Green Roofs as Carbon Sequestration Tools in Urban Environments

Green roofs have emerged as a critical nature-based solution for urban climate mitigation, offering potential for carbon sequestration alongside thermal regulation and stormwater management. This literature review synthesizes recent research (2020–2025) on green roof carbon dynamics, with emphasis on temperate climate zones and methodological approaches relevant to environmental impact assessment. We systematically analyzed 47 peer-reviewed studies published between 2020 and 2025 through comprehensive database searches, focusing on substrate composition effects, vegetation type performance, seasonal variation patterns, and Life Cycle Assessment methodologies. Key findings from extensive systems in maritime and temperate–arid climates reveal that substrate organic carbon typically dominates total carbon storage, significantly exceeding plant biomass contributions. Extensive green roofs demonstrate a wide range of annual carbon fluxes—from initial net emissions of +20.2 g C m−2 yr−1 during establishment phases to substantial net sequestration rates reaching up to −1762 g CO2 m−2 yr−1 in mature systems—depending strongly on substrate age, vegetation type, and local climate conditions. Native grass and forb mixtures consistently outperform Sedum monocultures in long-term carbon storage through enhanced root biomass and substrate organic matter accumulation. Substrate depth, composition, and moisture retention capacity emerge as primary controls on carbon balance, with recycled waste materials showing promise for enhanced storage. Life cycle assessment studies indicate that indirect carbon savings from reduced building energy consumption frequently exceed direct biological sequestration by one to two orders of magnitude. However, significant methodological heterogeneity, limited long-term monitoring datasets, and geographic gaps—particularly for Central and Eastern European temperate zones—constrain robust comparative analysis and transferability of findings. This review identifies critical research priorities, including standardized carbon accounting frameworks, dynamic life cycle assessments incorporating temporal sequestration trajectories, multi-decadal monitoring programs, and region-specific validation studies for temperate continental climates similar to Romania’s Cfb/Dfb zones.