The Planetary Boundary Framework (PBF) is a fundamental scientific concept in environmental science under constant development by scientists such as Steffen et al. (2015) and Richardson et al. (2023). The PBF aims to define a safe operating space for human societies and to ensure the long-term stability and health of our planet.

a. [5 pts] Explain how the PBF define a safe operating space for the Earth considering the history and possible trajectories of the Earth’s climate.

b. [5 pts] Explain what an environmental indicator is and how they are used in the PBF. Include one example of an environmental indicator used in the PBF to support your answer.

c. [5 pts] Describe one update or change to the PBF presented by Richardson et al. (2023), in comparison with Steffen et al. (2015), including a possible reason for the update or change.

References cited in this question:

Steffen et al. (2015). Planetary boundaries: Guiding human development on a changing planet.

Richardson et al. (2023). Earth beyond six of nine planetary boundaries.