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More people, more concrete, and lots more heat in Phoenix

An 'urban heat island' effect, fed by the city's growth, is trapping heat and making temperatures soar.

By Faye BowersStaff writer of The Christian Science Monitor / August 30, 2007


Arizona is poised to take another record. It's about as unwelcome as a couple of other firsts – No. 1 in the nation for most illegal immigrants crossing the border, or No. 1 in the nation for identity thefts.

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This "one" directly corresponds with another No. 1 – its status as the fastest-growing state in the nation. While news of global warming becomes as common as the wheeze of air conditioners here, Phoenix is fighting a different, if related, problem. In part because of heavy growth – particularly in the Phoenix metro area – heat is being reflected, trapped, and absorbed in concrete, rooftops, and a maze of buildings that blocks wind. At the same time, there's little vegetation to absorb the heat, and high energy usage generates more.

It's called the "urban heat-island effect," and whatever the impact of global warming here, this phenomenon is sending the mercury rising. On Tuesday, Phoenix tied the all-time record of 28 days at 110 degrees or greater in one summer, reached in 1979 and again in 2002. If the temperature rises to 110 degrees one more day this year, Phoenix will set a record.

"We're forecasting 111 for Wednesday, 109 for Thursday, and 110 again on Friday," says Keith Kincaid, a forecaster with the National Weather Service here. But if the temperature doesn't hit 110 on those days, he adds, "we have had 110-degree days in September before."

This summer is hot elsewhere, to be sure. But in few places can you fry an egg on a sidewalk as quickly and thoroughly as you can here. And you'd have to fry a lot of them: Experts say the main reason the number of 110-degree-or-higher days has risen so steadily – and steeply – is rapid growth. In the 1950s, for example, the temperature rose to 110 or higher an average of 6.7 days per year. In the 1960s it was 10.3 days per year; in the 1980s it was 19 days per year, and in the 2000s (through Aug. 21, 2007), 21.9 per year, according to the National Weather Service.

For Westerners living here, it's about as much fun as an earthquake, a drought, or, well, a 110-degree day. But it does have people's attention. True, it's not as difficult as this summer's devastating floods or fires elsewhere in the US. Many people have swimming pools, and most have air conditioning. But that, too, adds to the problem of the heat-island effect, experts say.

"Every time you use that mechanical air conditioner, you're throwing hot air back into the environment," says Jay Golden, an expert on urban climate and energy at Arizona State University in Tempe. "It's not only the sun and the pavement, but we're generating more heat because of human adaptation." And that's where global warming comes in: The hotter it is, the more we need to cool off; and the more we try to cool off – with air conditioning, for instance – the more heat-trapping greenhouse gases and "waste energy" we create, feeding both phenomena.

No escape in the Phoenix nights