The role of low carbon fuels towards net-zero in integrated assessment models and energy system models: A critical review

Low-carbon fuels (LCFs) are crucial for achieving net-zero CO 2 emission goals in integrated assessment model (IAM) and energy system model (ESM) scenarios. The absence of a standardized LCF classification system and inconsistencies in modeling approaches have obscured the integration of various LCFs within these models and makes a meaningful comparison of scenario outcomes difficult. This study addresses these issues by conducting a comprehensive critical review of the representation of LCFs in IAMs and ESMs, focusing on the fuel's role in shaping net-zero emission futures. We categorize LCFs into key groups, including electrification, hydrogen, synfuels, and biofuels. Our analysis reveals substantial gaps in technical modeling, lifecycle emissions data, incomplete modeling of environmental impacts beyond CO 2 emission, and discrepancies in LCF applications across sectors. To enhance the accuracy of future scenarios, we recommend adopting a unified LCF classification system, standardized input data, and more detailed sectoral applications. Additionally, we advocate for the integration of Life Cycle Assessment (LCA) into IAMs and ESMs to improve the evaluation of LCFs' full environmental impacts, providing a more comprehensive foundation for net-zero emission pathways. • Reviews LCF representation in IAMs/ESMs, identifying inconsistencies in definitions, modeling approaches, and scenario assumptions. • Proposes a categorization of LCF technologies based on production pathways and feedstocks, aligning with decarbonization strategies. • Analyzes scenario outcomes, highlighting sectoral variations and the roles of hydrogen, biofuels, and synthetic fuels in net-zero pathways. • Recommends improving transparency, high-resolution temporal and spatial modeling, and expanding LCF end-use sector representation. • Stresses the inclusion of non-CO 2 emissions, land-use impacts, and policy mechanisms to enhance the accuracy of decarbonization strategies.