By now, almost anyone can pick the world’s biggest polluters out of a lineup: power plants, automobile tailpipes and factories. Together they push nearly 70 percent of heat trapping greenhouse gases into the atmosphere. Not surprisingly, the trio drew considerable attention during the late 2015 Paris climate talks to limit global warming to 2 degrees Celsius, or 3.5 degrees Fahrenheit, by the end of the century.

But a new study released Tuesday says the agreement reached by governments after the United Nations talks will fail if they fail to confront another major source of greenhouse gas emissions: agriculture. Based on some estimates, meat, dairy and crop production emit as much greenhouse gas pollution in the form of methane and nitrous oxide as automobiles emit carbon. The study said farm emissions must fall by a billion tons per year by 2030.

According to the study, current regulations for agriculture will fall up to 5 percent short of what’s needed. “This research is a reality check,” said Eva Wollenberg, leader of the CCAFS Low Emissions Development research program at the University of Vermont’s Gund Institute for Ecological Economics. “Countries want to take action on agriculture, but the options currently on offer won’t make the dent in emissions needed to meet the global targets agreed to in Paris.”

The U.N.’s current solutions call for more water efficiency in rice production, better forestry practices and lowering food waste. But the study’s authors said governments will have to do better than that. The study advocates identifying specific breeds of cattle that produce less methane, along with a dietary inhibitor that reduce the gas by more than 25 percent.

The study, two years in the making, was published in the journal Global Change Biology. Its more than 20 authors represent research institutions from around the world, including the International Livestock Research Institute in Nairobi, the French National Institute for Agricultural Research in Paris, the International Rice Research Institute in Los Baños, Philippines, and the International Institute for Tropical Agriculture in Cali, Colombia.

“Part of the purpose is to stimulate people to think about these options,” Wollenberg said. “I think it just takes the political will.”

On Earth Day last month, Secretary of State John F. Kerry and the leaders of more than 170 nations signed an agreement to lower greenhouse gas emissions at the U.N. headquarters in New York, “the largest number of countries ever to sign an international agreement in a single day,” Secretary General Ban Ki-moon said on the occasion.

Ban called the global effort to fight global warming “a race against time.”

But the effort will fall short without “massive investment, information sharing and technical support to enable a global-scale transition” to address emissions from agriculture, according to a statement from the University of Vermont announcing the study. Agriculture had a 300 million ton carbon footprint in 2012 from food waste alone.

“Promising technical innovations on the horizon include recently developed methane inhibitors that reduce dairy cow emissions by 30 percent without affecting milk yields, breeds of cattle that produce lower methane and varieties of cereal crops that release less nitrous oxide,” the statement said.