การฟัง TOEFL

🎧 บทถอดเสียง

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. Why does this happen? Well, one major factor is the replacement of natural surfaces with materials like concrete and asphalt. These materials absorb and retain heat from the sun during the day, and then slowly release it at night, so the city doesn't cool down as much as the countryside. Another factor is the lack of vegetation. Trees and plants provide shade and also cool the air through a process called evapotranspiration, where water evaporates from leaves, taking heat with it. When you remove vegetation, you remove that natural cooling mechanism. Also, human activities, such as driving cars and running air conditioners, generate waste heat that adds to the overall temperature. So, the combination of heat-absorbing surfaces, reduced green space, and anthropogenic heat sources creates a significant temperature difference. Interestingly, the intensity of an urban heat island can vary depending on the weather and the time of day. It's often most pronounced on clear, calm nights. So, that's a basic overview of the urban heat island effect."