We proposed here an alternative view of future changes in the atmospheric circulation at northern mid-latitudes, considering the future trends in weather regime frequency and persistence over the Euro–Atlantic and Pacific–North American sectors, as projected by the CMIP5 and CMIP6 models. The CMIP6 ensemble shows a non negligible improvement in the reproduction of the weather regimes when compared to CMIP5 (Sect. 3.2). A better simulation of the regime patterns is in particular evident over the EAT sector; however, both sectors show an improvement in the other metrics considered (i.e. the variance ratio and the regime frequency bias; see Sect. 3.2). The model biases in simulating the observed regime centroids, frequencies and variance ratio are known and documented in the literature (Dawson et al., 2012; Weisheimer et al., 2014; Strommen et al., 2019; Fabiano et al., 2020). The improvements of the CMIP6 models compared to CMIP5 in this respect are therefore encouraging.

Over the EAT sector, an increase in the NAO+ frequency and persistence during the second half of the 21st century is observed in all scenarios with larger changes in SSP3–7.0 and SSP5–8.5 (Sect. 3.3.1). This increase is accompanied by a decrease in the AR frequency (and persistence) in all scenarios and a decrease in the SBL frequency, which is more pronounced in the most extreme scenarios. The NAO− regime shows a small positive trend in all scenarios. These trends are consistent with changes in the mean geopotential height state that shows an increase at high latitudes and a pronounced eastward shift in the stationary eddies (Sect. 4.1). A significant fraction of the spread of the model response over the EAT sector is related to the spread in the polar stratospheric temperature and the Arctic amplification in future projections (Sect. 4.2). The increase in the NAO+ regime is consistent with a squeezing of the jet around the central position (Peings et al., 2018; Oudar et al., 2020) and with a reduced meridional variability in the jet (Barnes and Polvani, 2013).

In the PAC sector, the future trends are characterized by an increase in the PT regime occurrence with a concomitant decrease in the BR regime frequency. The two PNA regimes do not show clear trends in the future scenarios. The inter-model spread in the PAC WR trends correlates significantly with the upper tropospheric warming in the tropics and the warming of the tropical North Atlantic (Sect. 4.2). The increase in the PT regime frequency indicates a larger relative importance of tropical forcing versus orographic forcing in perturbing the mean flow. The decrease in the BR regime is consistent with changes in the mean state (Sect. 4.1) and with a decrease in the blocking frequency in the Bering Strait (Davini and D'Andrea, 2020).

The regime perspective presented in this work provides a clear picture of future changes in the wintertime mid-latitude atmospheric circulation and also introduces a suitable framework to study the impact of extreme weather in the future scenarios. The projected changes in the regime frequencies are associated with important changes in the temperature and precipitation statistics over different regions. For example, an increase in frequency of a strong zonal flow regime (i.e. NAO+) over the Atlantic can lead to an enhanced flood risk due to its connection with stormy weather over north-western Europe and the British Isles (Yiou and Nogaj, 2004). In this respect, it is worth noting that the extreme rainfall in the UK during winter 2013–2014 resulted from this type of atmospheric circulation (Knight et al., 2017), and human-induced climate change was recognized as the major driver of such an extreme (Vautard et al., 2016). Also, the Mediterranean region might suffer from summertime dry spells and heat waves in response to a deficit in precipitation during winter (Vautard et al., 2007), which is more likely to occur with increased NAO+ frequency.