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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 are often warmer than surrounding rural areas, sometimes by as much as five degrees Celsius. Why? Well, one major factor is the materials we build with. Concrete and asphalt absorb and retain heat during the day, and then release it slowly at night. That's why cities stay warm even after sunset. Another factor is the lack of vegetation. Trees and plants provide shade and release moisture through transpiration, which cools the air. In cities, we've replaced green spaces with buildings and roads, so there's less natural cooling. But there are solutions. One is green roofs, which are covered with plants. These roofs not only insulate buildings, reducing energy costs, but they also absorb rainwater and help lower the surrounding temperature. Another solution is planting more street trees. Studies show that increasing tree canopy by just ten percent can reduce surface temperatures by up to four degrees Celsius. So, while the problem is significant, we have practical ways to mitigate it.