Monday, August 20, 2007

Gas or charcoal? Reducing carbon footprint is tricky business

Recently, the Home & Garden section reported ("Going green with holiday grilling takes a few backyard adjustments," June 30) that grilling outdoors using propane released less carbon dioxide into the atmosphere, and thus possibly contributed less to global warming, than grilling with charcoal.

But, like all things relating to your carbon footprint, the gas versus charcoal debate is not as straightforward as it may seem.

The Sierra Club came to its pro-gas conclusion with the help of calculations made by carbon-cycle expert Tristram West, a researcher with the Department of Energy's Oak Ridge National Laboratory Environmental Sciences Division in Oak Ridge, Tenn. West assumed that each type of grill - gas, charcoal, electric - would put out 35,000 British Thermal Units per hour, the amount of Btu most manufacturers say their grills will produce when all burners are turned on for one hour.

A Btu is the amount of heat energy required to raise the temperature of 1 pound of water by 1 degree Fahrenheit. Any fuel burned for heat has a per-pound Btu rating - propane is about 15,000 Btu per pound while charcoal is about 9,700 Btu.

West based his calculations on the use of common charcoal that contains coal and other additives, not pure wood lump charcoal that has a Btu rating of about 13,000.

Using this equation, West did the math on the carbon emissions for each type of fuel and determined that gas spews 5.6 pounds of carbon dioxide per hour, while a charcoal grill puts out 11 pounds. West pegged electric grills as the worst carbon offenders - even though they do not emit any carbon on-site - after taking into account the emissions created in the generation (mostly by the burning of coal and gas) and transmission of electricity - a whopping 15 pounds.

Case closed, gas wins. Right? Well, not exactly.

West concludes that burning charcoal made from wood completes the carbon cycle begun when the tree it came from sprouted, thus making it "carbon neutral." Advantage, charcoal. But why?

Gas, on the other hand, comes from nonrenewable fossil fuels. They can't be replaced. When gas is burned, although it produces less carbon dioxide than charcoal, its emissions do contribute to the ever-escalating carbon imbalance just like your, say, Cadillac Escalade.

"When a tree grows it takes up carbon dioxide. When we burn that wood it's releasing that same CO2" and another tree takes it up, West said. He also points out that charcoal, being 90 percent waste wood, would be burned anyway. "Nobody's going to cut down trees to make charcoal because that wood's too valuable," he said.

Not surprisingly, Kingsford briquette spokesman Drew McGowan agrees with West's conclusion but takes issue with the way West calculated the emissions.

"It's important to calculate the carbon emitted per cooked item, not per pound of fuel consumed," said McGowan. "In other words, we need to compare emissions created per cooking event, not per hour or pound of fuel. People barbecue until their food is cooked, not for a specific weight of fuel."

It turns out West agrees with McGowan and would like to re-do his calculations for charcoal based on the amount of briquettes used and what's being cooked.

But it gets even more complicated. That's because West would also like to consider the particulate matter emitted into the atmosphere when burning charcoal. He notes that in the making of charcoal in kilns, 310 pounds of particulate matter per ton are produced.

"My guess is you'll get some more when you burn it in your backyard." Then again, particulate matter is heavy and comes down to earth rather quickly; C02 can stay in air 100 years, said West.

Another factor is the fuel used to burn the wood to make charcoal. If it's a fossil fuel, that would cause charcoal to lose its "net carbon emitter" status, said West.

West admits that the amount of carbon your grill emits is insignificant. He's determined that for barbecue-grill carbon emissions - both gas and propane - to equal the 5.8 billion tons of carbon emitted by the United States in 2000, all the 60 million grills fired up on a typical July 4 would have to remain lit every hour of every day for the next three years.

When it comes to your carbon footprint, whether you use charcoal or gas "makes very little difference - it's .0003 percent of U.S. carbon emissions."

"It's clearly not the thing to be focusing on if we're going to be reducing carbon emissions," said West. He does, however, concede that the charcoal versus gas "green" debate is an "educational tool for people to learn about different types of fuels they're using."

So, now that you're armed with plenty of ammo, no matter what side of the charcoal/gas grilling carbon footprint debate you're on, relax and throw another shrimp on the barbie - Labor Day's right around the corner.