Listen to part of a lecture in an environmental science class. Professor: Today we're discussing urban heat islands—why cities are often warmer than surrounding rural areas. One major factor is the replacement of natural surfaces with materials like concrete and asphalt, which absorb and retain heat. Another is the lack of vegetation, since trees provide shade and release moisture through transpiration. But there's a less obvious contributor: waste heat from buildings, vehicles, and air conditioning units. In fact, studies show that air conditioning can increase outdoor temperatures by up to one degree Celsius in dense city centers. This creates a feedback loop—hotter air makes people use more AC, which generates more heat. To combat this, some cities are implementing cool roofs, which reflect solar radiation, and green roofs, which are covered with plants. These strategies not only lower surface temperatures but also reduce energy demand. The challenge is cost and maintenance, but long-term benefits are significant.
❓ 题目 What does the professor identify as a less obvious cause of urban heat islands?