Tokyo:The use of air conditioners to cool the inside of buildings can make citieshotter, said researchers who studied the summer temperatures of a Japanesecity.

Yukitaka Ohashi of the Okayama University of Science andcolleagues compared the summer temperatures in downtown Tokyo on weekends versus weekdays, reportedABC online (Australian Broadcasting Corporation).

The study showed that air conditioners dump enough heat intothe streets to raise the temperature at least one to two degrees Celsius.

Air conditioners remove not only ambient heat frombuildings, but they expel heat from their use of electricity. In other words,coolers don't just move heat from the inside to the outdoors, they also add newheat just by being machines that consume power, the repot said, quotingDiscovery News.

In fact, Tokyosucks up about 1.6 giga-watts of electricity for every two degrees of warmingon a hot summer day, the Japanese researchers say. That's equivalent to theoutput of one-and-a-half nuclear power plants.

"To accurately predict the air temperature in any big city,meteorologists need to better understand exactly how big buildings areexpelling heat," the study suggests.

US-based urban heat researcher Stuart Gaffin of the Centerfor Climate Systems Research at ColumbiaUniversity in New York suspects the Japanese researchersare right about the significant contribution of air conditioning to hottercities.