Changing dietary habits in the United States are leading to reduced gas emissions linked to food and global warming, and half of the reduction can be attributed to reduced beef consumption, according to a new study.
Every choice we make as consumers has an impact on the climate, which is often measured in terms of a ‘carbon footprint’, i.e. the amount of greenhouse gases emitted during the production of a good or the supply of a service.
“The greenhouse gases of our food system are one of the biggest parts of our footprint as a nation,” says Clare Bassi, who led the new study, which was published recently in the Journal of Cleaner Production., as a master’s student at the University of Wisconsin-Madison. Globally, food systems contribute about a quarter of all human-made greenhouse gas emissions.
It can be difficult for consumers to know how specific food choices relate to overall climate impact. A food’s carbon footprint includes the emissions associated with its production, processing, transportation, cooking and waste. And different foods have very different environmental impacts – animal products and processed foods are often much more carbon intensive than minimally processed and plant-based foods.
The new study explores the carbon footprint of Americans’ eating habits and how they have changed over the past few decades.
“I wanted to see where the impacts of climate change were on our diets and how they changed over time,” says Bassi. She also looked at trends based on demographic factors, such as gender, age, household income and race/ethnicity.
Bassi analyzed food habits reported each year from 2003 to 2018 and calculated the average daily greenhouse gas emissions associated with food. In just 15 years, the carbon footprint of the American diet has dropped by more than 35%, largely due to Americans eating less meat and other carbon-intensive foods. Decreased consumption of beef, dairy, chicken, pork, and eggs accounted for more than 75% of the diet-related carbon dioxide savings observed over the study period; beef alone was responsible for almost half of the decline.
“The trend is quite exciting,” Bassi says. “Over the study period, the national greenhouse gas savings due to dietary changes alone is roughly equivalent to offsetting the emissions of every passenger vehicle in the country for nearly two years.”
As an individual, it sometimes feels like you don’t have much power to make positive changes, notes Bassi. But her findings show that “our collective behavioral changes are making a difference,” she says. By choosing foods with a low carbon footprint, “you may feel able to reduce your impact significantly.”
Bassi calculated greenhouse gas emissions based on the individual daily diets reported by more than 39,000 American adults in the National Health and Nutrition Survey between 2003 and 2018. She looked at the changes in averages over time and examined trends based on demographic factors, such as gender. , age, household income and race/ethnicity.
Each demographic subgroup she analyzed showed a 30 to 50 percent reduction in diet-related greenhouse gas emissions over the study years. In general, women ate lower-impact diets than men. Women had an average diet-related carbon footprint of around two kilograms of carbon dioxide emissions per person per day in 2018; for men it was about three kilograms per person per day.
When the data was aggregated by race/ethnicity, the average carbon footprint was slightly higher among Hispanics than among non-Hispanic whites and lowest among blacks. In a breakdown by income level, the food-related carbon footprint was highest in the highest income group (annual household income above 1.84 times the federal poverty level, or about 46,000 $ for a family of four in 2018) and lowest in the lowest income group (annual income below 1.3 times the poverty line, or $32,600 in 2018).
The lowest income group also showed the largest percentage reduction, 46.4%, between 2004 and 2018, compared to 39.3% in the highest income group. When analyzed by age group, the youngest eaters showed the greatest reduction in diet-related carbon emissions, with a 47.2% decline over 15 years.
“All of these savings are basically coming from people eating foods that are less greenhouse gas intensive,” Bassi says. Caloric intake remained stable over the years of the survey, and the analysis used constant values for production-related emissions and other systemic factors to focus only on changes due to dietary habits. .
These positive trends are encouraging, she notes, but Americans still exceed our fair share of food-related emissions compared to other parts of the world. A 2019 scientific report by the International EAT-Lancet Commission identified global thresholds for diet-related greenhouse gases that would adequately feed the world’s population while keeping global warming below 2°C by 2050. The average U.S. food-related carbon footprint in 2018 was still nearly twice as high as global goals, she says.
“People’s actions make a difference,” Bassi says, “but we still have a long way to go.”
Bassi completed the research as a master’s student at the Nelson Institute for Environmental Studies at the University of Wisconsin-Madison and the Wisconsin Energy Institute. The article was co-authored with Rachael Maysels of Cauca University in Colombia and UW-Madison Professor of Biological Systems Engineering Rob Anex.