The planetary boundaries framework defines a safe operating space for humanity based
on the intrinsic biophysical processes that regulate the stability of the Earth system.
Here, we revise and update the planetary boundary framework, with a focus on the underpinning
biophysical science, based on targeted input from expert research communities and
on more general scientific advances over the past 5 years. Several of the boundaries
now have a two-tier approach, reflecting the importance of cross-scale interactions
and the regional-level heterogeneity of the processes that underpin the boundaries.
Two core boundaries—climate change and biosphere integrity—have been identified, each
of which has the potential on its own to drive the Earth system into a new state should
they be substantially and persistently transgressed.