Revisiting the application and methodological extensions of the planetary boundaries for sustainability assessment.

The planetary boundaries (PBs) delineating the safe operating space for human activities have been broadly recognized as a well-grounded framework for global sustainability assessment. This paper provides a comprehensive review of the application and methodological extensions of the PBs by linking with multiscale environmental sustainability assessments. We find that the targeted scales, sharing principles and sustainability perspectives jointly determine the downscaling of the PBs-a complex process that needs to take into account the biophysical, socioeconomic, ethical and cultural dimensions. Despite the varying sharing principles, in general both top-down and bottom-up approaches have been employed to define the environmental boundaries at sub-global scales on which the various PBs highly differ in their threshold behaviors. To clarify the responsibility of different stakeholders for sustainable development, the PB-informed sustainability assessment should refer to a specific perspective (i.e., production-, consumption-, or life cycle-based). Furthermore, the methodological extensions of PBs have the potential to monitor the progress and gaps of the globally consensus-based Sustainable Development Goals (SDGs). To achieve the SDGs within the PBs, there is a great need for a thorough transition of socioeconomic systems towards a prosperous, just and sustainable future.