Researchers have identified a way in which city-dwellers are inadvertently stoking up the heat of the night… by installing air conditioners. Because the cities are getting hotter as the climate changes, residents are increasingly investing in air conditioning systems, which discharge heat from offices and apartment blocks straight into the city air. And the vicious circle effect is that cities get still warmer, making air conditioning all the more attractive to residents.
In fact, a new study shows that the first transaction is not a wash at all. The air conditioning actually is heating up the outdoors. In Phoenix, a team from Arizona State University found that air conditioning didn’t make much of a difference in outdoor daytime temperatures, but at night, when temperatures drop to about 80 degrees, heat pushed outside by air conditioning heated up the ambient air by as much as two degrees.
Candace Pearson at BuildingGreen notes: “With extreme heat projected to increase this century, this positive feedback loop could prove a public-health concern or put further strain on electrical grids; in Phoenix, energy used for cooling already sometimes rises to half of the region’s total electrical consumption.”
At present, 87% of U.S. households have air conditioning, and the U.S., which is not one of the warmer nations, uses more electricity to keep cool than all the other countries of the world combined. To keep the people of Phoenix cool during periods of extreme heat, air conditioning systems can consume more than half of total electricity needs, which puts a strain on power grids.
The Arizona scientists simulated a 10-day period of unusually hot weather between July 10 and July 19, 2009, and used computer models and detailed readings from weather records to analyze the effect of air conditioning systems on local temperatures. Even though the biggest demand for air conditioning was in the daytime, they found the biggest difference was always at night.
The team focused on the role of air conditioning systems in the Phoenix metropolitan area, which is in the Sonora desert in Arizona, and conditions in the summertime are harsh there anyway. But, worldwide, normally warm countries are experiencing increasing extremes of heat, and conditions in cities have on occasion become lethal.
To cap this, cities are inevitably hotspots, and it’s not just because of global warming. The concentration of traffic, commuter systems, street and indoor lighting, central heating, light industry, tarmac, tiles, bricks, building activity and millions of people can raise temperatures as much as 5°C (9°F) above the surrounding countryside. Read more about the story here.