Diagnosing the role of internal variability over recent decades is critically important for both model validation and projections of future warming. Recent research suggests that for 1980-2022 internal variability manifested as Global Cooling and Arctic Warming (i-GCAW), leading to enhanced Arctic Amplification (AA) and suppressed global warming over this period. Here we show that the observationally derived i-GCAW is rare in CMIP6 large ensembles, but simulations that do produce similar i-GCAW exhibit a unique and robust internally driven global surface air temperature (SAT) trend pattern. This unique pattern of SAT change features enhanced warming in Barents and Kara Sea and cooling in the tropical Eastern Pacific and Southern Ocean. Given that these features are imprinted in the observed record over recent decades, this work suggests that internal variability makes a crucial contribution to the discrepancy between model-simulated forced SAT trend pattern and observations.

In this paper we assessed the representation of Arctic sea surface salinity (SSS) and liquid freshwater content (FWC) in the historical simulation of 31 CMIP6 models with comparison to 39 CMIP5 models, and investigated the projected changes in Arctic liquid FWC and freshwater budget in two scenarios (SSP245 and SSP585) of the CMIP6 models. While CMIP6 multi-model mean (MMM) shows an amelioration in representing Arctic SSS compared to CMIP5, no significant reduction is found in the overestimation of FWC and overall model spreads of future changes of Arctic freshwater budget. CMIP6 MMM projects a SSS decrease in most parts of the Arctic Ocean, a slight SSS increase in the Eurasian Basin, and the strongest increase in FWC along the periphery of the Arctic Basin. In the historical simulation, the MMM river runoff, net precipitation, Bering Strait and Barents Sea Opening freshwater transports are 93±34 mSv, 58±109 mSv, 80±32 mSv, and -20±17 mSv, respectively. In the last decade of the 21st century, these budget terms will increase to 138±47 mSv, 123±93 mSv, 83±35 mSv, and 33±47 mSv in the SSP585 scenario. Sea ice meltwater flux will decrease to about zero in the mid-21st century in both SSP245 and SSP585. Freshwater exports through Fram and Davis straits will be higher in the future, and the Fram Strait export will remain larger. The Arctic Ocean is projected to hold a total of 160,300±62,330 km3 freshwater in the SSP585 scenario by 2100, about 60% more than its historical climatology.