Planetary Boundaries, a framework developed by scientist Johan Rockström[1].
It defines nine safe operating limits for keeping the Earth system stable.
The nine boundaries are climate change, biosphere integrity, land-system change, freshwater change, biogeochemical flows, ocean acidification, atmospheric aerosols, ozone depletion, and novel entities; as of 2023, six of the nine had been breached, and as of 2025 it is seven — ocean acidification being the latest to cross.
The engine treats it as the detailed biochemical reality sitting underneath the broader 'persistent pollution' variable in system-collapse modeling.