  This study assesses the relative importance of time integration error in
present-day climate simulations conducted with the atmosphere component of the
Energy Exascale Earth System Model version 1 (EAMv1) at 1-degree horizontal
resolution. We show that a factor-of-6 reduction of time step size in all major
parts of the model leads to significant changes in the long-term mean climate.
These changes imply that the reduction of temporal truncation errors leads to a
notable although unsurprising degradation of agreement between the simulated
and observed present-day climate; the model would require retuning to regain
optimal climate fidelity in the absence of those truncation errors. A
coarse-grained attribution of the time step sensitivities is carried out by
separately shortening time steps used in various components of EAM or by
revising the numerical coupling between some processes. The results provide
useful clues to help better understand the root causes of time step
sensitivities in EAM. The experimentation strategy used here can also provide a
pathway for other models to identify and reduce time integration errors.
