Reanalysis-Based Attribution and Storylines of Extremes (ReBASE)

We introduce a novel approach to event attribution and developing storylines based on both recent and historical observed extreme events. Using the 20th Century Reanalysis system (20CRv3) we produce factual global reconstructions of observed events from different periods - the examples shown here are for a range of event types from 1910, 1976 and the last decade.

For modern events we produce a cooler counter-factual by reducing the SSTs used as boundary conditions and greenhouse gas levels in the reanalysis and assimilate the same surface pressure observations to produce the ‘same’ weather patterns in a cooler world. For the historical examples we produce a warmer counter-factual by increasing the SSTs and greenhouse gas levels to represent the same weather in a modern climate. The differences between factual and counter-factual provide estimates of the change in intensity of the observed event as represented by a modern numerical weather prediction model.

This approach allows a global perspective on extreme events and their impacts - the same experiments produce global factual and counter-factual reconstructions of every day in the chosen periods. The data will be made openly available to allow anyone to explore their own choice of extreme event anywhere in the globe. Counter-factuals will also be developed for future warmer climate conditions to understand how extreme events and their impacts will change, and help inform adaptation decisions.