Food is inextricably linked with climate

All our foods affect the climate. By adding actual figures to the impact of the production of individual foods, scientists can help consumers, farmers and society as a whole to make better decisions.

2017.01.21 | Janne Hansen

Many factors play a role when calculating the carbon footprint of milk. Photo: Colourbox

When you bite into a steak or a carrot, you also have an impact on climate change. On average, a steak is responsible for 14 kg CO2 per kg food produced, whereas the carrot only has an impact of approx. 0.2 kg CO2 per kg food produced. How does this work and how do other foods impact the climate?

Scientists from the Department of Agroecology at Aarhus University have been working on elucidating this. The results of their research efforts provide us with figures to help us make better decisions; ranging from the production process till we place the product in our shopping carts. 

A better understanding of how and to what extent our food consumption affects the climate can contribute to figuring out how and where to reduce the carbon footprint of food.  

Scientists put numbers on the whole picture

How do scientists add figures to the whole picture? Researcher Marie Trydeman Knudsen from the Department of Agroecology at Aarhus University explains:

- We carry out life cycle assessments of individual foods. A life cycle assessment is the calculation of a given product’s environmental impact. The impact on the climate is called the product’s carbon footprint. We estimate emissions throughout the entire chain. First, we identify the processes that the product went through, and then the input, output and emissions of each process.  

Milk is a good example of how to carry out a life cycle assessment of a given product and its carbon footprint:

The output of a dairy is milk, and milk production requires input in the form of e.g. energy for machinery. Energy consumption is connected to greenhouse gas emissions. Such emissions are part of the equation in life cycle assessments for the carbon footprint of milk.

Milk comes from a farm, the output of which is milk and beef. The input used to produce milk and beef includes e.g. feed concentrate and roughage. In addition, fertilizers and perhaps pesticides are used. Energy is required in factories as well as fields to produce these products, leading to greenhouse gas emissions. Animals are also part of the game. Cows emit greenhouse gasses in the form of methane when they metabolize feed in the rumen.

The importance of each individual part of the chain

One of the challenges is to identify and map all processes and their climate factors. Another challenge is to determine precisely the carbon footprint of each of these factors. In the milk example, this will depend on the type of energy sources used at the dairy, in the fertilizer factory and by the tractor as well as the type of feed fed to the cows.

Scientists from all over the world – including scientists from Aarhus University – are working on calculating the different types of emissions precisely. For this purpose they carry out measurements, develop calculation models and share their knowledge with each other. 

- In addition to Aarhus University’s own trials in fields and livestock buildings, we draw on figures and calculation methods from the literature and various databases such as the Intergovernmental Panel on Climate Change (IPCC), Ecoinvent and the SimaPro tool, which compares emissions in the entire chain and draws on the Ecoinvent database, Marie Trydeman Knudsen explains. 

Once the scientists have gathered all data, they convert the different GHG emission figures into CO2-equivalents per kg produced food or per ha depending on which is most relevant.

The emissions are converted to CO2-equivalents because the various greenhouse gasses impact the climate in different ways. One kg methane (CH4) impacts the climate just as much as 25 kg CO2 and one kg nitrous oxide (N2O) has the same impact as 265 kg CO2. A conversion into CO2-equivalents allows for a total carbon footprint calculation.


See the carbon footprint for a number of foods here (in Danish).


The idea behind life cycle assessments (LCA)

However, the job is not done when data is gathered and calculations made. The figures must be put to work.

The scientists work with three different approaches. One is to use LCA to estimate the climate impact in relation to an existing system that produces food or bioenergy in order to optimize and improve the system and look for hot spots (the parts of the process with the most significant climate impact). Identification of the hot spots allows the scientists to clarify which areas need increased focus and efforts. 

Another approach is to use LCA to compare different food or bioenergy systems in order to assess the advantages and disadvantages of the production systems. The scientists study the impact of the different systems on the climate when all aspects are included.  

Finally, LCA is an efficient tool when developing new innovative food or bioenergy systems and can be used as a guideline for developing the most sustainable and optimum system. 

- Life cycle assessments are often interdisciplinary and take place across departments and together with the industry in national or international projects, and the environmental life cycle assessment represents part of the project, says Marie Trydeman Knudsen. 

Still using the milk example, we might argue that the methane emission from cows constitutes a hot spot in relation to milk production. Consequently, much research currently focuses on this particular area.  


See examples of current research here.


Aquatic environment plans helped

Cows are not the only focus area. Cultivation systems also affect the climate. The role of nitrogen in relation to the environment constitutes an excellent example of the complex connections that impact the carbon footprint.

- A major part of the reduced nitrous oxide emissions we have seen is attributable to the aquatic environment plans. These plans resulted in reduced nitrogen emissions to the aquatic environment, to the benefit of not only the aquatic environment. The reduced use of nitrogen resulted in less nitrogen emissions from the fields. In addition, the reduced application of fertilizer has resulted in a reduced need for fertilizer production and thus reduced energy consumption, Marie Trydeman Knudsen explains.

The environmental impact of food in a broader sense

So far we have mainly considered the carbon footprint of food, but foods affect the planet and its resources in a number of ways.

- When measuring the environmental impact, we focus mainly on climate impact (emission of greenhouse gasses) and eutrophication the aquatic environment (nitrogen emission). However, the impact on biodiversity also constitutes a very significant environmental impact. Climate impact, eutrophication and biodiversity are the three major impacts to the planet. Mankind has already changed these processes so much that we have exceeded the planetary boundaries within which Earth can regain its equilibrium. We should not exceed these limits if we want a sustainable production, says Marie Trydeman Knudsen.

Besides including biodiversity and soil carbon changes in life cycle assessments, scientists from the Department of Agroecology have also started including new environmental areas. These comprise soil quality, water consumption and ecotoxicity.

- We want to look at the entire picture. If we only use the carbon footprint, we may risk a sub-optimization. This will happen if we improve one area – e.g. the carbon footprint – but produce a negative impact with regard to other parametres. Then we have accomplished nothing. As far as possible we should look at the big picture, says Marie Trydeman Knudsen. 


For more information please contact: Researcher Marie Trydeman Knudsen, Department of Agroecology, e-mail: mariet.knudsen@agro.au.dk, telephone. +45 8715 7958

Read more about how agriculture can mitigate its effects on the climate on out Climate Theme site.


Climate-Smart Agri-Food Systems is one of the research areas in which the Department of Agroecology is particularly strong and from which results are delivered in line with national and global societal challenges and goals.

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