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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. As you know, cities tend to be warmer than surrounding rural areas. This is mainly because concrete and asphalt absorb and re-radiate heat, and there are fewer trees to provide shade and cool through evapotranspiration. But there’s an interesting solution that some cities are adopting: green roofs. A green roof is a roof that is partially or completely covered with vegetation and a growing medium, planted over a waterproof membrane. These roofs can reduce surface temperatures by up to 40 degrees Fahrenheit compared to traditional roofs. They also improve insulation, which lowers energy costs for heating and cooling. Moreover, green roofs absorb rainwater, reducing stormwater runoff and the risk of flooding. Some cities, like Toronto, have even passed bylaws requiring green roofs on new large buildings. However, the initial cost is high, and maintenance can be challenging. Still, many experts argue that the long-term benefits outweigh the upfront expense, especially as climate change intensifies the heat island effect.