Storylines for unprecedented heatwaves based on ensemble boosting

Recent temperature extremes have shattered previously observed records, reaching intensities that were inconceivable before the events. Could the possibility of an event with such unprecedented intensity as the 2021 Pacific Northwest heatwave have been foreseen, based on climate model information available before the event? Could the scientific community have quantified its potential intensity based on the current generation of climate models? Here, we demonstrate how an ensemble boosting approach can be used to generate physically plausible storylines of a heatwave hotter than observed in the Pacific Northwest. We also show that heatwaves of much greater intensities than ever observed are possible in other locations like the Greater Chicago and Paris regions. In order to establish confidence in storylines of 'black swan'-type events, different lines of evidence need to be combined along with process understanding to make this information robust and actionable for stakeholders. Climate model ensemble boosting can yield physically coherent storylines for record-shattering climate extremes such as the 2021 Pacific Northwest heatwave. Combining information from storyline approaches with process understanding can inform planning for future extremes of unprecedented intensity.

Automated summary

Recent temperature extremes have exceeded previous records and it is questioned whether these intense events could have been predicted using climate models or if there are greater intensities to come. This study demonstrates how an ensemble boosting approach can generate physically plausible storylines for hotter heatwaves, indicating the possibility of even greater intensities in places like Greater Chicago and Paris. Combining different lines of evidence and process understanding is crucial in establishing confidence in such extreme events and informing planning for future unprecedented intensities.