We have developed a carbon calculator which is simple to use and will enable you to track your carbon footprint from year to year. The calculator is a spreadsheet which can be downloaded here.
We intend after it has had some use to implement a web based version, so please put any feedback in the comments section below.
Note that when you open the spreadsheet, you may find that it displays an error message about updating links. If it does please press No and it will continue into the spreadsheet. This will be fixed as soon as we have resources to deal with this issue.
What datasources do we use?
The calculator uses the following data sources:
- Greenhouse Gas reporting factors published annually by government.
- Annual Household expenditure statistics published by ONS
- Our world in data carbon impacts data. This has a download link for carbon footprints different basic foods.
- How bad are banana? book by Mike Berners-Lee
Why do we ask for the year?
There are two reasons that we ask for the year:
- Annually government produces factors that are used for company greenhouse gas (GHG) reporting, we need the year to determine which set of factors to use.
- We build a table of carbon footprints for each year, together with a set of targets for following years.
Home energy use
Home energy use can be calculated very accurately, particularly if the fuel you use is metered. You enter the amount of each of the following types of fuel you use in a year:
For some types you will need to make further selections for example you could use either mains gas or LPG
Standard factors for each year are applied to your home energy use to work out your footprint.
We have worked out a simple way of accomodating both conventional ICE vehicles, plug in hybrids (PHEV) and battery electric vehicles (BEV)
For each vehicle you need its annual mileage, which you can get from its MOT certificate (unless it is less than 3 years old), fuel consumption (petrol/diesel). Many cars have a trip computer which shows average consumption over the car’s life, this is the easiest way of getting your consumption.
If you don’t have a trip computer you need to gather data over a calibration period, and enter this into the calculator you can input the mileage and litres of fuel used in the period (it is clearly important to start and end with the same fuel gauge reading).
Plug-in vehicles (both BEV and PHEV) are often charged at home using electricity that has already been accounted for in your home electricity consumption, so you need to enter only mileage that does not use home electricity.
There is a separate section for electricity from public charging points that can be used for any plug-in vehicle. You need to enter your electricity consumption, you can probably get this from the car’s computer, and the mileage travelled on public charging electricity.
It would be nice if you could keep a food diary and enter the precise amount of each food you ate, and it worked out your carbon footprint. Unfortunately this would take a lot of your time, and would require a large amount of data to drive it. Some information on the carbon footprint of various foods is given by our world in data. This data gives raw foods, so could be a useful indicator, but leaves out things that are processed that we might eat such as biscuits, ready meals and so on.
Your food and drink expenditure should include both home and away from home consumption.
We have instead built an approach based on five diet types and your annual expenditure on food and drink:
- Plant Based
- Light meat eater
- Standard UK
- Heavy meat eater
Diets that are only plant based have far lower emissions than any other.
Vegetarian diets include dairy produce and eggs which have quite high emissions.
Light meat eater diets include poultry and fish and very occasional red meat.
The standard UK diet includes some red meat, and follows a similar profile to ONS household expenditure.
The heavy meat eater diet is one which has a portion of red meat almost every day. Red meat such as beef, lamb and venison has higher emissions than other foods. There is also much more variability in red meat emissions, depending on land use change, feed, and even breeding.
I have also looked into beef and lamb a bit more, as the figures given in the above are global averages. This link https://ourworldindata.org/environmental-impacts-of-food#you-want-to-reduce-the-carbon-footprint-of-your-food-focus-on-what-you-eat-not-whether-your-food-is-local shows that beef emissions vary between 9kg CO2e/100g and 105kg CO2e/100g. This is too big a range to ignore. I came across an industry report which seems to get emissions at a farm level http://beefandlamb.ahdb.org.uk/wp-content/uploads/2013/04/roadmap_3_-_down_to_earth_180112-final-report.pdf. This sort of thing might be more useful as it could direct consumers to good farms.
Stuff covers goods and services, it is everything else that you consume.
You enter the amount you spend annually on goods and a standard factor is applied to calculate your emissions.
A standard amount of emissions is allocated to emissions.
- Tobacco and Narcotics
- Clothing and footwear
- Maintenance and repair of dwellings
- Water supply
- Household goods and services
- Medical products, appliances and equipment
- Purchase of vehicles, spares and servicing
- Communications equipment (phones, etc)
- Audio-visual, photographic and information processing equipment
- Major durables for recreation
- Other Recreational items, gardens and pets
- Newspapers, books and stationery
- Personal care and personal effects
- Rent and mortgages
- Hospital services
- Postal and communication services
- Recreational and cultural services
- Package holidays
- Social protection
- Other services – professional, legal, banking, etc.
How is stuff calculated?
The calculation for stuff is the least accurate of our calculations.
For goods the underlying assumptions are:
- Emissions of 1100 kg CO2e per person, which CAT have calculated from UK industrial and commercial emissions.
- 2.3 persons per household to give household emissions of 2530 kg CO2e
- UK Consumption emissions of 784 Mt CO2e
- UK Production emissions of 503 Mt CO2e
- Household emissions are multiplied by the ratio of consumption emissions to production emissions (1.55) to give 3943kg CO2e
- This is divided by average household expenditure on goods of £8725 from analysis of ONS household expenditure data to give 0.4519 kg CO2e/GBP
This factor is multiplied by the amount you spend on stuff to give your emissions.
The fixed amount for services is based on an estimate of 3000kg CO2e per standard household of 2.3 people equivalent to emissions of 1304kg CO2e per person. Unlike the other estimates it isn’t based on expenditure, this is because things in this category that we spend a lot of money on such as rent, mortgage, council tax will have roughly the same emissions regardless of what is spent.