Carbon footprint….do you know what it is?

You’ve probably heard the expression carbon footprint many and many times. And you might even heard it daily if you are interested in environmental issues, or if you ready the newspaper, or listen to the radio and television news.  But do you actually know what does carbon footprint actually mean?

When talking about climate change, footprint is a metaphor for the total impact that something or someone has [that is why it is usually represented as a footprint. It’s the mark that something or someone leaves on the planet]. And carbon is a sum up for all the different greenhouse gases that contribue to climate change.

The term carbon footprint, therefore, is a shorthand to describe the best estimate that we can get of the full climate change impact of something. That something could be anything – an activity, an item, a person, a lifestyle, a company, a country or even the whole world.

And this is the scientific definition: Carbon footprint is “a measure of the total amount of carbon dioxide (CO2) and methane (CH4) emissions of a defined population, system or activity, considering all relevant sources, sinks and storage within the spatial and temporal boundary of the population, system or activity of interest. Calculated as carbon dioxide equivalent (CO2e) using the relevant 100-year global warming potential.” (1)

Therefore, everything has an associated carbon footprint, that count the emissions created by producing that product. The footprint is calculated through an analysis of the life of the product. Let say you’d like to know the carbon footprint of an apple you have to consider the energy necessary to grow it, pick it from the tree, transport it into the factory, put it into the package, transport to your local store, and finally keep it fresh in the store. If you think that  a lot of the fruit we find in UK supermarket come from different country you can easily see that the impact of transport is huge and it is also of immediate understanding why people always say to buy local product that are not packaged [because you cut emissions from at least 2 steps of the production circle].

Anyway, carbon emissions are expressed in kilograms. So what I think when I try to make sense of carbon emissions is something that has the actual weight of the emissions I am considering.

Image source: Data Visualisation

So for example, 1 kg of local oranges emits 1 kg of CO2, while 1kg of oranges that has been transported via plane emits 5.5 kilograms of CO2. Therefore, transport makes  a big difference.

What is CO2?

Climate change is blamed to be man made due to the release of certain types of gas into the atmosphere. The dominant man-made greenhouse gas is carbon dioxide (CO2), which is emitted whenever fossil fuels are burnt. But other greenhouse gases are also important. Methane (CH4), for example, which is emitted mainly by agriculture and landfill sites, is 25 times more potent per kilogram than CO2. Even more potent but emitted in smaller quantities are nitrous oxide (N2O), which is about 300 times more potent than carbon dioxide and released mainly from industrial processes and farming, and refrigerant gases, which are typically several thousand times more potent than CO2.

In the UK, the emissions break down like this: carbon dioxide (86%), methane (7%), nitrous oxide (6%) and refrigerant gases (1%). Given that a single item or activity can cause multiple different greenhouse gases to be emitted, each in different quantities, a carbon footprint could get even more confusing. To avoid this, the convention is to express a carbon footprint in terms of carbon dioxide equivalent or CO2e. This means the total climate change impact of all the greenhouse gases caused by an item or activity expressed in terms of the amount of carbon dioxide that would have the same impact.

What do you think? Can you visualise carbon emissions? Would you like some more information? Would you like some more scientific information, or you’d rather prefer more visualisation?

(1) Wright, L., Kemp, S., Williams, I. (2011) ‘Carbon footprinting’: towards a universally accepted definition. Carbon Management, 2 (1): 61-72.

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