Livestock farming causes a significant share of the world’s greenhouse gas emissions. According to a new study, the carbon footprint of milk may be considerably larger than commonly calculated when carbon released from the soil is also considered.
When discussing the climate impact of milk, attention usually falls on cow methane emissions. Changes in the carbon stored in soil organic matter rarely factor in farm-level carbon footprint assessments, because a standardized calculation method is still subject to debate. A study by the University of Helsinki and the Finnish Meteorological Institute shows that changes in the soil organic carbon stock can play a key role in the carbon footprint of milk production.
The study examined how changes in the soil organic carbon stock affect the total carbon footprint of milk production at the University of Helsinki’s Viikki research farm, on fields of grass and cereal crop rotation. The calculations used life cycle assessment, a method that calculates a product’s environmental impact by examining every step of its creation, from growing cattle feed to manure management.
Researchers compared three distinct ways of calculating soil carbon changes and found that each produced very different results. The simplest method, the IPCC Tier 1 default, clearly underestimated emissions compared with more detailed field measurements and carbon models.
The study identified a feature specific to the northern climate. Repeated freeze–thaw cycles during winter damaged the grass, which weakened growth and reduced the amount of carbon sequestered in the soil. Climate change is expected to bring more unpredictable impacts such as freezing and drought, which may further weaken the ability of fields to act as carbon stores.
On grassland, when the grass growth was weakened, the amount of carbon released from the soil to the atmosphere was significant. Yet when the grass was converted to cereal crop, the loss grew to nearly five times as much. When soil emissions were included in the total figures for milk production, the carbon footprint measured 41 percent higher than in assessments that ignored soil carbon changes.
“Grassland used as cattle feed can either sequester carbon in the soil or release it into the atmosphere. The belowground biomass of grass is an important source of carbon input to promote soil carbon sequestration. This is why the carbon balance of a field is part of the carbon footprint of milk, even though it is usually left out of calculations,” says Postdoctoral Researcher Yajie Gao from the Faculty of Agriculture and Forestry at the University of Helsinki. “The soil is a living carbon bank, and without accounting for it we cannot make an honest assessment of the climate impact of food production,” continues Gao.
“A multidisciplinary approach combining soil science, atmospheric measurements and environmental assessments is essential for an honest account of our food system’s impact. The study enables farmers to move from generic sustainability claims towards data-driven management,” says Research Coordinator Marja Roitto from the Faculty of Agriculture and Forestry at the University of Helsinki. “When the true ‘carbon cost’ of the soil is known, site-specific solutions that reduce emissions can be developed,” adds Roitto.
The study was a major multidisciplinary effort involving the University of Helsinki’s Future Sustainable Food Systems research group, the Environmental Soil Science group, the Viikki Research Farm in the Department of Agricultural Sciences, the Department of Food and Nutrition Sciences, the Institute for Atmosphere and Earth System Research, and the Finnish Meteorological Institute. Research is part of the COVERE2 project (EIT Food).
The International Journal of Life Cycle Assessment
Improving the carbon footprint assessment of milk production: a case study integrating soil carbon stock changes with eddy covariance and DeNitrification-DeComposition model
9-Mar-2026