Adaptive Strategies to Reconcile Diverse Equity Preferences in Climate Policies

Normative uncertainty, which arises from diverse ethical perspectives and uncertainty about distributional outcomes, poses a significant hurdle in climate policy negotiations. Such uncertainty illustrates the core challenge of achieving agreement on the moral principles or equity considerations that should guide the development of climate policies. Integrated Assessment Models (IAMs), while influential in shaping decisions, fall short in factoring in this normative uncertainty in climate policies. To address this issue, we developed an IAM framework called JUSTICE. JUSTICE leverages the economic insights of the RICE50+ model to explicitly account for spatiotemporal heterogeneity alongside probabilistic forecasting of the FaIR climate model for a better representation of climate uncertainty. We also reformulate the Social Welfare Function (SWF) in light of four distributive justice principles - Utilitarian, Sufficientarian, Egalitarian, and Prioritarian - to encapsulate the ethical pluralism of different stakeholders.  We search for adaptive mitigation policies by assimilating two established decision-making frameworks: Multi-Objective Robust Decision-Making (MORDM) and Evolutionary Multi-Objective Direct Policy Search (EMODPS). MORDM rigorously tests potential policies against deep uncertainties to find robust, Pareto-optimal choices. At the same time, EMODPS fine-tunes strategies to reconcile stakeholders' diverse objectives, ensuring policies are adaptive and robust.  Our findings demonstrate that adaptive policies facilitate deliberation. They identify common ground among policymakers with diverse perspectives by being robust across multiple realizations of deep uncertainties and flexible enough to accommodate conflicting ethical perspectives. Our approach designs climate policies that are both inclusive and adaptive, ensuring they account for immediate necessities while remaining responsive to unfolding future challenges—thereby upholding the tenets of both intra and intergenerational justice.   In summary, our study underscores the pivotal role of normative clarity in facilitating stakeholder dialogue and ensuring that climate policies are scientifically sound and socially equitable. Incorporating diverse normative perspectives and acknowledging normative uncertainties, our adaptive strategies limit overconfidence in climate policies, promote inclusivity without subjecting individuals to undue risks, and redefine the application of IAMs in crafting fair and just climate policies.   Keywords: Integrated Assessment Models, Climate policy, Distributive justice, Deep Uncertainty, Adaptive strategies, Social Welfare Function, Robust decision-making.