Global fossil fuel reduction pathways under different climate mitigation strategies and ambitions

This paper explores what the AR6-assessed scenarios, which are consistent with limiting long-term warming to 2°C or below, say about the speed, trajectory, and feasibility of different global coal, oil, and gas reduction pathways and why. Given the 2021 Glasgow Climate Pact’s emphasis on the 1.5°C limit, and the significant amplification of adverse climate impacts at 2°C relative to 1.5°C, the focus of the paper is on the “C1” group of scenarios that limit warming to 1.5°C with no or limited overshoot. 

The paper uses a range of different techniques on the scenario ensemble to understand the characteristics of different scenario groupings, and why they have those characteristics. This includes analysing the most important factors that lead to different levels of cumulative 2020–2100 supply for a given fossil fuel, using classification and regression tree analysis (CART), and given the variability of gas, an analysis of variance (ANOVA) to explore the influence of eight potential drivers. 

For the C1 group of scenarios, global coal, oil, and natural gas supply (intended for use in all sectors) decline on average by 95%, 62%, and 42%, respectively, from 2020 to 2050. However, the long-term role of gas is shown to be highly variable. A key finding from the paper is that pathways that have higher levels of gas are enabled by higher carbon capture and storage (CCS) and carbon dioxide removal (CDR). The paper highlights that these higher levels are likely associated with inadequate model representation of regional CO2 storage capacity and technology adoption, diffusion, and path-dependencies. The assumptions of the relevant models about CCS, renewables, and carbon pricing are key to determining the role of gas. 

The paper then considers what the fossil fuel reductions might be if CDR was constrained by limits derived from experts, and estimates reductions to be 99%, 70%, and 84% for coal, oil, and gas respectively. 

A number of policy insights are put forward: i) governments need to align their climate and energy policies by planning for and implementing an active transition away from fossil fuels, as per the Production Gap Report conclusions; ii) mitigation of methane emissions is important but not a substitute for fossil fuel phase out, as continued gas use is dependent on CCS/CDR and potentially delays renewable deployment; and iii) phase out rates are normative, based on the risks that governments are willing to take on future emission removals through CDR. A precautionary approach would reduce these risks and bring benefits on a number of other fronts, such as reducing air pollution. 

This paper can be used to highlight that many scenarios which project high levels of fossil fuels, notably gas, generate these projections due to specific model-based assumptions (particularly about the role of CCS/CDR), the plausibility of which are highly contestable. Insofar as such scenarios are used by fossil fuel proponents to justify proposed new supply projects, this paper can help to critique that evidence.