Join the dots on planetary boundary interactions

Abstract. Planetary boundaries (PBs) are complexly interlinked, as the transgression of either one can worsen the status of others. Such cascading processes can accelerate Earth system destabilization and shrink humanity's safe manoeuvring space. To demonstrate the crucial need to maintain multiple PBs, we unravel interactions between the three PBs for freshwater change, climate change and land-system change (representative of key biosphere–atmosphere feedbacks), and how they are linked via PB control and response variables. Thereby we exemplify how transgressions of these PBs are driven both directly by human activities and indirectly by biophysically or anthropogenically mediated effects of other PBs' transgressions. As we also highlight, measures to maintain a single PB – such as large-scale terrestrial carbon dioxide removal aimed at lowering pressure on the climate change PB – can unintentionally become a force of transgression of other PBs, creating new impacts. To identify fallacies and uncontrolled feedbacks that may put Earth system stability at further risk, we propose a systematic model-based assessment of interacting impacts of PB transgressions and of measures to maintain multiple PBs simultaneously.