Policy simulation modelling to inform national carbon budget pathways

Carbon budgets are emerging as a key policy tool to set cumulative targets on greenhouse gas emissions at a national and international level. In this paper, we develop a methodology for simulation modelling of energy demand and carbon dioxide (CO₂eq.) emissions to assess the implication of different scenarios on sectoral emissions ceilings and carbon budgets. We demonstrate how this simulation modelling approach to carbon budgets applies to Ireland's Climate Action Bill, which sets a legal obligation to keep within defined sectoral emission ceilings. The transport, residential, industry, and electricity sectors meet Carbon Budget 1 (2021–2025), and the residential and services sector meets Carbon Budget 2 (2026–2030) sectoral ceilings in the scenario presented. This paper also examines the interaction effect between these policy scenarios. The interaction effect between public transport and modal shift shows an additional emissions savings of 0.1 MtCO₂eq. The interaction effect also highlights a ‘double counting’ effect between the uptake of Electric Vehicles (EVs) and increased biofuel mixing for private car transport of 0.3 MtCO₂eq., and for Evs and passenger transport modal shift of 0.2 MtCO₂eq.