How to predict record-shattering weather events

livemint.com:

heatwave of 2021 was one of the most extreme deviations from meteorological norms ever recorded, anywhere. But others have come close. As the world gets hotter, phenomena once considered rare are becoming common and others, believed impossible, are happening.

This shift in weather patterns has inspired modellers to pay more attention to the tails of the frequency distributions of meteorological possibility which their models generate (see chart), in search of such unprecedented extremes. One recent exercise, led by Erich Fischer at ETH Zurich, a technology university in Switzerland, and presented at last year’s annual jamboree of the European Geosciences Union, shows how the heatwave that destroyed Lytton could have been foreseen with data available at the time. The approach Dr Fischer used, ensemble-boosting, is one of several developed recently.

Another, from Britain’s Met Office, is UNSEEN (Unprecedented Simulation of Extremes with Ensembles). This was first put to work by Vikki Thompson and her colleagues at the Met Office in a retrospective analysis of floods that had drowned parts of the country in 2014, resulting in £451m ($743m) of insurance claims. More than 130 years of English records had offered no indication such a biblical deluge was possible.

Yet, here it was. As Thierry Corti, a climate-risk analyst at Swiss Re, a reinsurance company, observes, “the risk landscape is evolving. So if you simulate probabilities of a rare event you need to take that against the backdrop of something that’s changing.