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Listen to part of a lecture in an environmental science class. Today we're going to talk about urban heat islands. Now, you might think that cities are just warmer because of all the concrete and asphalt, but it's more complex than that. One major factor is the lack of vegetation. Trees and plants provide shade and release moisture through transpiration, which cools the air. When we replace green spaces with buildings and roads, we lose that cooling effect. Another factor is waste heat from human activities—think of cars, air conditioners, and factories. These generate heat that gets trapped in the urban canyon. The shape of the city itself matters too. Tall buildings can block wind, reducing natural ventilation. Interestingly, the heat island effect is strongest at night, because the materials like concrete and brick slowly release the heat they absorbed during the day. This can make nighttime temperatures in cities significantly higher than in surrounding rural areas. This has real consequences for health, especially during heat waves, and for energy use, as people need more air conditioning. So, cities are experimenting with solutions like green roofs and reflective materials. But there's a trade-off, as these can be costly and sometimes change the look of historic buildings.