Decarbonizing cities from below: deep geothermal energy as a pillar of urban transformation

Cities are hubs of resource consumption and hotspots of vulnerability, yet they are also places where climate-neutral solutions need be co-designed, tested, and scaled. A central gap in many transformation pathways is that urban energy strategies are still planned largely “from the surface”, while the subsurface and its capacities and constraints remains underexplored in socio-technical and governance-oriented transformation research. This talk positions the subsurface as a core element of integrated urban energy infrastructure within the blue–green–red framing: ensuring groundwater and water quality (blue), and shaping land-use, nature-based solutions (green) interacting with low-carbon heat and power supply (red). We focus on geothermal heat as a practical, scalable option for decarbonizing urban heat supply, while it is reducing exposure to volatile fuel imports and supporting resilient district heating concepts. With a specific subsurface focus using Potsdam as an illustrative case, we outline what it takes to make geothermal a planning-ready solution. The key message is that the subsurface is not only a boundary condition but an indispensable factor and an enabling infrastructure layer for climate-neutral urban transformation. Bringing it systematically into planning and governance is essential for robust mitigation and adaptation strategies that meet cities’ sustainability and resilience targets.