Seasonal Controls of Biogenic Uptake and Anthropogenic Emissions on Carbon Dynamics in a Post‐Industrial Shrinking City

Abstract Urban carbon mitigation is increasingly urgent as global greenhouse gas emissions intensify. Post‐industrial shrinking cities such as Detroit face unique challenges and opportunities with widespread vacancy yet potential for extensive greenspace expansion. Here, we investigate the seasonal controls on net ecosystem exchange (NEE) of carbon dioxide (CO 2 ) in the post‐industrial shrinking city of Detroit, Michigan from August 2019 to June 2022. We combined eddy covariance measurements with a camera‐based greenness index and satellite‐based normalized difference vegetation index (NDVI) to parse daily and seasonal flux variability. We hypothesized that growing‐season vegetation uptake partially offsets emissions but is overshadowed by dominant anthropogenic sources. Results show Detroit is a persistent net carbon source with dormant‐season fluxes driven by fossil‐fuel heating and industrial plumes far exceeding the modest carbon mitigation provided by urban greenspaces in summer. A 1% increase in greenspace coverage was associated with a median NEE decrease of 0.21 gCO 2 m −2 d −1 . Feature importance analyses confirm that heating and traffic emissions are the primary drivers of daily flux variability. The COVID‐19 restrictions led to only brief emissions dips highlighting persistent anthropogenic sources. Although urban reforestation can partially offset emissions in the growing season, our findings show that large wintertime fluxes from heating and industrial processes keep Detroit in net source territory. Consequently, sustained emission reductions beyond greenspace expansion are essential for achieving substantial CO 2 mitigation in post‐industrial shrinking cities.