Earth system modeling of idealized overshoot scenarios under the TIPMIP ESM protocol using EC-Earth3-ESM

We present the first results of the TIPMIP ESM experiments using the post-CMIP6 model EC-Earth3-ESM. The main objective of the TIPMIP ESM is to study the risks and consequences of potential tipping events in the Earth system, as well as the potential reversibility of triggered events - as a function of e.g., magnitudes and durations of different global warming levels (GWLs) before cooling the climate back to lower GWLs and pre-industrial climate.

Following the TIPMIP ESM protocol, we performed a set of idealized emission-driven simulations, including 1) ramp-up runs with a constant CO2 emission that drives a global mean surface air temperature (GMSAT) warming rate of 0.2 K/decade; 2) stabilization runs with zero CO2 emission at multiple GWLs; and 3) ramp-down runs to the pre-industrial climate with a negative CO2 emission (same magnitude with the ramp-up run) branched after 50 years of stabilization runs.

We present and discuss the simulated responses in the large-scale features of the different components of the earth system in the ramp-up, stabilization, and first test runs of the ramp-down experiments, with a focus on, e.g., GMSAT, AMOC, sea ice, carbon pools/fluxes, and Greenland Ice Sheet. Our findings suggest that some fast climate system components are reversible, e.g., sea ice, but Arctic summer sea ice can show some delays in recovering at high GWLs. AMOC linearly declines during the ramp-up phase, stabilizes during the stabilization phase, and recovers during the ramp-down phase (with an overshoot). Melting in the Greenland Ice Sheet accelerates during the ramp-up phase, its mass loss continues with somewhat slower speeds during stabilization and hardly reverses during the ramp-down phase when branched at high GWLs.