A groundbreaking study conducted by a multidisciplinary team from Kyoto University, Hokkaido University, and the International Institute for Applied Systems Analysis (IIASA) presents one of the first thorough multi-model evaluations of what it truly takes to achieve a global energy system entirely free of fossil fuels. This research arrives at a critical juncture when international climate efforts are transitioning from debating the merits of fossil fuel phase-out to the pragmatic routes for achieving it.
Following the landmark COP28 agreement in 2023, which officially recognized the necessity of transitioning away from fossil fuels, global climate dialogues have moved decisively towards strategizing the practical steps to realize this shift. The new study, therefore, is instrumental in informing policy-making processes emerging from recent high-profile forums like the COP30 meeting in Belém, Brazil, the Santa Marta Conference, and the Transitioning Away from Fossil Fuels initiative. These platforms are actively exploring mechanisms to accelerate the replacement of coal, oil, and natural gas with sustainable alternatives at a global scale.
Led by Assistant Professor Shotaro Mori of Kyoto University, an alumnus of IIASA’s prestigious Young Scientists Summer Program (YSSP), the research distinguishes itself from prior work by emphasizing the nuanced difference between decarbonization and a complete fossil fuel phase-out. According to Mori, while decarbonization often implies reducing emissions through cleaner fossil technologies or integrating carbon capture, a full fossil fuel phase-out demands fundamentally different and much more accelerated transformations in energy production and consumption patterns.
At the core of the study is the application of two globally recognized integrated assessment models: the Asia-Pacific Integrated Model-Technology model (AIM-Technology) and the MESSAGEix-GLOBIOM framework. These sophisticated tools enable detailed scenario analysis contrasting conventional 1.5°C-compliant pathways, which still allow residual fossil fuel use with transitional technologies, with scenarios that envisage a total elimination of coal, oil, and natural gas between 2050 and 2100.
The findings are both compelling and daunting. Achieving fossil fuel phase-out by mid-century would necessitate a rapid and unprecedented expansion of renewable electricity generation infrastructure paired with the large-scale deployment of hydrogen-based energy carriers, including hydrogen itself, ammonia, and synthetic fuels. These energy vectors are vital for decarbonizing sectors such as heavy industry and long-haul transport, which pose significant challenges to direct electrification due to their high energy density requirements and operational realities.
The study reveals that zero-fossil fuel pathways require approximately 1.6 to 1.8 times more electricity generation by 2050 compared to conventional 1.5°C-aligned scenarios. This demand surge underscores the imperative for accelerating the solar and wind power build-out at rates far exceeding current global trends. Equally critical is the swift scaling up of green hydrogen production capacity through massive investment in electrolysis technologies powered exclusively by renewables, highlighting the complexity and interdependency of future energy infrastructures.
However, this ambitious transition carries enormous economic implications. The cumulative investments required for technology deployment and infrastructure development are significantly higher, necessitating mobilization of capital at scales 2.5 to 3 times greater than today’s investment patterns in non-fossil electricity generation. This marks a radical shift in global energy economics, infrastructure policy, and investment underwriting, accompanied by a comprehensive restructuring of supply chains, industrial processes, and global trade dynamics.
Importantly, the researchers emphasize that full fossil fuel phase-out scenarios inherently reduce reliance on carbon removal technologies such as bioenergy with carbon capture and storage (BECCS) and direct air carbon capture and storage (DACCS). This is a crucial advantage because these negative emissions technologies remain nascent, unproven at scale, and pose their own sets of ecological and ethical challenges.
Furthermore, the study finds that earlier fossil fuel elimination enhances the likelihood of stabilizing global temperatures at 1.5°C following any transient overshoot. This result highlights that beyond cost considerations, the complete abandonment of fossil fuels serves as a robust climate risk mitigation strategy, reducing uncertainties associated with future carbon removal capacities and technological readiness.
Despite these findings, the authors caution that the zero-fossil path is not a singular solution but one of several possible routes to meet the Paris Agreement targets. Cost-optimal scenarios that permit continued fossil fuel use coupled with carbon capture may appear economically attractive from a narrow techno-economic standpoint. However, zero-fossil pathways offer a strategic safeguard against climate uncertainties by fundamentally re-engineering the global energy system to minimize long-term dependencies on technologies with uncertain scalability and efficacy.
Equity and just transition considerations lie at the heart of the study’s implications. Countries heavily dependent on fossil fuel production and exports face profound socio-economic transformations that cannot be addressed by technology deployment alone. The researchers call for coordinated international cooperation, transition planning inclusive of affected communities and workers, and complementary policy frameworks that provide social and economic support to fossil fuel-reliant regions.
Coauthor Volker Krey, a principal research scholar at IIASA, stresses that the shift away from fossil fuels entails more than simple fuel substitution; it demands a deep systemic transformation. From infrastructure to industrial processes and macroeconomic patterns, the scale of change is enormous. Governments and financial institutions must prepare for a multi-trillion-dollar global mobilization of investments over the coming decades to realize this vision.
Siddharth Joshi, another coauthor and IIASA research scholar, highlights that the zero-fossil transition represents a comprehensive risk management strategy. The upfront capital requirements, while substantial, help build resilience into energy systems that are less vulnerable to geopolitical shocks, resource depletion, and carbon pricing volatility, ultimately securing sustainable pathways for energy security and climate stability.
Importantly, this research aligns closely with emerging international processes such as the Santa Marta Conference and the Transitioning Away from Fossil Fuels initiative. These forums emphasize the rapid scale-up of renewables and hydrogen infrastructure, prioritized reduction of CO₂ removal dependencies, and the socio-economic dimensions of fossil fuel phase-out, signaling a growing consensus on the diverse spectrum of challenges and opportunities in the global energy transition.
In conclusion, this study provides a critical evidence base for governments and stakeholders engaged in forging the next generation of climate policies and nationally determined contributions (NDCs). It clarifies the scale and complexity of the energy transformation required for a zero-fossil future, as well as the profound benefits and trade-offs involved, ultimately underscoring the urgency of decisive policy action to accelerate this unprecedented transition.
Subject of Research: Full phase-out of fossil fuels under the 1.5°C climate goal
Article Title: Challenges and opportunities of the full phase-out of fossil fuels under the 1.5°C goal
News Publication Date: 18-May-2026
Web References:
https://transitionawayconference.com/
https://docs.messageix.org/projects/models/en/latest/global/index.html
https://iiasa.ac.at/early-career/yssp
References:
Mori, S., Joshi, S., Krey, V., Oshiro, K., Fricko, O., Hara, T., & Fujimori, S. (2026). Challenges and opportunities of the full phase-out of fossil fuels under the 1.5°C goal. Nature Communications. DOI: 10.1038/s41467-026-72841-7
Keywords:
Energy transition, fossil fuel phase-out, renewable energy, hydrogen economy, climate change mitigation, decarbonization pathways, integrated assessment models, 1.5°C goal, carbon capture and storage, just transition
