Examining the Eastern European extreme summer temperatures of 2023 from a long-term perspective: the role of natural variability vs. anthropogenic factors

Abstract. Amidst unprecedented rising global temperatures, this study investigates the historical context of heat wave (HW) events in Eastern Europe. The record-breaking 2023 summer, featuring a HW lasting for 19 d in the southeastern part of Romania, extending up to Ukraine, necessitates a deeper understanding of past extreme events. Utilizing statistical methods on long-term station data spanning from 1885 to 2023, we aim to detect and analyze historical HWs, particularly focusing on events predating 1960. This extended time frame allows for a more comprehensive assessment of noteworthy extremes compared to recent decades. We used both a percentile-based threshold and a fixed absolute temperature threshold to identify HW events. Our analysis identifies two critical periods with increased HW frequency and intensity: 1920–1965 and 1980–2023, respectively, highlighting the most extreme events in August 1946, August 1952, July 2012, June 2019, and August 2023. Furthermore, reanalysis data show that historical HWs, similar to the 2023 event, were associated with large-scale European heat extremes linked to high-pressure systems, and they were accompanied by extreme drought, thus leading to compound extreme events. We find that while a clear trend emerges towards more frequent HWs from the 1980s onward, the analysis also uncovers substantial HW activity on daily timescales throughout the 1885–1960 period. Moreover, we highlight the intertwined impacts of climate change and multidecadal internal variability on HW patterns, with evidence suggesting that both contribute to the increasing frequency and intensity of these extreme events. Attribution analysis reveals that the extreme summer temperatures observed in 2023 would not have been possible in the absence of anthropogenic climate change. Regardless of future warming levels, such temperatures will occur every year by the end of the century. Our research highlights the value of extending the historical record for a more nuanced understanding of HW behavior and suggests that extreme heat events, comparable to those experienced in recent decades, have occurred throughout the analyzed period.