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Narrator: Listen to part of a lecture in an environmental science class. Professor: Today, let's talk about urban heat islands. As you know, cities tend to be warmer than surrounding rural areas. This is because concrete and asphalt absorb and re-radiate heat more than vegetation does. Additionally, waste heat from vehicles and air conditioners adds to the effect. But here's an interesting solution: green roofs. By covering rooftops with plants and soil, buildings can reduce heat absorption. Studies show that a green roof can lower the surface temperature of a roof by up to 40 degrees Celsius compared to a traditional black roof. This not only cools the building, reducing energy costs, but also helps mitigate the overall urban heat island effect. However, green roofs require regular maintenance, such as watering and weeding, which can be costly. Some cities offer tax incentives to offset these costs. So, while the initial investment is high, the long-term benefits—both environmental and economic—are significant.