Nitrogen, planetary boundaries, and the metabolic rift: Using metaphor for dietary transitions towards a safe operating space

The framework of planetary boundaries serves as a useful metaphor for a “safe operating space” if we are to maintain Earth as a viable habitat for humanity. Using another metaphor, that of metabolic rift, the chapter concentrates on one of the anthropogenically breached boundaries: the global biogeochemical flow of nitrogen. The disruption of the global nitrogen cycle is largely an unintended consequence of the widespread use of nitrogen-based fertilisers arising from the development of the Haber-Bosch process early in the twentieth century. The capability to synthesise atmospheric nitrogen into fertiliser has had a transformative effect on humanity’s ability to feed itself, with consequences for population growth and also dietary change. Reflecting upon the disturbed metabolic interaction between human society and the environment under the current global agri-food system, the chapter highlights how agricultural intensification has resulted in increasing production of animal feeds that, in turn, has made livestock products cheaper and more ubiquitous. Rising levels of meat consumption have problematic consequences both for human and planetary health and the chapter explores the prospect of planetary boundaries as a metaphor that may guide a process of dietary transition towards a safe operating space.