Carbon Footprints

It is not as easy to measure a person's or even a product's carbon footprint as some may think. In fact, it is close to impossible. As an example, let's take a pack of bacon:

There are many stages in the life-cycle of a food product: raw materials are produced and transported, the food is processed and packaged and then it is distributed to retailers where it is stored. But it doesn’t end there: once bought it must be transported home, stored again and consumed, all of which use energy. Lastly there is disposal – the packaging is collected and usually taken to landfill; a small amount is recycled or reused.

In each of these stages there are hundreds of complex processes, all of which will emit greenhouse gases, which can vary by each individual product. Taking the pack of bacon: At the start of the cycle we have a young pig. Its food is produced and transported to the farm where it lives. Immediately we must ask: How is it transported? By lorry, plane, rail? How is its food supply manufactured? How many tractors plough the corn field where its food is grown, and what are the emissions of each tractor? This can go on, and we are only on the first phase of the cycle. The pig farm machinery must also be taken into consideration – and each farm will be different. What of the emissions from each pig’s bodily functions?

This question may seem insignificant when compared to the many other factors, but it leads to another very important point: The carbon footprint of a product is a measure of its impact on the environment i.e. how much is it going to increase the greenhouse effect? The use of the word ‘carbon’ can be confusing here; there are other gases which when released into the atmosphere have a far greater global warming potential, relative to carbon dioxide.

And so this brings us to a pig’s fart: methane. It is emitted at other stages of the cycle too, like landfill sites where waste decomposes, releasing methane.

In carbon footprints, these other gases are accounted for and included. The trouble is that many of the carbon footprints quoted today can be somewhat misleading, because they are based on the global warming potential relative to CO2 over a 100 year period. If we had 100 years to address climate change, this would make sense. But it appears we have years, not decades, so it would be more meaningful to consider the effect over the next 20 years. One can see that methane is 3 times more potent over 20 years than it is over 100 years. The footprints of products would almost certainly be different if calculated on a 20 year basis.

Riverford, the largest supplier of organic food boxes in England, came across a good example of the complexity in measuring the carbon footprints of food and drink. Riverford carried out a study comparing the carbon footprint of its tomatoes grown locally to those grown in Spain. It would be reasonable to expect that the tomatoes grown abroad would have a higher footprint – they have further to travel and they must be conserved (refrigerated) on route. However the study showed that while they do indeed emit more CO2 in the transport stage, overall they are less carbon-intensive i.e. fewer greenhouse gases are released in the life-cycle of each Spanish tomato sold in the UK, than in a UK tomato sold in the UK! This is because in Spain, the tomatoes can be grown in the natural climate, but in the UK greenhouses are needed, heating is needed and the growing of the tomatoes requires energy – taken from the national grid. When this is weighed against the emissions from transport, the UK tomatoes have a higher carbon-intensity.

Now imagine trying to work out all of these stages for a person's lifestyle…air travel, packs of bacon eaten…it would be a lifetime calculation for about 100 Albert Einsteins working together. In fact, I heard that when a large British supermarket chain announced they would be offering carbon footprint labels on 1000s of products by next year, they had to quickly backtrack and now offer labels on just packets of crisps - and only one flavour, from one manufacturer.