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The Off-Ramp TemperaTour - Parts 1-5

JPL climatologist Bill Patzert (L) and Cal State LA meteorologist Steve LaDochy take readings at Griffith Park, as part of their Off-Ramp TemperaTour.
JPL climatologist Bill Patzert (L) and Cal State LA meteorologist Steve LaDochy take readings at Griffith Park, as part of their Off-Ramp TemperaTour.
John Rabe

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In 2007, during a nasty heat wave, two prominent weather experts -- Bob Patzert and Steve LaDochy -- drove around with John and took Southern California's temperature, exploring the region's trends, microclimates, and weather controversies along the way.

We asked JPL's Bill Patzert to bring us up to date on what he and Steve have been up to in the two years since we did the TemperaTour. Here's what he sent:


Since their temperature taking tour in September of 2007. Bill, Steve and their students continue to slice and dice California temperature data. Last year they published a attention grabbing scientific paper, "Heat Waves in Southern California: Are They Becoming More Frequent and Longer Lasting?' No mystery here, the answer is an unequivocal 'Yes'.

The summer 2008 in Southern California went down in the books as cooler than normal, and the thermometer in downtown Los Angeles topped 90 degrees Fahrenheit (32.2 degrees Celsius) just once in July, August and the first two-thirds of September, but don't expect last summer's respite from the usual blistering heat to continue in the years to come. The long-term forecast calls for increased numbers of scorching days and longer, more frequent heat waves.

Analyzing one hundred years of daily temperature data in Los Angeles, they found that the number of extreme heat days (above 90 degrees Fahrenheit or 32.2 degrees Celsius in downtown Los Angeles) has increased sharply over the past century. 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.

"We found an astonishing trend - a dramatic increase in the number of heat waves per year," says Arbi Tamrazian, one of authors of the study, and a senior at the University of California, Berkeley.

The team forecasts that in coming decades, we can expect 10- to 14-day heat waves to become the norm. And because these will be hotter heat waves, they will be more threatening to public health.

"The bottom line is that we're definitely going to be living in a warmer Southern California," says study co-author Bill Patzert, a JPL climatologist and oceanographer. "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. 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 last year," Patzert continued, "but the trend is still towards more extreme heat days and longer heat waves."

So what's behind this long-term warming trend? Patzert says global warming due to increasing greenhouse gases is responsible for some of the overall heating observed in Los Angeles and the rest of California. Most of the increase in heat days and length of heat waves, however, is due to 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."

(Click over to the left, under WEB RESOURCES, for more info.)