It is critically important that we have a sense of how challenging, or feasible, our pathways to a 1.5 °C future might be, considering technical, socio-cultural, political and economic factors. Incorporating such factors into integrated assessment models (IAMs), which dominate such analysis of low-carbon pathways, is one way of better exploring this level of challenge. Now two studies in Nature Climate Change, by Stephen Bi and colleagues1 and Greg Muttitt and colleagues2, incorporate current political ambitions behind transitioning away from coal power into their IAM pathways, to shine a light on how compatible such ambitions are with the 1.5 °C goal, thereby contributing to the assessment of feasibility. Taken together, the studies show that current 1.5 °C-compatible low-carbon pathways have rates of coal reduction that are far faster than even the most optimistic interpretations of real-world ambitions. This could be interpreted as a severe blow for the feasibility of such pathways. But it can also be taken as a call-to-arms for governments across the world to have much greater political ambition on phasing out coal, while also tackling oil and gas.

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Exploring the feasibility of low-carbon transitions using IAMs, for example, by comparing their rates of energy system transformation with historical experience, has become a growing field of climate change mitigation research. Some studies have constrained the rates based on historical data3,4. Other studies have explored the extent to which rapid transitions away from fossil fuel technologies have indicated that assets such as coal plants would become ‘stranded’ — which is to say too expensive to run, even though they haven’t yet reached the end of their useful economic lives5,6. It is this latter consideration around how fast coal power can feasibly be reduced that leads to the two new papers’ advances in better reflecting political commitments in low-carbon pathways analyses, to improve their realism around the overall feasibility of low-carbon transitions.

In the real world, many countries have agreed to phase out coal power as part of the Powering Past Coal Alliance (PPCA), an initiative launched by the United Kingdom and Canada at COP23 in 2017. The alliance now has over 160 members, including almost 50 national governments, with subnational governments and other organizations making up the remainder. The PPCA was launched with an aspiration that member countries should phase out unabated coal power by 2030 (for Organisation for Economic Co-operation and Development countries) and by 2050 (for the rest of the world)7. How these goals, which represent a level of ambition that arguably reflects political feasibility well, compare to modelled IAM pathways towards 1.5 °C, calculated on the basis of minimizing transition costs, thus lends key insights about how feasible these ‘least-cost’ pathways are in light of real-world political commitments.

The study from Bi and colleagues1 constructs scenarios in which different countries join the PPCA over time, on the basis of their rising gross domestic product per capita and falling coal-fired power generation as a share of total electricity generation (two factors that robustly predict PPCA accession). It then dynamically links these scenarios to an IAM to produce projections of the emissions, where the pathways and PPCA participation would mutually impact each other. The study also explores the ‘colour’ of post-COVID-19 recovery packages. Green packages see coal plant project completion rates fall, increasing the likelihood of accession to the PPCA, while by contrast brown packages see project cancellation rates fall and they prolong the life of coal plants, decreasing the likelihood. While some studies have incorporated current policy packages to understand where emissions are heading8,9, the dynamics of future political decisions such as PPCA membership had not yet been incorporated endogenously, as is done here.

The study finds that if PPCA coal phase-out commitments are restricted to the power sector, then non-power sectors and non-PPCA countries take much of the unwanted coal, in a process called ‘leakage’. This makes the PPCA highly ineffective at closing the gap between the coal used in current climate policies and what is required for a 1.5 °C outcome. In fact, only about 2% of this ambition gap is closed even with a green COVID-19 recovery. In other words, dealing with leakage across sectors and countries is essential, ideally through expanding the coal phase-out commitment beyond the power sector, as well as expanding the alliance. China is a critical player in this analysis, only simulated to join the PPCA in a green or ‘neutral’ COVID-19 recovery. If the recovery is brown, China doesn’t join, considerably diminishing the total amount of global coal that is phased out, even if PPCA membership is taken to mean phasing out unabated coal across all sectors of members’ economies (that is, not just their power sectors).

The second study, from Muttitt and colleagues2, sheds light on the PPCA’s compatibility, or otherwise, with 1.5 °C scenarios from a different angle. It considers the implications of constraining coal phase-out in power generation in the top ten coal-power-consuming countries according to the PPCA timelines. A key novelty is that the study first demonstrates that PPCA-compatible coal phase-out timelines generally sit near the fastest historical rates of decline of different power generation sources, including relatively drastic examples such as nuclear shutdowns in Japan after the Fukushima disaster. The resulting IAM-modelled pathway, aimed at 1.5 °C but constrained by PPCA coal phase-out rates, shows drastic differences from a pathway without such constraints. Most strikingly, the Global North has to go much faster on emissions reductions, with Europe’s CO2 reduction rate increased from 8% to 13% per year over the period 2020–2045, and the United States up from 10% to 17%. And much more of the global emissions reduction comes from earlier phasing out of gas and oil, to compensate for coal going slower. For example, the constrained scenario sees peak gas by 2025, rather than 2030 in the unconstrained scenario.

Together, these two analyses1,2 deliver some stark messages: the PPCA coal power phase-out timelines are certainly not unambitious compared to historical benchmarks of how fast power sources have declined, but at their current level of ambition could lead to very little in terms of reduced coal use and emissions, which are unlikely to get near the 1.5 °C target. This requires considerably enhancing coal phase-out ambitions, doubling down on other fossil fuels and calls for richer, industrialized countries to reduce their emissions much faster.

Both studies leave some key questions unexplored. These include the political feasibility of both expanding the PPCA beyond coal power and going faster on oil and gas reductions. They also only explore feasibility within the dynamics of the current economic system, with strongly growing underlying global gross domestic product driving demand for energy services. With a rapidly diminishing 1.5 °C carbon budget10, we should explore feasibility in the context that we may have to break with historical social and economic precedents, as well as current political commitments. Perhaps this is where these studies’ greatest utility lies — not as a cast-iron assessment of feasibility, but rather as an invaluable contribution to the evidence base on how we should reinforce our efforts if we are to stand any chance of meeting the 1.5 °C goal.