Debates about the future of wind and solar power are often framed around a false binary: either these technologies will continue accelerating or they are already losing momentum. Both views assume that renewables follow an S-curve with near-exponential expansion followed by slowdown. Using national deployment data, we show that renewables’ growth departs from ideal S-curves. Instead, it proceeds through a formative phase of erratic growth, followed by takeoff and brief acceleration that ends at low levels of market penetration (≈3% of electricity generation). Renewables then enter a prolonged steady growth phase punctuated by pulses of acceleration and deceleration, with an overall cruising speed that is slower than the first growth peak (≈0.7 percentage points [p.p.] year−1; interquartile range [IQR]: 0.4–1.5 for wind and 0.3–1.9 for solar). We develop diagnostic tools and metrics for these phases. Hindcasting shows that these outperform year-on-year trends and fitted S-curve parameters. Peak growth in front-runner countries provides a reliable upper bound for global expansion.

Abstract Non-Technical Summary European climate plans call for a doubling of onshore wind capacity by 2030, yet over the last 15 years growth has largely stagnated – contradicting technology diffusion theories that predict smooth acceleration until a substantial share of the market is reached. We show that early slowdowns in large countries were associated with the withdrawal or weakening of policy support, while reinstating support and higher electricity prices drove reaccelerations. Despite these pulses, the average deployment pace remained steady and below the first peak rate. Current targets aim for historical peak speeds, but forecasts revert to long-run rates, suggesting persistent limits that only sustained policy effort can overcome. Technical Summary Mainstream theories predict S-shaped technology growth with a single peak followed by slowdown, but recent literature has observed low-carbon technologies often departing from this pattern. We systematically show that over four decades, onshore wind trajectories in 16 of the 18 largest European Union countries have strongly deviated from S-curve expectations. Initial acceleration ended at just 2% of capacity potential (Interquartile range: 1–4%) or 4% of electricity (IQR: 1.5–6%), coinciding with the withdrawal or weakening of policy support. In 14 countries, the first slowdown was followed by secondary and sometimes tertiary reacceleration, forming distinct growth pulses, with peak growth rates at subsequent pulses statistically similar to the first. Pre-2021 reacceleration closely followed the reinstating or introduction of support schemes, while several post-2020 pulses were likely driven by better market conditions. Over the full period, the cruising speed – average additions after the first peak – was about one-quarter below the peak rate. National 2030 targets require growth close to historical peaks, yet the latest forecasts converge on the cruising speed. Germany is the sole outlier, consistent with unprecedented institutional reforms beyond financial incentives. Our multi-segment growth model, combined with growth metrics and policy mapping, can be extended to other policy-driven technologies. Social Media Summary Policy-driven technologies grow in pulses, not S-curves. Despite higher 2030 targets, EU wind expands at unchanged speed.

More than 70% of climate policies target low-carbon technologies, with hopes that policy support will trigger tipping points and self-reinforcing growth. In practice, however, trajectories of policy-driven technologies remain difficult to explain and anticipate because their growth is nonlinear and often constrained by backlash, policy reversals and systemic barriers. In this Perspective, we develop a framework to explain, diagnose, and anticipate the growth of policy-driven technologies through four phases. In the formative phase, rapid innovation, uncertainties and frequent failures lead to erratic growth; in the accelerating growth phase, increasing economic and political returns progressively increase deployment speed; in the steady growth phase, emerging barriers dampen acceleration leading to a pattern in which growth pulsates around its peak; and in the slowdown phase, barriers stall growth and technology reaches its limits. Surprisingly, the scale and complexity of supporting policies do not necessarily diminish as technologies mature. Effective acceleration requires phase-specific policies to support technical and commercial viability in the formative phase, amplify increasing returns in the accelerating growth phase, manage barriers in the steady growth phase, and withdraw or reinvigorate support during the slowdown phase. Further advancing this phase-aware understanding of the co-evolution of policy and technology is essential for improving climate policy design and for developing more realistic technology projections and climate mitigation scenarios. Accelerating the growth of low-carbon technologies is important for achieving climate targets and is the focus of many policies. This Perspective outlines four phases in the growth of policy-driven technologies and the policy requirements to achieve acceleration in each phase.

Small modular reactors (SMRs) are increasingly promoted as a flexible low-carbon energy source, yet their contribution to nuclear expansion remains uncertain. Drawing on a newly constructed database of 75 SMR designs, we develop a probabilistic framework that estimates when existing and future designs are likely to reach First-of-a-Kind (FOAK) operation. We find that vendor-announced FOAK timelines are systematically overambitious. Even under optimistic assumptions, only a median of 13 additional designs (P10–P90: 11–16) are projected to reach FOAK operation by 2035, far below the 34 implied by vendor announcements. By 2050, cumulative FOAK deployment reaches 24 SMRs in the Baseline scenario (P10–P90: 18–30) and 48 in the Accelerated scenario (P10–P90: 39–58). Near-term deployment remains concentrated in China and Russia, while later growth shifts toward OECD markets. These results define the deployment prospects for the global SMR pipeline and the feasible starting conditions for subsequent scale-up.

This paper examines the evolution of the European Union's (EU) renewable energy (RE) policy from 1990 to 2024, focusing on how changing perceptions of feasibility shape policy ambition, what drives implementation measures, and under what conditions targets are met. Using a simplified policy cycle framework and process tracing across four major policy cycles, we analyse the interplay between state goals, capacities, and feedback loops within co-evolving policy, technology, and market systems. While climate mitigation, energy security, and competitiveness have consistently guided EU RE policy, they do not fully explain shifts in specific targets or levels of effort. Instead, ambition has been strongly influenced by perceptions of what levels of renewable deployment are economically and politically feasible-particularly in relation to subsidy affordability. Policy targets tend to accelerate historical growth when subsidies can be expanded or are no longer required due to low costs and high electricity prices; in other contexts, targets generally track past trends. Subsidies can rise rapidly from low initial levels but eventually hit a ceilingaround 0.5% of GDP in the EU-beyond which growth slows or stalls. These patterns of target-setting and subsidy allocation help explain phases of policy-driven technology diffusion, particularly growth pulses and prolonged near-linear expansion. We further show that during formative or re-acceleration phases of diffusion, targets are often over-or underachieved because the techno-economic models informing policies cannot adequately capture the high technological and socio-political uncertainty of these phases. In contrast, during stable growth periods, targets tend to be more accurate. These findings contribute to broader debates on climate target credibility, policy-technology feedbacks, and the evolving role of policy in scaling low-carbon transitions.

Despite the recent surge of wind and solar power, both technologies need to accelerate to meet climate goals. Yet, there are no robust methods to assess the likelihood of such acceleration. Here we show that renewable energy deployment follows a recurring pattern across countries with prolonged periods of relatively steady growth punctuated by growth pulses. Based on this insight and on observed growth trajectories in early adopting countries, we develop a probabilistic model (PROLONG) for projecting global wind and solar power deployment. In our central projections, both wind and solar power grow similarly to Intergovernmental Panel on Climate Change 2 °C-compatible pathways and faster than in current policy scenarios. The COP28 pledge to triple renewables by 2030 is near the 95th percentile of our projections and requires that the growth of wind and solar photovoltaics in major economies accelerate by 1.4-3 times and 2-5 times, respectively. PROLONG can be adopted for data-driven projections of other policy-dependent energy technologies.

Energy security crises have historically been turning points for energy systems, exposing vulnerabilities, reshaping policy priorities, and boosting technological change. However, whether—and to what extent—such crises accelerate low-carbon transitions remains contested. This paper examines the effects of the 2022 energy crisis on the European Union (EU)’s energy transition, using policy analysis combined with a quantitative assessment of renewable energy trends, forecasts, and targets. We analyse the ambition, implementation, and outcomes of the REPowerEU plan, the main response to the crisis. In an unprecedented move, REPowerEU securitised renewable energy as a means to reduce dependence on Russian energy imports. However, the plan only moderately increased earlier renewable energy targets and did not reverse declining subsidies despite more forceful implementation measures. Its effects have been uneven across technologies. Already accelerating solar may overshoot its targets, onshore wind might only slightly accelerate beyond its current steady growth, and offshore wind remains constrained by economic and institutional uncertainties. Despite increased subsidies for fossil fuels, coal continued declining, oil remained stable, and natural gas dropped. Overall, REPowerEU sustained rather than transformed the EU’s low-carbon transition, illustrating both the potential and limits of accelerating decarbonisation under security crises.

Climate change mitigation requires the large-scale deployment of carbon capture and storage (CCS). Recent plans indicate an eight-fold increase in CCS capacity by 2030, yet the feasibility of CCS expansion is debated. Using historical growth of CCS and other policy-driven technologies, we show that if plans double between 2023 and 2025 and their failure rates decrease by half, CCS could reach 0.37 GtCO(2 )yr(-1) by 2030-lower than most 1.5 degrees C pathways but higher than most 2 degrees C pathways. Staying on-track to 2 degrees C would require that in 2030-2040 CCS accelerates at least as fast as wind power did in the 2000s, and that after 2040, it grows faster than nuclear power did in the 1970s to 1980s. Only 10% of mitigation pathways meet these feasibility constraints, and virtually all of them depict <600 GtCO(2) captured and stored by 2100. Relaxing the constraints by assuming no failures of CCS plans and growth as fast as flue-gas desulfurization would approximately double this amount.

Coal power phase-out is critical for climate mitigation, yet it harms workers, companies, and coal-dependent regions. We find that more than half of countries that pledge coal phase-out have "just transition" policies which compensate these actors. Compensation is larger in countries with more ambitious coal phase-out pledges and most commonly directed to national and regional governments or companies, with a small share going directly to workers. Globally, compensation amounts to over $200 billion (uncertainty 163-258), about half of which is funded through international schemes, mostly through Just Energy Transition Partnerships and the European Union Just Transition Fund. If similar transfers are extended to China and India to phase out coal in line with the Paris temperature targets, compensation flows could become larger than current international climate financing. Our findings highlight that the socio-political acceptance of coal phase-out has a tangible economic component which should be factored into assessing the feasibility of achieving climate targets. When countries phase out coal, they compensate affected companies, communities and workers. Today more than $200 billion are allocated for such payoff, but much larger amount will be needed if China and India also phase out coal to tackle climate change.

Decarbonising the power sector requires feasible strategies for the rapid phase-out of fossil fuels and the expansion of low-carbon sources. This study assesses the feasibility of plausible decarbonisation scenarios for the power sector in the Republic of Korea through 2050 and 2060. Our power plant stock accounting model results show that achieving zero emissions from the power sector by the mid-century requires either an ambitious expansion of renewables backed by gas-fired generation equipped with carbon capture and storage or a significant increase of nuclear power. The first strategy implies replicating and maintaining for decades the maximum growth rates of solar power achieved in leading countries and becoming an early and ambitious adopter of the carbon capture and storage technology. The alternative expansion of nuclear power has historical precedents in Korea and other countries but may not be acceptable in the current political and regulatory environment. Hence, our analysis shows that the potential hurdles for decarbonisation in the power sector in Korea are formidable but manageable and should be overcome over the coming years, which gives hope to other similar countries.

Climate change mitigation requires rapid expansion of low-carbon electricity but there is a disagreement on whether available technologies such as renewables and nuclear power can be scaled up sufficiently fast. Here we analyze the diffusion of nuclear (from the 1960s), as well as wind and solar (from the 1980–90s) power. We show that all these technologies have been adopted in most large economies except major energy exporters, but solar and wind have diffused across countries faster and wider than nuclear. After the initial adoption, the maximum annual growth for nuclear power has been 2.6% of national electricity supply (IQR 1.3%–6%), for wind − 1.1% (0.6%–1.7%), and for solar − 0.8% (0.5%–1.3%). The fastest growth of nuclear power occurred in Western Europe in the 1980s, a response by industrialized democracies to the energy supply crises of the 1970s. The European Union (EU), currently experiencing a similar energy supply shock, is planning to expand wind and solar at similarly fast rates. This illustrates that national contexts can impact the speed of technology diffusion at least as much as technology characteristics like cost, granularity, and complexity. In the Intergovernmental Panel on Climate Change mitigation pathways, renewables grow much faster than nuclear due to their lower projected costs, though empirical evidence does not show that the cost is the sole factor determining the speed of diffusion. We demonstrate that expanding low-carbon electricity in Asia in line with the 1.5 °C target requires growth of nuclear power even if renewables increase as fast as in the most ambitious EU’s plans. 2 °C-consistent pathways in Asia are compatible with replicating China’s nuclear power plans in the whole region, while simultaneously expanding renewables as fast as in the near-term projections for the EU. Our analysis demonstrates the usefulness of empirically-benchmarked feasibility spaces for future technology projections.

Climate policies are often assumed to have significant impacts on the nature and speed of energy transitions. To investigate this hypothesis, we develop an approach to categorise, trace, and compare energy transitions across countries and time periods. We apply this approach to analyse electricity transitions in the G7 and the EU between 1960 and 2022, specifically examining whether and how climate policies altered the transitions beyond historical trends. Additionally, we conduct a feasibility analysis of the required transition in these countries by 2035 to keep the global temperature increase below 1.5°C. We find that climate policies have so far had limited impacts: while they may have influenced the choice of deployed technologies and the type of transitions, they have not accelerated the growth of low-carbon technologies or hastened the decline of fossil fuels. Instead, electricity transitions in the G7 and the EU have strongly correlated with the changes in electricity demand throughout the last six decades. In contrast, meeting the 1.5°C target requires unprecedented supply-centred transitions by 2035 where all G7 countries and the EU must expand low-carbon electricity five times faster and reduce fossil fuels two times faster on average compared to the rates in 2015–2020. This highlights the insufficiency of incremental changes and the need for a radically stronger effort to meet the climate target.

Despite the consensus on the desirability of rapid wind and solar power expansion, scholars disagree over realistic projections of their deployment. Here, we address the challenge of using empirical data for projecting renewables growth and use hindcasting to illustrate how and why existing approaches over- or under-estimate deployment. We show that in the formative phase, when the use of renewables is under 0.6% of electricity supply nationally or under 0.2-0.3% globally, their growth is erratic and not representative of later phases with substantial deployment levels. Using national observations from countries with higher deployment of renewables, we derive S-curve parameters, test their robustness, and propose a new hybrid model which outperforms existing approaches in projecting the global use of renewables. Under the assumption of historically fastest deployment speeds being sustained in all countries, it is feasible for global wind and solar power to grow as envisioned in most 2°C-compatible scenarios.

Transitioning to net-zero carbon emissions requires phasing-out unabated coal power; however, recently it has only been declining in some countries, while it stagnated or even increased in others. Where and under what circumstances, has coal capacity reached its peak and begun to decline? We address this question with an empirical analysis of coal capacity in 56 countries, accounting for 99% of coal generation in the world. The peaks in national coal power have been equally spread per decade since 1970. The peaks are more likely to occur in country-years with high levels of electoral democracy, higher GDP per capita, slower electricity demand growth, and with low levels of political corruption. Normally, peaking coal power preceded rather than followed political coal phase-out pledges, often with long time lags. We conclude that though the cost of coal alternatives are declining and concerns over climate change increasing, coal power does not automatically peak even in situations with low demand growth, aging power plants and high import dependence. A quick and decisive destabilization of coal regimes requires, in addition, having sufficient economic capacities and strong democratic governance. Recently, the use of coal has declined in some countries, but remained stable or even grown in others. We investigate under what conditions coal power peaks, i.e. stops growing and then declines. Peaking coal power has mainly occurred in wealthy democracies with low corruption and slow electricity demand growth and has occurred with steady frequency since the 1970s despite cheaper renewables and climate concerns. We also find that political commitments to phase-out coal such as the Powering Past Coal Alliance generally follow rather than precede peaking coal. Graphical Abstract

The feasibility of different options to reduce the risks of climate change has engaged scholars for decades. Yet there is no agreement on how to define and assess feasibility. We define feasible as "do-able under realistic assumptions." A sound feasibility assessment is based on causal reasoning; enables comparison of feasibility across climate options, contexts, and implementation levels; and reflexively considers the agency of its audience. Global climate scenarios are a good starting point for assessing the feasibility of climate options since they represent causal pathways, quantify implementation levels, and consider policy choices. Yet, scenario developers face difficulties to represent all relevant causalities, assess the realism of assumptions, assign likelihood to potential outcomes, and evaluate the agency of their users, which calls for external feasibility assessments. Existing approaches to feasibility assessment mirror the "inside" and the "outside" view coined by Kahneman and co-authors. The inside view considers climate change as a unique challenge and seeks to identify barriers that should be overcome by political choice, commitment, and skill. The outside view assesses feasibility through examining historical analogies (reference cases) to the given climate option. Recent studies seek to bridge the inside and the outside views through "feasibility spaces," by identifying reference cases for a climate option, measuring their outcomes and relevant characteristics, and mapping them together with the expected outcomes and characteristics of the climate option. Feasibility spaces are a promising method to prioritize climate options, realistically assess the achievability of climate goals, and construct scenarios with empirically-grounded assumptions.This article is categorized under:Climate, History, Society, Culture > Disciplinary PerspectivesAssessing Impacts of Climate Change > Representing UncertaintyThe Carbon Economy and Climate Mitigation > Decarbonizing Energy and/or Reducing Demand

Ending the use of unabated coal power is a key climate change mitigation measure. However, we do not know how fast it is feasible to phase-out coal on the global scale. Historical experience of individual countries indicates feasible coal phase-out rates, but can these be upscaled to the global level and accelerated by deliberate action? To answer this question, we analyse 72 national coal power phase-out pledges and show that these pledges have diffused to more challenging socio-economic contexts and now cover 17% of the global coal power fleet, but their impact on emissions (up to 4.8 Gt CO _2 avoided by 2050) remains small compared to what is needed for achieving Paris climate targets. We also show that the ambition of pledges is similar across countries and broadly in line with historical precedents of coal power decline. While some pledges strengthen over time, up to 10% have been weakened by the energy crisis caused by the Russo-Ukrainian war. We construct scenarios of coal power decline based on empirically-grounded assumptions about future diffusion and ambition of coal phase-out policies. We show that under these assumptions unabated coal power generation in 2022–2050 would be between the median generation in 2 °C-consistent IPCC AR6 pathways and the third quartile in 2.5 °C-consistent pathways. More ambitious coal phase-out scenarios require much stronger effort in Asia than in OECD countries, which raises fairness and equity concerns. The majority of the 1.5 °C- and 2 °C-consistent IPCC pathways envision even more unequal distribution of effort and faster coal power decline in India and China than has ever been historically observed in individual countries or pledged by climate leaders.

While macroeconomic models highlight rapid coal phase-out as an urgent climate mitigation measure, its socio-political feasibility is unclear. The negative impacts of coal phase-out for companies, workers and coal-dependent regions, and the unequal global distribution of the coal phase-out burden has triggered resistance and calls for just transitions. Here, we construct a database of domestic and international just transition policies and partnerships that compensate affected actors of coal phase-outs. By comparing coal phase-out in countries which have compensation plans with those that don’t, we show that compensation policies are essential to realizing premature retirement of coal. The cost we estimate associated with these policies clarifies the financial cost of making coal phase-out politically feasible. We find that compensation costs are proportional to avoided emissions resulting from coal phase-out and are generally consistent with recent carbon prices. We find that the cost of implementing similar compensation policies in case of 1.5°C -consistent coal phase-out for China and India is 17 times higher than all existing compensation, and roughly comparable to global Official Development Assistance in 2021. We show that in the case of coal phase-out, political will and social acceptance have a tangible economic component which should be factored in to assessing the feasibility of achieving climate targets.