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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, a phenomenon where cities are significantly warmer than surrounding rural areas. Why? Well, one major factor is the replacement of natural surfaces with materials like concrete and asphalt. These materials absorb and retain heat during the day and release it slowly at night, so temperatures don't drop as much as in rural areas. Another contributor is the lack of vegetation. Trees and plants provide shade and release moisture through transpiration, which cools the air. When we remove them to make way for buildings, we lose that natural cooling effect. Also, human activities—like running air conditioners, cars, and industrial processes—generate waste heat. Interestingly, urban heat islands can affect local weather patterns, increasing the frequency of thunderstorms downwind of cities. To mitigate this, some cities are implementing green roofs, which are covered with vegetation, and planting more street trees. These measures not only lower temperatures but also reduce energy consumption for cooling. So, understanding these dynamics is crucial for sustainable urban planning.