This chapter examines two critical dimensions of climate progress under the Paris Agreement: the potential sources of change and the policy directions with the greatest capacity to deliver substantial CO₂ emissions reductions. Drawing on expert assessments from the OECD survey, the chapter identifies which policy directions are perceived as most effective and which are advancing most rapidly. The chapter also explores how perceptions of transformative potential align with, or diverge from, views on actual policy progress.
The Paris Agreement at Ten Years
Expert Views on Progress and Challenges for Climate Change Mitigation
Abstract
Policy intervention emerges as the primary pathway to bridge the ambition and implementation gaps. The survey included a dedicated component to collect perceptions about scaling up ambition and implementation. Respondents were asked to allocate 100 points across a range of potential channels, offering a comparative view on their expected contribution (Figure 5.1, upper panels). Market-based instruments, such as taxes, subsidies and trading schemes, ranked highest. These instruments receive 23-26% of the total voting points from study participants. Regulations follow closely with 21-24%, and policy measures to support green innovation are ranked third with 17-19%. Together, these three types of instruments represent 61-67% of total responses. Re-examining expert votes from the perspective of their top-ranked alternative (i.e. top-score prevalence) yields more refined insights. Around 9 in 10 experts rank one of these three instruments as the most important by placing it first (i.e. top-score prevalence).1 As shown in Table 5.1, these channels also attracted the highest level of expert consensus among study participants. This suggests that their prominence reflects broad agreement rather than the strong preference of a few respondents.
Voluntary and behavioural channels are seen as secondary, but not insignificant. Policymakers and experts expect individual voluntary action2 to contribute 6-7% of the emissions reductions, corporate voluntary action 7-9% of these reductions, and behavioural interventions3 8-11% of them. Combined, these channels account for a notable 21-27%. Although not directly linked to economic policy, these channels still rely on soft instruments such as nudges, awareness campaigns, and labelling. However, results should be interpreted with caution: expert views on these channels vary widely and the lower consensus levels suggest diverging views on their relative importance. Around 90% of experts do not rank any of the three channels as their top option.4
Autonomous, market-driven technological progress is expected to deliver a modest but non-negligible part of the total change (11-12%) needed to meet the goals of the Paris Agreement.5 However, expert consensus on the importance of this channel is weak, and only 6-9% of non-government experts and 8-9% of government experts rank it as the most important.
Percentage of credit allocated by experts to various approaches
Notes: In this component of the survey, each respondent was asked to evaluate the relative potential of seven competing approaches to bridging the implementation gap (upper left panel) and the ambition gap (upper right panel) and eight competing policy targets to achieve the goals of the Paris agreement (lower panel). In all three cases, the relative potential of alternative options was evaluated by allocating a total of 100 points across them. There was no constraint on the number of alternatives a respondent could credit. For example, allocating all 100 available points to a single alternative and 0 points to all the rest constitutes a valid response. Similarly, a response allocating 25 points to two alternatives and 10 points to another 5 factors is also valid. Blue bars and text labels indicate mean scores, which is also the percentage of all voting points directed to the alternative. Black solid lines indicate the 25th-75th percentile ranges and grey dashed lines indicate the minimum-maximum range.
Government experts respond to the three questions from a national perspective (i.e. “in your country’s NDC targets”, “policymakers in your country” etc.). Technical notes: statistical tests indicate that the number of points allocated to a factor in the upper left panel is not statistically different from the number of points allocated to the same factor in the upper right panel. All p-values lie well above 0.10, with the exception of “Policy measures to boost green innovation” (p-value < 0.05).
Source: OECD survey on the transformative effect of the Paris Agreement, 2025.
Percentage of points allocated by experts to various approaches
Notes: All notes of Table 4.1 and Figure 5.1 apply. In the context of this study: (i) bridging the implementation gap is defined as “Bridging the gap between current emissions and the target inscribed in your country's NDC” (government experts) and “Bridging the gap between current emissions and the targets inscribed in NDCs” (non-government experts); (ii) bridging the ambition gap is defined as “Bridging the gap between your country's NDC target and 1.5°C-aligned emissions reductions” (government experts) and “Bridging the gap between emission targets in current NDCs and 1.5°C-aligned emissions levels” (non-government experts).
Source: Calculations performed by the authors using data from the OECD survey on the transformative effect of the Paris Agreement, 2025.
The results on policy rankings are coherent when focusing on the implementation and ambition gaps. Statistical tests reveal no significant differences in the points allocated across the same factor when evaluating the implementation gap and the ambition gap. This indicates a belief that the identified policy mix - market-based instruments, regulations and innovation support - is perceived as equally relevant for addressing both gaps.
Electrification, energy decarbonisation and improvements in energy efficiency stand out as the pillars of the required changes. Experts and policymakers alike consistently prioritise these three strategies to meet the Paris Agreement’s goals: 66-69% top-rank one of them, and they allocate 50-52% of total voting points to the three factors. As a stand-alone strategy, electrification of various economic sectors receives 18-20% of the voting points and is ranked first by 29-32% of respondents (Figure 5.1, lower panel). Furthermore, consensus levels on its importance are high, as most experts agree on placing a high score on it (Table 5.1). Improving energy efficiency receives 15-16% of voting points and reducing the carbon intensity of energy use receives 16-18% of voting points. Reducing non-energy-related emissions, including those from the AFOLU sector, also gains traction (11-14%), with some government respondents allocating up to 30% of their points to this option. However, the importance placed on this lever widely differs, both across country policymakers and across other climate experts. Measures focused on curbing total consumption, for instance by changing consumption patterns, receive lower rankings but still capture meaningful attention. In contrast, carbon dioxide removal through carbon capture, use and storage (CCUS) and hydrogen deployment score just 7-8% of the points each, with very few experts ranking them as top priorities.
Government experts identify policies with the highest perceived transformative potential as linked to the energy sector and carbon sinks. The final part of the survey gathered the beliefs of respondents about the potential of various policy directions to achieve substantial GHG emission cuts, as well as the degree to which these policies have been deployed so far. Scaling up renewable energy, including through subsidies, phasing out fossil fuels in power generation,6 investing in green infrastructure,7 as well as protecting and expanding carbon sinks constitute policy directions that policymakers rated highest in transformative potential (all above 3.8 out of 5.0) (Figure 5.2).
The views on some policy directions enjoy more consensus than others. There is high agreement among respondents on the transformative potential of scaling up power generation from renewable sources. Most rate this policy 4 or 5 on the transformative-potential scale. In contrast, views diverge more widely on phase-outs or bans of fossil fuels in power generation and in final consumption. Policies whose transformative potential is perceived in widely different ways across respondents also include taxing the carbon content of electricity, consumption goods and services, as well as subsidising the use of existing CCUS technologies.
Policymakers and climate change experts broadly agree that the most transformative policies are also the ones that have advanced the most. Figure 5.3 shows a positive association between perceived transformative potential and reported policy progress since 2015. This suggests that implementation efforts tend to concentrate on the areas seen as most impactful. Although the positive correlation between transformative potential and policy advancement may underpin a causal relationship, it needs to be interpreted with caution. In some cases, policies may be prioritised because of their high perceived potential, while in others, limited progress may explain low expectations about their transformative impact. This is particularly plausible for options requiring large (and possibly prohibitive) upfront investments, which may currently be viewed as infeasible. The figure also reveals a notable divergence in perceptions between policymakers and climate experts. Experts, who provide perspectives from a global viewpoint, see greater room for progress in areas they consider highly transformative. For instance, all fossil fuel-related policies (black dots) are rated above 3.75 in transformative potential but only 2.2 - 2.9 in advancement. Conversely, policymakers see less scope for further progress in areas they already perceive as transformative. For example, renewable energy policies (red dots) are consistently rated highly transformative (3.6 - 4.1) and are also seen as relatively advanced (3.2 - 3.5).
Scores (1-5) allocated by policymakers and non-government experts across policy directions
Notes: Diamond points indicate mean scores, grey solid lines indicate the ±1 standard deviation range. A transformative potential of 1 indicates no transformative potential at all; a transformative potential of 5 indicates very strong transformative potential, suggesting that the policy direction is an essential component in a policy package. An advancement of 1 indicates that the policy has not progressed at all since 2015, while a score of 5 indicates that very significant policy efforts have been made.
Sources: OECD survey on the transformative effect of the Paris Agreement, 2025.
Perceived transformative potential of a policy direction (horizontal) and policy advancement (vertical)
Notes: Each point corresponds to one of the policy directions listed in Figure 5.2. The horizontal axis reports the average score for the perceived transformative potential of the policy, where a score of 1.0 indicates no transformative potential at all and a score of 5.0 indicates very high transformative potential, i.e. the policy direction is considered essential for inclusion in the policy package. The vertical axis reflects the perceived domestic (for government experts) and international (for non-government experts) advancement of each policy since 2015, where a value of 1.0 indicates no progress and a value of 5.0 indicates very significant policy efforts. Points on the left panel indicate mean scores across all government policymakers. Points on the right panel indicate mean scores across non-government climate change experts. The 45-degree diagonal dashed line represents an advancement frontier. Policies lying close to this line are perceived to have progressed in line with their perceived transformative potential. The further a dot lies below the advancement frontier, the more under-implemented the corresponding policy is considered relative to its transformative potential. The closer a dot is to the frontier, the less room respondents consider there is for advancing the respective policy in order to materialise its full transformative potential.
Source: Graph generated by the authors using data from the OECD survey on the transformative effect of the Paris Agreement, 2025.
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← 1. The figure aggregates the top score prevalence of “market-based instruments”, “regulations” and “policy measures to boost green innovation”.
← 2. The finding is in line with the extensive literature on the willingness to pay (WTP) for climate-friendlier consumer options, which predominantly reports moderate or low estimates. While a comprehensive review of this voluminous literature goes beyond the scope of this study, some estimates are noteworthy. Johnson and Nemet (2010[26]) reviewed 27 studies published up to 2010 and found a WTP range of USD 22-437 per household annually, with a median value of USD 135. Therefore, an indicative value of 10 tons of CO2 per household per year yields values below USD 14 per ton of CO2.
A substantial share of the literature is concentrated on voluntary carbon offsets (VCO) in aviation. Cordes, Baumeister and Käyrä (2023[25]) identified 332 and analysed 47 studies in this literature stream, published between 2004 and 2020. Most of the primary studies report WTP figures that vary considerably across geographic regions and socioeconomic characteristics. For instance, Brouwer, Brander and Van Beukering (2008[22]) estimated a mean WTP of € 25 per ton of CO2 in air travel. Other studies, e.g. MacKerron et al. (2009[23]), report a WTP per flight, which is not straightforward to convert to WTP per ton of CO2.
Furthermore, the WTP may be significantly influenced by a mandatory payment of a carbon price. For instance, the study by Choi (2015[24]) finds that the WTP for aviation carbon offsets may fall from AUD 10 to values not significantly different from zero when a carbon price is imposed.
Beyond aviation, Löschel, Sturm and Vogt (2013[20]) estimated the individual WTP for CO2 emissions savings in Germany at € 12 per ton of CO2. Another study from Germany found the mean individual voluntary contribution for a ton of CO2e to be € 6.30, and the respective median as low as € 0.30 (Diederich and Goeschl, 2014[21]). Aldy, Kotchen and Leiserowitz (2012[19]) estimated a willingness by consumers to pay a 13% premium for 80% cleaner electricity in the United States. In particular, for greener electricity, the meta-analysis by Sundt and Rehdanz (2015[27]) used values from primary studies ranging between zero and USD 0.065 per kWh.
← 3. A relevant series of OECD publications examines the prevalence of various consumer beliefs, individual habits and attitudes (OECD, 2023[14]), as well as their impact on energy use (Hassett et al., 2024[16]), transport (Tikoudis et al., 2024[15]), waste practices (Brown, 2024[17]) and food choices (Hassett et al., 2025[18]).
← 4. The figure aggregates the top score prevalence of all channels apart from “Behavioural interventions”, “Voluntary individual behavioural change” and “voluntary corporate action”.
← 5. The finding is in line with several contributions indicating an insufficient reduction of CO2 emissions without substantial policy interventions. IDDRI (Spencer, Robiou du Pont and Colombier, 2019[28]) labels the scenario in which “energy transition is driven by the economic competitiveness of zero-carbon technologies” as “autonomous transition”. Under this scenario, they describe the evolution of energy-related CO2 as “an emissions peak, plateau, and slow decline” rather “than the abrupt decline required to meet the 2°C goal”. While autonomous progress may represent only a limited part of total decarbonisation, it may constitute an important factor behind some of its drivers. Improvements in energy efficiency could be a characteristic example. Tikoudis, Mba Mebiame and Oueslati (2022[1]; 2023[2]) examine the effect of autonomous technical change on automobile fuel efficiency, and isolate this effect from the impact of relevant market forces (e.g. gasoline price fluctuations) and policy instruments (i.e. CAFE standards and fuel taxes). They find that policy-induced and autonomous innovation together are responsible for more than 60% of the observed progress in fuel efficiency of cars sold in the United States.
← 6. OECD (2024[4]) estimated that government support to fossil fuels amounted to USD 1.1 trillion in 2023. A detailed review of the literature on effective fossil fuel subsidies goes beyond the scope of this report. Relevant literature directly discussing fossil fuel bans and phase-outs includes, among others, Green (2018[6]) and Erickson, Lazarus and Piggot (2018[7]). Trencher et al. (2022[8]) systematically reviewed over 400 scientific articles focusing (among others) on the policy instruments various studies use in order to conceptualise fossil fuel phase-outs. The cost-effectiveness of phasing out fossil fuels in energy production has been investigated, among others, by Burniaux and Chateau (2014[3]) and Chepeliev and van der Mensbrugghe (2020[5]).
← 7. There is no universal definition of the term “green infrastructure”. In line with Wang and Banzhaf (2018[11]), it may be defined as a combination of sustainable use of spaces and ecosystem services in order to improve human well-being. Since no explicit definition was provided in the questionnaire, the term may have been interpreted broadly by respondents, potentially extending beyond urban green infrastructure. For instance, see Chen (2015[9]) and Ai and Yan (2024[10]). Green infrastructure may be understood to include any physical investment aiming to maintain ecosystems, reconnect fragmented natural areas and restore degraded habitats (Naumann et al., 2011[12]). It may also be perceived to encompass investments in active mobility, public transport or low-carbon buildings. The 6th Assessment Report of the IPCC (2023[13]) defines green infrastructure as “The strategically planned interconnected set of natural and constructed ecological systems, green spaces and other landscape features that can provide functions and services including air and water purification, temperature management, floodwater management and coastal defence often with co-benefits for human and ecological well-being. Green infrastructure includes planted and remnant native vegetation, soils, wetlands, parks and green open spaces, as well as building and street-level design interventions that incorporate vegetation”.