If you live near a city, you may have noticed that cities are often warmer than the surrounding countryside, especially on calm, clear nights. Even in a city like Athens, with a little over 100,000 people, we can see as much as a ten degree difference between downtown and the fields outside the city. Smaller cities can also have an effect, albeit smaller.
Dr. Marshall Shepherd of UGA posted a blog entry here on Forbes.com which explains this and also shows that for some cities, the extra trees and irrigation of yards can actually cause a cooling effect, particularly in desert areas like Phoenix.
