Physical processes leading to extreme day-to-day temperature change – Part 2: Future climate change

Abstract. Extreme temperature swings from one day to the next, whether warming or cooling, can significantly impact human health, ecosystems, and the economy. These effects may become more pronounced or attenuated in the future. Part 1 of this research identified the physical processes – advection, as well as adiabatic and diabatic temperature changes – that cause extreme day-to-day temperature (DTDT) fluctuations in the present climate. Extreme DTDT variations are projected to change under future warming; however, how and which processes drive these changes remain poorly understood. This study addresses this question globally by analysing physical processes in Community Earth System Model Large Ensemble (CESM–LE) simulations under a high–emission scenario, employing both Eulerian composite and Lagrangian backwards–trajectory analyses. The projected changes in (extreme) DTDT variations display a seasonal contrast: weakening in mid- to high latitudes and intensification in the tropics during December–February (DJF), while during June–August (JJA), tropical intensification is more widespread, and only some extratropical locations experience reductions in DTDT variations. The spatial pattern of projected changes in the DTDT variations is mostly associated with changes in the standard deviation of daily temperature, whereas changes in temporal autocorrelation give rise to regional variations in magnitude. In the extratropics during DJF, the weakening of DTDT extremes is mainly driven by reduced advection contributions due to Arctic amplification. However, during JJA, reductions in extremes result from changes in advection, diabatic, and adiabatic processes, with differences between events and regions in their relative contributions. Furthermore, changes in diabatic processes play a significant role in the projected intensification of extremes in JJA over land areas in the tropics and subtropics, while the tropical intensification during DJF results from local changes in diabatic and adiabatic processes. Our findings demonstrate that a regional and seasonal perspective that, in addition to the well–established role of advection, also accounts for diabatic and adiabatic heating processes is essential for understanding projected extreme DTDT changes and for developing suitable adaptation strategies.