Fig. 6.

The nine identified planetary boundaries. The green zone is the safe-operating space (below the boundary), yellow represents the zone of uncertainty (increasing risk), and red is the high-risk zone. In these potentially dangerous zones of increasing risk, there are likely continental and global tipping points for some of the boundaries, although not for all them. The planetary boundary itself lies at the inner heavy circle. A proposed boundary does not represent a tipping point or a threshold but is placed upstream of it, that is, well before the risk of crossing a critical threshold. The intent of this buffer between the boundary and a potential threshold in the dangerous zone is to allow society time to react to early warning signs of approaching abrupt or risky change. Processes for which global-level boundaries are not quantified are represented by grey wedges

(adapted from Steffen et al. 2015). Reprinted with permission