"The bottom line is that we're definitely going to be living in a warmer Southern California," said Bill Patzert, a NASA Jet Propulsion Lab climatologist and oceanographer who co-authored a study that examined Los Angeles' daily temperature data for a hundred year period.

What they found was that "the number of extreme heat days (above 90 degrees Fahrenheit in downtown LA) has increased sharply over the past century," the study's summary explains. "A century ago, the region averaged about two such days a year; today the average is more than 25. In addition, the duration of heat waves (two or more extreme heat days in a row) has also soared, from two-day events a century ago to one- to two-week events today."

"Summers as we now know them are likely to begin in May and continue into the fall. What we call 'scorcher' days today will be normal tomorrow," Patzert continued. "Our snow pack will be less, our fire seasons will be longer, and unhealthy air alerts will be a summer staple... We'll still get the occasional cool year like this year, but the trend is still towards more extreme heat days and longer heat waves."

But what's causing this? The obvious answer is global warming, but that wouldn't be correct.

While the study says global warming is "responsible for some of the overall heating observed in Los Angeles," the study points its finger at a phenomenon called the "urban heat island effect:"

Heat island-induced heat waves are a growing concern for urban and suburban dwellers worldwide. According to the U.S. Environmental Protection Agency, studies around the world have shown that this effect makes urban areas from 2 to 10 degrees Fahrenheit (1 to 6 degrees Celsius) warmer than their surrounding rural areas. Patzert says this effect is steadily warming Southern California, though more modestly than some larger urban areas around the world.

"Dramatic urbanization has resulted in an extreme makeover for Southern California, with more homes, lawns, shopping centers, traffic, freeways and agriculture, all absorbing and retaining solar radiation, making our megalopolis warmer,” Patzert said.

These trends may capture the attention of utility companies and public health officials. "We'll be using more power and water to stay cool," says study co-author Steve LaDochy of California State University, Los Angeles. "Extreme heat, both day and night, will become more and more dangerous, even deadly."

It appears that the full study are not online, but published only in the July 2008 issue of the Yearbook of the Association of Pacific Coast Geographers. More NASA Earth science missions can be found on their website.

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