It Was a Dark and Sweaty Night

So Payne, a 48-year-old Pasadena resident, takes his sheets to the backyard, where he and his dog, a Newfoundland mix, can finally fall asleep.

The arrangement has some complications: He must put his sheets in the dryer each day because of the morning dew. And a worker doing repairs on a nearby crane who saw him snoozing asked: "Did your old lady kick you out of the house last night?"

But it's worth it, Payne said: "The house just doesn't cool off."

A case of hot summer nights has made Southern California's heat wave feel even more miserable.

It just isn't cooling off enough at night, climatologists say. On Sunday, several minimum temperatures were unseasonably high, breaking records.

At 77, Burbank experienced the warmest nighttime low the city has ever recorded for July. Los Angeles International Airport, Long Beach, Woodland Hills and downtown Los Angeles also saw record high minimum temperatures.

The night heat is one reason so many power transformers failed: People cranked their air conditioners all night, giving the taxed systems less time to rest before sunrise.

"Back in the old days, it got a lot cooler at night. Now, we're not getting relief at night," said William Patzert, a meteorologist for the Jet Propulsion Laboratory in La Canada Flintridge.

Climatologists say global warming gets some of the blame. But the prime villain, they say, is the ever-increasing urbanization of the region. The rapid development of Southern California over the last 50 years has created structures and landscapes that retain heat better than dry desert chaparral.

Golf courses, shopping centers, housing developments and lush lawns trap heat during the day, keeping temperatures up at night.

The warm nights lead to torrid daytime temperatures because heating already warm air doesn't take long, he said.

"The extreme makeover Southern California got is impacting nighttime temperatures," Patzert said.

"Everybody wants to know why it's not cooling off at night. This is an urban land use 'heat island' effect."

The numbers tell the tale: Between 1901 and 2000, the average daytime temperature in Southern California has gone up by three degrees, Patzert said. But nighttime averages have risen by seven degrees.