Assessment of changes in extreme weather under a changing climate is hindered by the paucity of data relative to what is required to characterise rare events. Observationally-based products are fundamentally limited by the length of record, while publicly available couple atmosphere-ocean climate model products are both limited in sample size and have important biases arising from deficiencies in the coupling between the atmosphere and ocean. The International CLIVAR Climate of the 20th Century Plus Detection and Attribution (C20C+ D&A) Project aims to fill this gap for extreme weather over terrestrial areas by producing large ensembles of simulations with multiple atmospheric climate models, under recent observed boundary conditions and under various estimates of boundary conditions that might have been experienced in the absence of human interference.

This presentation presents various comparisons of output from the C20C+ D&A simulations against other data sources available for analysis of extreme weather, including observational products, reanalyses products, and other climate model simulation archives. These comparisons are designed to evaluate the relative appropriateness of C20C+ D&A in relation to other available resources with respect to understanding how extreme weather has been affected by human interference with the climate system.