In the 1970s and 1980s the International Institute for Applied Systems Analysis (IIASA) hosted several research projects, workshops and conferences in order to discuss the implications of rising carbon dioxide concentrations in the Earth’s atmosphere. A number of distinguished scholars, some of whom later became prominent protagonists within the United Nations’ Intergovernmental Panel on Climate Change (IPCC) and sustainability communities more generally, participated in these debates. Since those at IIASA did not engage in obviously related fields such as geophysics or climatology, there is a need to explain how, and via which contexts the issue entered the institute’s agenda. This article examines this historical context and contrasts two competing paradigms that emerged at IIASA in order to assess and respond to the carbon dioxide question: The first approach was related to the organisation’s research projects on the future of energy systems, which drew on physics, engineering, economics and applied system dynamical modeling; the second approach drew earlier research into ecological management and complex dynamical systems theory, and argued for the use of multiple methods to assess the carbon dioxide question. The first approach invoked ideas of techno-economical control mechanisms, the second resulted in a more embedded framing of climate change as one of a larger complex of issues relating to sustainable development. Based on resources from IIASA’s research repositories and institutional archive, this study retraces these competing discourse framings and outlines the specific research and modeling strategies, policies, and cultural and technological imaginaries related to them.