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Heat Island Effect

What's New 

A new International Space Station instrument helps measure heat islands, and more in the latest Heat Island Reduction Program Newsletter: December 11, 2018.

Check out our newly sprouted webpage, Using Green Roofs to Reduce Heat Islands!

Heat Island Effect

The term "heat island" describes built up areas that are hotter than nearby rural areas. The annual mean air temperature of a city with 1 million people or more can be 1.8–5.4°F (1–3°C) warmer than its surroundings. In the evening, the difference can be as high as 22°F (12°C). Heat islands can affect communities by increasing summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions, heat-related illness and mortality, and water quality.