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Narrator: Listen to part of a lecture in an environmental science class. Professor: Okay, so today we're going to talk about urban heat islands. As you know, cities tend to be warmer than surrounding rural areas. This is due to the abundance of concrete and asphalt, which absorb and re-radiate heat, as well as the lack of vegetation. But there's a lesser-known factor: waste heat from buildings and vehicles. Now, one common mitigation strategy is planting trees, which provide shade and cool the air through evapotranspiration. However, a recent study from a university in Arizona suggests that reflective rooftops, often called cool roofs, might be more effective on a city-wide scale. The study used computer models to simulate different scenarios. They found that if every rooftop in a typical city were painted white or covered with a reflective membrane, the average summer temperature could drop by about 1.5 degrees Celsius. In contrast, increasing tree cover by 20% would only lower the temperature by about 0.7 degrees. But, cool roofs have a downside—they don't provide other benefits like reducing stormwater runoff or improving air quality, which trees do. So, ideally, we should combine both strategies. Any questions?