The Paris Agreement aims to hold the increase in the global average temperature to well below 2°C above pre-industrial levels, and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels (Article 2.1(a)). It also states parties’ aim to achieve these long-term temperature goals by balancing anthropogenic emissions by sources and removals by sinks of greenhouse gases (commonly understood to mean “net zero emissions”) in the second half of the century (Article 4.1). From these objectives, a “carbon budget” can be determined to set a cap on the total emissions allowable to meet the Paris Agreement.  

These normative objectives provide a constraint that can be used to model pathways for their achievement. Note that there are varying views about what constitutes alignment with the Paris Agreement’s goals. Different carbon budgets are associated with different probabilities of limiting warming below a specific temperature goal. For example, most 1.5°C pathways adopt a carbon budget associated with a 50% probability of limiting average global temperature increase to that level. On the question of what constitutes Paris alignment, Schleussner et al (2022) provides guidance on how to translate the Paris Agreement’s objectives into climate goals. 

Experts have constructed models that incorporate fossil fuel production, so as to explore the implications of achieving one or another of these normative objectives for fossil fuel production. IEA’s 2021 Roadmap for the Global Energy Sector models scenarios to meet the goal of achieving net zero by 2050, widely used as a proxy for limiting warming to 1.5°C, and shows that investments in new oil, gas and coal production infrastructure are not required. The UNEP 2021 Production Gap Report does not model new pathways but rather compares the plans of 15 major fossil fuel-producing countries against pathways that are Paris-aligned, and finds that there is a growing gap between those national plans and what is required in terms of production decline. This provides a stark reminder of the need for fossil fuel phase out. 

Welsby et al (2021) model pathways under 1.5°C, suggesting that the vast majority of undeveloped fossil fuel reserves must remain unused and that most producing regions have peaked or will reach peak production within a decade. The earlier study by McGlade and Ekins (2015) models scenarios under 2°C pathways, finding that a large share of current gas, oil and coal reserves should remain unused until 2050, and that in some countries the proportion of fossil fuels that should remain unextracted is incredibly high. Trout et al (2022) also found that a large proportion of already developed oil and gas reserves cannot be burned to stay within the 1.5°C carbon budget, so undeveloped reserves must be considered unextractable. 

IISD’s 2022 report on Navigating Energy Transitions models pathways for limiting warming to 1.5°C, suggesting that new investments in fossil fuel extraction and infrastructure should not occur, confirming the conclusions of the IEA (2021). Another IISD 2022 report further indicates that no new fossil fuel infrastructure should be approved if we are to meet the 1.5°C goal.  

Across many of the climate scenarios published, the role of carbon capture and storage (CCS) and carbon dioxide removal (CDR) remains contentious, as highlighted in Welsby et al (2021) and IISD (2022). To the extent such technologies are applied, they would enable continued use of fossil fuels, but models often assume their application at a scale that many experts believe is not possible given the lack of progress on commercialisation of such technologies. Therefore, analyses that use scenarios that are heavily reliant on CCS/CDR should be interpreted with care. A recent paper by Achakulwisut et al. (2023) highlights the important role that CCS/CDR plays across many of the recent scenario modelling studies, particularly in enabling the continued production and use of fossil methane gas. Calverley and Anderson (2022) show that phase out of oil and gas needs to be extremely rapid where reliance on CCS/CDR is removed.  

These modelled pathways can be used to justify certain policy interventions needed to meet the objectives of the Paris Agreement. Modelling of Paris-aligned supply pathways can also be used to determine the Regional Distribution of Production consistent with the modelled pathway, which may be relevant to Equity Considerations in Fossil Fuel Phase Out. The types of supply-side policies that can be used to keep emissions within the global carbon budget are further assessed in National and Subnational Supply-Side Policies, and International Supply-Side Cooperation.