Wind power and geothermal heat aren’t enough to keep the world cool, according to a new study. Even if energy, transportation, and manufacturing go entirely green, emissions of greenhouse gases from the food system would put the world on track to warm by more than 1.5°C, a target set in the 2015 Paris climate agreement.
For the world to have a chance of preventing significant harm from climate change, the study authors say, all parts of food production need rapid and significant reform—everything from reducing deforestation for new fields to eating less meat. Peter Smith, a soil scientist at the University of Aberdeen who was not involved in the work, agrees. “In addition to a complete transition away from fossil fuels in the coming decades, we will also need a dramatic food system transformation.”
Michael Clark, a food systems modeler at the University of Oxford, and his colleagues tallied the climate-harming gases likely to be released by agriculture from 2020 to 2100 if it continues with business as usual. Carbon dioxide comes from many sources, such as cutting down tropical forests to make way for fields and pastures, running farm machinery, and manufacture of agrochemicals. Fertilizer also emits nitrous oxide, another greenhouse gas. And cows release methane, a powerful warming gas, in their burps and manure.
The team assumed no radical changes in how food is produced, but continuing increases in efficiency. They also took population forecasts from the United Nations and applied standard assumptions about how diets change when nations become wealthier. As incomes rise, people tend to eat more overall and consume more meat, dairy, and eggs—and animal products have a larger climate footprint than plant-based foods.
The researchers then performed a thought experiment in which all other sources of greenhouse gases were immediately halted. Think: a complete transition to electric vehicles, geothermally heated buildings, renewable power, and so on. Given that climate utopia, but no change in how food is produced, the situation is still “very frightening,” Clark says. The simulation suggests the food system alone would contribute enough climate-harming gases that the planet (the hypothetical one with no other emissions, that is) would probably warm above the 1.5°C target sometime between 2051 and 2063, the researchers report today in Science.
Food policy experts and researchers already knew that food production holds sway over warming. But the new model takes a more rigorous and sophisticated approach than previous analyses, says Tim Benton, a food systems expert at Chatham House, a think tank, who was not involved in the study. For example, the researchers looked in more detail at the impact of methane, which doesn’t last nearly as long in the atmosphere as carbon dioxide.
“The good news is that there’s a lot we can do,” Clark says. “But we have to do a little bit of everything.” The researchers looked at the impact of five agriculture-related strategies. They include boosting crop yields more rapidly, which could reduce deforestation; shifting to diets with fewer animal products; and halving food waste. None of these strategies alone results in a 67% chance of keeping global warming below 1.5°C, they found, even if all nonfood emissions have been eliminated. But starting right away and making significant progress on all five strategies could put that goal within reach.
That makes sense to Benton. “There is no silver bullet,” he says. He also agrees that the threat of climate change demands new attention to how people farm and eat. “The solution is not just about having electric vehicles and photovoltaics. It is also necessarily about dietary change.”