Storylines of plausible future climates for recent European heatwaves.

Abstract:

Under the ongoing global warming, heatwaves are becoming more frequent, intense, and longer-lasting; and this trend is expected to continue in the future. In this context, the recent 2018 and 2019 summers were exceptionally hot in large areas of the Northern Hemisphere, with embedded heatwaves, as for example the European July 2018 and June and July 2019 events, redrawing the temperature record map. Large-scale dynamics (mostly associated with blockings or subtropical ridges) play a dominant role in explaining these mega-heatwaves.

Conceptually, global warming can be split into two different contributions: Dynamic and thermodynamic changes. Whereas dynamic changes remain highly uncertain, some thermodynamic changes can be quantified with higher confidence. We exploit this concept by studying how these recent European heatwaves might develop in the future for 1.5C, 2C and 4C warmer climates (storyline scenarios). To this end we employ the spectral nudging technique to AWI-CM model (CMIP6) model, which is the combination of ECHAM6 AGCM + FESOM Sea Ice-Ocean Model. In this technique, large-scale dynamics are prescribed by reanalysis fields (using ERA5 data). Meanwhile, the model is run for different boundary conditions corresponding to preindustrial and future climates along the SSP370 forcing scenario. This complementary approach should be useful to help to understand and communicate what climate change will mean to people’s life and hence facilitate effective decision-making regarding adaptation to climate change. Our results show a higher-than-average warming for the analyzed heatwaves, making these events and their consequences even more dramatic than in the present. These simulations also highlight that in Northern and Central Europe the nighttime temperatures in a 4C warmer world would be similar to the daytime temperatures in a preindustrial world.