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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. As you know, cities tend to be warmer than surrounding rural areas. This is because concrete and asphalt absorb and re-radiate heat, and buildings block wind, reducing cooling. But there's a less obvious factor: the lack of vegetation. Trees and plants cool the air through a process called evapotranspiration, where water evaporates from leaves, similar to sweating. When we replace green spaces with parking lots, we lose this natural cooling. However, some cities are fighting back. For example, Chicago has been planting green roofs—rooftops covered with vegetation. These roofs not only absorb less heat than traditional black tar, but they also insulate buildings, reducing energy costs. Studies show that a widespread adoption of green roofs could lower a city's average temperature by up to 2 degrees Celsius. But there's a catch: green roofs require significant upfront investment and maintenance. So while they're promising, they're not a quick fix. The key is to combine them with other strategies, like planting street trees and using reflective pavement materials.