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Narrator: Listen to part of a lecture in an environmental science class. Professor: Today we're going to talk about a fascinating phenomenon known as 'urban heat islands.' Essentially, cities tend to be warmer than surrounding rural areas. Why is that? Well, one major factor is the replacement of natural surfaces with asphalt and concrete. These materials absorb and retain heat during the day and release it slowly at night. Another factor is the lack of vegetation. Trees and plants provide shade and cool the air through a process called evapotranspiration. When we remove them, we lose that natural cooling effect. Additionally, human activities—like running air conditioners, cars, and industrial processes—generate waste heat. Interestingly, the temperature difference can be as much as 5 to 10 degrees Fahrenheit. This can have serious consequences, such as increased energy consumption for cooling, higher air pollution levels, and even heat-related health issues. Some cities are tackling this by planting more trees, creating green roofs, and using reflective materials on buildings. These measures not only reduce temperatures but also improve quality of life. So, understanding and mitigating urban heat islands is crucial for sustainable urban planning.