The scenario architecture of climate research (Shared Socioeconomic Pathways, SSPs, and Representative Concentration Pathways, RCPs) represents socioeconomic futures and emissions trajectories but places little emphasis on how climate and clean-energy policies are actually implemented by governments, incumbent utilities, investors, and civil society. Hewitt, Cremades, Kovalevsky and Hasselmann (2020) analysed implementation experiences in the US, China, Germany and Spain and proposed four qualitative implementation scenarios (IS1 Civil Society Takes Control; IS2 Strong-arm Transition; IS3 Systemic Limits; IS4 Renewable Austerity), meant as coordinates in a 'policy landscape' of actor-context configurations. The open problem is to refine, test, and operationalize this implementation-scenario framework for use in integrated scenario assessment and policy planning: translate the qualitative narratives into quantitative, dynamic models that capture how shifts in actor coalitions move countries between implementation pathways, including transitions and tipping behaviour; extend and test the typology across further case-study countries, especially emerging economies, and further actor types; and develop the associated policy-design instruments (ring-fencing and green conditionality in bail-outs, anti-trust and grid-governance reform, enabling international policy spaces).

Background

Climate-change research organizes its long-term analyses around a paired scenario architecture. Representative Concentration Pathways (RCPs) are trajectories of greenhouse-gas concentrations and radiative forcing used to drive climate models; Shared Socioeconomic Pathways (SSPs) are five global narratives, with quantitative realizations, describing how population, economic growth, inequality and other socioeconomic drivers could evolve over the 21st century. Integrated assessment models (IAMs) couple the energy system, economy, land use and climate to compute emissions and mitigation pathways under these assumptions. A companion element, the Shared Policy Assumptions (SPAs) introduced by Kriegler et al. (2014), was designed to describe the climate-policy mixes that scenarios assume, but in practice policy has mostly been represented through idealized instruments such as globally harmonized carbon prices, and the scenario architecture places little emphasis on how policies are adopted, contested, and put into effect. This matters because of the implementation gap: under the 2015 Paris Agreement, the policies countries adopt, and the outcomes those policies achieve, both fall short of agreed temperature limits; the gap is conventionally decomposed into an adoption component and an outcomes component (Fransen et al., 2023). Hewitt, Cremades, Kovalevsky and Hasselmann (2020) approached this gap from implementation research, the study of how adopted policies are carried out by concrete actors (national and subnational governments, incumbent energy utilities, investors, and civil society) within specific institutional and economic contexts. Analysing the clean-energy transitions of the United States and China (the two largest emitters) and of Germany and Spain (two markedly diverging European trajectories, including Germany's 'Energiewende' energy transition and Spain's post-2012 renewable-energy moratorium after the financial crisis), they proposed four qualitative implementation scenarios for clean energy worldwide: IS1 'Civil Society Takes Control' (citizens and forward-thinking investors marginalize ideologically opposed governments); IS2 'Strong-arm Transition' (a single-party state drives the transition without civil society); IS3 'Systemic Limits' (whole-energy-system constraints such as grids, storage and ancillary services limit what renewable expansion alone achieves); and IS4 'Renewable Austerity' (an economic downturn lets anti-transition actors strip policy support, as happened after the 2007-2008 financial crisis). The scenarios are intended as coordinates in a 'policy landscape' (waypoints that indicate, but do not determine, outcomes) and are deliberately independent of governments' professed aspirations. A methodological route for quantifying such narratives already existed: actor-based system-dynamics models (Kovalevsky, Hewitt, de Boer and Hasselmann, 2017), in which decision-making actors are represented as state variables coupled by differential equations so that policy implementation emerges from simulated actor interactions; agent-based modelling, where many autonomous decision-makers are simulated individually, is the natural alternative. The paper's conclusions argue that such dynamic models could show how policy shifts driven by different actor coalitions move countries around the scenario landscape, producing outcomes richer than the dominant 'salvation or catastrophe' scenario framing. But this modelling, the extension of the typology to further countries and actor types, and the associated policy-design questions (ring-fencing of mitigation incentives in bail-out agreements, anti-trust and grid-governance reform against incumbent concentration, and opening international policy spaces for particular pathways) were all left as future work, and it is this agenda that defines the problem.

Problem Statement

The problem, as posed by Hewitt et al. (2020), is to refine, test, and operationalize the four climate policy implementation scenarios (IS1 'Civil Society Takes Control', IS2 'Strong-arm Transition', IS3 'Systemic Limits', IS4 'Renewable Austerity') for use in integrated scenario assessment and policy planning. Its components are jointly linked by that single common objective: (1) Quantitative operationalization: translate the qualitative implementation-scenario narratives into quantitative, dynamic models that show how policy shifts driven by different actor coalitions move a country around the implementation-scenario 'policy landscape', including transitions between scenarios and tipping behaviour, in place of the prevailing 'salvation or catastrophe' scenario framing. (2) Extension and testing: analyse the policy context of further case-study countries, especially emerging economies in Asia or Africa, and further actor types (for example donor countries or NGOs), to determine whether the four scenarios remain representative or require refinement or alternative narratives, and how implementation-aware elements can be integrated into the SSP/RCP/SPA scenario architecture used in integrated assessment. (3) Policy-design operationalization: develop and assess implementable instruments arising from the scenarios, including tightly ring-fenced climate-mitigation clauses in bail-out agreements and 'Green Deal'/'Green Marshall Plan'-style support for struggling economies, robust anti-trust and grid-governance reform to prevent concentration of incumbent power, and international policy spaces that enable locally appropriate implementation pathways (for example bottom-up civil-society-led transitions versus state-led industrial programmes). China's coal-fleet retirement consistent with its 2060 carbon-neutrality pledge is one illustration of components (1) and (2), not a separate question. The three components form a single objective, with components (1) and (2) to be demonstrated for at least one country beyond the original US, China, Germany and Spain cases.

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