Observationally constrained climate sensitivity implies high climate tipping risk

Global warming increases the risk of crossing critical temperature thresholds, so-called climate tipping points, which trigger large-scale, non-linear, and possibly irreversible changes in the Earth System accompanied by substantial impacts on the biosphere and human societies. However, precise temperature projections remain uncertain, largely due to the spread in climate sensitivity estimates. Equilibrium climate sensitivity (ECS) quantifies long-term temperature response to a doubling of atmospheric CO2. Here, we analyze how climate tipping risk is affected by ECS uncertainty by propagating a range of temperature projections from the simple climate model FaIR to PyCascades, a model of interacting tipping elements. Considered tipping elements are the West Antarctic Ice Sheet, the Greenland Ice Sheet, the Amazon rainforest, and the Atlantic Meridional Overturn Circulation. We find a nonlinear, logistic relationship between ECS and climate tipping risk for a wide range of atmospheric CO2 concentrations. The exact relation depends strongly on CO2 concentration, underlining the importance of both emissions and climate sensitivity in determining system stability. Higher ECS values strongly amplify the likelihood of crossing tipping points. Moreover, a recent observational constraint on ECS set a lower limit at 2.9°C, which implies a high tipping risk of at least 75 % for present-day atmospheric CO2 concentration. These results highlight the critical importance of narrowing ECS uncertainty and improving understanding of its drivers, as even moderate ECS estimates imply substantial long-term risks of triggering tipping events.