<p>The climate crisis mandates building renewable energy infrastructure faster, increasing the demand for primary materials with large environmental footprints. Sourcing these materials from urban mines can mitigate such impacts, but the potential of recycling depends on waste availability. Here, we use life cycle assessment and monetization of impacts to explore the environmental implications of recycling fossil infrastructure that may become obsolete during the transition. We find that among many materials in fossil infrastructure, recycling steel and copper is particularly appealing, as their stocks (1.34 gigatons and 10.03 megatons) align with the projected energy transition demands (145% and 32% of median demand between 2020–2050, respectively). Recycling steel and copper in fossil infrastructure could save up to 1.95 gigatons CO_2,eq and 11.69 trillion US Dollars in externality costs until 2050, while remaining competitive considering current production methods. Using recycled steel and copper would also reduce the carbon footprint of energy transition technologies—for example, wind and photovoltaic power—by one third.</p>