Natasha Frilingou

Rapid renewable energy deployment is essential for climate change mitigation but often faces opposition due to concerns over potential biodiversity implications. This ‘green versus green’ dilemma is particularly salient in biodiversity-rich nations like Greece, yet regional energy-system implications of spatially constrained renewables remain underexplored. Integrating the regionally disaggregated Greek energy-system model HERMES with geospatial data on existing development restrictions, Natura 2000 protected areas, and protected and endangered flora species distribution, we explore Greece’s decarbonisation pathways under progressively stricter biodiversity constraints for onshore and offshore wind energy. We find that protecting ecologically sensitive areas does not compromise national climate targets and only marginally increases system costs. However, it would force within-country reallocation of installed renewable capacity. We highlight regional energy dynamics related to islands’ energy autonomy and transition justice in coal-producing regions. We argue that strategic spatial planning is critical to reconcile biodiversity conservation with a resilient and just energy transition.

Energy-sector decarbonisation requires large-scale investment in low-carbon technologies, yet only a limited share flows to low- and middle-income countries, partly due to higher financing costs and perceived risks. Most modelling exercises do not fully account for how the cost of capital may vary across regions and technologies, potentially influencing policy insights. We examine how plausible, expert-informed long-term trends in de-risking clean energy and increasing risks for fossil fuels could shape decarbonisation pathways, using an empirical dataset differentiated by country and technology. We also evaluate a “corrective justice” policy that taxes corporate windfall profits and redistributes revenues to support low-carbon investments in higher-risk regions. Results suggest that incorporating differentiated cost-of-capital trajectories may improve mitigation outcomes and help narrow the gap between current commitments and long-term climate targets, while indicating potential underestimation of risks associated with bioenergy-based negative emissions technologies in mitigation scenarios for high-income nations.

Climate mitigation scenarios are typically evaluated for technical and economic feasibility, yet their implementation depends on whether they are considered acceptable within broader development priorities. Sustainable Development Goal (SDGs) interactions create trade-offs that shape how mitigation strategies are perceived across regions. Combining integrated assessment modelling and stochastic multicriteria acceptability analysis, we assess the acceptability of four narratives achieving a common mid-century climate target. We find that pathways with similar climate outcomes differ markedly in acceptability and that global rankings often mask regional divergences. Technology-led decarbonization is more acceptable in the Global South, enabling rapid gains in energy access and development. Conversely, regions in the Global North favour strategies that protect natural carbon sinks, reflecting greater ecosystem restoration benefits. These divergent preferences stem from structural SDG trade-offs, challenging universal win–win narratives. Explicitly accounting for these differences is essential for designing politically feasible and effective climate pathways.

Participatory approaches to integrated assessment modelling seek to bring a more diverse range of views into the modelling process, to build a better understanding of the societal context while supporting more inclusive and fairer decision-making. This need for co-creation reflects a growing trend towards societally engaged and action-oriented research across sustainability science. Efforts to integrate stakeholder inputs in IAM-based research to strengthen legitimacy and transparency of the scientific process and the desirability of its results have remained sparse, with participation often limited to top-down formats in which stakeholders are consulted but rarely able to directly shape choices, outputs, or policy prescriptions. Furthermore, there has been little practical how-to guidance for well-structured participatory IAM processes in a domain that has long acknowledged the added value. Any such process should go beyond well-structured procedures and offer flexibility to quickly adapt to a changing policy landscape and thus to shifting stakeholder priorities.We designed and implemented a participatory process intended to support acceptable, robust, and durable transition strategies, while strengthening trust between modelling researchers and stakeholders. The process was designed to produce outputs that are intelligible in terms of real-world implications and actionable in terms of concrete policy recommendations. In practice, the process began by scoping and prioritising relevant stakeholder groups and policy questions; it then engaged stakeholders in co-designing the analytical approach used to address these questions; interim results were iteratively refined based on stakeholder feedback; and dedicated discussions supported shared interpretation of findings, which were distilled into policy briefs.A key lesson from implementing this multi-stage process was the overly thematic structure: framing exchanges around broad “climate and energy transition” topics often diluted sector-specific dynamics and actionable insights. Going forward, engagement could be organised around key drivers and barriers within each sectoral system (e.g., infrastructure and technology constraints, investment and competitiveness, regulatory bottlenecks, distributional impacts, and feasibility). To operationalise this shift, we propose a re-design of the participatory approach into iterative sectoral conversations that enable continuous exchange between the research process and relevant international debates, drawing on prior experience with knowledge co-production and multidisciplinary transition research and aligning with established scholarship on knowledge co-production for sustainability research. The participation proceeds along two integration tracks: (i) interdisciplinary synthesis linking country-level sectoral findings with global-level analysis, and (ii) transdisciplinary exchanges with a small, carefully selected group of international sector experts, complemented by broader expert-facing events.

The European Union’s (EU) climate strategy, anchored in the European Green Deal, the Fit-for-55 package, and updated National Energy and Climate Plans (NECPs), requires a rapid transformation of the energy system to meet the legally binding target of net-zero greenhouse gas emissions by 2050 and a 55% reduction by 2030 relative to 1990 levels. Yet, how national plans align with EU-wide ambition, alongside the implications for investment, infrastructure, and power-system operation, remain insufficiently assessed. We address this gap by linking an EU-specific implementation of a prominent integrated assessment model with Member State-level disaggregation (GCAM-Europe) with a higher-resolution European electricity system model (EXPANSE). This modelling framework captures national heterogeneity, sectoral detail, and spatiotemporal variability in electricity demand, renewable supply, and storage, enabling the assessment of grid investments and infrastructure. We analyse four scenarios representing EU-wide (Fit-for-55) or national (NECP) targets, implemented through explicit policies (POLICY) or cost-optimal carbon caps (COST_OPTIMAL). Results show all scenarios achieve the −55% fossil CO2 reduction by 2030, with the electricity sector driving the largest chunk. Renewable energy nearly doubles, with POLICY scenarios accelerating electrification and heat pump deployment, while COST_OPTIMAL scenarios leaning more on biofuels. Efficiency targets are partially met, with POLICY scenarios distributing savings more evenly across Member States compared to concentrated reductions (COST_OPTIMAL). By 2035, power system transformation diverges strongly: COST_OPTIMAL scenarios expand about 1,250 GW of new capacity, concentrated in few resource-rich regions, while POLICY scenarios reach around 1,750GW with broader spatial distribution, requiring higher investments in renewables and grids. Average wholesale electricity prices are higher and more heterogeneous under POLICY scenarios, reflecting carbon costs, transmission bottlenecks, and reliance on fossil backup. Results highlight trade-offs between economic efficiency and equitable burden-sharing, underscoring the importance of coordinated EU governance, infrastructure planning, and complementary policies to balance cost-effectiveness with political feasibility and social acceptance.

The European Union’s (EU) climate strategy—anchored in the European Green Deal, the Fit-for-55 package, and updated National Energy and Climate Plans (NECPs)—requires a rapid transformation of the energy system to meet the legally binding target of net-zero greenhouse gas emissions by 2050 and a 55% reduction by 2030 relative to 1990 levels. Yet, how national plans align with EU-wide ambition, alongside the implications for investment, infrastructure, and power-system operation, remain insufficiently assessed. We address this gap by linking an EU-specific implementation of a prominent integrated assessment model with Member State-level disaggregation (GCAM-Europe) with a higher-resolution European electricity system model (EXPANSE). This modelling framework captures national heterogeneity, sectoral detail, and spatiotemporal variability in electricity demand, renewable supply, storage, and grid constraints. We analyse four scenarios representing EU-wide (Fit-for-55) or national (NECP) targets, implemented through either explicit policies (POLICY) or cost-optimal carbon caps (FREE). Results show that all scenarios achieve the − 55% fossil CO2 reduction by 2030, with the electricity sector driving the largest chunk. Renewable energy nearly doubles, with POLICY scenarios accelerating electrification and heat pump deployment, while FREE scenarios lean more on biofuels. Efficiency targets are only partially met, with POLICY scenarios distributing savings more evenly across Member States compared to concentrated reductions (FREE). By 2035, power system transformation diverges strongly: FREE scenarios expand about 1,160 GW of new capacity, concentrated in a few resource-rich regions, while POLICY scenarios reach around 1,680 GW with broader spatial distribution, requiring higher overall investment in renewables and grids. Average wholesale electricity prices are higher and more heterogeneous under POLICY scenarios, reflecting carbon costs, transmission bottlenecks, and reliance on fossil backup. These results highlight trade-offs between economic efficiency and equitable burden-sharing, underscoring the importance of coordinated EU governance, infrastructure planning, and complementary policies to balance cost-effectiveness with political feasibility and social acceptance.

Limiting global warming to well-below 2°C necessitates profound decarbonization, but how to distribute mitigation efforts over sectors remains a widely debated issue. While Integrated Assessment Models (IAMs) traditionally rely on "Least-Cost" optimization to answer this question, the resulting sectoral allocations vary widely and ignore impacts on other potential policy objectives. Connecting an IAM with portfolio analysis, this study applies a novel methodology to evaluate how sector-specific mitigation actions impact key indicators from Sustainable Development Goals (SDGs) related to poverty, health, water, economy, and land, and to identify Pareto-optimal and Paris-compliant mitigation portfolios that reveal the trade-offs between other sustainable development priorities. Furthermore, we define "SDG-balanced" portfolios that outperform standard least-cost scenarios across all five SDG indicators for an equivalent carbon budget. Our findings demonstrate that the simultaneous evaluation of a broader set of policy priorities is crucial to provide truly policy-relevant guidance for the climate transition.