def ensure_components(model_tracer_list):
    """If a CO2 flavor is detected for a model, ensure all flavors are present."""
    co2_components = {'CO2', 'CO2_OCN', 'CO2_LND', 'CO2_FFF'}
    models = set(m for m, t in model_tracer_list)
    new_list = []
    for model in models:
        m_tracers = set(t for m, t in model_tracer_list if m == model)
        if m_tracers.intersection({'CO2_LND+CO2_FFF'}):
            new_list.extend((model, t) for t in co2_components.union(m_tracers))
        else:
            new_list.extend([(model, t) for t in m_tracers])
    return new_list