Scientists from Kyoto University, the International Institute for Applied Systems Analysis, Hokkaido University and the National Institute of Environmental Studies in Japan have simulated scenarios for a complete global phase-out of coal, oil and gas to determine the cost of keeping global warming to 1.5°C without using them. Their study showed that a complete phase-out of fossil fuels by 2050 would require a 1.6–1.8-fold increase in global electrification compared to the business-as-usual scenario, leading to a 34% increase in energy investment. However, this difficult path has an important advantage: it sharply reduces the reliance on carbon capture technologies and increases the likelihood of bringing the climate to target levels even after temporarily exceeding the 1.5°C threshold.
Most of the contemporary climate scenarios assume that even if carbon neutrality is achieved, some oil, gas and coal will continue to be used, primarily in aviation, heavy industry, freight transport and chemical production, where it is especially challenging to phase out fossil fuels. It is planned to offset the remaining emissions via CO₂ capture and storage technologies. Following the decision of the UN Climate Change Conference (COP28) in Dubai, which for the first time explicitly called for a fossil fuel transition, politicians and the public have been increasingly discussing not just emissions reductions, but a complete phase-out of coal, oil and natural gas. However, economic models have previously shown that the cheapest way to limit global warming to 1.5°C is to retain a small share of fossil fuels and offset emissions with carbon capture technologies. The Japanese researchers have decided to test a more extreme scenario: what will happen if no loophole is left for fossil fuels.
To that end, they have used two global energy models: AIM-Technology and MESSAGEix-GLOBIOM. The former simulates energy technology and infrastructure development in detail, while the latter also takes into account the impact of the energy industry on land use, agriculture and the biosphere. The researchers set the same condition for both models: a global carbon budget of 500 gigatons of CO₂ for the period from 2018 to 2100. In other words, humanity can only emit a strictly limited amount of carbon dioxide into the atmosphere in order to maintain its chances of limiting warming to about 1.5°C. The zero-fossil scenarios have coal, oil and gas supplies drop to zero by a specific date between 2050 and 2100. As a point of comparison, the researchers used a standard 1.5°C scenario, which has no direct ban on fossil fuels.
In the mid-century phase-out scenario, the share of oil and gas in final energy consumption is nearly negligible, as they get replaced by electricity and hydrogen. Moreover, this is mostly green hydrogen, which is produced by water electrolysis using solar and wind energy. Total electricity generation by 2050 in this scenario is supposed to be 1.6–1.8 times higher than in conventional climate models. This means that the world will have to significantly speed up the construction of solar and wind power plants, energy storage systems and electrolyzers for hydrogen production.
A complete phase-out of fossil fuels also has major advantages. The resulting drop in CO₂ emissions from the energy industry could dramatically reduce the need for carbon capture and storage technologies. For instance, the volume of geological CO₂ storage by 2100 in the complete phase-out scenarios is lower by 37–77% compared to the conventional 1.5°C scenarios. The need for direct carbon dioxide capture from the atmosphere would be lower as well. However, this transition proves much more expensive, with total energy supply investments rising by up to 34%.
The models show different pathways to phasing out fossil fuels. The AIM-Technology model is focused on indirect electrification through synthetic fuels produced from hydrogen and CO₂. This approach makes it possible to preserve some conventional technology, such as internal combustion engines, but requires enormous amounts of electricity to produce hydrogen. By contrast, the MESSAGEix-GLOBIOM model places greater emphasis on direct electrification, i.e., a transition to electric vehicles, electric heating and heat pumps. This reduces the need for synthetic fuels, but requires consumer equipment to be replaced much faster.
The researchers also warn that an accelerated phase-out of fossil fuels could lead to a sharp increase in the use of biofuels, which would create additional risks for food security and biodiversity, since large areas of agricultural land would be allocated for energy crops.
