Nghe TOEFL

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Narrator: Listen to part of a lecture in an environmental science class. Professor: Today we're going to talk about urban heat islands—the phenomenon where cities are significantly warmer than surrounding rural areas. One major cause is the replacement of natural surfaces with concrete and asphalt, which absorb and retain heat. Another factor is the lack of vegetation, since trees and plants provide shade and release moisture through evapotranspiration. Now, many cities are adopting green roofs—rooftops covered with vegetation—to combat this effect. Green roofs not only reduce the heat island effect by cooling the air, but they also manage stormwater runoff and improve insulation, which lowers energy costs. However, the initial installation cost is higher than traditional roofs, and maintenance can be challenging, especially in dry climates. Despite these drawbacks, studies show that the long-term benefits often outweigh the costs, particularly in densely populated areas where green space is limited. So, the key is to weigh the upfront investment against the environmental and economic gains over time.