Comparative politics has traditionally viewed environmental issues as valence topics, universally supported to varying degrees. However, recent research challenges this notion, suggesting that parties adopt distinct positions on climate change mitigation. Why has the environmental debate become positional? This study argues that parties take clear stances on environmental issues when energy dominates the political agenda. Two mechanisms are proposed to explain this shift: the broad relevance of energy to multiple stakeholders and its connection to decarbonization. Energy’s centrality engages a significant portion of the population concerned about energy access and affordability. Additionally, decarbonization policies bring severe domestic distributional consequences, prompting parties to address the topic strategically. As energy dominates climate discussions, it creates opportunities for parties to mobilize voters. Parties’ positions depend on whether a pro- or anti-environmental strategy helps attract new supporters while maintaining existing voter alignments. This theoretical argument is tested using party manifestos from 24 European countries (1980–2023). I offer two pieces of evidence. First, I descriptively confirm that parties’ attention to energy issue has increased over time and has dominated the climate debate. Second, I use a novel measure of parties’ environmental positions, based on their manifestos, and show that parties’ positions polarize as energy issues dominate the political debate. These findings have significant implications for understanding party competition, demonstrating that debates over environmental issues are dynamic rather than static. The evolution of climate issues, particularly the centrality of energy, fundamentally shapes how parties position themselves, influencing the trajectory of environmental policy and voter alignment.