UPDATE: Former California State climatologist Jim Goodridge presents some data that suggests that ocean temperature may be an equal or greater driving force behind Los Angeles Temperature increases, see graph below.
Source: NASA JPL
UPDATE: Sea surface temperature anomaly versus Los Angeles air temperature:
Source: Former California State climatologist Jim Goodridge – click for larger image
Perhaps the adjuster should adjust the adjustments a bit. This press release from NASA Jet Propulsion Lab says that most of the increase in temperature has to do with ubanization:
[NASA’s JPL Bill] 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.
Then there’s station siting issues, like this station on a rooftop of a fire station in Santa, Ana, CA. Note the air conditioner units all around.
Santa Ana Station looking North. Click for a larger image
The temperature record from that station, courtesy the Orange County Register:
And my complete write-up on it is available here
Here is the scientifc paper by Patzert, Ladochy, and Tamrazian which is cited by the NASA JPL press release.