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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. You might think that planting more trees would always lower city temperatures, but recent research shows that the type of tree matters a lot. Some trees, like oaks, have broad leaves that provide shade and release water vapor through transpiration, which cools the air. However, other trees, such as certain pines, have dense canopies that trap heat and emit volatile organic compounds, or VOCs. These VOCs can react with pollutants to form ozone, a greenhouse gas. In a study comparing two city blocks in Los Angeles, the block with large deciduous trees was several degrees cooler than the block with evergreen pines. The researchers concluded that while all trees help absorb carbon dioxide, their microclimatic effects vary. So city planners should prioritize species that maximize cooling, especially in hot climates. This is not just about aesthetics; it's about public health, as extreme heat is a leading cause of weather-related deaths.