def load_variable_config(project_config):
    """Extract the variable configuration out of the project configuration.

    Args:
        project_config (dict-like): Project configuration.

    Returns:
        dict: Variable dictionary with name: [levels] (single level will have a list containing None.)
    """

    # Extract the different rank variables
    v2ds = project_config['variables_2d']
    v3ds = project_config['variables_3d']

    # Create a dictionary of variables to process keyed to an empty list of levels for 2D
    variables = {v2d: [None] for v2d in v2ds}

    # Add in the 3D variables, with levels this time
    for v3d, levels in v3ds.items():
        variables[v3d] = levels

    return variables