If demand for meat, poultry, eggs and dairy keeps pace with projections, by 2050 the environmental consequences of livestock production could be responsible for 70 percent of the total greenhouse gas emissions considered a safe threshold for the planet, new research says.

This leaves little room for all of the other sources of greenhouse gases, such as transportation and electricity, which now account for more than 80 percent of emissions.

Livestock could generate an even greater proportion of the sustainable threshold for other environmental indicators, the researchers report online today in Proceedings of the National Academy of Sciences.

“It’s sobering,” said study lead author Nathan Pelletier who did the work with Peter Tyedmers while at Dalhousie University in Halifax, Nova Scotia.

“We’re not suggesting that everyone in the world become vegan or vegetarian,” he emphasized. “We really stress the importance of policies aimed at production and consumption over time by changing not just how much we eat, but what we eat and how frequently we eat it.”

The pair considered three aspects of global livestock production: greenhouse gas emissions, biomass consumption and nitrogen emissions. They looked at estimates of current and future levels for each of these and compared them with projections for the Earth’s limits, beyond which these systems may become dangerously or irreversibly out of whack.

For greenhouse gases, a 2006 United Nations report estimated that livestock production in 2000 produced about 14 percent of global greenhouse gas emissions, largely via nitrous oxide emissions from fertilizer used to grow feed and from manure and via digestive methane emissions from cows and other ruminants.