1 The IMACLIM-R Model: Infrastructures, Technical Inertia and the Costs of Low Carbon Futures under Imperfect Foresight*

Abstract. This paper analyzes the transition costs of moving towards a low carbon society when the second-best 15 nature of the economy is accounted for. We emphasize the consequences on mitigation costs of considering the interplay between a) technical systems inertia, including slow infrastructure turnover in transportation and construction; and b) imperfect foresight influencing investment decisions. To this end, the hybrid general equilibrium modeling framework IMACLIM-R is employed as it allows for transitory partial adjustments of the economy and captures their impact on the dynamics of economic growth. The modeling exercise quantitatively 20 emphasizes the i) specific risks that the interplay between inertia and imperfect foresight leads to high macroeconomic costs of carbon abatement measures; ii) opportunities of co-benefits from climate policies permitted by the correction of sub-optimalities in the reference scenarios. The article draws insights for the framing of future climate architectures by studying the role of measures that act complementarily to carbon pricing in the transport sector. In particular, reallocating public investment towards low-carbon transport 25 infrastructure significantly reduces the overall macroeconomic costs of a given GHG stabilization target an