Climate change, biodiversity loss, and pollution constitute the triple planetary crisis, which calls for site-based mitigation actions including those at university campuses. This study introduces a spatial “tree proximity scenario” approach to assess the carbon balance of Universitas Negeri Semarang, Indonesia. The analysis focused on the Faculty of Mathematics and Natural Sciences (FMIPA), integrating tree carbon sequestration around buildings with building electricity emissions. Emissions were calculated from an inventory of electrical equipment and electricity consumption (baseline) multiplied by the Indonesian grid emission factor (0.844 kgCO₂e/kWh). Sequestration was estimated from a tree inventory (DBH ≥10 cm) using tropical allometric equations, with biomass converted to carbon (0.5) and carbon to CO₂e (3.67). Each tree was mapped relative to building footprints derived from UAV imagery and classified into distance rings: <5 m, 5–10 m, and 10–15 m. Results indicate annual electricity emissions of 526.81 tCO₂e. Annual vegetation sequestration reached 1,230.09 tCO₂e (all trees), with proximity-based scenarios yielding 378.45 (<5 m), 725.18 (≤10 m), and 971.65 tCO₂e (≤15 m). The ≤10 m zone already offsets electricity emissions by 137.65%, while the ≤15 m zone provides substantial surplus sequestration (184.44%), highlighting the dual role of trees as direct carbon sinks and indirect emission reducers through microclimate regulation. These findings underscore the relevance of prioritizing tree protection and planting within 10–15 m corridors around building masses as an effective and replicable mitigation strategy for tropical suburban campuses, aligned with the Net Zero Emission 2060 agenda.