Nghe TOEFL

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Listen to part of a lecture in an environmental science class. The professor is discussing the concept of 'urban heat islands'. Professor: Now, we've talked about how cities tend to be warmer than surrounding rural areas. This is known as the urban heat island effect. But what causes it? Well, one major factor is the replacement of natural surfaces with materials like concrete and asphalt. These materials absorb and retain heat from the sun much more than vegetation does. Trees and plants provide shade and release moisture through a process called evapotranspiration, which cools the air. In cities, we lose that cooling effect. Another factor is waste heat from human activities—think of cars, air conditioners, and industrial processes. All of these generate heat. Also, the tall buildings in urban areas can trap heat by reducing wind flow and creating what we call an urban canyon. This can make the heat even more intense. So, when you combine these factors, it's not surprising that cities can be several degrees warmer than the countryside around them. Now, there are strategies to mitigate this, like planting more trees or using reflective materials on rooftops. But we need to think about how these solutions can be implemented effectively in different climates.