Are the Sustainable Development Goals self-consistent and mutually achievable?

On September 18, 2015, the United Nations General Assembly adopted the 2030 Agenda for Sustainable Development, which sets out wide-ranging ambitions for global development. In response to the 2030 Agenda, the International Council for Science (ICSU), in partnership with the International Social Science Council (ISSC), subsequently published a detailed commentary on the Sustainable Development Goals (SDGs) and the linkages between them. The ICSU-ISSC Report raises the possibility that the SDG framework as a whole might not be internally self-consistent, and the report itself calls for a wider "systems perspective." In this paper, we use the ICSU commentary as the basis for a quantitative theoretical analysis of the SDGs from a systems perspective. We provide a mathematical definition of self-consistency and show that the linkages we infer from the ICSU-ISSC report imply that the SDGs are not self-consistent. However, using a simple dynamical model to investigate the combined outcome of direct efforts at tackling each Goal and the indirect effects on progress due to network effects, we show that network effects could be used to secure better outcomes on every Goal than would be possible if linkages between Goals did not exist at all. These better outcomes would be possible through an unequal, targeted reallocation of direct efforts. Unequal distribution of direct effort can therefore make the SDGs mutually achievable. These conclusions contribute to the ongoing debate on the development of global strategies for the achievement of the 2030 Agenda, their implementation, and the definition and monitoring of progress towards the Goals.