Narrator: Listen to part of a lecture in an environmental science class. Professor: Today we're going to talk about urban heat islands. As you know, cities tend to be warmer than surrounding rural areas. This is because concrete and asphalt absorb and re-radiate heat more than vegetation does. But there's a lesser-known factor: the waste heat from buildings and vehicles. When we use air conditioning, for example, the heat is pumped outside, adding to the ambient temperature. This creates a feedback loop: hotter cities lead to more AC use, which leads to more waste heat, which makes it even hotter. One solution is to increase albedo—that is, reflectivity—by painting rooftops white or using reflective materials. Studies show this can lower city temperatures by a few degrees. Another approach is green roofs, which absorb heat and also provide insulation. However, both methods have trade-offs. White roofs work best in hot climates but may increase heating costs in colder seasons. Green roofs require maintenance and water. So, cities must weigh these factors based on their climate and resources.
❓ Question What is the main point the professor makes about the urban heat island effect?
A. It is caused solely by lack of vegetation in cities.
B. Waste heat from air conditioning contributes to a feedback loop.
C. Painting rooftops white is the most effective solution in all climates.
D. Green roofs are cheaper to maintain than white roofs.
✅ Correct Answer
Waste heat from air conditioning contributes to a feedback loop.
TOEFL Listening Tips
Skim the questions first to predict the content
Watch for signal words in lectures and conversations (however, actually, in fact)
For main idea questions, focus on the beginning; for detail questions, focus on examples and data
For attitude questions, pay attention to the speaker's tone and word choice
Take notes on keywords; don't try to write down every word
