A carbon footprint is the total amount of greenhouse gases emitted by something. That might be a person’s lifestyle, a product’s supply chain, an organisation, or an activity. Everything from a banana to a ship has a carbon footprint.
In simple terms, it equates to the environmental impact that someone or something has.
To begin with, this term referred to just the carbon dioxide (CO₂) emissions being released into the atmosphere. CO₂ is the most common greenhouse gas. But it’s not the only one. There are other gases that contribute substantially to climate change, such as methane and nitrous oxide. Carbon footprints usually now incorporate those too.
These are often added together and expressed as the carbon dioxide equivalent (CO₂e): the amount of carbon dioxide that would create the same amount of warming.
According to the World Wide Fund for Nature’s online calculator, my annual carbon footprint is about 7.7 tonnes. The average for the UK is 8.8, and the global average is 6.3 tonnes.
That footprint can be reduced by buying more stuff secondhand rather than new, lowering the temperature on the thermostat in my house by a couple more degrees and composting much more of my food waste at home, or perhaps switching to an ethical bank that doesn’t invest in fossil fuels.
The carbon footprint concept stems from the life-cycle assessment, a way to measure the impact of a product or system over its entire lifetime. From the sourcing of raw materials to manufacturing processes, transport and distribution, plus the energy used to dispose of a product once its no longer needed.
Measuring your carbon footprint is an important first step (forgive the pun) to improve our carbon literacy and environmental awareness. Knowing that baseline is crucial. Only then can progress really be quantified as time goes on.
But the problem is that carbon footprints can be measured in different ways and to varying degrees. In his book How Bad are Bananas?, Mike Berners-Lee, a professor at Lancaster University, says that most carbon footprint calculations are more like toe prints, because they don’t give the full picture.
Experts talk in terms of three different levels of emissions, called scope one, scope two and scope three emissions.
Scope one emissions include any greenhouse gas emissions that are in your direct control, or that of a company. So that includes the fuel you put in your car if you have one. Or the emissions that come from heating your home by putting logs on an open fire.
Scope two emissions include indirect greenhouse gas emissions from the energy used. So the emissions from generating the electricity used to light your home, for example.
Scope three is even broader. It includes all of the indirect emissions in the entire supply chain for a product or a service. So, for example, the shipping emissions from importing the bananas in your fruit bowl or the emissions released during the incineration of packaging waste that can’t be recycled.
Scope three emissions are usually the highest and the hardest to reduce because we have much less control over them.
Carbon footprint has become a household term. But as Marcelle McManus, a professor of energy and environmental engineering at the University of Bath highlights, it’s popularity is all down to oil companies actively promoting it.
She explains that the idea of measuring personal carbon footprints – in other words, calculating the emissions we’re responsible for as individuals – was originally promoted by oil giant BP to shift the burden of action (and blame) from fossil fuel companies to consumers.
So, the onus is on us. But even if we all reduced our personal carbon footprints that might never be enough.
“In a world where just 100 companies are responsible for 71% of global emissions,” McManus says, “we need a total overhaul of the carbon-intensive systems around us instead.”
