Observed Subdecadal Variations of European Summer Temperatures

Abstract

We identify subdecadal variations in European summer temperatures in coupled and uncoupled century‐long reanalyses. Spectral analyses reveal significant peaks at 5–10 years in the midtwentieth century. The subdecadal variations show substantial amplitudes of ~1–1.5 °C, associated with extremely warm summers during their positive phases. We use forced ocean model experiments and show that the European summer temperature variations are associated with the subdecadal coupled North Atlantic climate system. A positive winter NAO‐like forcing is associated with changes in the ocean circulation and mass and heat convergence occurring 1–2 years prior to European summer temperature rise. Ocean heat content and sea surface temperature increase in the subtropical North Atlantic. The atmospheric response is barotropic and induces wave activity fluxes toward the European continent, modulation of the jet positions, and blocking frequency. The atmospheric response establishes a pathway connecting the subdecadal coupled North Atlantic climate system to European summer temperature.

Weather and Climate Extreme Events in a Changing Climate

“…The large-scale modes of variability (Annex IV) affect the strength, frequency and persistence of these meteorological patterns and, hence, temperature extremes. For example, cold and warm extremes in the mid-latitudes are associated with atmospheric circulation patterns such as the Pacific-North American (PNA) pattern, as well as atmosphere-ocean coupled modes such as Pacific Decadal Variability (PDV), the North Atlantic Oscillation (NAO), and Atlantic Multi-decadal Variability (AMV) (Section 11.1.5; Kamae et al, 2014;Johnson et al, 2018;Ruprich-Robert et al, 2018;Yu et al, 2018Yu et al, , 2020Müller et al, 2020;Qasmi et al, 2021). Changes in the modes of variability in response to warming would therefore affect temperature extremes (Clark and Brown, 2013;Horton et al, 2015).…”

The Role of the North Atlantic for Heat Wave Characteristics in Europe, an ECHAM6 Study

“…While the FOCI ocean component is not used in our setup, atmosphere and land models are coupled. The atmosphere component is ECHAM, version 6.3.05p2, with a spectral truncation of T63 (about ∼1.8° in longitude and latitude) and 95 hybrid sigma‐pressure levels in the vertical (Müller et al., 2019). The land component used in FOCI is JSBACH, version 3 (Brovkin et al., 2009; Reick et al., 2013).…”

Extreme heat and drought typical of an end-of-century climate could occur over Europe soon and repeatedly

“…However, changes in the frequency and intensity of heat and drought stress depend not only on the level of global warming; they can also be dampened or amplified by internal variability on interannual to multi-decadal scales 2,26,33 . For example, the slowly evolving variability in the North Atlantic system affects European temperatures in observations [35][36][37] , and modulates past observed trends in concurrent heat and drought over European croplands 26 . This linkage has been also identified in idealized numerical experiments imposing slowly evolving sea surface temperature (SST) patterns to emulate different phases of Atlantic Multidecadal Variability (AMV), which lead to a marked increase in temperature and slightly lower decrease in precipitation under positive versus negative AMV phases 27,28 .…”