When an estimated 60 million Americans fire up their barbecue grills this Fourth of July, they'll be burning the equivalent of 2,300 acres of forest and consuming enough energy to meet the residential demand of a town the size of Flagstaff, Ariz., for an entire year.
Tristram West of the Department of Energy's Oak Ridge National Laboratory also calculated that the grills would emit nearly 225,000 metric tons of carbon dioxide. A metric ton is equal to about 2,200 pounds. West's estimate includes carbon dioxide emissions from production and combustion of the fuel. Carbon dioxide, considered a greenhouse gas, is increasing in the atmosphere each year and is thought to be a major factor in climate change.
July 4 is by far the most popular day of the year for cookouts, according to a Hearth, Patio & Barbecue Association (http://www.hpba.org/index.cfm) survey that found that 76 percent of the nation's grill owners use at least one of their grills that day. The survey also found that 76 percent of American households own a grill and 42 percent own more than one. Sixty-one percent own a liquefied petroleum gas grill; 48 percent own a charcoal grill; 9 percent own a natural gas grill; and 7 percent own an electric grill.
West, a researcher in ORNL's Environmental Sciences Division, assumed a 35,000 British thermal unit per hour output for the average grill and one hour of operation for each grill. In making his calculations, West took into account the carbon content and carbon dioxide emissions for each type of fuel.
"While more grills are fueled with liquefied petroleum gas, the majority of carbon dioxide emissions are from grills using charcoal briquettes, because the amount of carbon per Btu of gas is about one-third that of charcoal," West said.
Although electric grills emit no on-site carbon dioxide, West said they have the highest emissions per hour of all the grills when accounting for fossil fuel emissions from producing and transmitting electricity. A liquefied petroleum gas grill operated for an hour would emit 5.6 pounds of carbon dioxide while a charcoal grill would emit about 11 pounds. An electric grill would account for about 15 pounds of carbon dioxide.
West's calculations were based on the common charcoal typically sold at grocery and convenience stores, as opposed to charcoal that is made solely from wood. Common charcoal has a heating value of 9,700 Btu per pound while solid wood charcoal has a heating value of about 13,000 Btu per pound.
If the nearly 34 million liquefied petroleum and natural gas grills expected to be in use July 4 were instead charcoal grills, they would emit an additional 89,000 metric tons of carbon dioxide, West said. That's about a 40 percent increase in emissions. If, however, the nearly 23 million charcoal grills were fueled by liquefied petroleum gas, carbon dioxide emissions could be reduced by about 26 percent, or about 59,000 metric tons.
In making the estimate of energy consumption, West assumed an average household in the United States uses about 101 million Btu per year. That information is contained in a 1997 DOE Energy Information Administration document. Flagstaff has about 21,000 households. West's forest estimate assumes trees common to East Tennessee - oak, hickory and pine.
West cautioned against letting this data spoil your holiday fun, saying, "Considering that the U.S. emitted 5.8 billion tons of carbon dioxide in 2000, the emissions from grills are relatively insignificant. In fact, all of the grills in use July 4 would have to remain lit every hour of every day for three years to approximately equal the average annual U.S. carbon dioxide emissions.
"So I suggest that you fire up the grill and relax. However, also remember that when the coals are no longer on the grate and the gas is no longer in the tank, the coals and gas are not gone. They're in the atmosphere."
ORNL is home to the Carbon Dioxide Information Analysis Center (http://cdiac.ornl.gov/), which includes the World Data Center for Atmospheric Traces Gases. The center is the primary global change data and information analysis center for the Department of Energy. The center responds to requests for data and information from users from all over the world.
ORNL is a multiprogram facility managed for DOE by UT-Battelle.