Today in our environmental science lecture, we'll discuss urban heat islands. Cities tend to be warmer than surrounding rural areas because concrete and asphalt absorb and re-emit heat. One surprising solution is green roofs, which are covered with plants. A study in Chicago found that green roofs can reduce building temperatures by up to 5 degrees Celsius, cutting air conditioning costs by 20%. However, the initial installation is expensive, and maintenance requires regular watering. Despite this, many cities now offer tax incentives to encourage adoption.