Climate change contribution to the 2023 autumn temperature records in Vienna

Global monthly mean temperature continuously broke records in the year 2023 since June till October. This also happened widespread at September and October in Austria, but monthly temperature records on a local scale, such as in the mid latitudes like Austria, show less persistence than global or continental averages. This makes the autumn temperature extremes in Vienna (Austria) even more striking. Considering the compound occurrence of such an event at actual climate results in a return period of 324 years, which makes it extraordinary itself. Considering climate change, the compound event of two consecutive extreme high temperature records in autumn 2023 yields return periods of about 10,000 years until the second half of the twentieth century, which partly exceeds the length of the Holocene. Focusing on moderate compound extremes of the last 10 years (2014-2023), these reach return periods of 100 years up to 1960, but are now likely to happen every 15 years. Compound extremes in summer (July and August) present a higher decrease of the return period in Vienna over the last 250 years, possible leading to even more severe impacts on ecosystems and society.