Spend based carbon footprinting

The data for your carbon footprint is already in your bank statement

Calculating your core business finances is fairly simple. Gather your bank statements. How much income did you earn? How much did you spend? Is your profit matching your target?

Calculating your carbon footprint seems a lot more complicated. You’ve got bills showing the kilowatts of energy used for your own gas and electricity, so that’s straightforward. But what about all the products in your supply chain? How do you measure the carbon in an email, or from your insurance package? Where do you look to get any data on the climate impact of things you buy and the things you do as a business? It’s all there – in those same bank statements.

There are 2 key benefits to using your spend data to calculate your greenhouse gas emissions. The first is that you already have it, in your procurement logs. The second is that spend data can be used with an input-output model, a model that uses computing power to keep going back and back through supply chains to give a really complete emissions factor.

If you can calculate how much you spent on different things for your business, you can use the same data to calculate the carbon footprint from your supply chain.

How input-output models take biscuits to infinity

An input-output model takes the amount of money you spend in any one industry, and calculates the emissions from the full supply chain. The Small World input-output model has data on the emissions from each of 103 industries, and data on the other industries that they spent money with. As you pick your favourite biscuit to dunk in your brew, and think about where all the emissions come from in its production, how far back can you go?

If you buy some biscuits in the UK, the input-output model knows the direct emissions from this first-tier industry, which is easy to imagine as the energy needed to heat the baking ovens. The model also knows how much the baking industry spends on packaging, transport and digital advertising as well. So, it calculates the smaller amount of emissions from the amount spent on those second-tier industries. The packaging industry has direct emissions, and it also spends money on other industries, like paper production, and insurance. So the model calculates the emissions from these third-tier industries. The model keeps going up and up through the tiers, going through an infinite number of tiers, adding ever smaller amounts of emissions to the total. The result is a complete carbon footprint from the amount you’ve spent on a year’s supply of dunkable biscuits.

Using spend-based data with an input-output model gives a really complete emission factor, but it lacks specifics. It doesn’t know the difference between spending on organic chocolate biscuits or macaroni cheese, which have very different ingredients and so will have different carbon footprints.

Input-output models give system-complete carbon emissions, but lack specificity. Avocados and brussel sprouts are both vegetables, but have quite differnet carbon footprints.

Life Cycle Analysis and Hybridisation

“Life Cycle Analysis, or an LCA comes from the bottom up,” says Matt Bond, Senior Consultant at Small World Consulting. “It starts with the specific components of a product, and then looks at the other components needed for those. But because it's done manually it generally stops after 2 or 3 tiers.”

So this way of calculating carbon would capture the difference between chocolate biscuits and pasta and the different things needed to supply those, like sugar and wheat for the biscuits, and eggs and cheese in our macaroni dish. It would then look at those second tiers, the products and services needed for sugar or for eggs, and the emissions from those. But as LCAs are calculated manually by people, going to infinity isn’t a workable option. This means that LCAs are much more specific, but they don’t go as far up the tiers, so are not as complete and underestimate the full carbon in the supply chain.

That’s why we analyse LCAs, work out which tiers they’ve stopped at, and then use our input-output model to calculate the emissions from those missing tiers.

“Using hybridisation gives you the best of both models,” says Matt Bond, “we look at how many tiers are in the LCA and what’s been truncated, or left out. Then we use the input-output model to give a calculation for those missing tiers. Adding the two together gives us the most realistic carbon footprint for a product.”

Using our own input-output model also allows us to make adjustments to the data when we know specific details of a spend.

Having this level of detail in your carbon footprint is a huge benefit. It gives you the most reliable emissions factor, so you know that the actions you take to lower your emissions are really having an impact. And it means that when you change your spending choices to reduce your supply chain emissions, those reductions can be shown in your footprint reports year on year. If you change your biscuits to ones with a lower carbon footprint, our calculations can show that in your emissions report.