Spaces of anthropogenic CO2 emissions compatible with planetary boundaries

Abstract The concept of planetary boundaries delineates the Earth system’s limits within which humanity can sustainably prosper. Here, we introduce a new modelling framework to translate four climate-related boundaries: global warming, ocean acidification, sea level rise, and Arctic sea ice melt. Using a reduced-form model, we map a range of anthropogenic CO2 emissions and removals pathways consistent with the boundaries, optionally adding solar radiation management (SRM) measures to the picture. Our framework estimates safety levels as probabilities to stay within the boundaries considering the physical uncertainty of the Earth system. If CO2 emissions peak in 2030, net-zero CO2 is reached in 2100, CDR deployment capacity is 10 PgC per year, and SRM is not allowed, remaining within the global warming boundary is ensured with a safety level of 66%. This level is 50% for the sea level rise or the Arctic sea ice boundary; it is 26% for the ocean acidification boundary. When all four boundaries are considered together, it drops to only 12%, indicating a complex interplay of planetary boundaries in determining the safety level. Our results suggest a need to assess planetary boundaries holistically to develop sustainable future strategies.