Planetary Boundary for Novel Entities: Time for a Reboot.

Novel entities are diverse and complex; hence, defining their Planetary Boundary through control variables, indicators, and acceptable limits is challenging. Here, we highlight shortcomings of the current quantitative boundary, which applies a purely precautionary interpretation of safety that defines the safe operating space as zero novel entities that are not fully characterized. In practice, the zero limit is unattainable and undesirable for human societies that rely on services provided by novel entities. Furthermore, it is not operational within the framework of other boundaries, which have risk-based thresholds. We therefore propose a reboot of the Planetary Boundary for Novel Entities and recommend governance and monitoring strategies based on: (a) clarification of the "safe operating space" for novel entities, distinguishing pure precaution ("safe from the unknown") from operational precaution that tolerates a workable, non-zero level of uncertainty; (b) complementary, multilayer control variables spanning pressures, states, and impacts; (c) extensions to existing monitoring systems to provide quantitative indicators of distribution, accumulation, exposure, and impacts for subsets of novel entities to communicate the status and trends of stress from novel entities on the Earth system; and (d) recognition of regulatory and policy-related success stories that illustrate comprehensive, protective, and operational governance of novel entities.