European heat extremes under net-zero emissions

Abstract Projections of European heat extremes have been widely explored in the context of continued global warming. However, analyses of recent Earth system model simulations point to substantial climatic changes over multi-centennial timescales in net-zero emissions futures. Focusing on Europe, we address the gap in characterising heat extremes in long-term net-zero stabilised climates. We quantify the long-term effects of delayed mitigation on annual maximum daily maximum temperatures (TXx) in European regions using 1000 year-long stabilised simulations with ACCESS-ESM-1.5, reaching net-zero CO 2 emissions at different times over the coming decades. We evaluate ACCESS-ESM-1.5 against the ERA5 reanalysis for European maximum temperatures using rank frequency analysis and compare present-day maximum temperatures to their long-term future likelihood. Across all European regions, any delay in achieving net-zero emissions shifts the distribution to higher annual maximum temperatures, remaining elevated at the same levels for centuries. European regions show two- to five-fold frequency increases for heat events as strong as current records, while the Mediterranean region could experience 30-fold increases if emissions cessation is delayed until 2060. When comparing extreme heat distributions at global warming levels, we find substantial differences between transient and net-zero emissions quasi-stable climate states, with larger differences at higher warming levels. We provide the first comprehensive assessment of European extreme hot temperatures in net-zero stabilised climates, paving the way for further investigations of other extreme event types or regions in net-zero futures.