The Pace of Urbanization Regulates Global Urban Gross Primary Productivity Trends

Urban expansion replaces vegetated land with impervious surfaces, significantly reducing urban Gross Primary Productivity (GPP u ). Conversely, rising CO 2 levels and warming associated with climate change can enhance GPP u . The interplay between these opposing effects on GPP u remains poorly understood, resulting in considerable uncertainties for estimating the long‐term dynamics of urban carbon storage. Using an improved Carnegie‐Ames‐Stanford approach (CASA) model that accounts for urban CO 2 , we evaluated the long‐term trends and driving factors of GPP u in 2126 cities worldwide, spanning both historical and future periods. The study revealed that the average urban expansion rate (UER) of global cities from 1982 to 2024 was 21.3 km 2 /year. Rapid urban expansion was predominantly observed in cities in China and North America; whereas, cities in Europe exhibited relatively slower expansion rates. The response of GPP u to urban expansion was found to be dependent on the UER. In cities with faster UERs than 5.83 km 2 /year, the negative impact of urban expansion surpassed the positive effects of climate change on long‐term GPP u , resulting in a downward trend in GPP u (−2.48 g C/m 2 /year). Conversely, in cities with slower UERs (commonly observed in Europe), an opposite pattern was observed, leading to an upward trend in GPP u (1.21 g C/m 2 /year). The projected future response and driving factors of GPP u to urbanization were expected to resemble those observed in the historical period. These findings highlight that the pace of urbanization acts as a fundamental regulator of GPP u , underscoring the need for growth‐rate‐specific strategies to sustain regional carbon sequestration.