Thermal response timescales and associated spatial patterns in ESMs to pulse injections of climate forcers

The Earth system response to climate forcers can be broken down to multiple timescales, with the land surface responding within a few years to a change in forcing while the deep ocean layers have only fully equilibrated after several hundreds to thousands of years. In this work we assume that there is a number of distinct timescales represented in the thermal response to pulse injections of different climate forcers in the Coupled Model Intercomparison Project Phase 6 (CMIP6) Earth System Models (ESMs), which can be estimated by fitting a sum of decaying exponential responses  to a set of non-noisy Empirical Orthogonal Functions of each model. Using these exponential decay functions and a regression-based pattern scaling approach we are able to emulate the gridded transient surface temperature response to an input forcing timeseries. We determine that for the abrupt-4xCO2 experiment the thermal response in most CMIP6 ESMs can be represented by a similar set of timescales, but early results suggest diverse spatial warming patterns. This work introduces the concept that the evolving spatial patterns associated with the thermal response on different timescales for pulse injections of different climate forcers can be simply and accurately emulated and ultimately be used to predict transient simulations.