Studies on urban heat island (UHI) have been more than a century after the phenomenon was first discovered in the early 1800s. UHI emerges as the source of many urban environmental problems and exacerbates the living environment in cities. Under the challenges of increasing urbanization and future climate changes, there is a pressing need for sustainable adaptation/mitigation strategies for UHI effects, one popular option being the use of reflective materials. While it is introduced as an effective method to reduce temperature and energy consumption in cities, its impacts on environmental sustainability and large-scale non-local effect are inadequately explored. This paper provides a synthetic overview of potential environmental impacts of reflective materials at a variety of scales, ranging from energy load on a single building to regional hydroclimate. The review shows that mitigation potential of reflective materials depends on a set of factors, including building characteristics, urban environment, meteorological and geographical conditions, to name a few. Precaution needs to be exercised by city planners and policy makers for large-scale deployment of reflective materials before their environmental impacts, especially on regional hydroclimates, are better understood. In general, it is recommended that optimal strategy for UHI needs to be determined on a city-by-city basis, rather than adopting a “one-solution-fits-all” strategy

Exacerbated heat stress has resulted in a series of environmental issues in urban areas. Mounting empirical evidence shows that urban trees are effective in mitigating the thermal stress in the built environment, whereas large‐scale numerical simulations remain scarce. In this study, the effects of shade trees on the built environment, in terms of radiative cooling, pedestrian thermal comfort, and urban land surface energy balance, were evaluated over the contiguous United States. The projected scenario was simulated using a coupled Weather Research and Forecasting‐urban modeling system, incorporating the radiative shading of urban trees only. Results show that on average the mean near‐surface air temperature in urban areas decreases by 3.06 °C over the entire contiguous United States with the shading effect. Analysis of pedestrian thermal comfort shows that shade trees improve the thermal comfort level in summers, but could be detrimental in winters for cities located in temperate or subpolar climate zones. In addition, it was found that trees alter the surface energy balance by primarily enhancing the radiative cooling, leading to significant changes in the sensible heat but the ground heat comparatively intact.

Rooftop photovoltaic (RPV) is often understood as a niche contribution to climate change mitigation. However, the global potential of RPVs to mitigate global warming is unknown. Here we map the global rooftop area at 1-km resolution, quantifying 286,393 km² of rooftops worldwide through geospatial data mining and artificial intelligence techniques. Using nine advanced Earth system models from the coupled model intercomparison project phase 6, we reveal that RPVs could substantially contribute to reducing global temperatures by 0.05–0.13 °C before 2050. Region-specific analysis underscores the variability in RPV potential and the necessity of tailored approaches to optimize RPV deployment, considering local solar resources, existing infrastructure and grid carbon intensity. Our findings reveal that leveraging RPV systems offers a viable and impactful strategy for reducing carbon footprints and combating climate change globally, while advocating targeted interventions to enhance the benefits of RPVs, particularly in areas with high solar radiation or rapid urbanization.