The concept of planetary boundaries, which was first introduced in 2009, describes the resilience of our planet and analyzes human influence on various parts of the Earth system. Scientists have identified nine planetary boundaries, the observing of which collectively form the basis for human life on Earth:
- Climate change
- Change in biosphere integrity (biodiversity loss and species extinction)
- Land-system change (e.g., deforestation)
- Freshwater change
- Biogeochemical flows (including the use of phosphorus and nitrogen, e.g., in fertilizers)
- Ocean acidification
- Atmospheric aerosol loading
- Stratospheric ozone depletion
- The introduction of “novel entities” (i.e., chemical substances such as microplastics and pesticides)
A “safe operating space” is defined for each of these dimensions, exceeding which would jeopardize the planet’s resilience and expose humans to significant risks. Building on earlier scientific work (e.g., from the years 2015 and 2023), all nine boundaries were globally assessed for the first time in 2023. This assessment revealed that the safe operating space has been exceeded for six of them. While humanity is currently within the safe operating space for stratospheric ozone depletion, atmospheric aerosol loading, and ocean acidification, pressure is also growing there – particularly in the latter two areas.
In this context, it is pertinent to highlight the proposed distinction between “safe” and “just” boundaries. “Safe” boundaries refer to maintaining the functionality of the Earth system and the extent to which it supports the survival of humans and other living organisms. “Just” boundaries recognize the additional circumstances needed to prevent significant harm to people and enable a life in dignity. Considering the aspect of justice imposes additional constraints, for example on aerosol pollutants. In other words, although a condition may be within “safe” boundaries, it can still harm people in certain locations and be deemed unjust.