Physical climate impacts in overshoot scenarios

With ongoing greenhouse gas emissions it becomes increasingly unlikely that the global mean temperature (GMT) can be stabilized at 1.5°C without considerable negative emissions. As a result, most emission scenarios that would allow to reach 1.5°C GMT at the end of the century are overshoot scenarios: In these scenarios GMT warms until net-zero emissions are reached and slowly starts to cool afterwards. Here we want to have a closer look at the local climate responses after peak warming to get a first idea of potential consequences of overshoots.

The analysis is mainly based on the overshoot scenarios SSP119 and the SSP534-over from the “Coupled Model Intercomparison Project (Phase 6)”. We identify regions in which precipitation or temperature has an asymmetric response to GMT changes around peak warming. In some regions, and especially for temperature related variables, the asymmetries could result from lagged responses in the climate system. However, there are also a number of dynamic mechanisms that could influence local climate signals after peak warming and there are only few regions where analyzed earth system models (ESM) agree on the sign of change.

In many regions, the projected trends in precipitation or temperature after peak warming are in the range of trends that can be found in control runs without anthropogenic forcings. Here, single model initial-condition large ensembles (SMILEs) are necessary to estimate the forced response in overshoot scenarios. For a comprehensive understanding of the mechanisms explaining these non-linear responses to GMT changes around peak warming, more large ensemble simulations of idealized overshoot scenarios for different ESMs would be required.