This chapter examines how the goal of objectivity in scientific policy assessments can be achieved despite the value-laden nature of Integrated Assessment Models (IAMs). It begins by outlining the legitimacy challenge faced by scientific assessments: if IAMs embed specific value judgments, they risk unduly influencing policy decisions and undermining their perceived neutrality. To address this, the chapter proposes three principles for ensuring legitimate and objective scientific assessments with IAMs. Value Transparency: Value judgments in IAMs must be made explicit and presented as separate premises of the results. Value Plurality: IAM scenarios should represent a diverse range of viable value outlooks, ensuring that different kinds of mitigation strategies are supported by scientific evidence. Democratic Endorsement: Deliberative venues should be established to involve the public in legitimizing the value judgments embedded in models and scenarios, fostering democratic endorsement. These principles offer a provisional solution to the problem of legitimacy, demonstrating how scientific assessments can remain credible and authoritative while acknowledging the normative dimensions of IAMs.