Listen to part of a lecture in an environmental science class. Professor: Today we’re going to discuss a surprising factor in urban heat islands—trees. Now, you might think planting more trees always cools a city, but that’s not entirely true. A study in Melbourne, Australia, found that while trees provide shade, they also release water vapor through transpiration. This process can actually trap heat at night, especially in dry, low-wind conditions. The researchers used sensors to measure temperatures in different park areas. They discovered that on calm, clear nights, the temperature under dense tree canopies was up to 2 degrees Celsius warmer than nearby open spaces. Why? Because the water vapor acts like a blanket, absorbing outgoing radiation. However, during the day, the shade effect dominates, cooling the ground. So the net effect depends on the climate and the type of trees. In humid regions, transpiration is less effective, so trees are more beneficial. This complexity means city planners must consider local weather patterns before designing green spaces.
❓ 题目 What does the professor say about the effect of trees on nighttime temperatures in the Melbourne study?
A. Trees always cool the air at night due to shade.
B. Dense tree canopies can trap heat, making nights warmer.
C. Trees have no measurable effect on nighttime temperatures.
D. Transpiration only occurs during the day, not at night.
✅ 正确答案
Dense tree canopies can trap heat, making nights warmer.
