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, cities tend to be warmer than surrounding rural areas. This is known as the urban heat island effect. It occurs because materials like concrete and asphalt absorb and retain heat during the day, then release it slowly at night. Additionally, tall buildings trap heat and reduce wind flow. Vegetation, which provides shade and releases moisture through transpiration, is often scarce in urban areas, so cooling is limited. Interestingly, the intensity of the heat island effect varies. It is typically strongest on clear, calm nights, when the heat stored in buildings and pavement is released back into the air. In contrast, cloudy and windy conditions mix the air and reduce the temperature difference. Now, some cities are adopting green roofs and increasing tree cover to combat this effect. These measures not only lower surface temperatures but also improve air quality and reduce energy consumption for cooling. However, the initial costs can be high, which is a barrier for many municipalities."