Urbanization Contributes Little to Global Warming but Substantially Intensifies Local and Regional Land Surface Warming

Increasing urbanization causes an urban heat island (UHI) effect and exacerbates health risks of heat waves due to global warming. The surface UHI (SUHI) in large cities has been extensively studied, yet a systematic evaluation on the impacts of urbanization on local-to global-scale land surface warming is lacking. We propose a new procedure to quantify the warming effects of urbanization at local, regional, and global scales using high-resolution satellite observations. We find strong local warming effects for 88% of the urban-dominated pixels across the globe and cooling effects for the rest of the urban lands on a diurnal mean timescale, with a global urban mean intensity of 1.1 degrees C in 2015. The SUHI effects differ substantially by time of day, season, and climate zone, and are closely related to surface evapotranspiration. By extending local effects to the entire land surface, we estimate a diurnal mean warming of only 0.008 degrees C globally. However, urbanization can have large warming effects regionally, especially in eastern China, the eastern United States, and Europe. In addition, we show that global urban expansion results in over three-quarters of SUHI effects in 1985-2015, and its effect will likely increase by 50%-200% by the end of this century. The SUHI-added warming could be up to 0.12 degrees C in summer in Europe by 2100 under a fossil-fueled development pathway. Our results reveal that urbanization substantially intensifies local and regional land surface warming and that prioritized attention should be given to the SUHI-added warming in highly or rapidly urbanized regions.