A carbon footprint indicates the total greenhouse gases (GHGs) caused directly and indirectly by a person, product, activity or event expressed as equivalent to carbon dioxide (CO2e). Carbon dioxide equivalent (CO2e) number includes carbon dioxide and other greenhouse gases which are converted into CO2 equivalent and therefore the value of CO2e will always be higher than CO2 for any particular fuel, electricity or product, etcetera.
Direct emissions come from direct use of energy such as natural gas combustion for hot water or cooking at home. Indirect emissions can be of two types, one from direct consumption of electricity at home which is generated at power stations, resulting in CO2e and other by purchasing products and services such as consumption of bread at breakfast. Every loaf of bread has a carbon footprint associated with its production, packaging, storage and delivery also known as life cycle carbon emissions. This takes into account the emissions at each step from wheat production to Supermarket for sale and packaging recycling.
The carbon footprint of fruit and vegetables in agriculturally rich countries such as India and Pakistan could be much less than those who rely on export but it is also dependent on energy efficiency and carbon and water intensity of the producing country. India’s carbon intensity at grid was approximately 0.7429kgCO2e/kWh which is more than double the UK’s carbon of 0.35156kgCO2e/kWh for the same year.
To calculate Carbon Footprint, we need the conversion factors often available from government portals and vary country by country. In the UK, the department for environment, food and rural affairs (DEFRA) publishes CO2e factors for electricity, combustible liquids & gases and transport, etcetera. I have listed some carbon factors for 2019 as follows:
Electricity – 0.2556kgCO2e/kWh
Gas – 0.18385kgCO2e/kWh
Diesel – 0.24462CO2e/kWh
Petrol – 0.23373CO2e/kWh
Coal – 0.30561CO2ekWh
Water Supply – 0.344CO2e/m3
How to calculate the Carbon Footprint?
In addition to my example of calculating energy saving in my previous article, we can now calculate the carbon savings associated with energy-saving.
The electricity savings from turning-off a 20Watt LED bulb for one hour for 365 days 7.3kWh/yr. The associated carbon footprint (CO2e) savings would be:
7.3kWh × 0.2556kgCO2e/kWh = 1.87kgCO2e or 0.00187tonnesCO2e.
Calculating the Carbon Footprint of a typical household
Following example looks at calculating the carbon footprint of a typical household excluding indirect emissions from consuming food, using products and services including public transport.
Annual grid electricity consumption – 2,430kWh
Annual electricity generation and consumption from solar – 450kWh
Annual gas consumption – 858m3
Diesel consumption for 2.0Ltr car – 200litres
Petrol consumption for 1.3Ltr car – 70litres
Water Use – 300m3
| Energy Source | Formula | Carbon Footprint (kgCO2e/year) |
| Grid Electricity | 2,430 × 0.2556 | 621.1 |
| Solar Electricity | 450 × 0 | 0 (Carbon intensity for electricity generated from renewables including solar is zero) |
| Natural gas Converting from m3 into kWh: 858 × 1 × 39200÷3600 = 9,343kWh | 9,343 × 0.18385 | 1,717.71 |
| Diesel Converting Diesel litres into kWh: 200 (litres) × 10.60 (kWh/litre) = 2,120kWh | 2,120 × 0.24462 | 518.59 |
| Petrol Converting Diesel litres into kWh: 70 (litres) × 9.44 (kWh/litre) = 660.8kWh | 660.8 × 0.23373 | 154.44 |
| Water Use | 300 × 0.344 | 103.2 |
The household carbon footprint is approximately 3,115kgCO2e or 3.12teCO2e. The above results are shown in graphical form below.
Carbon Offsetting
In the above example, we might be able to reduce our carbon footprint by 75% by first reducing our energy consumption (via behaviour change and energy efficiency), switching to electricity supply from renewable sources and replacing gas heating with electricity, nevertheless, we can’t achieve 100% reduction to achieve zero emissions. In this case, the carbon footprint can be offset by purchasing carbon credits equivalent to the carbon footprint to achieve carbon neutrality or net-zero emissions. Several schemes are operating in the UK and worldwide who are investing in renewable energy and afforestation projects registered for carbon offsetting.
Conclusion
It is essential to understand our carbon footprint in order to start making strategies for reduction. Behaviour change and energy efficiency should the starting steps followed by renewable energy generation and purchasing from renewable sources. With decreasing UK grid carbon intensity, average household emissions are dropping and therefore the application of heat pump can be more viable than ever before. Savings achieved from energy savings could be used for renewable projects or carbon offsetting.
Do you know your carbon footprint? Which energy source is the highest contributor?
Click here to calculate your carbon footprint using an easy-to-use calculator.
Factbox
Did you know…
– One standard email results in 4 grammes (g) of CO2e and one email with a large attachment results in as high as 50gCO2e.
– In the UK, every day 64m emails are sent unnecessarily resulting in approximately 23,500 tonnes of CO2e according to a research carried out by OVO Energy.
– Every whole-grain loaf of bread (approx 800g) results in 0.5kgCO2e. Every day, an estimated 12 million loaves of bread are sold in the UK.