Nghe TOEFL

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Narrator: Listen to part of a lecture in an environmental science class. Professor: Today we're talking about urban heat islands, a phenomenon where cities are significantly warmer than surrounding rural areas. This happens because materials like concrete and asphalt absorb and re-emit heat more than natural landscapes. Also, waste heat from vehicles and buildings adds to the effect. But there's a lesser-known factor: the loss of trees. Trees provide shade and release moisture through transpiration, which cools the air. When we remove trees for development, we lose that cooling effect. One study in Phoenix found that neighborhoods with dense tree cover were up to 5 degrees Celsius cooler than nearby treeless areas. So, city planners are now considering 'green infrastructure'—like planting more trees and creating green roofs—to combat this. However, some argue that trees require water, which is scarce in arid regions. But researchers point out that the water used is often offset by the energy saved from reduced air conditioning use. So, the net benefit is still positive.