Analysing the pace of the energy transition under different cumulative CO2 budgets

• Model FENICE allows to study the impact of CO 2 constraints along energy transition. • Expansion of infrastructures appears as a key enabler of decarbonisation. • Different CO 2 budgets yield different CO 2 network structures. • Import of clean energy vectors is a key and challenging aspects. • Stricter CO 2 budgets anticipate renewables and negative emission techs deployment. Under the pressing need for decarbonisation, most industrialized countries are targeting net-zero CO 2 emissions by mid-century. The pathway to the net-zero configuration is as important as the final goal, since a lack of containment of the cumulative CO 2 emissions may enhance climate impact effects and force larger efforts for negative emissions. The main objective of this article is to investigate the effects of cumulative CO 2 emission budgets in shaping the long-term transformation of national energy systems, using Italy as a case study. By comparing three scenarios with different budgets, the analysis provides insights into their impact on technology deployment, infrastructure development, and timing of decarbonisation actions. The analysis is developed with the open-source model FENICE (Future Energy traNsition multI-seCtor model), which is here fully presented for the first time. It provides a comprehensive multi-period approach to analyse multi-vector energy systems with multi-node and multi-sector resolutions. Based on the oemof framework, FENICE considers the five main energy carriers (electricity, hydrogen, fossil and biogenic CH 4 , liquid fuels, biomass), detailing their transmission infrastructures and tracking the CO 2 flows. Results confirm the expected surge of renewable energy sources in all scenarios, combined with programmable technologies (power generation or energy storage) as well as carbon capture. Energy infrastructures emerge as key enablers of decarbonisation, facilitating renewables installation and highlighting the relevance of their detailed modelling. Under low CO 2 budgets, the system development is impacted by installation rate limits and the urgency of new measures forces large negative emission contributions, leading to diverse CO 2 pipeline designs and transport dynamics.