Today in our environmental science lecture, we will discuss the impact of urban green spaces on local climate. Recent studies show that parks and gardens can reduce surrounding temperatures by up to 5 degrees Celsius during heatwaves. This cooling effect is mainly due to shade provided by trees and the process of evapotranspiration, where plants release water vapor. However, the effectiveness depends on the size and density of the green area. For instance, a single tree can cool a small area, but a network of parks across a city can create a significant 'cool island' effect. Interestingly, even small rooftop gardens contribute, though their impact is more localized.