Fossil CO ₂ emissions from warehouse and distribution centers in Southern California’s Inland Empire

Abstract The rise of e-commerce has led to a rapid expansion of warehouses and distribution centers (W&DCs). However, impacts of e-commerce logistics, including emissions of fossil fuel-derived carbon dioxide (ffCO 2 ) on urban greenhouse gas inventories, remain poorly quantified. Here, we developed a 40 year tree-ring radiocarbon ( 14 C) record to isolate ffCO 2 enhancements within a W&DC cluster and in the urban background of Southern California’s Inland Empire, a region of concentrated W&DC growth during this period. Our results reveal elevated ffCO 2 concentrations (15–23 ppm) before 1984 in the residential tree, followed by a shift to lower levels that may reflect both the tree’s establishment history (likely transplanted from a more polluted environment during this period) and broader regional air quality improvements. Post-1984, urban background emissions increased alongside population growth. Strikingly, the W&DC cluster exhibited 12 ppm higher ffCO 2 than the urban background from 2000 to 2019, representing a threefold enhancement. This ffCO 2 enhancement occurred during a period when local traffic volume doubled (from approximately 4500–11 000 average daily trips between 2007 and 2023) at arterial roads directly serving the W&DC cluster and a 30% increase in traffic volumes at the nearby I-215/SR-60 interchange, the main transportation hub connecting the cluster to the Ports of Los Angeles and Long Beach. Our findings demonstrate that tree-ring 14 C records effectively detect W&DC emissions in complex urban environments and highlight the need for additional W&DC emissions observation and regulation. Future work should identify whether fleet modernization, traffic management or dwell-time controls would be most effective for achieving carbon neutrality objectives.