Transient climate response in the DICE integrated assessment model of climate-economy

Abstract

Integrated assessment models (IAMs) couple the interdependent dynamics of geophysical and economic systems. By solving an optimal control problem for a nonlinear, time-varying system, IAMs enable the determination of economically optimal pathways for emissions of greenhouse gases such as carbon dioxide (CO 2 ). Central to any IAM is a climate model capturing the dynamic response of global surface temperature to changes in net downward radiative forcing due to the atmospheric accumulation of heat-trapping greenhouse gases. The transient climate response (TCR), defined as the temperature change at the time of CO 2 doubling under a scenario in which CO 2 concentrations increase by 1%yr−1, plays a central role in quantifying the economic impacts of climate change on policy-relevant timescales. In this paper, we propose an optimization-based methodology for computing the parameters of a climate model in such a way that the resulting model exhibits a specified TCR. The methodology developed in this paper targets the climate model parameterization employed in DICE (Dynamic Integrated model of Climate and the Economy), a widely-studied IAM for which TCR is only indirectly specified. Results reported herein enable policymakers using DICE to compute optimal CO 2 emissions pathways which directly reflect the TCR of state-of-the-art climate models documented in the most recent (Fifth) Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC).