American diners are eating fewer burgers, steaks and meatballs, and that's making a noticeable dent in the nation's greenhouse gas emissions, a new study found.

U.S. beef consumption fell by nearly one-fifth -- or 19 percent -- on a per capita basis from 2005 to 2014, the Natural Resources Defense Council (NRDC) said Wednesday in a report. Eating less beef resulted in pollution reductions equal to removing 39 million cars from U.S. roads.

"I'm used to bad news on climate, but this is a rare bright spot," said Sujatha Bergen, the study's lead author and a policy specialist in NRDC's food and agriculture program.

"It doesn't mean that we've done all we can, but it's very motivating to know we've made some emissions reductions," she said.

However, some of those environmental gains were undermined by rising consumption of other carbon-intensive foods, such as cheese, yogurt and butter, according to NRDC.

Cattle industry groups also disputed some of the report's takeaways, arguing that rising beef exports -- not a new distaste for meat -- could explain the drop in per capita beef eating.

Regardless, diet-related emissions are declining in the U.S., federal data show.

Cows have an outsized climate impact for a few main reasons.

The animals eat an abundant amount of feed, which is grown with petroleum-based fertilizers and typically comes from industrial corn and soy fields. Forests around the world have been cleared to accommodate cattle grazing and feed production as well.

Cow burps and farts also emit significant levels of methane, a potent greenhouse gas. Copious piles of cow manure are spread across pastures, a practice that results in greenhouse gas emissions as well.

Globally, the livestock sector accounts for about 14.5 percent of total human-caused greenhouse gas emissions, according to the U.N.'s Food and Agricultural Organization.

For the NRDC report, Bergen and her colleagues scoured the U.S. Department of Agriculture (USDA)'s Food Availability data set. The agency estimates how much food is produced for domestic consumption for more than 200 basic commodities, including beef, flour and sugar.

Next, researchers examined the Environmental Protection Agency's inventory of U.S. greenhouse gas emissions. They compared every year from 2006 to 2014 against emissions in 2005.

By eating less beef, the U.S. avoided an estimated 185 million metric tons of greenhouse gas emissions over that 10-year period, the NRDC said. Lower consumption of other products -- including milk, pork, shellfish and high fructose corn syrup -- brought the total to about 271 million metric tons of avoided climate-warming pollution.

"Whether they know it or not, Americans have been fighting it with their forks," Bergen said in an earlier blog post.

The NRDC didn't examine why U.S. consumers are eating less beef, though Bergen said it may be a "welcome side effect" of people becoming more concerned about the environmental and personal health impacts of eating too much red meat.

But beef industry experts suggested the reason for beef's decline is likely due to reasons other than changing consumer tastes.

Lance Zimmerman of CattleFax, an industry information service, noted that record drought in Texas and other cattle-growing areas drastically lowered the headcount of cattle in recent years.

U.S. beef production has since recovered, but not all of that extra meat stayed home. The United States was a net exporter of beef from 2011 to 2013, meaning that even though the nation was producing more beef -- likely resulting in higher emissions -- Americans weren't actually the ones eating it, Zimmerman said.

Globally, meat consumption is expected to soar by nearly 73 percent by 2050 unless people make a concerted effort to cut back, the Food and Agricultural Organization estimated.

Beyond chowing down on fewer burgers, consumers should waste less of the meat they do eat.

About 20 percent of edible beef ends up in the trash, as do about 40 to 50 percent of fruits and vegetables, said Sarah Place, the senior director of sustainable beef production research for the National Cattlemen's Beef Association, a trade group.

"If we could cut beef waste in half, we'd improve the sustainability of the whole industry by 10 percent overnight," Place said.

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