Evaluation of Summer Non-Uniform Multidecadal Temperature Variations Over Eurasia in CMIP6 Models

The summer surface air temperatures (SAT) over Eurasia exhibit a non-uniform multidecadal pattern since the 1990s, with amplified warming over Europe-West Asia (EWA) and Northeast Asia (NEA) but weak warming over Central Asia. However, current climate models may inadequately capture this regional pattern. In this study, we evaluated the performance of 44 coupled models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) in simulating the decadal variability of Eurasian temperatures. Results show that all the CMIP6 models generally reproduce the largest SAT trends from 1985 to 2020 over EWA and NEA. However, the models fail to capture the non-uniform warming pattern and the SAT magnitudes are underestimated in most CMIP6 models. We compare "good" and "poor" ensemble, which represent the best and worst simulations of the non-uniform warming, in order to understand the inter-model spread. The BMME models capture the teleconnection wave trains from northwest Europe to East Asia, and the associated summer North Atlantic Oscillation like circulation changes. In contrast, the WMME models fail to reproduce such teleconnections. The contrast between the BMME and WMME simulations give a measure of confidence that the non-uniform warming pattern over Eurasia is tightly coupled with the upper-tropospheric wave-like pattern over Eurasia. If such atmospheric circulation changes cannot be reproduced, the non-uniform warming pattern over Eurasia will not be captured. Our results suggest a fundamental pattern of atmospheric circulation changes that determine the non-uniform warming variations in model simulations.