What phenomenon makes cities warmer than nearby rural areas?

The phenomenon that makes cities warmer than nearby rural areas is called the urban heat island effect.

Buildings, roads, and pavements absorb solar energy during the day and release it slowly after sunset. Cities also have less vegetation and exposed soil, so less incoming energy is used for evapotranspiration. Waste heat from vehicles, buildings, industry, and air-conditioning systems adds another source of warmth.

The effect is often strongest at night, when rural surfaces cool quickly but urban materials continue releasing stored heat. Calm, clear conditions can make the temperature difference more noticeable because wind and clouds would otherwise mix or reduce the contrast.

Urban heat islands are not the same as global warming. The former is a local effect caused by land cover and human activity, while the latter is a long-term change in Earth’s climate system. Trees, green roofs, reflective surfaces, and cooler pavements can reduce urban heat.