Hotspots of extreme temperature resulting from constructive interference of anthropogenic and natural forcing factors

In the context of global warming, the increase in amplitude and frequency of extreme temperature events represents a topic of significant scientific interest and socio-economic concern. An important problem related to this variable is related to the attribution of extreme temperature events and patterns to anthropogenic and natural factors, which is typicaly peformed using model simulations. Although extremely useful, this type of attributions are sensitive to computing power limitations and to model imperfections. Alternatively, here we isolate two global patterns of monthly maximum of daily maximum temperature (TXx), one associated with the atmospheric CO2 concentration and another corresponding to the Atlantic Multidecal Oscillation. The separation of these two modes is performed through multivariate analyses of the monthly global fields from the ERA5 dataset extending over the 1950–2024 period, The analyses are performed for all motnhs of the year, but we focus on only one month for each season (January, April, August and October). The attributions are made based on the similarities between the temporal and spatial properties of the two isolated global modes identified here and those shown in previous studies, in relation with their forcing factors. Based on the separations and attributions performed here we highlight hotspot regions in which the two factors interfere constructively and quantify their contributions to TXx anomalie in these areas. In particular, we identify Europe as one of the hotspot regions in August and suggest that the large summer extreme temperatures recorded on this continent in the last two decades results from the contructive contributions of the anthropogenic forcing and of the Atlantic Multidecadal Oscillation.