Currently, it is in to assess the effects of food on the climate – and with good reason – but according to a group of researchers at Aarhus University and their European colleagues, it is not enough.  

Impacts on field biodiversity and soil carbon change, and effects of nutrients and pesticides on the aquatic environment (eutrophication and ecotoxicity, respectively) should also be included when assessing the environmental footprint of food, according to an article published in the Journal of Cleaner Production.

The aim of the researchers’ study was to elucidate the importance of including soil carbon sequestration, ecotoxicity and biodiversity in assessments of organic and conventional milk production.  

Biodiversity, ecotoxicity and carbon sequestration should be included

The environmental footprint of milk has previously primarily been assessed by looking at carbon footprint, eutrophication and acidification. When a litre of organic milk is compared to a litre of conventional milk in this way, the environmental impact is more or less the same per litre milk.   

However, these three factors do not show the full picture. Soil carbon storage is very important for the climate and organic systems often have a higher soil carbon sequestration due to, among other things, a large proportion of grass in the crop rotations. In addition, the past 30 years’ of research have shown that biodiversity is 30 percent greater in organic fields, and that the effect of pollutants such as pesticides in the environment can influence a range of conditions.   

- We should therefore take these additional three factors into consideration when assessing the effect of food on the environment, says Marie Trydeman Knudsen from the Department of Agroecology at Aarhus University and main author of the scientific article.   

Three systems compared

In recent years, researchers from Aarhus University have worked on developing the methods for including soil carbon changes and biodiversity in life cycle assessments. 

The researchers chose to look at three different types of organic and conventional production systems in Europe: mixed systems with milk production and arable crops, grass-based milk production and milk production in mountainous areas. 

Across the three systems, the carbon footprint per kg organic and conventional milk was somewhat the same when the contribution from soil carbon changes was not included.  

There was a tendency that the contribution from the cows’ methane-rich burps was lowest in the conventional systems compared to the organic systems due to a higher milk yield in the conventional cows. On the other hand, the homegrown feed in the organic systems had a smaller carbon footprint than in the conventional systems due to the absence of mineral fertiliser in the organic systems. The absence of mineral fertiliser also meant that the organic systems contributed less to resource depletion in the form of e.g. minerals. 

When the effect of milk production on soil carbon sequestration was included, the carbon footprint of primarily organic milk was less because the carbon that was stored in the soil was removed from the atmosphere. Carbon sequestration in the organic milk production system reduced the climate footprint of milk by 9-18 percent. 

Organic milk better for biodiversity and ecotoxicity

With regard to ecotoxicity, all three types of organic systems affected the environment significantly less than the conventional systems.   

- There was a clear difference. On average, the effect of organic milk production on ecotoxicity was only two percent of the effect of conventional milk production, says Marie Trydeman Knudsen. 

More or less the same was the case with regard to the effect on biodiversity, which was assessed as the potential reduction in biodiversity compared to natural conditions. The organic systems had on average only one third of the effect on biodiversity than the conventional production systems had.  

- Including more grass in the rations of dairy cows increases soil carbon sequestration and decreases the negative effect on biodiversity, says Marie Trydeman Knudsen.   

You can read the article “The importance of including soil carbon changes, ecotoxicity and biodiversity impacts in environmental life cycle assessments of organic and conventional milk in Western Europe” here.

For more information please contact

Researcher Marie Trydeman Knudsen, Department of Agroecology, email: mariet.knudsen@agro.au.dk, telephone: +45 8715 7958