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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. This happens mainly because of the abundance of concrete and asphalt, which absorb and re-emit heat from the sun more than natural landscapes do. Additionally, waste heat from vehicles and buildings adds to the effect. But there are mitigation strategies. For example, planting trees and creating green roofs can provide shade and cool the air through evapotranspiration. Another approach is using cool pavements that reflect more sunlight and absorb less heat. However, these solutions aren't always equally effective. Cool pavements work best in hot, sunny climates, while green roofs are more beneficial in temperate regions. Interestingly, a study in Los Angeles found that increasing urban vegetation by 10% could lower surface temperatures by up to 4 degrees Celsius, but it would also increase humidity, which might make people feel less comfortable. So, it's a complex trade-off that city planners must consider.