Fig. 1: Development of the control variables for planetary boundaries over time, historic period and assuming BAU for 2030 and 2050 (SSP2, BAU).

a–d, Control variables for planetary boundaries for 1970 (a), 2015 (b), SSP2 2030 (c) and SSP2 2050 (d). The green zone is the safe operating space, the pale orange represents the zone of uncertainty (increasing risk), and the dark orange is the high-risk zone. The planetary boundary itself lies at the intersection of the green and pale orange zones. The control variables have been normalized to the reference value, planetary boundary and the upper end of the uncertainty zone, as explained in the Methods. The control variables and values used are indicated in Table 1. The planetary boundary figures are a useful conceptual visualization tool, but still subject to limitations, as discussed in the literature⁵⁰.