The CESM2 Large Ensemble Community Project

The ICCP is pleased to announce the launch of the CESM2 Large Ensemble in partnership with the National Center for Atmospheric Research in Boulder, USA. The CESM2 Large Ensemble consists of 100 members at 1-degree spatial resolution covering the period 1850-2100 under CMIP6 historical and SSP3-7.0 future radiative forcing scenarios. Calculations were completed in May 2021, and are released to the public as of June 14th via: with transfers of all of the full 3-D variables from the IBS Supercomputer to the public server due to finish by late July or early August 2021.

Unlike the CESM1 Large Ensemble, the CESM2 Large Ensemble uses a combination of different oceanic and atmospheric initial states to create ensemble spread as follows.

1) Members 1-10: These begin from years 1001, 1021, 1041, 1061, 1081, 1101, 1121, 1141, 1161, and 1181 of the 1400-year pre-industrial control simulation. This segment of the control simulation was chosen to minimize drift.

2) Members 11-90: These begin from 4 pre-selected years of the pre-industrial control simulation based on the phase of the Atlantic Meridional Overturning Circulation (AMOC). For each of the 4 initial states, there are 20 ensemble members created by randomly perturbing the atmospheric temperature field by order 10^-14K. The chosen start dates (model years 1231, 1251, 1281, and 1301) sample AMOC and Sea Surface Height (SSH) in the Labrador Sea at their maximum, minimum, and transition states.

3) Members 91-100: These begin from years 1011, 1031, 1051, 1071, 1091, 1111, 1131, 1151, 1171, and 1191 of the 1400-year pre-industrial control simulation. This set includes the extensive “MOAR” output, which can be used to drive regional climate models.

The initialization allows assessment of oceanic (AMOC) and atmospheric contributions to ensemble spread, and the impact of AMOC initial-condition memory on the global earth system.

The reference paper for these simulations is Rodgers et al. (2021) (preprint available at, with an associated DOI (

The full list of output variables is available at:

Please direct questions to any of the following project leads: Dr. Keith Rodgers (, Dr. Axel Timmermann (, Gokhan Danabasoglu (, and Dr. Clara Deser (