Air Conditioners Heat Up Cities
14 February 2007
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The use of air conditioners to cool big city buildings is making it hotter outdoors, say Japanese researchers.
A study comparing the summer temperatures in downtown Tokyo on weekends versus weekdays shows air conditioners dump enough heat into the streets to raise the temperature at least 2 to 4 degrees F (1 to 2 degrees C).
In turn, the heat blasting from the rear-ends of air conditioners is contributing to the “heat island” effect that makes cities hotter and their weather sometimes more severe.
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Ohashi and colleagues have published their results in the latest issue of the Journal Applied Meteorology and Climatology.
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Air conditioners remove not only ambient heat from buildings, 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 new heat just by being machines that consume power.
In fact, Tokyo sucks up about 1.6 gigawatts of electricity for every 2 degrees of warming on a hot summer day, the researchers reported. That’s equivalent to the output of one-and-a-half nuclear power plants.
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The bottom line, he said, is that to accurately predict the air temperature in any big city, meteorologists need to better understand exactly how big buildings are expelling heat.
“Such heat is not fully appreciated in urban heat island discussions,” said urban heat researcher Stuart Gaffin of the Center for Climate Systems Research at Columbia University in New York. He suspects the Japanese researchers are right about the significant contribution of air conditioning to hotter cities.
The heat islands created by big cities in warm climates — like Atlanta or Dallas — have been recognized as having noticeable and sometimes violent effects on stormy weather that crosses their path.
Even non-urban areas downwind of cities have been known to get more violent thunder storms as a result of the supercharging of storms by city heat.
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