Lipfert et al. (2026) Comparing 600 years of extremely hot Central European summers to future projections

Identification

• Journal: Scientific Reports
• Year: 2026
• Date: 2026-04-01
• Authors: Laura Lipfert, Ralf Hand, Stefan Brönnimann
• DOI: 10.1038/s41598-026-45507-z

Research Groups

• Institute of Geography and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
• Deutscher Wetterdienst DWD, Offenbach, Germany

Short Summary

This study compares 600 years of Central European summer heat extremes (1421-2008) using paleo-reanalysis and model simulations with future CMIP6 projections, revealing that historical events like 1540 and 1590 were more extreme relative to their contemporary climate than 2003, and similar anomalies in the future will be significantly hotter in absolute terms.

Objective

• How unusual are the hot summers of the 20th and 21st century in light of extreme summers in the past 600 years, and how do they compare with simulated future summers?

Study Configuration

• Spatial Scale: Central Europe (0-20° E, 47-57° N)
• Temporal Scale: Historical period: 1421-2008 (600 years); Future projections: 2070-2100. Seasons analyzed: April-September (AMJJAS) and June-August (JJA).

Methodology and Data

• Models used: ModE-RA (20-member global monthly paleo-reanalysis), ERA5 (reanalysis), ModE-Sim (20-member atmospheric general circulation model ensemble based on ECHAM6), CMIP6 (multimodel ensemble from ScenarioMIP, including ssp585 and ssp126 scenarios).
• Data sources: ModE-RA assimilates natural proxies, documentary data, and instrumental data into ModE-Sim. ModE-Sim uses prescribed SSTs (HADISST2 and reconstructions), volcanic forcing, solar irradiance, greenhouse gas concentrations, tropospheric aerosols, and land surface conditions. ERA5 provides daily mean surface temperature. CMIP6 simulations are from the Scenario Model Intercomparison Project. Anomalies are calculated relative to a fixed climatology (1950-2008) and a moving climatology (LOESS regression, approximately 31-year window).

Main Results

• Using a fixed 1950-2008 climatology, 2003 was the hottest summer in ModE-RA and ERA5, with a June-August (JJA) anomaly of 2.78 °C in ModE-RA.
• Using a moving climatology over the 1421-2008 period, 1540 was identified as the hottest extended summer (April-September, AMJJAS) with an anomaly of 2.17 °C, and 1590 as the hottest JJA summer with an anomaly of 2.80 °C, both surpassing 2003 (1.12 °C AMJJAS, 2.13 °C JJA).
• The 1540 event was a prolonged heat and drought (11 months) driven by internal atmospheric variability, characterized by a northward-shifted Atlantic-European jet and positive 500 hPa geopotential height (Z500) anomalies (Omega blocking in some ensemble members).
• The 1590 summer was a short but extremely hot JJA event, also driven by internal atmospheric variability, with Z500 anomalies extending further east (Rex/Dipole blocking in some ensemble members).
• The ModE-Sim ensemble (11,760 model years) produced 0.14% of AMJJAS summers and 0.24% of JJA summers with temperature anomalies exceeding those of 1540 and 1590, respectively, with the largest JJA anomaly exceeding 4 °C.
• CMIP6 future projections (2070-2100) show that anomalies comparable to 1540 and 1590 are rare but occur (0.9% for AMJJAS > 1540, 0.8% for JJA > 1590). These future summers, while having similar anomalies relative to their moving climatology, will be significantly hotter in absolute temperatures due to global warming.
• Extreme future summers in CMIP6 show a connection to negative sea surface temperature (SST) anomalies over the North Atlantic. For individual ModE-Sim extreme summers, both strong negative and positive North Atlantic SST anomalies were observed.

Contributions

• Provides a unique and comprehensive framework by combining a 600-year paleo-reanalysis (ModE-RA), reanalysis (ERA5), and large ensemble model simulations (ModE-Sim, CMIP6) to analyze Central European summer heat extremes.
• Identifies and characterizes historical extreme summers (1540 and 1590) that were more extreme relative to their contemporary climate than the well-known 2003 event, detailing their distinct temporal developments and atmospheric drivers.
• Offers a deeper understanding of rare past climate extremes and their underlying mechanisms, contributing to the limited existing literature on events like 1590.
• Compares the frequency and magnitude of past extreme anomalies to future climate projections, highlighting the dramatic increase in absolute temperatures for similar relative anomalies in a warming climate.
• Validates the ModE-Sim and ModE-RA datasets as valuable tools for exploring extreme climatic anomalies and their drivers across centuries.

Funding

• European Commission through H2020 (ERC Grant PALAEO-RA 787574)
• Swiss National Science Foundation project DVDW (219746)
• Swiss Supercomputer Centre CSCS (for ModE-Sim simulations)

Citation

@article{Lipfert2026Comparing,
  author = {Lipfert, Laura and Hand, Ralf and Brönnimann, Stefan},
  title = {Comparing 600 years of extremely hot Central European summers to future projections},
  journal = {Scientific Reports},
  year = {2026},
  doi = {10.1038/s41598-026-45507-z},
  url = {https://doi.org/10.1038/s41598-026-45507-z}
}