The Spanish Constitution's 'State of Autonomies' framework has led to increasing regional government influence on climate policy and the renewable energy transition (RET). Research suggests pro-decentralization parties act as climate pioneers at the regional level, using environmental issues to assert greater subnational authority. This study investigates whether this dynamic extends to the national level by analyzing party manifestos from three recent Spanish national elections. The central research question is whether pro-decentralization parties are more likely to prioritize climate change and the RET in their national platforms. The importance of this study lies in its contribution to understanding the interplay between multilevel governance, party competition, and climate policy preferences, specifically addressing the under-researched connection between decentralization and climate action within a multilevel democracy.

Existing research on climate federalism highlights the benefits of decentralized systems in addressing climate challenges. Decentralization fosters experimentation, mutual learning, and competition among subnational entities, increasing the likelihood of finding effective strategies. The concept of 'compensatory federalism' demonstrates that regions may take climate action even when the central government does not. The RET provides incentives for subnational governments to develop independent energy strategies, enhancing their autonomy and potentially boosting regional economies. Decentralization also improves policy adaptation to local contexts, enhances public participation, and fosters 'energy democracy' through citizen engagement in energy production and consumption. The rise of renewable energy cooperatives (RECs) further supports the potential of decentralized energy systems. Studies on 'Green Nationalism' show how minority nationalist parties often connect environmentalism and autonomy, emphasizing locally adapted solutions to climate change. This literature suggests that pro-decentralization parties are more likely to prioritize climate and energy issues, both to advance their regional agendas and because these issues align with the principles of Green Nationalism.

The study employed a mixed-methods approach. First, a qualitative analysis assessed the presence and structural integration of climate change within the manifestos of major political parties in the 2016, 2019, and 2023 Spanish general elections. The parties included both Statewide Parties (SWPs) and Non-Statewide Parties (NSWPs), reflecting Spain's left-right and center-periphery political cleavages. SWPs operate nationally, while NSWPs represent specific regions and advocate for regional autonomy. The second phase involved a quantitative analysis using 'quasi-sentences' (as defined by Schmitt and Wüst) as the unit of observation. A hand-coded database of 49,816 quasi-sentences was created. Four categorical variables were used: one measuring the overall salience of climate-related content (pro-climate, anti-climate, neutral, not relevant), and another breaking down 'pro-climate' and 'anti-climate' into finer subcategories (e.g., pro-renewable energy, pro-roads, pro-fossil fuels). The independent variable, measuring parties' stance on decentralization, used two measures: the first based on hand-coded quasi-sentences for and against decentralization in each manifesto; the second, available only for the 2016 and 2019 elections, utilized the 'Decentralization' and 'Centralization' variables from the MRG/CMP/MARPOR database. The data were then analyzed to examine correlations between parties' pro-decentralization positions and the salience of climate-related content, particularly pro-renewable energy content, in their manifestos. The party MP-E was excluded from the final analysis due to its unusually high climate salience scores. Key quasi-sentences were also qualitatively analyzed to gain deeper insight.

The analysis revealed a significant focus on pro-climate content across party manifestos, particularly in the 2019 elections. The results showed a positive correlation between a party's pro-decentralization stance and the salience of climate-related content in its manifesto. NSWPs consistently exhibited higher values for climate salience than SWPs, suggesting that pro-decentralization parties, even those on the political right, tend to prioritize climate change and the RET more strongly. Tables 1 and 2 present the percentage of content related to climate code variables and pro-climate policy subcategories for each party. Figures 1-4 visually represent the relationships between pro-decentralization positions and the salience of climate change and pro-renewable energy content. The findings confirm the two hypotheses: (1) the salience of climate content in manifestos increases with a party's pro-decentralization stance; (2) the salience of renewable energy content in manifestos increases with a party's pro-decentralization stance. Analysis of selected quasi-sentences from the manifestos further demonstrates the strategic use of climate policy by NSWPs to advocate for greater regional autonomy and control over energy resources. This is evident in their emphasis on regional control over renewable energy generation and their criticism of central government actions that limit regional energy independence.

The findings support the theoretical arguments of climate federalism and Green Nationalism. Decentralized systems are more effective in adapting climate policies to local contexts and enhancing public participation. The results show that pro-decentralization parties in Spain, regardless of their ideological leaning, tend to champion climate action and the RET strategically to gain greater regional autonomy. NSWPs’ prominent role in advocating for these issues at the national level indicates that subnational politics significantly shape national climate agendas. The study bridges a gap in the literature by demonstrating a direct link between decentralization and climate policy preferences within a multilevel governance system. The strategic use of climate and energy policies by NSWPs to advance their territorial interests highlights the complex interplay between environmental concerns and regional autonomy.

This study provides strong empirical evidence for a positive correlation between pro-decentralization political party stances and the prioritization of climate change and RET policies in Spain. The findings underscore the importance of multilevel governance and the strategic role of subnational actors in shaping national climate agendas. Future research could explore the causal mechanisms linking decentralization and climate policy preferences further, examining factors beyond manifestos, such as actual policy implementation and electoral outcomes. Comparative studies in other multilevel democracies would also enrich our understanding of this dynamic.

The study focuses solely on party manifestos, which may not perfectly reflect actual policy implementation. Furthermore, the analysis of decentralization preferences relies on two distinct, though related, measures, which might introduce some variation in results. Finally, the exclusion of MP-E from the final quantitative analysis due to its outlier status could limit the generalizability of some findings to a lesser extent.