Nghe TOEFL

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Listen to part of a lecture in an environmental science class. The professor is discussing the concept of urban heat islands. "Now, we all know that cities tend to be warmer than surrounding rural areas. This is called the urban heat island effect. But why does it happen? One major factor is the materials we use to build our cities. Concrete and asphalt absorb and retain heat much more than natural surfaces like soil and vegetation. During the day, these materials soak up solar radiation, and at night, they slowly release it, keeping the city warm even after the sun goes down. Another factor is the lack of vegetation. Trees and plants provide shade and release moisture through a process called evapotranspiration, which cools the air. When we replace green spaces with buildings and roads, we lose that cooling effect. Also, human activities—like driving cars, running air conditioners, and using electricity—generate waste heat that contributes to the overall temperature. So, the urban heat island is not just a simple phenomenon; it's a combination of design choices, loss of natural cooling, and human energy use." Now, the professor discusses the urban heat island effect. What is one factor mentioned that contributes to this effect?