We've never met. But Paul Stern knows a lot more about me than I care to admit.

He knows that while I'm racing around turning out lights and turning off the shower while I suds up, my attic is like a giant sieve, with cold winds zipping through.

In other words, I'm being the energy equivalent of penny-wise and pound-foolish.

Stern studies people's environmental behaviors for the National Research Council, an arm of the National Academy of Sciences.

More than a year ago, he began rating the most effective actions households can take to curb climate change.

Most people's feelings of helplessness aside, households represent a huge reservoir of untapped potential for reducing carbon emissions.

According to Stern and co-researcher Gerald T. Gardner, a psychology professor at the University of Michigan-Dearborn, U.S. households - including their vehicles - account for 38 percent of the U.S. carbon emissions. It's larger than the industrial sector. Larger than any nation's emissions except for China's.

Since technologies like solar and wind energy still need improvement, simply cutting back on energy offers the fastest, cleanest, and cheapest way to move forward.

In a paper published last year in the journal Environment, Stern and Gardner concluded that U.S. households could reduce energy consumption by 30 percent without making major economic sacrifices or lowering their quality of life. (Caution: Opinions may vary.)

The secret was in making wise choices. The problem was that, beyond a plethora of simplistic 50-things-you-can-do books, there was little guidance.

Or practicality. They noted that one of the so-called essential skills outlined in The Live Earth Global Warming Survival Handbook was this: "If all else fails . . . buy a camel."

Faced with no more than a laundry list, "you'll most likely do none or one," Stern said recently. "And you'll do an easy one. It will make you feel good, but it won't matter."

Stern and Gardner came up with a list of effective actions. At the top was, ahem, installing or upgrading attic insulation and ventilation.

Another good thing about weatherization is that it's a onetime deal. Conversely, turning the lights out requires a decision every time you leave the room.

Other actions included carpooling, or at least getting frequent tune-ups and driving gently. No fast starts or stops.

Also high were subbing 85 percent of incandescent bulbs with Compact Fluorescent Light bulbs and changing thermostat settings - down in winter, up in summer.

So how come more people don't do it? In a study published recently in the Proceedings of the National Academy of Sciences, Stern, Gardner, and their coauthors looked at behavior.

Studying 17 effective actions, they factored in the proportion of "nonadopters" who could be induced to take action by, for instance, a really good incentive program.

In 10 years, the nation could see a 20 percent reduction in household emissions - again, "with little or no reduction in household well-being."

Topping the list of both effective and "achievable" emissions reductions was getting a fuel-efficient vehicle, weatherization, and buying more efficient appliances.