Nghe TOEFL

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Listen to part of a lecture in an environmental science class. Professor: Today we're going to discuss the impact of urbanization on local ecosystems, specifically the phenomenon known as the urban heat island effect. This occurs when cities become significantly warmer than surrounding rural areas. Why is that? Well, buildings, roads, and other infrastructure absorb and re-emit the sun's heat more than natural landscapes do. Additionally, vegetation is often reduced in cities, which means less shade and less evapotranspiration—plants release water vapor that cools the air. Another factor is waste heat from vehicles and air conditioning. Interestingly, the effect can be mitigated by green roofs, which are covered with vegetation. Studies have shown that green roofs can lower rooftop temperatures by up to 30 degrees Celsius and reduce energy consumption for cooling. Moreover, they help manage stormwater runoff. However, the initial cost of installing green roofs is high, and maintenance can be challenging. Despite these drawbacks, many cities are adopting them as a sustainable solution.