The Planetary Boundaries concept identifies nine global priorities relating to human-induced changes to the environment. The science shows that these nine processes and systems regulate the stability and resilience of the Earth System — the interactions of land, ocean, atmosphere and life that together provide conditions upon which our societies depend. Four of nine planetary boundaries have now been crossed as a result of human activity: climate change, loss of biosphere integrity, land-system change, altered biogeochemical cycles (phosphorus and nitrogen). Two of these, climate change and biosphere integrity, are what the scientists call "core boundaries". Significantly altering either of these core boundaries would drive the Earth System into a new state.
Source: Stockholm Resilience Centre, 2015.