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Listen to part of a lecture in an environmental science class. Professor: Today, let's discuss the concept of 'urban heat islands.' As cities grow, they replace natural surfaces like soil and vegetation with asphalt, concrete, and buildings. These materials absorb and retain heat much more than natural landscapes do. During the day, they soak up solar radiation, and at night, they slowly release that heat, which keeps urban areas warmer than surrounding rural areas. This effect is especially pronounced in densely built downtown areas. But there are solutions. One strategy is to increase green spaces, such as parks and rooftop gardens, which cool the air through evapotranspiration. Another is to use 'cool roofs' made with reflective materials that bounce sunlight back into the atmosphere. Cities like Los Angeles have experimented with coating streets with a pale, heat-reflective sealant. These measures not only reduce energy consumption for air conditioning but also improve public health by lowering heat-related risks. However, implementing them broadly requires significant investment and policy changes, which can be challenging for some municipalities.