Assessing urban green roofs for CO2 removal via enhanced rock weathering in Europe

Abstract

Green roofs represent a novel and promising platform for integrating enhanced rock weathering (ERW) as a carbon dioxide removal (CDR) strategy within urban environments. By utilising underused rooftop spaces, rock (feedstock)-amended green roofs for ERW could contribute meaningfully to climate mitigation targets while fitting within existing markets and policy frameworks. Despite this, a comprehensive assessment of opportunities and barriers to deployment is missing. Here, we provide a conceptual assessment, serving as a benchmark for the potential for large-scale ERW green roof deployment in Europe, examining literature from similar applications and estimating theoretical CDR potential at European and global scales, and identifying key opportunities and challenges. Our estimates suggest that, under conditions where 100% reactivity is achieved, green roofs in Europe could theoretically remove tens of millions of tonnes of CO2 via ERW (in addition to plant uptake) by 2060, assuming expanded rooftop coverage. However, these findings are based on maximum geochemical capacities rather than empirical data from real-world conditions. Globally, theoretical removal potential ranges from tens to hundreds of millions of tonnes CO2 per year, with major contributions from Central Asia, North America, Latin America and the Pacific. Beyond CDR benefits, ERW green roofs can enhance photovoltaic performance by improving energy efficiency and reducing evaporation, although weight capacity of each rooftop must be evaluated. This approach offers a promising pilot-scale research opportunity, bridging the gap between laboratory experiments and potential field-scale applications, but the feasibility and effectiveness of large-scale deployment will require further empirical investigation, especially concerning climatic conditions, infrastructure, costs and policy support.