Narrator: Listen to part of a lecture in an environmental science class. Professor: Today we're going to talk about urban heat islands. Now, cities tend to be warmer than surrounding rural areas. Why is that? Well, there are several reasons. First, concrete and asphalt absorb and re-radiate heat, unlike vegetation, which provides shade and cools through evapotranspiration. Second, buildings and roads trap heat, and waste heat from vehicles and air conditioners adds to it. Third, the lack of green spaces reduces airflow and cooling. So cities can be several degrees warmer, especially at night. But there's a solution: green roofs. By planting vegetation on rooftops, we can reduce surface temperatures, improve insulation, and even manage stormwater. Some studies show that green roofs can lower a building's cooling costs by up to 25 percent. However, they require more maintenance and have higher upfront costs than traditional roofs. Despite that, many cities are now offering incentives for green roof installation. So, while they're not perfect, they're a promising strategy for mitigating the heat island effect.
❓ 题目 What is the main topic of the lecture?
A. The causes and mitigation of urban heat islands
