A crucial distinction in the global-warming balance sheet—and another stumbling block for beginners starting to count carbons—is that researchers treat fuel from current plant growth as causing zero net greenhouse- gas emissions. Yet burning wood pellets or corn-based ethanol certainly releases carbon dioxide, and in some cases more than fossil fuels. For instance, cooking your burgers over charcoal briquettes made from wood produces 11 pounds of carbon dioxide an hour, versus 5.6 pounds from propane gas. But the thinking is that the carbon dioxide emitted by renewable sources will eventually get reabsorbed through photosynthesis, as trees, corn, and other biofuel sources grow back.

The problem arises when you alter this “natural” balance by pulling fossil fuels from underground, with no means of reabsorbing the carbon. Dukes found that in a single year, 1997, the human population burned the equivalent of more than 400 times the total plant matter grown that year throughout the world, including oceanic plankton. The implication is that doing this year after year will eventually overwhelm the system.

In 2005 the concentration of carbon dioxide in the atmosphere, 380 parts per million, is a third higher than in preindustrial times. Optimistic estimates are that it will merely double over the rest of the century. But our rapidly increasing consumption of fossil fuels suggests that an optimistic scenario is unwarranted. The United States now adds 21 percent more carbon dioxide to the atmosphere annually than in 1990, almost all of it from fossil fuels. Greenhouse-gas emissions from China have increased by 50 percent in that period and will double within 20 years.

The good news is that roughly 33 percent of the American production of all greenhouse gases, or the equivalent of 17,422 pounds of CO2 per person, comes from sources under our direct control—our cars and houses. And partly because we are so profligate, cutting that number by half may not entail much pain or inconvenience.

For instance, generating a kilowatt-hour of electricity in the United States (about what an iron uses in an hour) produces 1.64 pounds of carbon dioxide. So the typical household uses enough electricity to add more than 2,000 pounds a month of CO2 to the atmosphere. Where I live, it took about two minutes on a computer to fix this. I simply switched, via my local utility, to a supplier that gets its electricity from windmills, small hydroelectric plants, and methane from landfills. This instantly removed more than 18,000 pounds of annual pollution from the dark side of my family’s ledger.

This seems too easy, of course.“Nobody can assure you that the electrons coming into your house are going to be green or any other color,” a utility executive told me. Whether the electrons come from a coal-fired plant in a neighboring state or the nuclear power plant down the road, they all mix together in the grid. So switching is in a sense just moral bookkeeping. I pay $6 or $7 extra a month for the warm feeling that I am doing the right thing. But nothing much changes. Moreover, if everybody started acting as if global warming mattered, there wouldn’t be nearly enough green electricity to go around. In my area, low- or nonemitting sources generate just 4.5 percent of the total supply.

What I accomplish by contracting for electricity from renewable energy sources is to create a market so that someone somewhere on the grid can produce more of the stuff, displacing electricity from dirtier sources. This is no small thing, another utility executive suggests: “A ton of carbon dioxide reduced someplace in the world is a ton of carbon dioxide that’s not in the atmosphere.”

Unfortunately, switching to renewables isn’t enough. Solar and wind power require acreage, they cost more per kilowatt-hour, and they are unlikely to make much of a dent in conventional energy sources anytime soon. Getting energy directly from this year’s plant crop, in the form of biofuels, is cleaner and more efficient than getting it from coal or oil, but Dukes found that if we tried to supply current worldwide energy demand entirely from biofuels, it would consume at least 22 percent of the production of all land-based plants annually. The lack of good alternatives has caused some people to make global warming an argument for increasing our reliance on nuclear power. But I already live within 10 miles of two nuclear power sites that are likely to remain radioactive for thousands of years. The implication, at least for me, is that we need to consume less energy.

Like a lot of American homes, my house is a little too big and too well equipped with light fixtures, appliances, computers, cars, and yard machinery. I could ask my family to give up certain things in the spirit of righteous suffering, but they would ignore me. So my approach is to address global warming in ways that make our lives more comfortable, not less.

For instance, my daughter’s bedroom is at the end of the run for heating and air-conditioning and never gets completely comfortable. A contractor could fix that using sealants to block leaks in the ductwork. The technology can reduce heating expenses by 10 to 20 percent, with a commensurate drop in greenhouse-gas emissions, according to a spokesman for Carrier, which makes furnaces and air conditioners. But what people really notice, the spokesman says, “is that they can actually cool their upstairs bedroom in summer.”

Other emissions-cutting moves also qualify as improvements, not hardships. Replacing some of the lawn with groundcover would mean spending less weekend time behind a power mower, which produces more carbon dioxide, not to mention noise, per mile than any automobile. In the office, a liquid crystal display flat-screen computer monitor uses 50 to 70 percent less energy than the clunky cathode-ray tube on my desk. Because I work on my computer more than 12 hours a day, switching would eliminate 135 pounds of carbon dioxide emissions a year. Installing a dozen compact fluorescent lightbulbs around the house would eliminate 550 pounds of carbon dioxide emissions a year, and the lower electric bills would pay back their cost in just three months.

The peculiar psychology of the payback period often determines what changes we are willing to make, with four years or less the magic number. For instance, I balk at installing solar power because it would cost about $20,000, even with state subsidies, and the payback would take about 17 years. Other ways of cutting energy use—for instance, adding insulation—are more cost-effective. But focusing too much on short-term payback may be misguided. The recent doubling in the price of oil suggests that energy may cost far more than we assume at the time of a purchase. Looking for a quick payback also ignores consequences that last for centuries.

“We apply this cost-effectiveness criterion to energy efficiency, but why only to this decision?” asks Danny Parker, a researcher at the Florida Solar Energy Center. “What’s the cost-effectiveness of really fine kitchen cabinets?What’s the cost-effectiveness of a Mercedes? It’s just not discussed.”He suggests that if you look at global warming from a cost-effectiveness perspective, you might decide that the Earth is not worth saving.

With some purchases, the Internet now makes hidden costs dismayingly clear. Say you were thinking about buying an SUV like the Ford Excursion. Driving it 15,000 miles a year, you’d be producing 25,350 pounds of carbon dioxide annually. Add in methane and other by-products from burning fossil fuels and you end up with 38,000 pounds of greenhouse gas, according to www.greenercars.com, a website that compares different car models. This is equivalent to lofting the vehicle’s own weight into the atmosphere once every 10 weeks. After a year, your SUV would be trailing the equivalent of five SUVs in its wake, like Jacob Marley’s chains. Multiply that by the 20 million SUVs on the road and you start to see Alaskan villages subsiding under the Arctic seas.

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Homemade CO₂
A typical American house is an energy guzzler that produces a surprising amount of greenhouse gas. In the last 25 years, the average size of a single-family house—and consequently the amount of space that must be heated, cooled, and lit—has increased from 1,740 square feet to 2,330 square feet. These annual carbon dioxide emissions figures are based on national averages for a 2,000- to 2,500-square-foot house.

Space heating
54,900 cubic feet of natural gas
6,643 pounds of CO₂

Lighting and appliances
8,998 kilowatt-hours of electricity
14,757 pounds of CO₂

Air conditioning
2,784 kilowatt-hours of electricity
4,566 pounds of CO₂

Water heating
19,700 cubic feet of natural gas
2,384 pounds of CO₂

Source: U. S. Department of Energy, 2001 Residential

Of course, it’s too easy (but nonetheless fair) to pick on SUVs. I drive a Volvo V70 Cross Country station wagon, a favorite of exurban environmentalists. My car annually produces 26,000 pounds of greenhouse-gas emissions—more than two killer whales’ worth of pollution. If I switched to a lightweight SUV like the Ford Escape hybrid, I could cut my greenhouse-gas emissions to 18,000 pounds. But with a lighter hybrid, like a Toyota Prius sedan, I could get down to 10,000 pounds.

But the truth is that a lot of American families, mine among them, can’t afford to replace their cars right now. “That’s OK,” says Jim Kliesch of the American Council for an Energy-Efficient Economy, the nonprofit behind www.greenercars.com. The idea is simply to get people thinking about environmental consequences next time they buy a car. Even stepping up from the Volvo V70 to a car that gets an extra two miles a gallon avoids about a ton of greenhouse-gas emissions annually. By neglecting to think about such things, Kliesch says, we get locked into purchases we could regret for years, or generations, to come.

For a lot of people and organizations feeling stuck on the wrong side of the global-warming balance sheet, one solution is to offset the emissions they cannot eliminate. In essence, they pay somebody else not to pollute, or they pay for activities like planting trees that are assumed to remove carbon dioxide from the atmosphere. As a practical alternative for individual consumers, the retail market in emissions offsets is promising—but not yet ready for prime time.

Most trading in carbon dioxide offsets now occurs only on a large scale. It works like this: One company installs new equipment to cut its emissions by 5,000 tons. Then it sells the right to emit 5,000 tons to a buyer for whom new equipment would be too costly. To avoid simply swapping pollution from one place to another, these so-called cap-and-trade systems usually involve a gradual, government-ordered reduction in overall emissions. As the cheaper reductions get put into place, participants move on to the more difficult reductions, and the trades become steadily more pricey. Selling emissions rights helps defray the cost of making reductions.

To some people, reforestation projects, like the ones the Rolling Stones arranged, seem like the most appealing way to offset emissions. In one case, a power company paid $13.7 million to reforest 100,000 acres of U.S. Fish and Wildlife Service land in Mississippi in the expectation that every acre of trees would absorb enough carbon dioxide to offset 150 tons of greenhouse-gas emissions over the life span of the trees. But critics say such these schemes are much less effective than advertised.

“Basically, they’re selling a warm, fuzzy feeling,” says Dennis King, a University of Maryland researcher and the author of an EPA-funded study of carbon sequestration. Young trees don’t actually start to sequester significant amounts of carbon dioxidefor 20 years, he says, and it takes a tree 100 years to remove a measly 3,000 pounds of carbon dioxide from the atmosphere—assuming the tree survives drought, fire, flood, disease, and other afflictions. But, King says, the buyer “gets to dump a ton of carbon into the atmosphere with 100 percent certainty” today. Moreover, most of the carbon that gets sequestered in these forestry projects will eventually be released again when the trees die and decompose—or get harvested. “The numbers don’t look good when you work them out,” King says.

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Planes: Domestic flights average 877 miles and produce 270 pounds of CO₂ per passenger, or 1,080 pounds for a family of four.

Trucks: A new SUV is typically driven 15,000 miles the first year, burns 882 gallons of gas, and produces 22,050 pounds of CO₂.

Autos: A typical midsize car is driven 12,000 miles annually, burns 494 gallons of gas, and produces 12,350 pounds of CO₂.

Mileage and fuel-efficiency statistics compiled by the Environmental Protection Agency.