Imagine a grain field in Western Jutland, winter wheat standing tall and golden. Now picture it being ploughed up and replaced with clover grass: one of the crops intended to drive the green transition in Danish agriculture. On paper, it sounds climate-friendly: a form of production-oriented extensification that results in more plant-based protein, less imported soy, and biomass for biogas. But what really happens when we change just one piece of the enormous puzzle that is agriculture?
That question has been explored by researchers at Aarhus University using the CIRKULÆR model: a new tool that calculates climate and environmental effects of changes in farming practices at regional and national levels. The model was developed to help policymakers understand the consequences of the green transition before rolling out new measures.
“Agriculture is not a simple, closed system. When we change one thing, a chain reaction occurs,” explains Henrik Thers from the Department of Agroecology at Aarhus University.
The model’s results are both encouraging and unsettling. When grain is replaced with high-yielding clover grass with relatively high nitrogen fertilization for biorefining, direct greenhouse gas emissions from agriculture increase. This is partly due to more ammonia and nitrous oxide from green manure and biogas residues returned to the soil.
But something else happens: carbon is stored in the soil on a large scale. Over 20 years, the stored carbon can more than offset the extra emissions. The net effect? A significant climate benefit.
It’s a paradox that challenges the political logic that “green initiatives” always mean lower emissions here and now.
“We have to face the fact that, under the assumptions used in these scenarios, replacing winter wheat with clover grass fertilised with relatively high nitrogen is an intensification of the system, not the opposite, even if it might seem intuitive at first glance,” says Henrik Thers.
Policymakers often work with simple equations: less fertiliser equals less emissions. But the CIRKULÆR model shows reality is far more complex. If we only look at one part of the system; for example field emissions, we risk making decisions that do more harm than good in the long run.
“It’s about understanding the entire cycle,” says Henrik Thers. “When we introduce new crops or technologies, it affects everything from feed rations to biogas production and the amounts of slurry and mineral fertiliser applied including methane emissions and carbon returned to the soil. That whole picture must be part of the decisions.”
The model also reveals that crop choice matters greatly:
The CIRKULÆR model is not just a research project, it’s a tool. It can help design support schemes that reward holistic solutions and prevent us from introducing measures that look green on paper but aren’t from a systems perspective.
“We need models like this if we are to meet climate targets without creating new problems,” says Henrik Thers.
Partners: Department of Agroecology, Aarhus University
Funding: Developed with funding from the Danish Agricultural Agency (Grant No. 33010-NIFA-19-732; Program: NIFA projects under the Climate Research Initiative in Agriculture).
Conflict of interest: None
Read more: The publication “ The CIRKULÆR model – A national and regional static flow model of agricultural production, environmental and climatic impacts ” is published in Agricultural Systems . Authors: Henrik Thers, Lars Uldall-Jessen, Asbjørn Mølmer Sahlholdt, Mette Vestergaard Odgaard, August Kau Lægsfaard Madsen, Tommy Dalgaard, Troels Kristensen, and Jorge Federico Miranda-Vélez.
Contact: Henrik Thers, Department of Agroecology, Aarhus University. Email: thers@agro.au.dk
Agricultural Systems
The CIRKULÆR model – A national and regional static flow model of agricultural production, environmental and climatic impacts