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-emit heat. However, a recent study in Melbourne found that increasing tree canopy by just 20% could reduce surface temperatures by up to 4 degrees Celsius. The researchers also noted that green roofs, while helpful for insulation, had a smaller impact on street-level cooling. Interestingly, the study emphasized that the placement of trees is more critical than the total number, as shade on western-facing walls proved most effective during afternoon heat peaks.