On the system properties of the planetary boundaries

Rockström et al. (2009) identified a set of critical sustainability issues where perturbations resulting from human activities present a risk of unacceptable global environmental change. They attempted to quantify a boundary level for each one, using the range of variability observed during the Holocene as the marker for the safe operating space for humanity. Together, the set of boundaries (Table 1) represents an important conceptualization of global sustainability through the lens of resilience and Earth system science, already influencing research and policy agendas worldwide. Rockström et al.'s (2009) multidisciplinary expert deliberative process took into account several decades of Earth system research, and their text frequently signals the profound influence of systems approaches in their analysis (notably Supplementary Discussion 1).

However, their article is not explicit about the system properties of the boundaries themselves, resulting in conceptual tensions, discussed below. Debates remain about the definitions of the boundaries and what kinds of measures should be control variables (e.g., Carpenter and Bennett 2011). Systems analysis approaches provide a theoretical containing structure for these debates as the boundaries are redefined or refined, and for the further development of the planetary boundaries concept.