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Agriculture accounts for about 15% of the current global warming trend. Clear-cutting new land, the use of synthetic fertilizers, farm energy use, and cow burps, for example, all release greenhouse gases into the atmosphere. Agricultural production alone accounts for nearly half the methane, two thirds of the nitrous oxide, and 3% of the carbon dioxide (CO2) the world emits annually, the authors noted. These greenhouse gases vary in their heat-trapping ability and persistence in the atmosphere.

Methane—mostly emitted by the production of animals and rice—can absorb more than 100 times more heat than CO2. However, whereas CO2 can last for hundreds of years in the atmosphere, methane stays around for only about a decade: It is a potent, but short-lived, greenhouse gas. Nitrous oxide emitted by synthetic fertilizers is even more potent and long-lasting than methane: It traps 250 times more heat than CO2 and lingers in the atmosphere for about a century.

Previous research fell short of accounting for emissions changes and downplayed the real impact of these gases in the long term.

Some studies report emissions in carbon dioxide equivalents, which is a simpler way of reporting a gas’s effects, said John Lynch, a biologist and climate modeler at the University of Oxford in the United Kingdom who was not involved in the new study. Climate model–based research must break out the individual contributions of each greenhouse gas, but smaller-scale studies (those that consider emissions from agricultural systems, for example) tend to simplify data with carbon dioxide equivalents, he said.

By measuring pollutants only in carbon dioxide equivalents, previous research on food production’s climate effects fell short of accounting for emissions changes and downplayed the real impact of these gases in the long term, said study lead author Catherine Ivanovich, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory.

To account for these differences throughout food production, Ivanovich and her colleagues isolated the emissions of each greenhouse gas from 94 foods using data from more than 100 studies. They then scaled annual emissions by gas, based on five different projections for population growth and food consumption in 171 countries.

After that, they fed the data to a simplified global-scale climate model to project the impacts of these five emissions scenarios on temperature changes in the atmosphere.

Keeping our current consumption patterns, the world can expect an almost 1°C increase in current warming levels, according to the analysis. The costliest foods are methane-intensive red meat, dairy, and rice: Together they account for 75% of projected food-related warming.

It was surprising “how well the results align with previous studies,” Ivanovich said. “It was satisfying to see that even by using a novel approach, the findings…still aligned well with the understanding that we had.”

The results are not without limitations. The scenarios that maintained current food consumption levels did not consider how land use and climate change might influence food production in the future, Ivanovich said. Whether some crops will be viable in certain locations in the future could have an impact on food production, but the study did not address this, she added.

The 1°C increase in warming from food might therefore be overestimated, Ivanovich said. On the other hand, she added, “the fact that the global demand for ruminant meat, and animal products more broadly, is projected to dramatically increase in the following century would render our results an underestimation.”

“These actions need to work in tandem to make meaningful change.”

“Normally, when we see big reports or papers released on food system contributions to climate change, they report the different greenhouse gases as CO2 equivalent emissions,” Lynch said. But teasing out the effects of each gas, as Ivanovich and her colleagues did, helps scientists see the impacts of changing diets and technologies, such as shifting cow farming practices to reduce methane emissions, he said.

The authors looked at mitigation actions such as reductions in retail-level food waste, improved production practices, and a massive adoption of a healthy diet, finding that these strategies combined can cut the increase in warming by 55%. “These actions need to work in tandem to make meaningful change,” said Ivanovich.

“[Change] is hard but is possible. And it takes time,” said Ana María Loboguerrero, head of global policy research at the CGIAR Research Program for Climate Change, Agriculture and Food Security. “Policies are key to the changes we need,” she said.

—Meghie Rodrigues (@meghier), Science Writer