Kate Galbraith at the NYTimes' Green Inc. blog dives into that question in a recent post, "Deciphering California's Energy Efficiency Success." Galbraith looks at a new study critical of the attempts frequently made by climate and energy efficiency advocates to hold up California's low per-capita electricity use as proof that cutting carbon emissions won't be all that hard.

Talk to any California utility or environmental advocate, and at some point they are bound to cite - with pride - the flattening out of the state's per-capita electricity use.

Since 1975, the amount of electricity per person has grown by almost 50 percent in the rest of the country, but California's numbers have stayed nearly level.

Advocates often credit energy-efficiency measures taken by utilities, at the behest of the state.

Unfortunately, matters aren't that simple it seems, according to a new study from Cynthia Mitchel and two colleagues at Energy Economics, which suggests that many of the drivers behind California's low per-capita electricity consumption have nothing to do with the state's battery of policies encouraging energy efficiency.

Galbraith has the scoop:

Writing in the industry publication Public Utilities Fortnightly, Ms. Mitchell proposes several additional factors that could have caused the state's appetite for electricity to stabilize, on a per-capita basis, in recent decades.

First, California's electricity prices have risen far faster than those elsewhere - 35 percent between 1970 and 2005, as compared with 4 percent across the nation. Higher prices will, of course, prompt people to use less electricity. A second possible reason is the nice weather. Because California's climate is mild compared with most other states, it has not seen an equivalent surge in air-conditioning usage as families became wealthier.

Housing is another area where California's trends run counter to the nation's. The number of people living in an average housing unit has increased in California since 1980, whereas it has fallen nationwide. (Presumably, heavy immigration into California is part of the reason.) Also, the proportion of inhabitants in multi-family and attached housing has risen in California, whereas it has remained stable across the nation. These factors are important, because when more people live in a home -- especially a compact home -- they can share air-conditioning and other electricity-consuming essentials.

There is also an intangible that Ms. Mitchell calls California's "conservation chic," meaning that Californians award status points for turning out the lights or doing away with the air-conditioner. (On the other hand, of course, California is the high-tech capital of the United States, with many of its companies specializing in designing or building electricity-guzzling gadgets. And for all the talk of the greening of Hollywood, the stars' enormous mansions do not always accord with "less is more.")

Then there is the changing economy: some energy-intensive industries such as aluminum have declined more in California than elsewhere.

Ms. Mitchell does give some credit to utilities' efficiency policies, such as encouraging efficient light bulbs or promoting better insulation. She also credits other state government policies, such as tighter building codes and regulations that force appliances like refrigerators or air-conditioners to meet minimum efficiency requirements.

But the overall picture is complex, and understanding the various factors behind California's impressive achievement, Ms. Mitchell writes, will help other states as they decide how to translate California's experience into their own policies.

Finally, Ms. Mitchell notes that stabilization of per-capita electricity use may not be good enough from an environmental perspective. That is because the population, in California and the nation, is growing swiftly. Despite the leveling off of the average person's usage, California's overall electricity consumption has risen about 2 percent annually in recent decades. In the battle against climate change, she writes, California's lessons are therefore "limited at best."