Quantifying future Arctic and Antarctic climate change from a storyline perspective using global variable-resolution models

Here, we use three variable-resolution, global models to explore storylines of future Arctic and Antarctic climate change previously derived by Levine et al. (2024; 10.5194/esd-15-1161-2024) and Williams et al. (2024; 10.1175/JCLI-D-23-0122.1). The models are the Community Earth System Model (CESM), the ICOsahedral Nonhydrostatic model (ICON), and the Model for Prediction Across Scales (MPAS). The pair of Arctic storylines examined represent 1) weak Arctic amplification combined with strong SST warming in the Barents-Kara Seas and 2) strong Arctic amplification combined with weak SST warming in the Barents-Kara Seas. Over Antarctica, the storylines explored are 1) high Southern Hemisphere (SH) sea-ice loss combined with a shorter delay in SH vortex breakdown, and 2) low SH sea-ice loss combined with a longer delay in SH vortex breakdown. 

Sea surface temperatures (SSTs) and sea ice concentrations (SICs) from CMIP6 models that are representative of these storylines were provided to the variable-resolution models to perform a number of AMIP-style experiments. We performed experiments for the recent past and for the future with uniform and refined horizontal resolution over the polar regions. The result is a novel and comprehensive set of experiments based on three different variable-resolution models (CESM, ICON, MPAS), two different SST and SIC forcing fields for the Arctic and two for the Antarctic (from 4 different CMIP6 models), two different resolutions (refined and unrefined), and two different time periods (recent past and future). 

We use this experiment set to explore the extent to which results from the variable-resolution experiments resemble the CMIP6 models that have been selected to represent the storylines that the SSTs and SICs are taken from, focusing on near-surface temperature, precipitation, and 850-hPa zonal wind. Furthermore, we quantify the influence of the storyline model, the influence of the variable-resolution model, and the influence of the resolution on the future responses. Results show that the influence of the storyline and the variable-resolution model is larger than the influence of the resolution for all variables and seasons in both the Arctic and Antarctic. In the Antarctic, the storyline influence moreover tends to be larger than the model influence, meaning that the model differences are smaller than the differences associated with the phase of the remote drivers (high/low SH sea-ice loss & short/longshort SH vortex breakdown delay). While we find similar results for near-surface temperature in the Arctic, the storyline and model influence are more comparable for precipitation and zonal wind. Overall, our results suggest that for the large-scale climate change responses considered here, careful selection and sampling of storyline drivers and model structural uncertainty is more critical than increased horizontal resolution in the polar regions.