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Listen to part of a lecture in an environmental science class. Today we're going to talk about urban heat islands, a phenomenon where cities are significantly warmer than surrounding rural areas. One major cause is the replacement of natural surfaces with asphalt and concrete, which absorb and retain heat. Another factor is the lack of vegetation, since trees and plants provide shade and release moisture through evapotranspiration. To combat this, many cities are implementing green roof initiatives. A green roof is a rooftop covered with vegetation and a growing medium. These roofs can lower surface temperatures by up to 40 degrees Celsius compared to conventional roofs. They also reduce stormwater runoff by absorbing rainwater, and they improve air quality by filtering pollutants. However, the initial installation cost is higher than traditional roofing, which is a barrier for some building owners. Nevertheless, over time, the energy savings from reduced cooling needs can offset the upfront expense. So, while the initial investment may seem steep, the long-term benefits are substantial.