If you're driving your SUV to the farmer's market to buy local asparagus — and thinking you're making a difference for the planet — not so fast. You're focused on a detail and ignoring the gas-hogging elephant in the room.

Likewise, if you're badgering your kids to turn out the lights and the bulbs are still incandescent, you could make more progress — and probably add harmony to your household — if you replaced those old energy-sucking bulbs with efficient ones.

As the authors of a new book point out, you'd have to leave the old bulbs off three out of four days to get energy savings comparable to that of CFL or LED bulbs.

The book is Cooler Smarter: Practical Steps for Low-Carbon Living, by the Union of Concerned Scientists.

Experts at the science-based nonprofit spent two years calculating the direct and indirect carbon emissions from 500 categories of consumer activity.

"We tracked everything from clothes and cars to health care and day care," said Brenda Ekwurzel, a UCS climate scientist and coauthor of the book.

They found a lot of low-hanging fruit, which may be good news because UCS wants all of us to reduce our emissions 20 percent over the next year.

And they found that many of the steps they recommend don't just reduce a person's carbon footprint. "They can also improve the quality of your life, save you money and time, and even improve your health," the authors say.

Along the way, they sorted out a barrage of green advice and selected actions that deliver the biggest savings. So it's a guide to making a difference, instead of worrying about whether to use a paper towel or the electric hand dryer in a public bathroom.

The way some people fret about the details, you'd think we had all the big stuff licked. Far from it. An American's lifestyle, on average, results in 21 tons of carbon dioxide entering the atmosphere every year, about four times the global average.

So perhaps we could consider the 20 percent reduction UCS is advocating a down payment on what many scientists say we need — an 80 percent reduction in emissions by the middle of the century. Or consider it a matter of doing your part because the government isn't doing enough.

Praise for the book is mounting. "Whatever your view may be about climate-change projections, there are no good arguments that favor wasting energy and launching the world's climate into an uncertain future," said Neal Lane, a former White House science adviser in President Bill Clinton's administration.

Recognizing that not everyone is in the same situation, the book offers more of a menu than a blueprint.

But some things clearly stand out. For most Americans, what matters most is how you drive, the energy you use at home, and what you eat, in that order.

At 28 percent, personal transportation is the largest portion of the average carbon footprint. So unless you are already an eco-hero by taking public transportation, that means your car.

If you have one that gets 20 miles per gallon — average for today's vehicles — and you replaced it with one that gets 40 m.p.g., you'd cut your annual carbon emissions by four tons, nearly enough to meet the 20 percent goal in just one action.

Plus, you'd save $18,000 on gas over the life of the car, UCS figures.

Home heating and cooling account for 17 percent of the average footprint, and the UCS scientists say you can make significant reductions by installing a programmable thermostat.

I've written before about how difficult these are for many people to use, but clearly we're going to have to figure them out. Or get a techno-savvy teen to help. Having one automatically adjust the heating and cooling when you're asleep or not home can reduce energy use 15 percent a year.

Likewise, sealing leaks in floors, doors, and around windows has a big effect.

Other home energy use amounts to 15 percent of the footprint, and here — after you've replaced the lightbulbs — the biggest culprit for most people is their refrigerator. (No, not the super-inefficient old refrigerator in the basement or garage, because you've already ditched that one, right?)

Manufacturers have achieved such remarkable efficiency gains that any fridge made before 2003 is likely worth replacing now, said Jeff Deyette, assistant director of energy research for UCS. With lower electricity use, you can recoup the cost in as little as three years.

The vampire power your cellphone charger uses when it's still plugged in? Knock yourself out by unplugging it. Any reduction is good. But if you haven't taken the big steps … .

Now let's get to the meat of what you eat. If it's beef, back off, the UCS experts advise.

"Our analysis showed that, by any measure, producing red meat causes more global-warming emissions than almost any other type of food," said John Rogers, a UCS senior energy analyst. A pound of beef is responsible for 18 times the global-warming emissions of a pound of pasta.

There are many, many reasons to support local agriculture. But if you're eating a big steak every night, that's where you should reduce.

On average, Americans eat 270 pounds of meat a year. Halve that, and your emissions shrink three tons or more a year, said Rogers.

I was surprised that "things we buy" didn't rate more attention from the authors. But that's because much of what we buy is services and health care, and you wouldn't shop for most of those based on global-warming emissions. Still, they note that buying fewer consumer goods is important.

The book has many more tips, of course, and it can help you figure out which ones are right for you.

"GreenSpace" appears every other week, alternating with Art Carey's "Well Being" column. Contact Sandy Bauers at 215-854-5147 or sbauers@phillynews.com, or follow on Twitter @sbauers. Visit her blog at www.philly.com/greenspace.