Across the globe, many cities in industrialized countries are considerably hotter than the surrounding rural areas. With a temperature difference between cities and outlying areas of five to 10 degrees, the impact is significant.

Man-made structures such as buildings and roads absorb heat from the sun, especially in areas with little vegetation or soil moisture. This causes ambient temperatures to increase surface and ambient air temperatures. Urban heat islands can even cause changes in regional weather patterns, increase smog levels, and boost cooling costs.