ACE2S-SHiELD+

The newest member of the Ai2 Climate Emulator (ACE) family, and the first ACE model filed here: a stochastic spherical Fourier neural operator on a 1° grid with a 6-hour step and an energy-conservation constraint, trained to emulate NOAA's SHiELD atmosphere model about 68 times faster than the physical model. The accompanying paper addresses a failure of earlier ACE versions, which were accurate only where sea surface temperature and CO₂ were correlated in training and behaved unphysically under a +4 K SST perturbation or an abrupt CO₂ quadrupling; the "+" training separates the two forcings so the emulator responds correctly to each. Weights released 10 September 2026 under Apache 2.0; the parameter count is not stated on the card.