Carbon-negative transition by utilizing overlooked carbon in waste landfills

<p>Landfills play a crucial role in urban climate solutions, as the decomposition of their “hidden” carbon stock contributes to 8.8% of global methane emissions. While controlling landfill gas emissions is the most commonly used intervention, a systematic approach to manage the carbon cycle in landfills remains elusive. In this study, we developed a quantitative solid-water-gas coupling model to estimate the carbon stock in landfills across 346 cities in China. Our findings reveal a standing landfill carbon stock 506.3 ± 4.2 Tg, which could potentially substitute for 20% of soil organic carbon in green spaces and 1 year of residential electricity consumption of cities. Our scenario analyses show that by implementing a life-cycle package of interventions (incl., input minimization, stock utilization, and leakage reduction), the total carbon stock in landfills could be reduced to 230.1 Tg with a negative annual carbon emission (-57.1 Tg CO<sub>2</sub> eq/year) reached by 2030. These interventions could cumulativly cut greenhouse gas (GHG) by 753.3 Tg, representing 62.2% of the landfill-related GHG emissions and 2.0% of China’s carbon debt towards the 1.5°C warming targets. Landfill mining contributes 52.3% of these reductions, while in-situ aerobic restoration accounts for 14.4%, positioning landfills as a potential carbon-negative sector that can drive cities towards carbon-neutrality.</p>