The globe’s cities are warming primarily due to declining albedo, not CO2 radiative forcing.
According to a comprehensive new study published in Remote Sensing of Environment, CO2 fertilization has led to an enhanced greening trend in 72.6% of cities across the world since 1985, accelerating to 89.2% since 2001.
Per the authors, this greening trend is the key factor lowering the albedo reflecting incoming solar radiation in urban areas, amounting to a +2.76 W/m² increase in solar radiation reaching the surface from 1986-2020.
In contrast, the clear-sky-only trend from CO2 surface forcing only amounts to 0.2 W/m² per decade (22 ppm), or 0.02 W/m² per year, in the 21st century. (This trend only represents the forcing from CO2 in an imaginary world where no clouds exist.)
Thus, the positive radiative imbalance from the declining trend in albedo explains urban warming far better than an enhanced greenhouse effect from a clear-sky-only CO2 radiative forcing.