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-radiate heat. One effective mitigation strategy is increasing green spaces, such as parks and green roofs. However, a recent study in Melbourne found that planting trees along streets can reduce local temperatures by up to 2 degrees Celsius during summer afternoons, but only if the trees are mature and have a wide canopy. Younger trees have less impact. Additionally, the study noted that light-colored pavements reflect more sunlight, but they don't cool the air as much as trees do.
❓ According to the lecture, what condition is necessary for street trees to significantly reduce local temperatures?
A. They must be planted in large numbers.
B. They need to be mature with a wide canopy.
C. They should be placed near buildings.
D. They require light-colored pavements around them.