Today in our environmental science lecture, we're discussing urban heat islands. A key point is that cities tend to be warmer than surrounding rural areas due to human activities and the concentration of buildings. For instance, concrete and asphalt absorb and re-emit heat more than natural landscapes. One effective mitigation strategy is increasing green spaces, such as parks and green roofs, which can lower local temperatures significantly. However, the lecturer emphasizes that the most cost-effective solution is planting street trees, as they provide shade and cool the air through evapotranspiration. While reflective materials on buildings also help, they are more expensive to implement on a large scale.