Nghe TOEFL

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Listen to part of a lecture in an environmental science class. Professor: Today we're going to talk about urban heat islands. As you know, cities tend to be warmer than surrounding rural areas. This is because of a combination of factors. First, concrete and asphalt absorb and re-radiate heat more than vegetation does. Second, buildings block wind, reducing natural cooling. Third, waste heat from vehicles and air conditioners adds to the effect. The temperature difference can be as much as five degrees Celsius at night. Interestingly, the heat island effect is not uniform across a city. Parks and green spaces can be several degrees cooler than nearby dense commercial areas. This has led some cities to implement cool roof programs, where rooftops are painted white or covered with reflective materials. These roofs can lower building temperatures and reduce air conditioning needs. But there's a trade-off: in winter, the same reflective surfaces may increase heating costs. So, urban planners must weigh the seasonal benefits carefully. Now, let's consider a specific example...