The main reason for the consideration of adaptation in global welfare-maximizing IAMs is to assess the sensitivity of mitigation targets to different assumptions about the magnitude and effectiveness of adaptation. Because IAMs have generally been designed to be applied in one of these decision-analytical frameworks, it is common to speak of policy optimization models, policy evaluation models and policy guidance models, respectively. There is, however, some overlap between these categories, as witnessed by the application of some policy evaluation models (e.g. PAGE) and policy guidance models (e.g. ICLIPS) in policy optimization mode.