This Policy Brief synthesizes the messages and policy insights of the REEEM project. It is based on the impact assessment of three deep decarbonisation pathways co-designed with stakeholders: Coalitions for a Low-carbon path, Local solutions and Paris Agreement. For these, it highlights often hidden challenges and opportunities of decarbonisation, which emerge when considering the connections between sectors and the cascade effects between scales. Those scales range from EU-wide, to regional, national and local. Recommendations are provided to policy makers to exploit the opportunities and minimise the challenges. A set of tools is presented to facilitate engagement.