An inside look at the footprint of salmon

You probably know that the carbon footprint of different products varies – the footprint of beef, for example, tends to be higher than that of tomatoes. But where do those numbers come from? To learn how carbon footprints are calculated, let’s take a deep dive inside one calculator that WWF devised with the Global Salmon Initiative (GSI). This calculator is being used by GSI member companies to track their progress towards an ambitious benchmark we call “The Salmon of 2030” and to accelerate mitigation efforts through shared knowledge. The core calculator was developed by Blonk Consultants and IDH.

Step 1: What is included?

A calculator looks at a product within certain boundaries. For example, a footprint that is cradle-to-retail indicates that all the inputs, processing, and transport emissions are included up to the point of sale; a footprint that is cradle-to-grave would also include emissions from the use (or consumption) phase and disposal.

In this case, we included four critical phases that are most relevant for salmon aquaculture – feed production, salmon farming, processing & packaging, and transportation to distribution centers. The figure below shows the range of footprint contributions from each phase — measured in kilograms of CO2 equivalents per kilogram of edible weight (EW) — according to a literature review conducted by WWF.

Each stage can contribute a lot of emissions to the footprint. But note that their contributions can also vary greatly. Therefore, we need to directly estimate what that contribution is for each salmon-producing company to help them understand how best to lower their emissions.

Step 2: Gathering information about the processes occurring in each stage

Carbon footprints are calculated by gathering data about the different processes that emit greenhouse gases. For example, to understand the emissions from purchased feed, we would ask about the amount of feed purchased and then multiply that amount by the emissions factor for that feed.

The bullets below show key questions we ask each company for the processing and packaging phase. We also provide clarifying notes on what each question means and the units we are expecting, because there can be many interpretations that could influence the results.

• How much of the live-weight is wasted? (tonnes) This includes any salmon products from slaughter or processing that are not used.
• How much electricity is used? (kWh)
• How much fuel is used? (L) Please also specify which fuel is used (diesel, gasoline, etc.)
• How much packaging is used? (tonnes) Please also specify which type of packaging is used.

Step 3: Calculating the climate impact of each process

We then use the data generated in Step 2 to estimate the amount of greenhouse gases emitted in each relevant process. To do this, we often must make assumptions; in this case, those assumptions were tested by collecting a large amount of additional data from all the GSI member companies to ensure that the questions we asked captured the most important components contributing to the footprint.

Let’s go through calculating the climate impact from each of those questions from Step 2:

• How much of the live-weight is wasted? We take this number, in combination with how it is treated, to calculate the emissions from disposal. Different methods of disposal generate different emissions. For example, if 1 kg of organic material is composted, it generates about 0.01 kg of CO₂e; if it is landfilled it generates about 0.7 kgCO₂e.¹ So, we would multiply the kg that are composted by 0.01 and add it to the kg that are landfilled multiplied by 0.7.
• How much electricity is used? Different types of electricity production have different greenhouse gas emissions. For example, hydropower produces about 0.02 kgCO2e/kWh while coal produces about 1 kg.² So, in a similar manner to above, we take the total amount of electricity supplied by each source and multiply it by that emissions factor. If the producer gets electricity from a regional grid that uses multiple sources, we use the average across those energy sources.
• How much fuel is used? Similar to electricity sources, different fuels generate different amounts of GHGs when burned. For example, burning a gallon of diesel generates about 10 kg of CO2e, while a gallon of liquid petroleum gas generates about 5.9. We then multiply the amount of each fuel by its emissions factor.³
• How much packaging is used? Greenhouse gas emissions are also produced in making packaging materials. To calculate how much, typically those researchers will do their own analyses (following similar steps) to calculate the total footprint of that product. For a plastic, this might be about 2-4 kgCO₂e / kg depending on the type of plastic or about 1 kgCO2e / kg of paper packaging — multiplied, of course, by the emissions factor.⁴

From each of these steps we’ll get a total amount of greenhouse gas emissions in CO₂e. Now we just need to do the final step: divide the sum of greenhouse gas emissions by the amount of salmon produced. This gives us the contribution of processing and packaging per unit of salmon.

Step 4: Compare results over time & look for mitigation opportunities

This step is the most important. We can look at these results over time and see how much progress the company is making towards lowering the footprint or understanding how events like switching processing facilities or an algal bloom impact the footprint. We can also look at the individual contributions from each of the four stages, or compare, say, the contributions of electricity vs. packaging. From this, we can understand both what the biggest sources of emissions are and strategize how to reduce them. One strategy might be to reduce the amount of electricity used, for example, but we could also think about switching to a different electricity source.

Because GSI member companies are all using the same tool to make these calculations, they can directly compare their values and share lessons about what strategies helped them lower their footprints the most effectively.

¹Data from: DEFRA 2023
²https://data.nrel.gov/submissions/171
³DEFRA 2023
⁴DEFRA 2023