The global energy system is undergoing a profound transition driven by the urgency of climate change mitigation, energy security concerns, and the commitment to limit global warming to 1.5 °C. While electricity decarbonization has received substantial attention, thermal energy remains a largely overlooked yet critical component of the energy transition, accounting for approximately 50% of global final energy consumption and representing the largest source of energy-related CO₂ emissions. This review critically examines the role of thermal energy across key sectors of the global energy system, including power generation, industrial processes, buildings, and transportation. Conventional and low-carbon thermal power technologies—such as nuclear, geothermal, biomass, and concentrated solar power—continue to play a vital role in providing dispatchable electricity and maintaining grid stability amid increasing penetration of intermittent renewables. In industry, where process heat contributes nearly 18% of global greenhouse gas emissions, decarbonization pathways centered on electrification, bioenergy, and waste heat recovery are evaluated. The building sector is assessed with emphasis on high-efficiency heat pumps and district heating and cooling systems as scalable solutions for reducing fossil fuel dependence. Additionally, the evolving role of thermal energy in transportation is examined, highlighting advances in waste heat recovery, thermal management of electric vehicles, and carbon-neutral synthetic fuels for hard-to-abate sectors. Despite significant technological potential, the deployment of modern thermal energy solutions is constrained by high capital costs, technical integration challenges, regulatory barriers, and sustainability concerns. This review underscores the necessity of repositioning thermal energy at the center of energy transition strategies, supported by targeted policies, financial mechanisms, and technological innovation, to achieve a resilient, low-carbon, and secure global energy system.
MOMOH et al. (Tue,) studied this question.