AC use heats up summer nights

Using air conditioners makes it hotter — at least in cities.

According to researchers at Arizona State University, increased use of indoor air conditioning is driving up urban temperatures, especially at night. In the Phoenix area, the model for the study, outdoor nighttime temperatures are believed to be more than 1 degree Celsius (1.8 degrees Fahrenheit) warmer because of widespread AC use.

As the climate warms, periods of extreme heat increase along with average global temperatures. Those heat waves motivate more people to install air conditioning units, and those units produce heat that is vented into the surrounding environment. That increases the air temperature, which spurs more AC use, which raises the outside temperature even more.

It is a vicious cycle, exacerbated by urban environments, which both generate and retain substantially more heat — as much as 5 degrees Celsius (9 degrees Fahrenheit) — than the surrounding countryside.

In the United States — which is not one of the world’s hotter places, actually — 87 percent of households have air conditioning, and the U.S. uses more energy to keep cool than the rest of the world combined.

So, what’s a planet to do?

Well, the first thing it shouldn’t do is send city-dwellers to the countryside. Though there is much to bemoan in an inefficient city, much about dense urban life actually saves energy — shorter commutes, less car ownership, more mass transit use, biking and walking, and multi-unit buildings with shared walls all actually reduce per capita carbon emissions when compared with surrounding suburbs.

As for the AC, that heat doesn’t actually have to go to waste. The Arizona State study suggests that using the heat produced by air conditioning can be put to other household uses, such as producing hot water. Such cogeneration coupled with optimized electrical usage could save cities more than 1,200 Megawatts of electricity per day, the study says.

This is not to let big buildings off the hook, of course. Large office buildings produce 40 percent of America’s climate pollution; within cities, that number can look more like 50 to 75 percent. But simple and often low-cost fixes, such as more efficient lighting, motion detectors that turn of lights, smarter thermostats and reflective paint, can save millions of dollars and millions of tons of CO2 if implemented across America’s major cities.

The fear is that while the U.S. could be a leader in those conservation measures, it will more likely be, at least in the near future, the pattern for energy consumption in countries with expanding consumer classes. According to recent studies, the demand for air conditioning is expected to grow exponentially in China, India and other emerging economies.

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Correction: The main study in this post was produced at Arizona State University, not the University of Arizona as previously indicated. We regret the error.