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 retain heat. However, a recent study in Melbourne found that increasing tree canopy coverage by 20% could reduce surface temperatures by up to 4 degrees Celsius during summer afternoons. Interestingly, the effect was strongest in residential areas with low-rise buildings, not in high-density commercial zones. The researchers also noted that green roofs, while helpful, had a smaller impact than street trees. Therefore, city planners are now prioritizing tree planting along main roads and in parks.