Second, a key question is how biophysically “safe” targets can be achieved while also meeting goals for human well-being and justice. For example, meeting the social goals of Agenda 2030 without widespread transformations may lead to crossing safe targets for the biophysical state of the Earth system (Sachs et al., 2019). Achieving biophysical targets, such as 1.5°C for climate or increasing ecosystem protection, can undermine well-being, if, for example, bioenergy competes with food production, or protected areas undermine local livelihoods (Hasegawa et al., 2020).

First, an “unsafe” world is likely to increase inequality, so “safe” would seem a necessary pre-condition for “just”—but not always a sufficient one. A “safe” target from a biophysical perspective may not be adequate to prevent large-scale risks to humans in specific contexts. For example, there are large risks for many human populations even with a 1.5°C climate target (Hoegh-Guldberg et al., 2018).