Adaptive emission reduction approach to reach any global warming target

The parties of the Paris Agreement agreed to keep global warming well below 2 °C and pursue efforts to limit it to 1.5 °C. A global stocktake is instituted to assess the necessary emissions reductions every 5 years. Here we propose an adaptive approach to successively quantify global emissions reductions that allow reaching a temperature target within ±0.2 °C, solely based on regularly updated observations of past temperatures, radiative forcing and emissions statistics, and not on climate model projections. Testing this approach using an Earth system model of intermediate complexity demonstrates that defined targets can be reached following a smooth emissions pathway. Its adaptive nature makes the approach robust against inherent uncertainties in observational records, climate sensitivity, effectiveness of emissions reduction implementations and the metric to estimate CO2 equivalent emissions. This approach allows developing emission trajectories for CO2, CH4, N2O and other agents that iteratively adapt to meet a chosen temperature target.