Myriam Khodri and her team have been awarded ~40 millions hours of HPC as part of the PRACE 21st call for proposals (October 2020 to September 2021). Their proposal, ASSIM2K, aims to assess climate models’ ability to reproduce natural climate variations. Proxy records (corals, speleothems, etc.) documenting the last 2000 years (2K) provide evidence for the wide range of natural variability. ASSIM2K proposes to use a novel cutting edge method to reconstruct and attribute sources of recent climate changes, through the seamless integration across the last 2000 years of external (natural and anthropogenic) forcings and the assimilation of observations (instrumental and proxy) in the massively parallelized very-low resolution (VLR) IPSL-CM6 climate model. The proposal will rely on a particle filter method, which uses a Linear Inverse Model as an emulator of the IPSL model. The trajectory of hundreds of simulations can thus be optimally guided by proxy records available worldwide. The PRACE allocation will generate breakthrough outcomes allowing (i) benchmark against observations and documented historical events, the ability of CMIP-class climate models to capture the processes of natural climate change, (ii) identify when, where and with which level of confidence anthropogenic climate changes emerge out of the natural “noise” and (iii) compare historical and modern societies’ resilience to past and recent climate changes.