines the concepts 'environment' and 'expertise'. It is argued that these concepts, while having long and diverse individual histories, acquired new meaning through a process of mutual co-production which occurred largely in the period 1920-1960, thus significantly preceding the common understanding of environmentalism as a phenomenon emerging in the 1960s. It is further argued that environmental expertise is much predicated on natural science in a range of fields that were integrated into a comprehensive understanding scaling upwards from the local to the global. Quantitative analysis, observing, measuring, and monitoring rates of change of a growing set of indicators were other key features of this emerging understanding of the environmental. Yet another key aspect was the self-proclaimed ability of environmental expertise to predict rates and directions of current and, crucially, future changes of global environmental conditions, increasingly assuming that these changes were largely of human origin. In addition to thus presenting a brief history of environmental expertise the article also makes the point that the environmental was, despite changed by human action, essentially regarded as something that did not in itself belong to the human or the social and thus the implicit prerogative of the natural sciences. The article argues, on the contrary, that there is solid historical evidence to suggest that 'environment' should also, perhaps primarily, be understood as a social concept, or rather as an extension of the social into nature. As conventional environmental expertise has failed to provide the advice needed to question the driving forces behind environmental degradation and lack of sustainability it is here instead suggested that environmental expertise be fundamentally reconfigured to include the social sciences and humanities, and that concerted research efforts are directed to the understanding of the formation of environmental expertise.