New York City's 90 degree-plus temperatures last week may not have set new records for the month of May, but it was certainly a sign of the sweltering months to come. Even though we deal with this every year—temperatures that are often 5 degrees Fahrenheit higher during the day than nearby non-urban areas, and up to 22 degrees higher at night, due to the urban heat island effect—what can be done about it?
It doesn't take deep thinking to understand why built-up urban areas are notably hotter than surrounding, less developed places: It's a combination of asphalt, pavement, and buildings, absorbing and retaining heat, furthered by a lack of trees and planted surfaces, plus traffic and exhaust from building cooling systems venting waste heat. We experience the urban heat island both in terms of increased surface temperatures (roofs and pavements can be 50-90°F hotter than the air) and increased air temperatures (the 5-22°F temperature differences mentioned above).
For the rest of the story: http://motherboard.vice.com/blog/how-to-cool-our-sweltering-cities-without-air-conditioners