More realistic simulations of our Earth system with increased mode l complexity do not necessarily lead to improved dynamical understanding , while simpler models can often be used to address the gap between simulation and understanding. The multi-column ocean mode l (MCOM) is a new ocean component of the Community Earth System Mode l version 2 (CESM2). MCOM extends the CESM2 ocean mode l hierarchy by disabling the lateral ocean processes while retaining the vertical processes , thus simpler than a full 3-D ocean mode l. It prognostically calculates mixed layer and entrainment features that are absent in a slab ocean mode l. Comparisons between multi-century-long CESM2 simulation s with these three different choice s of the ocean mode ls are us e d to study the respective roles of lateral and vertical ocean processes in climate variability.