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Carbon Assumptions

Carbon Assumptions

Carbon Footprint Calculations

We understand that everyone lives very busy lives, which is why we have kept our lifestyle questionnaire short and sweet. Our questionnaire covers 5 main areas to get an estimate of your carbon footprint: day-to-day travel, flights, diet, products and home.

We have listed below all of the assumptions and sources for data used in our calculations.

Day-to-day travel

Instead of asking you to figure out the number of miles you travel across various modes of transport in an average a week, we ask you how much time you spend traveling. We then work out your distance with average speeds for each mode of transport which is multiplied by the appropriate 2020 UK government emissions factors .

An emissions factor tells us how much carbon is emitted by traveling one mile using each type of transport. These emissions factors vary depending on things like the size of car, type of bus and type of train.

We have assumed an average car size for emissions factors relating to cars. Travel by train is assumed to be national and travel by bus is assumed to be a local bus. For ease, we have assumed travelling by Uber means you are traveling in a hybrid car.

Flights

In the same way that we calculate day-to-day travel, we can use the 2020 UK government emissions factors and the average speed of a plane (900Km/hour) to understand the carbon emissions from flights.

Again, to make things simple we provide you with four options on flight times and take the median time per category: short haul (2 hours), medium haul (6 hours), long haul (10 hours) and extra long haul (14 hours).

We have assumed that you will fly economy class and have opted for emissions factors that include radiative forcing. Radiative forcing includes emissions of nitrous oxides and water vapour when emitted at high altitude.

Diet

A study from the University of Oxford, Poore & Nemecek (2018) , analysed the carbon footprints of various foods in our diet. We ask you about your monthly eating habits to find a monthly footprint and then extrapolate to a year.

We have assumed that everyone eats their vegetables so have added the emissions for a standard vegan diet onto your footprint if you didn’t select a vegan diet.

Products

Everything we consume has a carbon footprint and the organisation Carbon Footprint has provided estimates for how much carbon is emitted from spending on various products and services.

Whilst the list is large of all the possible things you can buy, we have kept it simple with fashion, toiletries and electronics.

Home

We have included spending on furniture and appliances as an emission from your home, with data being provided by Carbon Footprint .

Waste at home can either go to landfill or to recycling and the carbon emissions are different depending on where your waste ends up. DEFRA estimates that the average home recycles only around 45% of their waste. We know from UK statistics on waste that the average home produces 0.975 tonnes waste each year. Using 2020 UK government emissions factors we can then calculate the average emissions per home from waste going to landfill and to recycling plants. This number is then divided by the number of people living in your household to find your share of the household emissions.

Emissions also arise from the supply and treatment of water for your home. Energy Savings Trust estimates the average UK home uses 349 litres of water every day. We multiply this by the 2020 UK government emissions factors to work out the emissions from water supply and treatment in the average UK home. This is then divided by the number of people living in your home to find your personal share of the household emissions.

If you said that you are on a renewable energy tariff or if your gas is carbon neutral then you won’t have any emissions from home gas or electricity.

If you aren't on a renewable tariff or have carbon neutral gas, we use Ofgem data for average energy usage per UK home, which is 2,900 kWh electricity and 12,000 kWh gas each year. We multiply this by the 2020 UK government emissions factors for the UK average fuel mix. This number is then divided by the number of people living in your household to find your share of the household emissions.


Unavoidable Emissions

Carbon Independent calculates that everyone in the UK is responsible for 0.18 tonnes per year per person of food emissions they can't avoid. This is down to things like methane emissions from soil management, and carbon emissions from operation of retail stores and farming.

Carbon Independent also estimates that everyone in the UK is responsible for 1.1 tonnes of emissions over which they have no direct control. These unavoidable emissions are things like the NHS, armed forces, social services and schooling.


Your Carbon Equivalent Metrics

Below, we document how we calculate the equivalent metrics displayed back to our community to help them understand the carbon they’ve reduced through funding our offsetting solutions

Equivalent Metric

Data Source

Source Link

Calculation Methodology

Comments

Flights from London to Rome

2020 BEIS Conversion Factors

Here

  1. Multiply emissions factor by distance from London to Rome (1,440 km)

  2. Divide total carbon by carbon offsetted for each journey, giving us number of flights

Output is rounded to nearest 0.5

Car trips from London to Manchester

2020 BEIS Conversion Factors

Here

  1. Multiply emissions factor by distance from London to Manchester (208 miles)

  2. Divide total carbon by carbon offsetted for each 208 mile journey, giving us the number of car trips

Output is rounded to nearest 0.5

Beef Steaks Consumed

Poore & Nemecek (2018)

Here

Assumption of 225g serving of steak taken 23.19 kg CO2e (0.02319 t)

We divide the total carbon offsetted by the emissions above which gives us the number of steaks consumed equivalent.

This source includes the emissions caused by all farm-to-fork aspects including methane generation, meat production and logistics

We round this equivalent to the nearest whole integer as the CO2 emissions from one beef steak is relatively small in comparison to our other offsetting figures.

Parcel Deliveries

ASOS (via DPD & Hermes)

Here

Medium sized parcels generate approx. 3.68kg CO2

We divide the total carbon reduction by the data point above, which gives us the number of parcel deliveries equivalent.

We round this equivalent to the nearest whole integer as the CO2 emissions from one delivery is small (especially relative to our other emissions factors)

M2 of sea ice saved

Notz (2016)

Here

Three square meters of Arctic summer sea ice disappears for every tonne of CO2 a person emits, wherever they are on the planet.

We then assume that for every tonne of carbon dioxide someone prevents through our projects, three square meters of sea ice has been saved.

Of course, causation is not proven in this study, but we love including this sort of metric as it is spatial, physical and relevant.

We round to the nearest .5 meter squared

Days Online Streaming

IEA (2020)

Here

36g of CO2 for each hour of online streaming

We then calculate the total number of hours of online streaming your total carbon reduction is equivalent to, before dividing by 24 to reach the total number of days.

We round this equivalent to the nearest whole integer as the CO2 emissions from one delivery is small (especially relative to our other emissions factors)

Months of Home Electricity

BEIS Methodology Paper for base electricity conversion (2020)

Ofgem (2020)

Here

Here

We take the emission factor 0.25792 kgCO2e / kWh from BEIS, and match this with the average electricity consumption from Ofgem’s Typical Domestic Consumption Values for 2020 (3,941 kWh per household).

An average UK household therefore emits 1,016.46 kgCO2e across a year, or 84.705 kgCO2e per month. We then divide the total carbon reduction (in kg) by 84.705 to get our months of home heating.

The output of months can also be divided by 12 in case we display years of home heating


Other Assumptions

We're constantly communicating emissions reduction impacts in different ways. Whilst we update this page bimonthly, please just let us know if you see any other metric you'd like us to give you the data assumptions for.