Hot L.A. Nights Caused By Urban Heat Island Effect

The recent heat wave has L.A. residents without air conditioning resorting to sleeping in backyards, or renting motel rooms. Energy demand is continuing to strain the region's power grid into the night, because unlike during past heat waves, evening temperatures are remaining high. And the high night temperatures only make the next day that much hotter.

"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."

"The extreme makeover Southern California got is impacting nighttime temperatures," said William Patzert, a meteorologist for the Jet Propulsion Laboratory.

"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."