Temperatures between the suburbs and downtown Athens on hot summer afternoons can vary some 14 degrees Celsius (26 degrees Fahrenheit), according to new research by Athens University’s meteorology department into «heat islands» – or certain districts of cities that are hotter than others. «Known for a century, it is the most documented climatic change phenomenon and the most frequently observed of the effects of urbanization,» said Professor Matthaios Santamouris, who led the survey. The survey, which began in Athens in 1996 and is still ongoing, has shown that temperature discrepancies between the coolest and hottest parts of the city are quite considerable. On a windless day in summer, the temperature in dense locales is often very high: 44C (111F) on Ippocratous Street, 41C (105F) in Korydallos and 39C (102F) on both Ermou Street and Kifissias Avenue. On the same day, the eastern suburb of Ilioupolis will register 30C (86F). «Generally when there is a gentle northerly breeze blowing, the temperature differences between the center and the suburbs ranges from 5-8C,» Santamouris said. The temperature rises according to a pattern: It begins at about 10 a.m., peaks between 2 and 3 p.m., and drops again at about 7 p.m. At night, temperatures remain high in the city center compared to the suburbs because buildings and roads emit the heat accumulated during the day. Heat islands also occur in winter, when temperatures between the city center and suburbs can vary by 8C 15F). When it’s cold, this phenomenon benefits downtown residents, who save up to 30 percent in power bills. According to the US Environmental Protection Agency, heat islands form because of a densely constructed city, long narrow streets that do not allow air to circulate freely, a lack of greenery and the kind of building material used (concrete and asphalt, for instance, absorb large amounts of solar radiation.) Measurements in Athens streets during the summer showed asphalt temperatures of up to 60C (140F). City streets that are designed in a way that trap ultra-violet radiation are also to blame. Santamouris estimates that a building in the center of Athens needs twice the amount of energy for air conditioning as one in the northern or southern suburbs. Energy consumption is 50 percent higher in densely populated western Athens, where there is very little greenery, than in the rest of the suburbs. This translates into about 200 euros annually per resident for air conditioning alone. Higher city temperatures also mean a reduction in the effectiveness of air-conditioning units of up to 25 percent in the center, creating a vicious circle. Meanwhile, producing more energy means burning more lignite and therefore more atmospheric pollution with greenhouse gases.