Storyline simulations suggest dampening of 2020 Siberian heatwave analogues in warmer climates

Siberia experienced an exceptionally warm first half of 2020, with temperatures peaking on 20th June, when the weather station at Verkhoyansk registered 38ºC – the highest-ever temperature recorded north of the Arctic Circle. This event led to a state of emergency declaration due to a wide range of natural and human disasters, including permafrost collapse or wildfires. Several previous attribution studies have found anomalous synoptic atmospheric circulation and human-caused climate change as major drivers of this event. However, it remains unclear how such an event would unfold in warmer climates.

In this work, we have constructed analogues of this extreme event in past and future climates, so-called “storylines”, employing spectral nudging experiments using the coupled climate model AWI-CM1. In these simulations, large-scale free-troposphere winds are constrained toward ERA5 data, and the model is run for different boundary and initial conditions (pre-industrial, present, +2K, +3K, +4K climates). By doing so, this approach focuses on the less uncertain thermodynamic influence of climate on extreme events, constraining the much more uncertain dynamical changes.

Our present-climate simulations realistically reproduce the observed Siberian heatwave and the exceptionally warm conditions before the event. When the different background climates are considered, on the one hand, a robust global warming amplification is obtained until spring. On the other hand, a future global warming dampening or even local cooling is observed in phase with the heatwave peak. We examine the mechanisms that damp warming during the heatwave analogue, especially changes in soil moisture and radiative fluxes.