Sounds Good, But...

We can't afford to make any more mistakes in how to 'save the planet.' Start by ditching corn ethanol.

You can stop berating yourself for buying that Spanish clementine or New Zealand lamb. Although lists of "what you can do to save the planet" include eating locally—buying food that is grown nearby—to reduce your carbon footprint, the calculation is more complicated than counting up your food's frequent-flier miles. If the local tomato comes from a greenhouse that gobbled up electricity produced from coal and was trucked in via an 8 miles-per- gallon pickup, and a long-distance one was grown in sunny fields and transported by a 400mpg train, you'll leave a smaller carbon footprint if you opt for the latter. Each calculation depends on the food and where you live, but studies find that dairy products imported by Europe from New Zealand leave half the carbon footprint as local ones, while imported New Zealand lamb (which is pasture-raised) leaves one quarter the carbon footprint as local kinds that rely on energy-intensive feed. While bottled water from the South Pacific is an eco-no-no, "you can't say that food from thousands of miles away is [worse for the environment]," says Jonathan Harrington, author of the new book "The Climate Diet." "Transportation is only one piece of it."

Veterans of the diaper wars know that environmental costs aren't always what they seem. But if we learned anything from that endless debate, it is that to determine a product's impacts you must include all of them—power to run the washer and dryer for cloth diapers, not just the landfill impact of disposables, for instance. (Cloth comes out only a little bit ahead; it's a clear winner if you run your appliances on sun or wind.) We can't afford to keep getting it wrong. We have already overshot the level of carbon dioxide in the atmosphere that "will preserve a planet [like] that on which civilization developed and to which life on Earth is adapted," climatologists James Hansen of NASA and colleagues argue in a new paper. Anything beyond 350 parts per million of carbon dioxide threatens widespread glacial melting and a rise in sea levels. We are at 385 and counting.

Yet errors have plagued efforts to green the planet. On the personal front, although recycling is better than tossing aluminum, plastic, glass and paper in the trash, the order of priority is "reduce, reuse, recycle." Instead of recycling two-quart juice bottles, we should have been telling people to buy 12-ounce concentrates and refill that bottle 100 times before putting it in the blue bin. Even hybrid electric cars aren't a clear plus. If your outlet gets its juice from the standard U.S. electricity mix (half of which is generated by burning coal), hybrid electrics emit half the greenhouse gases as standard gasoline cars. But if your utility burns dirty coal inefficiently, hybrid electrics are worse. If you plug in at night, when most people do, you'll also be using more coal-generated electricity. Perhaps the greatest folly, in time lost and dollars wasted, has been the push for ethanol to replace gasoline. In the United States, almost all ethanol comes from corn. When you tote up the carbon emissions caused by clearing land to grow corn, fertilizing it and transporting it, corn ethanol leaves twice the carbon footprint as gasoline.

The greenwashing doesn't end there. Only half of all hybrid vehicles on the U.S. market are more fuel-efficient than their non-hybrid versions, researchers at the Union of Concerned Scientists find: some models pair a big gas-guzzling engine with hybrid technology in a way that enhances only performance, not fuel economy, explains UCS's David Friedman. "Don't assume that because something's a hybrid it's better for the environment," he says (though the Prius is). The Web site sorts out the true greens from the impostors.

If the complexity of all this makes you decide to live however you want and make it up to the planet by buying carbon offsets, think again. Offsets are transactions in which you pay someone else, usually through a middleman, to reduce or soak up carbon emissions equal to those from eating, flying or just plain existing. In one common offset, you pay to have enough trees planted to absorb the amount of carbon dioxide from driving your car. But offsets do not necessarily lead to activities that compensate for the carbon you're feeling guilty about. If the project—a wind farm in the developing world, say—was going to happen anyway, you haven't accomplished much. More problematic, there is no guarantee that trees you pay to plant will live long enough to absorb the carbon on your conscience. "There is no agreed-upon standard for what constitutes a genuine offset," says Joseph Romm of the Center for American Progress. "Anyone can call anything an offset."

The greatest folly is the "what you can do" fairy tale. Yes, every bit of saved energy—by insulating homes, driving less—helps. But we shouldn't fool ourselves that individual eco-conscious behavior can prevent dangerous global warming. That will require "serious interventions from governments to change how we produce and use energy," says Gabrielle Walker, coauthor of the new book "The Hot Topic" with Sir David King, Britain's former science adviser. "Everyone can try to do our bit, but it's not the sort of thing that individuals can greatly influence by themselves." Some problems are too big to solve one weatherstrip at a time.