>[!abstract] >The planetary boundaries framework, introduced by [[Rockström et al., 2009|Rockström et al. (2009)]], identifies nine Earth-system processes that define a "safe operating space" for humanity, beyond which ecological destabilization risks catastrophic change. These boundaries include climate change, biosphere integrity, land-system change, freshwater use, biogeochemical flows (nitrogen and phosphorus), ocean acidification, stratospheric ozone depletion, atmospheric aerosols, and novel entities (e.g., chemical pollution). Crossing these thresholds can trigger [[Nonlinear system|nonlinear]], potentially irreversible shifts in Earth's systems. The concept reframes sustainability by emphasizing biophysical limits and the need to keep human activity within planetary-scale boundaries to preserve long-term resilience. >[!related] >- **North** (upstream): [[Earth system science]] >- **West** (similar): [[Doughnut economics]] (Kate Raworth's model linking planetary boundaries with social foundations) >- **East** (different): [[Infinite growth paradigm]] (classical model assuming no biophysical limits) >- **South** (downstream): —