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 a surprising factor that can affect local climate: the color of roofs. Dark roofs absorb more solar radiation, which can raise the temperature of a building and the surrounding air. In cities, this contributes to the 'urban heat island' effect, where urban areas are warmer than nearby rural areas. To combat this, many cities are now encouraging 'cool roofs' – roofs painted white or made of reflective materials. These roofs reflect sunlight, reducing heat absorption. Studies have shown that cool roofs can lower a building's cooling costs by up to 20 percent. They also help reduce smog, because cooler air slows the chemical reactions that create ground-level ozone. However, cool roofs are not a panacea. In colder climates, they might increase heating costs in winter, since less heat is absorbed. Therefore, the decision to install a cool roof depends on the local climate and the balance between cooling and heating needs.