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Abstract The mitigation scenarios database of the Intergovernmental Panel on Climate Change’s Sixth Assessment Report is an important resource for informing policymaking on energy transitions. However, there is a large variety of models, scenario designs, and resulting outputs. Here we analyse the scenarios consistent with limiting warming to 2 °C or below regarding the speed, trajectory, and feasibility of different fossil fuel reduction pathways. In scenarios limiting warming to 1.5 °C with no or limited overshoot, global coal, oil, and natural gas supply (intended for all uses) decline on average by 95%, 62%, and 42%, respectively, from 2020 to 2050, but the long-term role of gas is highly variable. Higher-gas pathways are enabled by higher carbon capture and storage (CCS) and carbon dioxide removal (CDR), but are likely associated with inadequate model representation of regional CO 2 storage capacity and technology adoption, diffusion, and path-dependencies. If CDR is constrained by limits derived from expert consensus, the respective modelled coal, oil, and gas reductions become 99%, 70%, and 84%. Our findings suggest the need to adopt unambiguous near- and long-term reduction benchmarks in coal, oil, and gas production and use alongside other climate mitigation targets.

Long-term mitigation scenarios developed by integrated assessment models underpin major aspects of recent IPCC reports and have been critical to identify the system transformations that are required to meet stringent climate goals. However, they have been criticized for proposing pathways that may prove challenging to implement in the real world and for failing to capture the social and institutional challenges of the transition. There is a growing interest to assess the feasibility of these scenarios, but past research has mostly focused on theoretical considerations. This paper proposes a novel and versatile multidimensional framework that allows evaluating and comparing decarbonization pathways by systematically quantifying feasibility concerns across geophysical, technological, economic, socio-cultural and institutional dimensions. This framework enables to assess the timing, disruptiveness and scale of feasibility concerns, and to identify trade-offs across different feasibility dimensions. As a first implementation of the proposed framework, we map the feasibility concerns of the IPCC 1.5 °C Special Report scenarios. We select 24 quantitative indicators and propose feasibility thresholds based on insights from an extensive analysis of the literature and empirical data. Our framework is, however, flexible and allows evaluations based on different thresholds or aggregation rules. Our analyses show that institutional constraints, which are often not accounted for in scenarios, are key drivers of feasibility concerns. Moreover, we identify a clear intertemporal trade-off, with early mitigation being more disruptive but preventing higher and persistent feasibility concerns produced by postponed mitigation action later in the century.

The implementation of ambitious climate policies consistent with the goals of the Paris Agreement is fundamentally influenced by political dynamics. Yet, thus far, climate mitigation pathways developed by integrated assessment models (IAMs) have devoted limited attention to the political drivers of climate policymaking. Bringing together insights from the political science and socio-technical transitions literature, we summarize evidence on how emissions lock-in, capacity, and public opinion can shape climate policy ambition. We employ a set of indicators to describe how these three factors vary across countries and regions, highlighting context-specific challenges and enablers of climate policy ambition. We outline existing studies that incorporate political factors in IAMs and propose a framework to employ empirical data to build climate mitigation scenarios that incorporate political dynamics. Our findings show that there is substantial heterogeneity in key political drivers of climate policy ambition within IAM regions, calling for a more disaggregated regional grouping within models. Importantly, we highlight that the political challenges and enablers of climate policy ambition considerably vary across regions, suggesting that future modeling efforts incorporating political dynamics can significantly increase the realism of IAM scenarios.

Transitioning away from fossil fuels presents substantial challenges, given the growing mismatch between pledges submitted to international climate negotiations and the mitigation strategies that limit warming to below 1.5 °C or 2 °C presented in the Intergovernmental Panel on Climate Change Sixth Assessment Report. The scientific case for phasing out coal-fired electricity is clear, and many countries are progressing towards this. However, despite widespread concerns about risks and trade-offs, natural gas is often considered a bridge fuel, and there is currently no progress towards phasing down its capacity. Previous work on the political feasibility of coal phase-out only considered limited socio-political factors, missing the importance of governance quality and policies supporting the energy transition. There is even more limited understanding of factors associated with gas phase-down, while Europe and North America fall behind trajectories required to limit warming below 1.5 °C. We use multivariate regression and clustering analyses on over four decades of data to investigate the drivers and synergies of coal and gas transitions. This reveals opportunities to overcome fossil fuel lock-in through renewable energy expansion, energy policy reforms, and power market restructuring. Countries with greater reliance on fossil fuel infrastructure and workforce face additional difficulties in phase out. Social factors such as higher belief in climate change are positively linked with more ambitious coal phase-out efforts. However, disentangling these links for gas remains difficult given the limited historical evidence of phase-down progress. We identify four archetypes (Coal Reliance, Gas Reliance, Limited Policy, and Transition Underway) that illustrate different ways countries have transitioned from coal and gas over time. These provide blueprints for potential future transitions in other countries. Recognizing the diverse social, political, and institutional factors that shape transitions can inform the design of politically relevant future scenarios.

Questions around the technical and political feasibility of deep mitigation scenarios assessed by the Intergovernmental Panel on Climate Change have increasingly been raised as have calls for more directly analyzing and incorporating aspects of justice and fairness. Simultaneously, models are increasing the technical representation of novel carbon-dioxide removal (CDR) approaches to provide policy-relevant analyses of mitigation portfolios in the context of the rising number of net-zero CO 2 and GHG targets made by parties to the Paris Agreement. Still, in most cost-effective mitigation scenarios developed by integrated assessment models, a significant portion of mitigation is assumed to take place in developing regions. We address these intersecting questions through analyzing scenarios that include direct air capture of CO 2 with storage (DACCS), a novel CDR technology that is not dependent on land potential and can be deployed widely, as well as regional variations in institutional capacity for mitigation based on country-level governance indicators. We find that including novel CDR and representations of institutional capacity can enhance both the feasibility and fairness of 2 °C and 1.5 °C high-overshoot scenarios, especially in the near term, with institutional capacity playing a stronger role than the presence of additional carbon removal methods. However, our results indicate that new CDR methods being studied by models are not likely to change regional mitigation outcomes of scenarios which achieve the 1.5 °C goal of the Paris Agreement. Thus, while engineered carbon removals like DACCS may play a significant role by midcentury, gross emissions reductions in mitigation pathways arriving at net-zero CO 2 emissions in line with 1.5 °C do not substantially change. Our results highlight that further investment and development of novel CDR is critical for post-net-zero CO 2 mitigation, but that equitable achievement of this milestone will need to arrive through technical and financial transfers, rather than by substantial carbon removals in developed countries before mid-century.

Climate action is shaped as much by politics as by technology and economics. The Shared Socioeconomic Pathways (SSPs), central to mitigation and adaptation assessments, do not yet include a quantitative representation of political development. We outline a research agenda to systematically integrate political dimensions into climate scenario modelling.

A large-scale transformation of the energy system, which climate mitigation entails, is a global and highly politicized problem. This thematic issue brings together scholars who work with Integrated Assessment Models (IAMs)—which are used for Intergovernmental Panel on Climate Change (IPCC) reports and other key analyses of future climate trajectories—and social scientists working on climate and energy issues to highlight how the two strands of research could benefit from combining insights across different disciplines and methods. One of the key messages across almost all contributions is that the more technical perspectives could benefit from adjusting their assumptions to reflect the patterns observed in quantitative and qualitative social science. Combining different disciplines is methodologically challenging but promising to ensure that the mitigation strategies developed are considered technically and politically feasible, as well as just.

There is growing criticism aimed towards global integrated assessment models (IAMs) and an ongoing academic debate on how justice considerations can be incorporated in those models. By relying on 39 interviews with a multidisciplinary group of experts, we map three shapes of change containing multiple avenues for incorporating justice considerations into IAM tools and scenarios: to improve representation within IAMs (Shape 1), to couple to new models and expand points of access to disciplines and users (Shape 2), and to refine the role of IAMs within a wider array of practices (Shape 3). These shapes reflect multi-disciplinary agreements and divergences over the capacity of IAMs to incorporate justice considerations—regarding kinds of representation, greater involvement of new disciplines and users, and the objective of mitigation scenarios in climate policy. Our analysis is among the first to describe and integrate a variety of opinions from different communities, fostering a more holistic understanding of the opportunities and challenges of incorporating justice into IAMs.

Some experts contend that addressing global climate challenges requires consideration of technologies such as Carbon Dioxide Removal (CDR) and, possibly, Solar Radiation Modification (SRM). Previous studies, primarily centered on the OECD region, have indicated that most of these technologies are contentious, eliciting low levels of public support. By conducting a set of nationally representative surveys examining seven CDR and three SRM technologies in 30 countries, we show that public skepticism is most prominent in wealthier countries. Respondents from these countries express lower confidence in the potential of science and technology to address climate change, diminished trust in industry, and expect to experience less personal harm from climate change. At the same time, there are many countries, not previously studied, where the levels of support for CDR and SRM are relatively high. As middle-income countries, their capability to effectively implement these technologies may be deficient; additionally, there is a risk of the unilateral implementation of certain technologies with uncertain implications in terms of their impacts on climate. This underscores the necessity for long term climate strategies that are context-specific and tailored to individual countries, while moreover emphasizing the imperative for extensive international collaboration, including through technological and financial transfers. Finally, strong international governance structures, especially in the context of SRM, are crucial to ensure a responsible approach towards these technologies.

Many households worldwide face substantial gaps in decent living standards (DLS), universal and essential material preconditions for achieving well-being and inclusive development. Here, we use subnational Demographic and Health Survey data from 75 low and middle-income countries (1990–2021) to explore the distribution and trends of ten living standards. We estimate that 94.9% of households in our dataset lack the material prerequisites for at least one of the ten standards, and 63.6% for one-third of them. Stark inequalities persist both within and between countries, with regions in sub-Saharan Africa experiencing the most severe deprivations. Despite some improvements, progress remains limited in critical areas such as health care, sanitation, housing, and education. Within countries, rural, agrarian households with low levels of educational attainment are particularly disadvantaged. These granular findings at the subnational level can help direct policy efforts and resources towards those populations most in need. Using subnational Demographic and Health Survey data from 75 low and middle-income countries, the authors show that many households lack access to decent living standards as basic prerequisites for human well-being. Major inequalities exist within and across countries and by socio-economic backgrounds.