Please cite this article in press as: Slamersak et al., Post-growth: A viable path to limiting global warming to 1.5 C, One Earth (2023), https://doi.org/ 10.1016/j.oneear.2023.11.004 ll OPEN ACCESS Perspective Post-growth: A viable path to limiting global warming to 1.5C a Slamers Aljos ak,1,* Giorgos Kallis,1,2 Daniel W. O’Neill,3,4 and Jason Hickel1,5,6 1Institutde Ciencia i Tecnologia Ambientals (ICTA-UAB), Universitat Autonoma de Barcelona, Barcelona, Spain 2Catalan Institution for Research and Advanced Studies, ICREA, Barcelona, Spain 3School of Economics, Universitat de Barcelona, Barcelona, Spain 4Sustainability Research Institute, School of Earth and Environment, University of Leeds, Leeds, UK 5International Inequalities Institute, London School of Economics and Political Science, London, UK 6Department of Anthropology, Universitat Autonoma de Barcelona, Barcelona, Spain *Correspondence: aljosa.slamersak@gmail.com https://doi.org/10.1016/j.oneear.2023.11.004 SUMMARY Existing climate mitigation scenarios assume future rates of economic growth that are significantly higher than what has been experienced in the recent past. In this article we explore how assuming lower rates of growth, in line with the hypothesis of secular stagnation, changes the range of mitigation possibilities. We compare scenarios with moderate and strong policy ambition under both high-growth and low-growth as- sumptions. The results show that low growth makes it more feasible to decrease emissions in a way that is consistent with 1.5 C–2 C of warming. Moreover, low growth reduces the need to rely on unprecedented buildout of low-carbon energy infrastructure, and the unprecedented rates of energy-GDP decoupling that characterize existing scenarios. By contrast, pursuing higher growth rates, such as those represented in IMF projections, jeapordizes the Paris Agreement. The challenge is that lower growth is commonly associ- ated with recession, which raises concerns about equity between and within countries, social stability, and the ability to finance a low-carbon energy transition. Recent literature on achieving a ‘‘post-growth’’ tran- sition points to novel policies that could address these problems, which should be explored and evaluated in future mitigation scenarios. INTRODUCTION important consideration, as lower growth rates may change the mitigation possibility space.10 Indeed, secular stagnation Measures to contain the coronavirus pandemic caused the may already have kept emissions lower than they would other- largest reduction in global carbon emissions since the Second wise have been. For example, Burgess et al. show that global World War,1 with emissions dropping by 6% in 2020 alone.2 CO2 emissions would likely have remained near the upper range Yet the impact of this event on the global temperature trajectory of the IPCC’s projections if it were not for the low growth rates proved to be small, as only two years later, emissions exceeded between 2005 and 2018.4 pre-pandemic levels.3 The rebound in emissions can be ex- Although several high-income countries have achieved abso- plained by the fact that recovery efforts were focused in large lute decoupling of GDP from emissions in recent years,11 their part on increasing economic growth. decoupling has been insufficient to respect the carbon budgets Growth tends to increase energy use relative to what it otherwise for 1.5 C and 2 C.12,13 Moreover, it has taken place during a might be, which in turn makes decarbonization more difficult to period of economic stagnation, and faster growth could have achieve. This tension is evident in existing climate mitigation sce- eroded these modest reductions. narios assessed by the Intergovernmental Panel on Climate For these reasons, there is an urgent need to consider climate Change (IPCC).4 Existing scenarios tend to assume all countries mitigation scenarios that do not rely on high economic growth as pursue high growth, regardless of how wealthy they already are. the default assumption. The case for ‘‘post-growth’’ scenarios To reconcile this assumption with the Paris Agreement targets, ex- has already been articulated in the literature,10,14 but such sce- isting scenarios rely on an unprecedented decoupling of energy narios are not yet represented in existing climate mitigation sce- use from economic output5 alongside the application of unproven narios, such as the Shared Socioeconomic Pathways negative emission technologies.6,7 (SSPs),15,16 which have been used as the main point of reference It is worth noting, however, that existing mitigation scenarios in the IPCC scenario literature.17,18 tend to over-project economic growth compared to recent The first question motivating this article is then: does lower trends, without taking into account studies that suggest high-in- growth make a difference to climate mitigation pathways, and come economies may have entered into a prolonged period of if so, how important is this difference? We find that low growth secular stagnation.8,9 The possibility of secular stagnation is an does make a difference, as it can reduce the need for One Earth 7, January 19, 2024 ª 2023 The Authors. Published by Elsevier Inc. 1 This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Please cite this article in press as: Slamersak et al., Post-growth: A viable path to limiting global warming to 1.5 C, One Earth (2023), https://doi.org/ 10.1016/j.oneear.2023.11.004 ll OPEN ACCESS Perspective A B Figure 1. Historical trends and IPCC projections of per-capita GDP The graphs show per-capita GDP growth for (A) the world, (B) high-income countries, and (C) lower-in- come countries.27 The black dashed line shows the annual values, whereas the blue line shows the 5-year rolling average of historical values. The gray dashed line shows the average rate of change for the periods from 1994 to 2006 and from 2007 to 2022. The data were partitioned with regard to the financial crisis of 2007–2008, which represents a clear break in the trend of global economic growth. The red envelopes show the interquartile range of the projections from the 33 IPCC scenarios, and the red line depicts the average rate of change in these scenarios. C ports, historical trends, and pledges. Our analysis reveals that growth is an impor- tant mitigation lever. Scenarios of lower economic growth can achieve decarbon- ization fast enough to keep temperatures below 2 C without having to rely on un- precedented changes of both the energy efficiency and the deployment of low-car- bon energy. Finally, we address the con- unprecedented energy efficiency improvements, but this finding cerns that low growth may pose higher mitigation challenges raises additional questions. Without appropriate policy interven- and perpetuate social inequalities, distinguishing between an tions, low growth may lead to rising inequality in high-income unplanned and inequitable ‘‘low-growth’’ scenario and a countries19,20 and less development in lower-income coun- purposefully managed and equitable ‘‘post-growth’’ scenario. tries,21,22 which would make it difficult to mobilize the broad sup- By delineating five key post-growth interventions, we seek to port needed for climate action. We therefore distinguish between inform the development of novel, equitable post-growth mitiga- ‘‘low-growth’’ scenarios and ‘‘post-growth’’ scenarios, with the tion scenarios. latter characterized by interventions intended to improve mitiga- tion capacity, equity, and social outcomes.23,24 CHALLENGES UNDERLYING A HIGH-GROWTH, LOW- Regardless of where one stands on the debate over the desir- CARBON TRANSITION ability of a post-growth future, it is clearly important to explore the conditions under which low-growth economies can be stable Over the past few years, an increasing number of scholars have and equitable. To illustrate the difference that lower growth might raised doubts about the feasibility of some of the key assump- make when it comes to climate mitigation, we explore six indic- tions that underpin existing climate mitigation scenarios. Here ative scenarios that differ in terms of their assumptions regarding we review these concerns, focusing on four key issues. four factors that drive carbon emissions: population, per-capita gross domestic product (GDP), the energy intensity of the econ- GDP growth: The unquestioned norm omy, and the carbon intensity of energy. Unlike existing sce- Existing IPCC scenarios of ambitious mitigation have over-pro- narios from the IPCC literature, which typically derive energy jected annual per-capita GDP growth since 2010 (Figure 1A), and emissions pathways by cost-optimizing the deployment of with a projected GDP growth rate of 3.1%–3.2%, exceeding energy-efficient and low-carbon technologies, the mitigation the actual average growth rate from 2010 to 2020 by 2 percent- pathways in our scenarios are derived in relation to existing age points. We find that IPCC scenarios have over-projected growth trends and existing plans of climate action. economic growth rates by 1.3 percentage points for high-in- Our intention is not to develop state-of-the-art scenarios. come countries, consisting of the Organization for Economic Instead, we use a simple modeling analysis to illustrate the Cooperation and Development [OECD] countries and European importance of considering slower growth trajectories. With Union [EU] member states and candidates (Figure 1B). For mid- this, we hope to start—and inform—a debate on the topic, hope- dle-income and low-income countries (hereafter ‘‘lower-income fully leading to the development of more advanced post-growth countries’’), we find that existing scenarios have over-projected models and scenarios. economic growth rates by 2.1 percentage points (Figure 1C). In this article, we develop scenarios of climate mitigation ac- In addition to over-projecting economic growth, none of the tion in the period 2022–2030, the last decade when decisive existing scenarios of ambitious mitigation compatible with climate action can still prevent the overshooting of the Paris 1.5 C–2 C of warming consider the possibility of lower GDP Agreement goals.18 Our scenarios rely on informed choices for growth in the near future.28,29 The global annual per-capita growth, energy use, and decarbonization based on policy re- GDP growth rate for the 33 scenarios considered in our analysis 2 One Earth 7, January 19, 2024 Please cite this article in press as: Slamersak et al., Post-growth: A viable path to limiting global warming to 1.5 C, One Earth (2023), https://doi.org/ 10.1016/j.oneear.2023.11.004 ll Perspective OPEN ACCESS A B Figure 2. Historical trends and IPCC projections of population The graphs show population growth for (A) the world, (B) high-income countries, and (C) low- income countries. The blue line shows the 5-year moving average of the historical population. The gray dashed line shows the average rate of change for the periods from 1994 to 2006 and from 2007 to 2022. The red envelopes show the interquartile range of the projections from the 33 IPCC scenarios, and the red line depicts the average rate of change in these scenarios. C ences,34 an aging population,19 high levels of debt,35 damage from climate change,36 and losses from stranded fossil capital.37 Vollrath, for example, predicts a long- term per-capita growth rate for the United States economy of no more than 1% per year.34 The shift to lower growth may also be due to changes in global political econ- omy. After the period of stagflation in the 1970s, growth rates in high-income econo- mies were boosted by neoliberal globaliza- tion.38 Structural adjustment programs is in the range of 2.6%–3.6% per year (2020–2030), with five of imposed across much of the global South during the 1980s these scenarios assuming growth rates that exceed 4.0%. As depressed the prices of labor and resources, removed capital Figure 1A shows, these growth rates are unprecedented in the controls, cut trade tariffs, and privatized public assets. The struc- contemporary period: since 1990, the period 2004–2007 was tural adjustment thereby opened new frontiers for foreign invest- the only period when global per-capita GDP growth exceeded ment, and multinational firms shifted production to poorer coun- 2.0% per year for more than three consecutive years. In contrast tries to take advantage of cheaper inputs.39 to the high-growth projections in existing scenarios, if we were to However, this process has now largely run its course. The pri- extrapolate the growth rates from the 2007–2022 period, an ces of Southern labor and resources are increasing, the margins average growth rate of 0.9% per year could be assumed for to further decrease tariffs and capital controls are small, and the period 2022–2030. This rate corresponds to an average there are few territories remaining that have not been integrated growth rate of 1.0% per year in high-income countries and into the international capitalist system. Several theorists argue 1.6% in lower-income countries. that global capitalism now faces the prospect of prolonged stag- The gap between the projections and data can only partly be nation.40,41 explained by the economic downturn during the first phase of As for lower-income countries, structural adjustment has had the COVID-19 pandemic, which could not have been anticipated several long-term negative effects. For one, these economies by the pre-pandemic scenarios. However, the gap already ex- were largely reorganized around exports to high-income coun- isted before the recession and was due to overestimating growth tries, which means that declining growth rates in the latter rates for the recovery period after the financial crisis of have led to slowdowns in the former. In addition, they have 2007–2008.4 generally been prevented from using protective tariffs and sub- The period of low growth since 2008 may be an anomaly after sidies to build up domestic industrial capacity and have been which the global economy will eventually return to high growth, prevented from using fiscal expansion to stimulate domestic de- as the International Monetary Fund (IMF) suggests.30 However, mand.42 A combination of economic reliance on high-income two recent studies claim that the uncertainty of long-term GDP countries, rising levels of debt, and the lack of sovereign indus- projections is substantially larger than in the forecasts of the tries may help explain the declining growth that lower-income IMF and World Bank, upon which the economic growth projec- countries have experienced over the past decade (Figure 1C). tions in the SSPs are based.31,32 These studies project that long-term global per-capita GDP growth could be as low as Population growth in existing scenarios 1% per year. Moreover, the global supply-chain crisis and the While mitigation scenarios tend to over-project economic war in Ukraine are likely to weigh down global economic growth growth, they underestimate global population growth rates in the years to come. (Figure 2). During the period 2010–2020, real population growth Indeed, some authors argue that high-income countries have rates were higher than assumed in the IPCC mitigation sce- entered a period of secular stagnation, whereby low growth is narios. The mitigation scenarios assume that lower-income likely to persist over the long term, given a slowdown in innova- countries have lower population growth rates than the United tion and productivity,33 a shift to services,34 changes in prefer- Nations (UN) projections suggest. However, the difference is One Earth 7, January 19, 2024 3 Please cite this article in press as: Slamersak et al., Post-growth: A viable path to limiting global warming to 1.5 C, One Earth (2023), https://doi.org/ 10.1016/j.oneear.2023.11.004 ll OPEN ACCESS Perspective A B Figure 3. Historical trends and IPCC projections of global energy intensity and global carbon intensity The graphs show the rate of change of (A) global energy intensity (energy use per unit GDP) and (B) global carbon intensity (CO2 emissions per unit GDP). The black dashed line shows the annual values, whereas the blue line shows the 5-year rolling average of historical values. The gray dashed line shows the average rate of change for the periods from 1994 to 2006 and from 2007 to 2022. The red envelopes show the interquartile range of the projections from the 33 IPCC scenarios, and the red line depicts the average rate of change in these scenarios. scenarios do not account for macro-eco- nomic rebound effects, whereby savings from efficiency improvements induce additional consumption, thus driving up to- tal energy demand or at least eroding a significant proportion of the gains.52,53 Achieving global energy efficiency im- only 0.2 percentage points globally (0.3 in lower-income coun- provements may be further complicated by the socioeconomic tries and 0.1 in high-income countries), which is an order of context of lower-income countries. To resolve the trade-off be- magnitude less than the 2-percentage-point difference in global tween economic growth and emissions from increased energy per-capita GDP projections. Therefore, the inconsistency in pop- use, existing scenarios assume industrialization in lower-income ulation growth projections has much lower impact on emissions countries but without growth in energy use.54 This is a strong projections than the inconsistency in economic growth pro- assumption, considering that lower-income economies mainly jections. depend on agriculture, which tends to be less energy intensive compared to industrial production.55 To accomplish industrial Betting on energy efficiency development without energy growth, lower-income countries Existing scenarios of ambitious mitigation have also over-pro- would have to achieve equal or even faster energy efficiency im- jected energy efficiency improvements for the period from provements than high-income countries.56 Such improvements 2010 to 2020 (Figure 3A). The average energy intensity improve- would require lower-income countries to industrialize by import- ment across the 33 SSPs is 2.5% per year, which substantially ing the most advanced ‘‘frontier technologies.’’ Unless high-in- exceeds actual improvements (1.2% per year over the period come countries initiate extensive programs of technology trans- 2007–2022). In fact, long-term average energy intensity improve- fer and financial assistance for industrial development, the ments have been stuck at approximately 1% since the 1990s. envisaged efficiency improvements seem implausible. For 2020–2030, the scenarios assume even more dramatic en- The difficulty of achieving the energy efficiency projections of ergy intensity improvements. Over this period, average energy in- ambitious mitigation scenarios is reflected by the modest global tensity improvements across the 33 scenarios are assumed to be energy intensity improvements estimated from existing national 4.0% per year. At the upper range of scenario assumptions, the energy plans (Figure 3A). Even the most ambitious target to ‘‘Low Energy Demand’’ scenario by Grubler et al.26 assumes im- improve energy intensity, the EU’s target of 3.0% per year, falls provements of 6.7% per year. Modelers are assuming an absolute short of the average efficiency improvements of 4.0% assumed decoupling of GDP from energy, such that energy use declines as in mitigation scenarios. GDP grows. Assumptions about rapid efficiency improvements are defended on the grounds that existing conversions of primary Betting on low-carbon energy to final energy are highly inefficient and can be feasibly improved. Existing scenarios of ambitious mitigation have accurately pro- Indeed, bottom-up studies show that existing provision of energy jected a small decline in the carbon intensity of energy, averaging services is much less efficient than what can theoretically be 0.2% per year from 2007 to 2022 (Figure 3B). The scenarios as- achieved with existing technology.25,26,43 sume that the decarbonization rate of the energy system will However, a number of studies have questioned whether such dramatically accelerate to 1.5%–4.2% per year (median 2.4%), ambitious efficiency improvements are feasible in practice, from 2020 to 2030. To hit this target, an immediate global imple- particularly at the global scale.44,45 A recent systematic review mentation of policies driving rapid decarbonization is needed. of the evidence on decoupling shows no absolute decoupling Historical growth rates of renewables—solar energy in partic- of GDP from energy at the global level,46 while a model-based ular—indicate that it is possible to achieve a rapid build-up of analysis suggests that absolute decoupling is unlikely to be renewable energy capacity, as the figures exceed even the achieved globally in the future.47 Whereas several studies find most ambitious projections documented in past IPCC reports.57 evidence of decoupling as a result of growing energy efficiency However, gains in renewable capacity in the period from 2010 to in high-income countries,48,49 these have been linked to the off- 2020 have been outstripped by increased fossil fuel use.58 In shoring of energy-intensive activities.50,51 Moreover, existing other words, renewable energy is being added on top of fossil 4 One Earth 7, January 19, 2024 Please cite this article in press as: Slamersak et al., Post-growth: A viable path to limiting global warming to 1.5 C, One Earth (2023), https://doi.org/ 10.1016/j.oneear.2023.11.004 ll Perspective OPEN ACCESS fuel energy rather than replacing it. Moreover, projections based In our ‘‘high growth and high climate ambition’’ scenario (HG- on extrapolated historical trends may overestimate the possible High), we assume that the whole world rolls out ambitious decar- build-up of low-carbon infrastructure, as the supply of material bonization and energy efficiency improvements similar to those resources required and the production of necessary compo- pledged by the European Green Deal.71 We assume a boosting nents may not match the speed at which low-carbon energy of investment in clean energies, which shows up in our calcula- needs to replace fossil fuels in existing scenarios.59–61 tions as an increased share of low-carbon energy in final energy Furthermore, studies warn that a fast low-carbon transition consumption and faster improvements in energy intensity may lead to disruptions to the economy, as construction of achieved by a gradual shift to less-energy-intensive lifestyles low-carbon infrastructure will direct investments away from and investments in energy efficiency. We also model a ‘‘high more productive sectors of the economy62 and reduce the re- growth and moderate climate ambition’’ scenario (HG- sources available for other economic activities63,64 due to the Moderate), representing a middle-of-the-road trajectory be- substantial materials and energy needed to scale up a low-car- tween current trends and the HG-High scenario. In terms of bon energy system. Supply-side constraints may be aggravated per-capita GDP, the assumptions in these scenarios remain by public opposition to big energy projects, triggered by the the same as in the HG-Current scenario: growth of more than adverse social and environmental impacts of mineral extraction 2% per year, in line with IMF predictions.30 and land grabbing.65,66 For comparison, we present three low-growth scenarios: ‘‘low Here, the problem is not only the faster decarbonization rate growth and high climate ambition’’ (LG-High), ‘‘low growth and expected from 2020 to 2030 compared to the previous decade weak decoupling’’ (LG-Weak-Decoupling), and ‘‘low growth but also the difficulty of catching up if projected decarbonization and current climate ambition’’ (LG-Current). The LG-High sce- rates do not come to pass. Missing decarbonization targets in nario incorporates the decarbonization and energy intensity one year means that the targets must be set even higher in sub- improvement aspects of the European Green Deal, but also as- sequent years. sumes economic growth to be lower (in line with what it has been from 2007 to 2022). The LG-High scenario reflects what could be achieved if the Green Deal type of policies take place in the Toward alternative mitigation scenarios context of lower economic growth.72 In the LG-Weak- Our analysis suggests that existing mitigation scenarios tend to Decoupling scenario, we assume ambitious decarbonization over-project economic growth and energy efficiency improve- equal to the LG-High scenario, while improvements in energy in- ments. Moreover, while decarbonization rates in these scenarios tensity stay in line with the historical trend. This scenario repre- are consistent with historical trends, an increase in decarboniza- sents a future where mitigation policies succeed in decarboniz- tion rates is required without delay. Large uncertainties ing the economy but energy use remains tightly coupled to regarding the mitigation levers lead us to the conclusion that ex- economic growth. The LG-Current scenario is used to estimate isting scenarios over-represent optimistic mitigation outcomes the implications of lower economic growth as the sole mitigation but do not adequately consider the possibility that one or more lever, i.e., without any changes relative to existing decarboniza- of the mitigation levers may fail to perform.14 tion and energy intensity plans. We illustrate this gap by examining a series of mitigation path- We assume the same trajectories of population growth across ways over the 2022–2030 period. We project carbon emissions all six scenarios, given the small differences in the range of pop- using projections of final energy intensity, per-capita GDP, popu- ulation projections across the scenarios from 2020 to 2030. We lation, the share of low-carbon energy in final energy consump- take our projections of population growth from the medium tion, and the use of different fossil fuels (see experimental proced- fertility scenario of the UN World Population Prospects from ures). We compare emissions in each of our six scenarios with the 2019. For a detailed description of scenario assumptions, see 33 IPCC scenarios. These include a range of 14 SSPs compatible Table 1, Figure 4, and ‘‘scenario narratives and assumptions’’ with 1.5 C (SSP-1.9) and 19 SSPs compatible with 2 C (SSP-2.6). in experimental procedures. The SSPs are obtained from the Integrated Assessment Modeling Consortium (IAMC) 1.5 C Scenario Explorer.68 RESULTS SIX FUTURES AFTER THE PANDEMIC The most ambitious low-growth scenario (LG-High) is the only one that is fully consistent with the emissions pathways that are neces- In our ‘‘high growth and current climate ambition’’ scenario (HG- sary to limit global warming to 1.5 C (Figure 5A). The LG-Weak- Current), policies to support fossil fuel technologies and infra- Decoupling scenario and the HG-High scenario only overlap with structure lead to an increase in energy use and emissions similar the upper range of the 1.5 C pathways. The upper range encom- to those that followed the 2008–2009 recession.68,69 Per-capita passes pathways that substantially rely on negative emissions in economic growth continues at a rate that exceeds 2% per year, the second half of the 21st century (see the illustrative pathways in line with IMF predictions.30 Carbon intensity improvements in in the IPCC’s Special Report on Global Warming of 1.5 C.18 this scenario are broadly compatible with existing climate plans Emissions continue to increase in the HG-Current scenario, from nationally determined contributions (NDCs), as estimated while emissions in the low-growth variant of current climate ac- by the International Renewable Energy Agency (IRENA).70 Even tion (LG-Current scenario) remain constant. High emissions in though HG-Current is the least ambitious of our six scenarios, both scenarios put their emissions beyond the less ambitious the assumed improvements in carbon intensity are more ambi- 2 C global warming pathway. It is also worth noting that in the tious than what has been achieved historically. majority of the SSPs that we use as a reference in the envelopes, One Earth 7, January 19, 2024 5 6 One Earth 7, January 19, 2024 10.1016/j.oneear.2023.11.004 Please cite this article in press as: Slamersak et al., Post-growth: A viable path to limiting global warming to 1.5 C, One Earth (2023), https://doi.org/ OPEN ACCESS ll Table 1. Six post-recovery scenarios Annual global Annual change in carbon Historical data per-capita Annual population Annual change in Annual change in intensity due to fuel switching and scenarios GDP growth growth final energy intensity carbon intensity between fossil fuels Historical trends d 2007–2022: 1.4% d 2007–2022: 1.1% d 2007–2022: 1.2% d 2007–2022: 0.2% d 2007–2022: 0.2% High growth and d 2023: 1.8% d 2023–2030: 0.9% d 2023–2030: d From 0.6% in 2023 d 2022–2030: 0.2% current climate d 2024: 2.0% (UN World Population 1.2% (continuation to 0.9% in 2030 (IRENA current strategies) ambition d 2025–2026: 2.3% Prospects) of 2007–2022 trend) (IRENA current strategies) (HG-Current) d 2027: 2.2% High growth and d 2028–2030: 2.1% From 2.1% in 2023 d From 1.2% in 2023 d 2022–2030: 0.3% moderate (IMF baseline) to 2.5% in 2030 to 2.0% in 2030 (IRENA transformative climate ambition (NDC estimate) (middle-of-the-road) energy scenario) (HG-Moderate) High growth and high d 2023–2030: 3.0% d From 2.2% in 2023 climate ambition (EU Green Deal) to 4.6% in 2030 (HG-High) (EU Green Deal) Low growth and current d 2023–2030: 0.9% d 2023–2030: 0.9% d 2023–2030: 1.2% d From 0.7% in 2023 climate ambition (continuation (UN World Population (continuation to 0.9% in 2030 (LG-Current) of 2007–2022 trend) Prospects) of 2007–2022 trend) (IRENA current strategies) Low growth and weak d 2023–2030: 1.2% d From 2.3% in 2023 d 2022–2030: 0.3% decoupling (LG-Weak- (continuation to 4.6% in 2030 (IRENA transformative Decoupling) of 2007–2022 trend) (EU Green Deal) energy scenario) Low growth and high d 2022–2030: 3.0% d From 2.3% in ambition (LG-High) (EU Green Deal) 2023 to 4.6% in 2030 (EU Green Deal) Note on the economic growth assumptions in low-growth scenarios: the annual global historical per-capita GDP growth rate from 2007 to 2022 of 1.4% per year can be broken down into an average growth rate in high-income countries of 1.0% per year (with a steady trend), and an average growth rate in lower-income countries of 3.3% per year (with a decreasing trend). For the period from 2023 to 2030, we extrapolate the recent trends in both regions which leads to a lower average per-capita global growth rate of 0.9% (this breaks down to 0.9% for high-income countries and 1.6% for lower-income countries). IMF, International Monetary Fund; UN, United Nations; NDC, nationally determined contributions; IRENA, International Renewable Energy Agency. Perspective Please cite this article in press as: Slamersak et al., Post-growth: A viable path to limiting global warming to 1.5 C, One Earth (2023), https://doi.org/ 10.1016/j.oneear.2023.11.004 ll Perspective OPEN ACCESS A B Figure 4. Recent historical trend and future projections underlying our six post-recovery scenarios and the IPCC scenarios This figure corresponds to Table 1. It shows the historical rate of change since 2007 and projected trajectories of (A) per-capita GDP, (B) population, (C) energy intensity, and (D) carbon intensity. The blue line shows the 5-year rolling average of historical values. The gray dashed line shows the average rate of change for the period from 2007 to 2022. The red envelopes show the interquartile range of the projections from the 33 IPCC scenarios, and the red line depicts the average rate of change in these scenarios. The orange, purple, and green lines show the future projections for our six scenarios. Note that the orange line in (A) represents all of the scenarios that assume high growth, while the purple line represents all of the low-growth scenarios. C D and consistent with the recent trend. All of the scenarios except for the HG- Current and LG-Current scenarios reduce the overall energy from fossil fuels (Fig- ure 5D). Per-capita GDP projections in our six post-pandemic scenarios diverge sub- stantially from the SSP scenarios, with the divergence starting in the aftermath of the 2007–2008 crisis (Figure 5E). The gap between the projections and our scenarios remains relatively constant in the high- growth scenarios, whereas in the low- the projected emissions from 2020 to 2030 are higher than they growth scenarios the gap continues to grow. The scenarios otherwise would be because the scenarios assume significant also differ, albeit less so, with respect to population growth amounts of carbon removal later in the century. The LG- (Figure 5F). Population growth in our scenarios is slightly faster Current scenario shows that lower economic growth can help than projected in the SSPs. Here too, the divergence between to halt the growth in emissions, but it alone cannot accomplish SSPs and our scenarios starts around 2010, as the SSPs have the emissions reductions without additional mitigation action. historically underestimated population growth. Emissions in the LG-Weak-Decoupling scenario are closely Our scenarios reveal the challenging path to stabilizing global comparable to the emissions in the HG-High scenario, which warming at 1.5 C–2 C if we fail to act on all mitigation levers. shows that lower economic growth can reduce the need for ab- Achieving the necessary emissions reductions without lower solute decoupling between GDP and energy use. economic growth and improvements in energy efficiency re- The HG-Moderate scenario falls short of the emissions reduc- quires much faster growth in low-carbon energy than assumed tions necessary to comply with the 1.5 C goal, although it comes in most existing scenarios, as illustrated by the LG-Weak- close to the upper range of the 2 C emissions pathways. In other Decoupling and HG-High scenarios (Figure 5C). Moreover, the words, existing pledges, unprecedented as they are and with LG-Weak-Decoupling and HG-High scenarios show that a dra- questions regarding the ability of nations to achieve them, are matic increase in low-carbon energy alone cannot achieve the not sufficient if the rate of economic growth turns out to be high. emissions reduction required to align with the 1.5 C pathway. The HG-Moderate, LG-Current, and LG-Weak-Decoupling However, a lower growth trajectory, if combined with improve- scenarios all use an increasing amount of energy, thus overlap- ments in energy efficiency, enables substantial emissions reduc- ping with the upper ranges of the 1.5 C and 2 C pathway enve- tions with less low-carbon infrastructure. Lower growth, other lopes (Figure 5B). Meanwhile, the HG-Current scenario over- mitigation levers being equal, makes the transition easier, but shoots these respective upper ranges. Scenarios with higher of course other mitigation levers may not be equal, and it is to energy efficiency improvements (the HG-High and the LG-High this issue that we now turn. scenarios) succeed in stabilizing or decreasing energy use and thus conform to the envelope of 1.5 C energy pathways. From low-growth to post-growth The HG-High, LG-Weak-Decoupling, and LG-High scenarios Our scenarios show that lower rates of economic growth, in line roll out low-carbon energy much faster than the upper range of with recent trends, make climate mitigation easier in important 1.5 C transition pathways (Figure 5C). The growth of low-carbon respects. Lower growth would make it more feasible to achieve energy in the LG-Current and HG-Current scenarios is slower the necessary emissions reductions with more reasonable One Earth 7, January 19, 2024 7 Please cite this article in press as: Slamersak et al., Post-growth: A viable path to limiting global warming to 1.5 C, One Earth (2023), https://doi.org/ 10.1016/j.oneear.2023.11.004 ll OPEN ACCESS Perspective A B Figure 5. Six post-pandemic scenarios compared with a range of IPCC 1.5 C and 2 C pathways The graphs show projections of (A) emissions from fossil fuels, (B) final energy, (C) low-carbon energy, (D) energy from fossil fuels, (E) per-capita GDP, and (F) population for our high-growth and low-growth scenarios. The envelopes show the interquartile range of the SSP scenarios that are consistent with 1.5 C (light green) and 2 C (light blue) of global warming by 2100. In (E), the orange line shows the GDP trajectories for all of the high-growth sce- narios, whereas the purple line shows GDP in both of the low-growth scenarios. (F) shows the popula- tion trajectory based on the median scenario of the UN World Population Prospects that we use in all of C D our scenarios. growth.76,77 Moreover, existing studies generally assume that growth in low-car- bon technology sectors depends on the growth rates in the economy at large.78 However, innovation and mitigation measures primarily depend on where in- vestment is directed, not growth. Aggre- gate growth may not entail growth in low- carbon sectors if investments are directed E F elsewhere (for instance, if higher-carbon sectors are more profitable). On the other hand, a push for a ‘‘green stimulus,’’ including through public finance or derisk- ing strategies, may enable low-carbon sectors to grow faster than the rest of the economy.79 Second, low growth might entail unde- sirable social outcomes, such as unem- ployment and inequality. Under existing conditions, growth can counteract techno- logical unemployment. It can also help to improve the material conditions of the poorest and maintain investment in public services without needing to challenge the distribution of income and access to re- sources, which can be politically difficult. Conversely, lower growth means lower tax revenue and lower overall investments, which may create trade-offs between in- vestment for a low-carbon energy transi- tion and socially needed investments.80 rates of low-carbon energy deployment and less ambitious, but Finally, lower growth may make it more challenging to replace still considerable, energy efficiency improvements compared lost jobs and to hedge against stranded assets from fossil fuel to those assumed in existing mitigation scenarios. However, companies. the prospect of lower growth raises additional concerns that Moreover, if the return on capital remains constant around its need to be addressed. historic 5% per year, lower growth rates mean that more and First, a low-growth scenario might make it more difficult to more of the income produced ends up in the hands of the wealth- achieve necessary innovations in technology and efficiency. Ex- iest, thus increasing inequality.19 Under such conditions, lower isting scenarios assume that growth is associated with techno- growth could lead to increased unemployment, lower living stan- logical development and efficiency improvements.73–75 These dards for the working classes, increasing inequality, and distri- scenarios assume that growth fosters the development of butional conflict. Such a scenario could make it more difficult advanced technologies that can offset emissions from fossil to achieve political consensus for ambitious climate mitigation. fuels and decouple energy and resource use from economic Lower growth in lower-income countries also risks perpetuating 8 One Earth 7, January 19, 2024 Please cite this article in press as: Slamersak et al., Post-growth: A viable path to limiting global warming to 1.5 C, One Earth (2023), https://doi.org/ 10.1016/j.oneear.2023.11.004 ll Perspective OPEN ACCESS global inequalities and could make it more difficult to achieve scenarios, progress would be measured in terms of specific social development goals. and environmental objectives rather than in terms of GDP. Core However, such outcomes could also be prevented through policies might include the following. policy choices. For instance, legislation to facilitate a reduction in working time or introduce job guarantees could prevent unem- (1) Reducing inequality. Progressive taxation of income and ployment in a low-growth scenario, while enabling lower-income wealth can help reduce the unnecessary excess consump- countries to use fiscal and industrial policy could improve devel- tion of the rich, exemplified by the fact that the wealthiest opment outcomes. Wealth and income taxes, or public owner- 1% of the world’s population currently capture 20% of ship of productive assets, can redistribute resources to the global income83 and are responsible for 23% of current working class, while public investment and industrial policy greenhouse gas emissions.84 Moreover, reducing can ensure that the energy transition and innovation are sus- inequality would ensure a fairer distribution of the national tained even in the absence of growth.81 product and give citizens more control over production. In this respect we find it useful to distinguish between ‘‘low- (2) Ensuring decent living standards for all. This objective may growth’’ scenarios and ‘‘post-growth’’ scenarios. We see low- be pursued through a program of universal public ser- growth scenarios as a continuation of the involuntary stagnation vices,85 a right to affordable housing,86 living wage pol- period from 2007 to 2022, with rising inequalities and without any icies,23 a green job guarantee,72 and working-time reduc- additional policy intervention. Post-growth, however, refers to the tion87 to eliminate unemployment and mobilize labor for process whereby governments would move beyond the pursuit of socially and ecologically necessary production. Revenues increasing GDP to focus directly on social and ecological goals from increased taxes on wealth could be used to finance and actively prepare to manage lower rates of growth by introducing expanded social investments in these policies. policies designed to counteract potential negative outcomes.14 (3) Increasing public investment for the energy transition. We want to emphasize that the low-growth scenarios we Monetary and fiscal policy could be used to directly in- represent here are unjust. By not differentiating responsibilities crease investment in renewable energy deployment, en- for mitigation between regions, and by extrapolating existing ergy efficiency improvements, public transportation, trends of economic growth (which may be inadequate for devel- building insulation, and installation of efficient appliances. opment in many lower-income countries), they effectively allo- Investments in response to the COVID-19 pandemic and cate an unjust mitigation burden to the lower-income countries the invasion of Ukraine exemplify how governments can while constraining their rights to develop. This falls foul of the eq- steer the economic system toward the production of uity principles established in the Paris Agreement. An equitable essential goods and services (vaccines and alternative allocation of mitigation burdens would enable lower-income energy supply) to confront these crises. There is no countries to achieve higher economic growth, while high-income reason why the looming climate crisis could not be con- countries would need to achieve much faster emissions reduc- fronted with the same—if not greater—urgency. tion to limit warming to 1.5 C–2 C. In such a scenario, high-in- (4) Reducing less-necessary forms of production and con- come countries would need to pursue post-growth strategies sumption. This objective may include phasing-out fossil to reduce energy and material use.128 fuels,88 regulations limiting SUVs,89 frequent flier levies Scholarship in ecological economics indicates that with the for aviation,90 and measures to curb industrial meat pro- appropriate policy mix, economies can achieve successful post- duction91 and fast fashion,92 among others. These mea- growth scenarios, maintaining economic stability and even sures would directly reduce the most inefficient uses of improving social outcomes.23,24 Here we explore possible post- materials and energy and enable faster decarbonization. growth policy interventions that could address issues related to (5) Aiming for convergence in material and energy use be- climate mitigation and social outcomes under low growth and tween the global North and South to safe and sufficient point out the main barriers to realizing these interventions. In doing levels.93 High-income countries must recognize their his- so, we identify the constitutive elements of post-growth scenarios torical responsibility for climate change. Countries of the and differentiate them from low-growth scenarios. global North have emitted more than 50% of cumulative emissions since the pre-industrial period,94 meaning Outline of post-growth scenarios they have already exhausted their fair share of the carbon We propose that post-growth climate mitigation scenarios should budget consistent with the Paris Agreement.95 To ensure simulate the effects of core post-growth policies. The overall a just distribution of mitigation burdens, these countries objective of such policies is to prioritize production of what is must pursue a faster decarbonization of their economies important for human well-being and environmental sustainability and provide lower-income countries with the necessary while reducing less-necessary forms of production and consump- means for mitigation. Doing so will require programs of tion. Recent estimates of the energy requirements for a decent life technology transfer and additional financial transfers suggest that basic needs could be universally provided at approx- from North to South.96,97 imately half of the current global energy generation.21,82 Yet, even at present-day high energy use, billions of people remain without access to basic energy services,21 demonstrating the degree of Barriers to a post-growth transition wasteful inefficiency in the current economic system. In line with It is worth acknowledging that while many of the above policies this, post-growth scenarios would emphasize feasible efficiency are popular according to surveys and citizens’ assemblies,98,99 improvements but also embrace sufficiency and equity. In such transition to a post-growth economy is likely to face resistance One Earth 7, January 19, 2024 9 Please cite this article in press as: Slamersak et al., Post-growth: A viable path to limiting global warming to 1.5 C, One Earth (2023), https://doi.org/ 10.1016/j.oneear.2023.11.004 ll OPEN ACCESS Perspective from specific social classes, companies, and institutions that growth rates in a post-growth scenario could be a direct result benefit from the current configuration of the economy.100 of the downscaling of the carbon-intensive ‘‘brown sectors’’ of First, in terms of cultural values, post-growth goes against the the economy, while the ‘‘green economic sectors’’ driving the common notion that growth is needed for social progress and for low-carbon transition could still grow substantially. Major solving societal problems.101 In line with such ‘‘growthist’’ narra- emissions reductions could be achieved independently of tives, the measures that call for a decrease in economic economic growth via a societal shift toward sustainable life- throughput are often framed as bringing societies back to times styles, more equitable energy use, and reduced consump- of scarcity. Outrage against the appeal of the Spanish minister of tion.105,106 These mitigation actions do not require high consumption to reduce meat consumption in the country dem- economic growth and are therefore compatible with a post- onstrates the difficulty that post-growth ideas may have in re- growth narrative. shaping the common sense of desirable social transfor- Second, post-growth scenarios should construct overarching mations.102 narratives that allow lower-income countries to capture a fairer Second, in terms of economic reform, post-growth scenarios share of global economic production in order to achieve human assume substantial wealth and income redistribution, which development goals, while high-income economies develop would benefit lower-income groups and reduce the consumption frameworks for ensuring strong social outcomes without growth. and power of the wealthiest. To achieve a global convergence in Future research should craft post-growth scenarios and wealth, high-income countries would have to substantially in- model their effects on the economy and emissions using existing crease their financial transfers to lower-income countries.96 or new integrated assessment models (IAMs). Working-time Post-growth policies would likely require an increase in govern- reduction, for example, has the potential to reduce carbon emis- ment spending, which could lead to higher public deficits, con- sions while increasing employment at a given level of trary to existing fiscal rules.103 Realization of these policies would output.107,108 Given that existing IAMs rely extensively on spec- require an increased role of the state in the economy.104 ulative negative emissions technologies and contentiously high It should also be acknowledged that the present political outlook levels of decoupling between GDP and energy use, there is no is not conducive to such policies, as even the most progressive reason why they should not also include visionary social and governments are not contemplating dropping the pursuit of eco- economic trajectories to explore the full range of possible mitiga- nomic growth from their agendas, and redistributive policies within tion pathways.109 and between nations face substantial obstacles. Post-growth pol- itics may be further complicated by the rise of far-right populism EXPERIMENTAL PROCEDURES and climate denialism in high-income countries. Resource availability The political and cultural changes required for post-growth are Lead contact historically unprecedented and challenging to realize at the pace Requests for further information should be directed to the lead contact, Aljosa necessary for staying within 1.5 C–2 C. Post-growth may be as Slamersak (aljosa.slamersak@autonoma.cat). Materials availability difficult to achieve politically as negative emissions or high en- This work did not produce any novel materials. ergy–GDP decoupling are to develop technically. Data and code availability d The workbooks containing the historical data and our six scenarios are Conclusion available in an online data repository, accessible at https://osf.io/efv89/ Regardless of what one thinks about the desirability of lower ?view_only = 283f2994a68d4d87b7133ac419e230c6. growth, it appears to be a likely future. Our analysis has illustrated d Energy and emissions data for the SSP energy transition pathways were the difference that lower growth makes when it comes to achieving obtained from the IAMC Scenario Explorer repository: https://data.ene. iiasa.ac.at/iamc-1.5c-explorer/. climate mitigation consistent with 1.5 C–2 C. Lower-growth sce- d Historical emissions were obtained from the Global Carbon Budget Proj- narios make it more feasible to achieve necessary emissions ect repository of ‘‘fossil fuel emissions and industry’’ data, accessible at reductions with a slower build-up of low-carbon energy and less https://globalcarbonbudgetdata.org/latest-data.html. d Historical data for final energy, gross/primary energy, and the share of energy–GDP decoupling. By contrast, pursuing higher growth low-carbon energy in final energy consumption were taken from the on- rates - such as those represented in IMF projections - jeapordizes line International Energy Agency (IEA) Data and Statistics database, the Paris Agreement . Still, even in our lower-growth scenarios, the accessible at https://www.iea.org/data-and-statistics. mitigation pathways compatible with 1.5 C require an extremely d Historical data for per-capita GDP at constant 2015 US$ prices were taken from the online World Bank database, available at https://data. ambitious acceleration of decarbonization and energy efficiency worldbank.org/indicator/NY.GDP.PCAP.KD. improvements, equivalent to the whole world immediately adopt- d The high-growth projections for per-capita GDP were taken from the on- ing and achieving the targets established in the EU Green Deal. If line IMF Datamapper tool, available at https://www.imf.org/external/ datamapper. such rapid mitigation cannot be realised, then achieving the Paris Agreement objectives would likely require a further deceleration of economic growth. To ensure a just distribution of mitigation bur- Decomposition of emissions drivers dens, and to ensure the ability of lower-income countries to To estimate carbon emissions in our six post-pandemic scenarios, we adapt a simple decomposition formula, known as the Kaya identity,110 which is widely develop, high-income nations would need to pursue post-growth used to study the drivers of emissions from the energy sector.111,112 We derive demand reduction strategies. the extended decomposition, starting from a formula that relates emissions to We identify two major tasks for a post-growth scenario the product of the primary energy intensity of the economy (EIPE), carbon inten- research agenda. First, advanced modeling studies should sity of primary energy (CIPE), population (P), and economic activity per capita (GDPpc ) (Equations 1, 2, and 3): explore the conditions and limits of ambitious mitigation in the context of lower economic growth. In theory, declining CO2 = EIPE 3 CIPE 3 P 3 GDPpc ; (Equation 1) 10 One Earth 7, January 19, 2024 Please cite this article in press as: Slamersak et al., Post-growth: A viable path to limiting global warming to 1.5 C, One Earth (2023), https://doi.org/ 10.1016/j.oneear.2023.11.004 ll Perspective OPEN ACCESS changes in energy–emissions factors (presented in Table 1 and Figure 4). Values of energy–emissions factors in a particular year are calculated by multi- PEtot plying their values in the preceding year by their respective annual changes, as EIPE = ; (Equation 2) P 3 GDPpc shown in Equation 11: CO2 yt+1 = yt 3 ð1 + Dy% Þ: (Equation 11) CIPE = : (Equation 3) PEtot To calculate the annual growth rates of factors from our scenarios and the SSPs that are portrayed in Figure 5, we use the compound annual growth for- We further expand the equation by disaggregating primary energy intensity mula, shown in Equation 12: into final energy intensity and the ratio of final energy to primary energy (Equa- tions 4, 5, and 6), following the approach described by Koomey et al.113 This  Dt1 yt+Dt expansion allows us to distinguish between the efficiency improvements in Dy% =  1: (Equation 12) the economy that lead to higher economic output at lower energy use (Equa- yt tion 5) and the improvements in energy conversion efficiency from primary en- ergy to final energy (Equation 6), accomplished by the reduction in energy los- ses along the energy supply chain from the point of extraction to the point where energy enters the economy.114 Scenario narratives and assumptions High-growth scenarios FEtot PEtot In the HG-Current scenario, we assume that the rate of final energy intensity CO2 = 3 3 CIPE 3 P 3 GDPpc ; (Equation 4) P 3 GDPpc FEtot changes in line with the average of 1.2% per year for the period 2007 to 2022.116 FEtot Continuation of the long-term historical trend in the annual changes to the EIFE = ; (Equation 5) final energy intensity of 1.2% by 2030 is used in reference to the argument P 3 GDPpc that absolute decoupling between economic growth and energy is difficult to achieve globally.5,44 FEtot hsys = : (Equation 6) For GDP, we follow the current IMF baseline projections, with 2.8% global PEtot growth in 2023, 3.0% growth in 2024, 3.2% growth in 2025–2026, and 3.1% in 2027, followed by 3.0% growth per year until 2030.30 For our population as- sumptions, we follow the median scenario of the UN World Population Pros- Final energy intensity can be decreased either via end-use efficiency improve- pects.117 We decided to only use the median fertility scenario after conducting ments in the conversion of energy to goods and services or through structural a preliminary sensitivity analysis, which showed that the low-fertility and high- changes in the economy (i.e., by undertaking a transition from a high-intensity fertility variants of the UN projections make very little difference to the final en- industrialized economy to a lower-intensity service economy). The final-to-pri- ergy and emissions trajectories by 2030. mary energy ratio changes when one energy carrier replaces another (e.g., To estimate final energy, we combine the assumed changes in final energy electricity replaces gasoline) and by improving energy conversion efficiencies intensity and GDP growth. This results in an average final energy growth of from primary to final energy. The ratio will increase if power generation from 1.9% per year from 2022 to 2030. We assume that low-carbon final energy fossil fuels is replaced by more efficient energy sources, typically renewables, grows at a rate of 4.0% p.a., increasing the share of low-carbon energy by or if obsolete power generation facilities are replaced by modern facilities with 6.5%, from 17.4% in 2018 to 23.9% in 2030, as assumed in the assessment higher energy conversion efficiency. of current energy policies by IRENA. We arrive at the final decomposition formula by decomposing the carbon in- To calculate the annual change in the carbon intensity of fossil fuels, we use tensity of primary energy into the factors of low-carbon energy share (Equation the annual growth rate equation (Equation 12), assuming the share of coal and 7) and the total carbon intensity of fossil fuels (Equation 8), following the oil in total final energy from fossil fuels decreases by 0.3% per year from 2022 approach of Peters et al.115 Here, we define the low-carbon energy share as to 2030 while the share of gas increases by 0.6% per year Our assumptions on the share of low-carbon energy in final energy consumption, which includes fuel switching correspond to the dynamics of the primary energy shares of energy from renewables, biomass, and nuclear power. We obtain the different fossil fuels, from 2018 to 2030, according to the assessment of exist- expanded equation for carbon intensity (Equation 9) by first expressing total ing energy policies by IRENA. primary energy as total final energy divided by the final-to-primary energy con- We see the HG-Current scenario happening if countries invest in existing version ratio (Equation 6); and, in the next step, by describing total final energy fossil fuel infrastructure and polluting industries and reject energy and carbon as a function of low-carbon energy share (LCshare) (Equation 7). taxation. This scenario could occur if countries maintained a supply of energy FEFF FEFF from fossil fuels and removed incentives for structural changes in energy con- ð1  LCshare Þ = = ; (Equation 7) sumption and improvements in energy efficiency. The latest emissions–energy FEtot FELC +FEFF data from the IEA118 link current policies with continued growth in energy use and emissions by 2025, suggesting a possible return to a business-as-usual CO2 CIFF = ; (Equation 8) carbon-intensive economy. FEFF We design two high-growth scenarios that both include a major boost in in- vestment in low-carbon energy and substantial improvements in energy effi- CO2 FEtot CO2 FEtot CO2 ciency. We design the HG-High scenario to represent the high end of foresee- CIPE = = = ð1 LCshare Þ 3 : (Equation 9) PEtot PEtot FEtot PEtot FEFF able mitigation efforts over the next decade, assuming global implementation of the decarbonization and energy efficiency targets from the European Green Deal.119 In the HG-Moderate scenario, we assume that global policy goes Finally, we obtain an expression that allows us to distinguish the effects of halfway toward meeting the decarbonization and efficiency targets of the Eu- changes in energy efficiency from both the mitigation efforts to decarbonize ropean Green Deal. the energy system (which depend on the share of low-carbon energy alongside In the HG-High scenario, final energy intensity decreases by 3.0% per year changes in the carbon intensity of final energy from fossil fuels) and the effects by 2030 (compared to 1.2% per year before the pandemic). We estimate this of economic growth (Equation 10). This formula is used alongside the underlying rate of efficiency improvement by referring to the policy goal of the EU’s energy scenario assumptions from Table 1 to estimate the emissions in our six scenarios. efficiency directive,120 which aims to reduce final energy consumption from 2018 to 2030 by 17%,121 alongside the projected economic growth in the FEtot CO2 CO2 = 3 ð1 LCshare Þ 3 3 P 3 GDPpc : (Equation 10) EU of +1.8% per year over the same period.122 P 3 GDPpc FEFF Final energy intensity in the HG-Moderate scenario decreases by 2.5% per year each year from 2022 to 2030, which corresponds to the improvements that would be needed if Goal 7 of the UN Sustainable Development Goals were to be met.123 The improved energy efficiency in our scenarios can be Calculating energy and emissions thought of as the result of intentional policies to increase the price of fossil fuels To calculate energy and emissions pathways for each of the six mitigation sce- (e.g., energy and carbon taxes in the highest-emitting countries) and an orga- narios shown in Figure 5, we use the scenario assumptions for the annual nized shift toward fewer carbon-intensive activities (e.g., by making bailouts One Earth 7, January 19, 2024 11 Please cite this article in press as: Slamersak et al., Post-growth: A viable path to limiting global warming to 1.5 C, One Earth (2023), https://doi.org/ 10.1016/j.oneear.2023.11.004 ll OPEN ACCESS Perspective and government loans conditional on compliance with climate targets and jections of population growth. After 2023, we assume that per-capita GDP accelerating the retirement of older, inefficient energy infrastructure).124 En- growth continues in line with the trend from 2007 to 2022, which results in a ergy efficiency also improves when there is a higher share of renewable en- constant per-capita growth rate for high-income economies of 1.0% and a ergy, as this reduces the energy conversion losses from primary to final gradually decelerating growth rate from the value of 2.0% in 2023 for energy.26 lower-income countries (decelerating approximately by 0.1% each year). The decarbonization in the HG-High scenario increases the share of low- For high-income countries, the LG-High scenario roughly represents a sce- carbon energy by 18.5% from 2022 to 2030. We calculate that this could be nario that has been referred to in the literature as a ‘‘Green New Deal accomplished by an average growth rate of low-carbon energy of 8.0% without growth.’’72 each year. We calculate the resulting rates of carbon intensity improvements According to the IEA, high-income countries consumed 37% of final en- starting from 0.6% per year in 2022, improving to 4.6% in 2030. In the ergy in 2018 and lower-income countries consumed the remaining 63%. HG-Moderate scenario, we increase the share of low-carbon energy by For the sake of simplicity, we assume the same final energy intensity im- 9.3% from 2022 to 2030. As a result, carbon intensity falls from 0.6% per provements for both regions. A sensitivity analysis, in which we assume year in 2022 to 2.0% in 2030. Although less ambitious than the HG-High sce- higher energy intensity improvements (1%) in high-income countries, al- nario, the decarbonization in the HG-Moderate scenario is still two times faster lows energy use in lower-income countries to increase by 0.3% yet implies than the trend in the HG-Current scenario. a 1% faster reduction of energy use in high-income countries. This suggests To estimate the effects of fuel switching between different fossil fuels, we that the degree of energy intensity improvements in high-income countries follow IRENA’s Transforming Energy Scenario, an energy transition scenario only weakly affects the required energy intensity improvements in lower-in- that emphasizes fast mitigation through renewable energy. We apply the same come countries if we assume the same average global energy intensity im- fuel-switching assumptions in both the HG-Moderate and HG-High scenarios. provements. We estimate that fuel switching can decrease the carbon intensity of fossil fuels by 0.3% per year Thus, fuel switching has a much lower potential to decar- bonize the economy in comparison to the share of low-carbon energy. This is ACKNOWLEDGMENTS because: (1) switching between fossil fuels decreases emissions but does not eliminate them completely, unlike when fossil fuels are replaced by low-carbon We acknowledge financial support by a scholarship from ‘‘la Caixa’’ Founda- alternatives; and (2) carbon intensity improvements through fuel switching are tion (ID 100010434, LCF/BQ/IN17/11620039). We also acknowledge support constrained by the inflexibility of the fossil fuel infrastructure and the inability by the European Research Council (ERC-2022-SYG REAL, reference number of end-use appliances to change between different fuels (e.g., natural gas is 101071647). Finally, this work was supported by the ‘‘Marı́a de Maeztu’’ Unit of not a good substitute for petroleum in the transportation sector, especially Excellence (MDM-2015-0552) grant from the Spanish Ministry of Economy when considering the existing fleet of petroleum-powered vehicles). and Business (MINECO). The HG-Moderate and HG-High scenarios would be most likely to occur if countries adjusted their economic policies to comply with climate objectives, which would accelerate the retirement of older, less efficient energy infrastruc- AUTHOR CONTRIBUTIONS ture.125 Introducing carbon taxation would suppress growth in energy demand and carbon emissions. Faster deployment of renewable energy together with All authors contributed to designing the project and writing up the results. additional investment in energy efficiency would speed up decarbonization of A.S. led the project, developed the method, collected and analyzed the the energy system. data, and produced the results, under the supervision of G.K., D.W.O., Low-growth scenarios and J.H. In the LG-High scenario, countries boost green investments and low-carbon energy increases by the same share as in the HG-High scenario. We also as- sume the same decline in final energy intensity as in the HG-High scenario. In DECLARATION OF INTERESTS addition to a shift to a more efficient energy system with a higher share of low- carbon energy, we assume the global GDP growth rate continues to decline in The authors declare no competing interests. line with the trend from 2007 to 2022. Assuming the same energy intensity im- provements as in the HG-High scenario, this leads to a decline in the growth of final energy by 0.9% per year. We assume the same fuel switching from coal REFERENCES and oil to gas as in the HG-High scenarios. 1. (2020). Unexpected times. Nat. Clim. Change 10, 479. The LG-Current scenario assumes the energy intensity improvements in line with the 2007–2022 average of 1.2% per year. This scenario assumes the 2. IEA (2021). World Energy Outlook 2021. same mitigation ambitions as the HG-Current scenario, describing a future 3. 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