NPR: What’s The Environmental Footprint Of A Loaf Of Bread? Now We Know

A new study published Monday in Nature Plants breaks down the environmental cost of producing a loaf of bread, from wheat field to bakery. It finds that the bulk of the associated greenhouse gas emissions come from just one of the many steps that go into making that loaf: farming.

The study was conducted by a team of researchers at the University of Sheffield, in the U.K. They wanted to understand the environmental impacts of the entire life cycle of a common staple. They chose bread and used a “real-world supply chain,” says Liam Goucher, the lead author of the study and a research fellow at the Grantham Center for Sustainable Futures at the University of Sheffield. “We focused on a specific farm, which was in Lincoln, in the U.K., and we focused on a specific mill and a specific [commercial] bakery.”

They collected and analyzed data for emissions involved at every step of the process, including growing the wheat, fertilizing it, harvesting the crop, transporting the grains to the mill, grinding the grains into flour, transporting the flour to a bakery and then baking and packaging a loaf of bread. Scientists call this a life cycle analysis.

Many stages were energy intensive and involved with emissions — for example, the machinery involved with tilling the soil, harvesting, and irrigation, or the electricity required to operate the mill and the bakery. But the vast majority of emissions — nearly 66 percent — came from growing wheat.

“We found that over half of the environmental impacts of producing a loaf of bread come from wheat cultivation,” says Goucher. “The interesting thing is that 40 percent is attributable just to the use of ammonium nitrate fertilizers alone, which is a huge amount, when you consider it.” The fertilizers also cause a lot of water pollution when they run off into streams and rivers.