托福听力

🎧 听力原文

Narrator: Listen to part of a lecture in an environmental science class. Professor: So, when we talk about urban heat islands, we're referring to the phenomenon where cities are significantly warmer than surrounding rural areas. This happens because concrete and asphalt absorb and re-radiate heat more than vegetation does. Now, one common solution is planting more trees, but there's a less obvious factor: the albedo effect. Albedo is a measure of how much solar radiation a surface reflects. Light-colored surfaces, like white roofs, have high albedo, meaning they reflect more sunlight. Dark surfaces, like black tar roofs, have low albedo and absorb heat. A study in Los Angeles found that if all roofs were painted white, the city's average temperature could drop by about 1.5 degrees Celsius. However, there's a catch: white roofs might cause more cooling in winter, increasing heating costs. So, the strategy needs to be region-specific. In tropical climates, the benefits are clear, but in colder areas, a balance between summer cooling and winter heating is crucial.