NEW YORK — Rising greenhouse gas emissions from worldwide food production will make it extremely difficult to limit global warming to the targets set in the Paris climate agreement, even if emissions from fossil-fuel burning were halted immediately, scientists reported.

But they said that meeting one of the targets, limiting overall warming this century to 1.5°C could be achieved through “rapid and ambitious” changes to the global food system during the next several decades, including adopting plant-rich diets, increasing crop yields and reducing food waste.

“If we’re trying to meet the 1.5°C target there is no single silver bullet that is going to get us there,” said Dr Michael Clark, a researcher at the Nuffield Department of Population Health at the University of Oxford in England and the lead author of the new research, an analysis of the climate effects of global food production published in the journal Science.

“But together all of them will.”

Meeting the 2-degree target would be easier, Dr Clark said. But in both cases, he added, the analysis is based on immediately reaching “net zero” emissions from the burning of fossil fuels for electricity, transportation and industry.

Although countries have pledged to reduce them, current fossil-fuel emissions are nowhere near zero, and once they are factored in, he said, “any food transition probably needs to be larger and faster”.

Food production results in emissions of carbon dioxide, methane and other planet-warming gases in many ways, including land clearing and deforestation for agriculture and grazing, digestion by cattle and other livestock, production and use of fertilisers and the cultivation of rice in flooded paddies.

Overall emissions are equivalent to about 16 billion metric tons of carbon dioxide a year, or about 30 per cent of total global emissions.

While the world tends to focus on reducing emissions from fossil-fuel burning, the new study shows cutting emissions from food is crucial, too, the researchers said.

“Food systems are sort of the dark horse of climate change,” said Dr Jason Hill, senior author of the paper and a professor at the University of Minnesota.

The researchers forecast how emissions would change in coming decades as the world population grows, diets and consumption patterns change as some countries become more affluent, and crop yields increase.

They found that food-related emissions alone would quite likely result in the world exceeding the 1.5°C limit in 30 to 40 years. Food emissions alone would bring the world close to the 2-degree limit by 2100.

Dr Brent Loken, the global lead food scientist for the World Wildlife Fund, who was not involved in the research, said the study was “one more piece of evidence that supports what many people are saying,” that climate goals cannot be reached without changes in the food system.

“It’s really less about where food system is today, and more about where it’s heading,” he said.

Analyses in recent years have pointed to the need to alter diets and make other changes in the food system both to improve human health and make the system more sustainable.

Dr Loken, for example, was a co-author of a report by the EAT-Lancet Commission, an international group of scientists, that recommended a 50 per cent reduction in global consumption of red meat and some other foods by 2050.

Dr Loken said that without changes, food emissions were expected to double by 2050.

“And the wiggle room to meet the Paris limits is so small,” he said.

Dr Hill said that the study did not consider potential shifts like the entire world population adopting a vegan diet.

“We wanted to present the ones that were realistic goals,” he said.

“A plant-rich diet is a realistic goal. We’re not saying in this paper to hit these targets we have to give up animal products. But there need to be some dietary shifts toward the healthier diets.”

Dr Clark said that he was optimistic that dietary shifts and other changes in the food system could be made in time to have an effect on global warming. He and others are working on determining what policies and behavioral changes it may be possible to implement.

“Maybe it’s a combination of nudges at grocery stores, and top-down policies from governments,” he said. “It could be very bureaucratic or individualistic.”

“There are so many different ways we can do this,” Dr Clark added. “Every person has a role to play, every corporation as well. Through collective action and political will we can actually do this pretty rapidly.” THE NEW YORK TIMES