Quicksilver Carbon Calculator Methodology
Last worked on 4/3/2011
Introduction
Our development of the Quicksilver Calculator has been guided by three key principles:

A comprehensive approach:
We aim to build up a complete picture of the carbon resulting from all aspects of a household’s
domestic life.

Providing a benchmark that encourages lower carbon behaviour:
The key purpose of the calculator is to provide a benchmark against which to measure behaviour
change. By measuring their carbon footprint on an annual basis, households will get feedback
about the impact of carbon cutting activities they may have undertaken. With this in mind, we
have focused on capturing details of data and lifestyle choices which will reward positive
behaviour change with a reduced carbon footprint.

Focusing on actual consumption rather than proxy measures:
We have chosen to use consumption data rather than indicative measures where ever possible.
Where direct measurement is not possible, especially in areas relating to lifestyle choices, it is harder to
provide a precise measurement of carbon emission relating to these areas. Instead we have asked
questions to ascertain the carbon intensity of the lifestyle and scaled the emissions accordingly.
Although we have attempted to be as accurate as possible, it is important for users of the service to be
aware that we are only able to provide an estimate of their carbon footprint. In part because the CO2
emissions relating to some activities are hard to accurately measure, but also because carbon intensity
factors of fuels are based on UK averages.
Ultimately we want to provide households with a tool to enable them to benchmark the current impact of
their activities on climate change, and provide them with feedback about how changes in their lifestyle
can reduce this impact.
Section 1: About you and your household
Here we capture basic household information.

Name and address, to identify to owner of the footprint.

Occupants – we count children as a “whole” person when it comes to breaking down the
household footprint to an average per individual, but in a number of calculations we assume
children to have a lower impact eg food consumption.

There is an option to take into account people you may share your home with for all or part of the
year. They will be allocated a share of the domestic energy emissions, but are excluded from
calculations relating to lifestyle and travel.

House type information is collected to enable us to use the results of the footprints we carry out to
estimate an overall community footprint based on housing stock types.

Participants are also asked their permission to use their data (in an anonymised format) to build up
an overall group footprint and community wide carbon footprint, as well as for other carbon
footprinting. A data protection clause is also be signed by the participant.
Section 2: Your Domestic energy consumption
This section looks at the fuel used to power your home.
A. Energy use in your own home
For most fuels, we calculate the carbon emissions associated with powering your home using actual
consumption data and conversion factors taken from DEFRA GHG Conversion Factors 2010.
Nb we used the gross Calorific Value (CV) basis factor and do not include indirect emissions.
Source: http://www.defra.gov.uk/environment/business/reporting/pdf/101006-guidelines-ghg-conversion-factors.pdf
To convert
Distances
Gas
Electricity (rolling grid av 2008)
100% renewable electricity
Heating Oil
LPG
Coal
Wood (not from DEFRA)
from
miles
KwH
KwH
KwH
Litres
Litres
Kilos
Kilos
to
kilometres
Kg CO2
Kg CO2
KgCO2
Kg CO2
KgCO2
Kg CO2
Kg CO2
multipler
1.609
0.18523
0.54522
0
2.5421
1.4920
2.8814
0
Electricity – based on electricity consumed, rolling grid average.
Nb these factors have increased from last year, in part because they now include other GHG emissions
such as CH4 and N2O.
Where the amount of fuel used is not available, for example for households using pre-paid meters, there is
an option to estimate fuel used based on money spent. We only recommend this option when no actual
consumption data is available.
Householders can input the actual cost per unit of their fuel. Our suggested default figures are based on
Ebico prepayment tariff:
Gas: 4 p a unit
(Ebico EquiGas: 4.011p a unit (inc VAT) at 25.1.11)
Electricity 13.5p
(Ebico Equipower, Southern Region:13.45p a unit (inc VAT) at 25.1.11)
Wood
For wood, we assume there is no net direct resultant carbon – although this is debatable, as it can be
argued that although over its lifetime wood is carbon neutral, it takes many years for trees to grow, and so
recapture the CO2 released by burning wood, and it is the levels of CO2 in the short term which are
driving climate change. Carbon emissions also result indirectly from the production of wood, eg
transporting it. However, as we exclude indirect emissions from other fuels, we also exclude them here
for consistency.
B. Green Energy
1. Are you signed up to a green energy tariff?
Householders are asked to indicate whether they have a green energy tariff. The result of this answer does
not impact on their carbon footprint.
2. Does your supplier invest in renewable energy beyond that required by law?
If the householder purchases electricity from a company for whom renewable energy makes up a greater
percentage of its fuel mix than that required under the Renewables Tariff, (ie 12% or more,) we reduce
the contribution of their electricity usage to 0 kg/KwH.
According to the Which Switch website, the following companies achieve this: Good Energy, Green
Energy, Ecotricity, OVO Energy (www.Which.co.uk/Switch 29 September 2010)
The DEFRA conversion factor for electricity is calculated based on the overall generation mix for the
UK. In theory, this means that if we use a lower conversion factor for people on green energy tariffs we
are double counting the impact of renewable energy. However, as the key purpose of our calculator is to
encourage individuals to reduce their carbon footprint, and switching to a green energy tariff is a part of
this solution, it felt important to reflect the theoretical impact of this choice.
With this in mind, we had decided to use a lower conversion factor for people who purchase their energy
from a company which
We use a conversion factor of zero for 100% renewable energy. Although there are indirect emissions
associated with renewable fuels, we do not include these for other fuels, so use zero to remain consistent.
2. Home based renewable generation
The impact of these technologies will already be reflected in reduced energy consumption from other
sources. We are capturing information about these technologies in this questionnaire in order to feed into
the second pledge sheet section (still under development).
C. Your heating
If electricity is used as the main heating source we attribute a proportion of electricity usage towards
heating, if not, all electricity usage is attributed to appliances and lighting. See summary below for split.
D. Your lighting
Data about low energy light bulbs is collected here to feed into the pledging section.
Summary
We allocate emissions by activity as follows:
1.
In gas heated homes:
heating & hot water
Appliances & lighting
cooking
2.
All gas, oil , coal and wood
100% electricity
As this is relatively small proportion, and a complex calculation to
accurately model, we have not split out cooking in this calculator.
In electric heated homes:
heating & hot water
Appliances & lighting
cooking
70.5% of electricity plus 100% of oil, coal and wood
29.5% of electricity
As this is relatively small proportion, and a complex calculation to
accurately model, we have not split out cooking in this calculator.
Section 3: Transport
This section looks at the emissions relating to journeys made by all members of your household in your
own vehicles, public transport, lifts from others and flights. We ask people to exclude all travel directly
relating to their work, but to include their journey to and from work.
Vehicle Travel
A.
Vehicles that you own
Ideally, we would have liked to base vehicle emissions on the annual consumption of fuel, as this would
not only provide us with an accurate measure of carbon emissions, but would also reward “greener
driving” techniques as people need less fuel to travel the same distance. However, this information is
rarely available, so we have had to use mileage as an indication of fuel consumption.
Calculation:
First we calculate the basic CO2 emissions for each vehicle:
Take the annual mileage.
Times by 1.609 to convert to km,
Times by the manufacturers quoted g/km emissions.
Times by a Real World Uplift of 15%
Real World Uplift
The manufacturers’ data for their fuel consumption is based on test conditions and doesn’t take into
account specific usage patterns by any one driver. Actual fuel consumption can be impacted on by traffic
conditions, driving style, maintenance, air pressure of tyres and use of air conditioning. To factor these
in, Act on CO2 uses a 15% uplift factor, which we have also adopted.
Embodied Energy
As well as factoring in the fuel used by vehicles, we wanted to illustrate the impact of vehicle ownership.
For example, two households may clock up the same amount of mileage in a year, but one owns three
vehicles, the other only one. We wanted to reflect the fact that the multiple car owning household would
have the larger carbon footprint for transport. We do this by this by apportioning a share of the emissions
associated with the creation of the vehicle.
There are several different ways of skinning this cat. For example, David McKay cites the figure of 30
500KwH as the net life-cycle energy cost of a car from Burnham et al 2007.
In our calculations, we wanted to reflect the CO2 associated with the manufacturing process of the
vehicle. Simon Barnes of the SMMT (the Society of Motor Manufacturers & Traders) says “Vehicle
manufacturers report an average of 0.6 tonnes per vehicle of CO2 generated from manufacturing, But we
need to at least treble this figure to take into account component and material manufacture.” This gives a
figure of 1.8 tonnes for manufacture, but this does not to take into account the embodied energy in the
materials used.
The European Environment Agency Report “Towards a resource efficient transport system” 1
which attributes 8% of a car’s lifecycle emissions to its production and a total of 77% towards energy
used to run it. Further details of this study are available in IMPRO-Car “Environmental Improvement of
Passenger Cars”2
1
ISSN 1725-9177
2
http://ec.europa.eu/environment/ipp/pdf/jrc_report.pdf
petrol
1240
diesel
1463
average
1351.5
Production
Spares
End of Life
embodied
energy
4.3
0.4
0.1
4.7
0.5
0.1
4.5
0.45
0.1
4.8
5.3
5.05
well to tank
tank to well
running costs
7.4
43.9
51.3
8
44.6
52.6
7.7
44.25
51.95
grand total
56.1
57.9
57
weight (kg)
Source: IMPRO-Car
This gives an average of around 5 tonnes for the cost in carbon terms for the lifecycle of the car –
excluding its running costs.
We then attempt to reflect the fact that larger cars use more raw materials and take more energy to build.
So, we have factored in the relative size of a vehicle when allocating its share of embodied energy. We
use the figures below as average weights for each class. 5 tonnes works out as 3.73kg CO2e per kg of car
or 370 kg for each year of an average car’s life.
We then shared the total embodied energy per year of average vehicle lifespan - 13.5 years.3
Vehicle
Best seller
Average kerb
Weight
Motorbike
Small car
Medium car
Honda CBF125
Ford Fiesta
Ford Focus Zetec
128kg
From 1096kg
From 1229kg use
1300kg av
Large
car/MPV
Vauxhall Zafira
4x4
Landrover Freelander
Van
Ford transit
for vehicle
(kg)
kg per year of
ownership
478.283
4095.302
4857.566
35
303
360
5821.606
431
1425kg
5324.639
394
1800kg
6725.860
498
1558
www.autotrader.co.uk/.../CARS/news/NEWCARS/49771.html
http://www.offroadmasters.com/vehicles.cfm
Finally, the calculator allows you to adjust for ownership of vehicles for under a year.
This calculation is of course a very approximate and crude ways of calculating the embodied energy of
any specific vehicle. I have ignored the fact that many of the component materials can be salvaged at the
end of the car’s life, reclaiming some of this energy, as well as the energy required to scrap a car. I also
suspect transport of components has been underreported. However, there is little agreement about the
CO2 emissions linked to the lifecycle of a car. We aim for this basic approximation to be sufficient to
ensure that the embodied energy of vehicles we own – the largest single purchase many people make – is
not overlooked and to encourage a reduction in car ownership and a shift to smaller vehicles.
3
http://www.wasteonline.org.uk/resources/InformationSheets/vehicle.htm
B.
1.
Commuting:
Using your own Vehicle
Calculation: Table Calc 1
To calculate the CO2 emission attributable to a particular journey over a year:
Times the distance in miles, by the number of times a journey is travelled in a week and again by the
number of weeks in which that journey was undertaken a year. This gives the total miles travelled a year.
Divide this mileage by the total annual mileage of the appropriate vehicle, to find fraction of total travel
in that vehicle attributable to that commute journey.
Multiply that fraction by total CO2 emissions for the relevant vehicle.
Finally, this is shared by the total number of occupants in the car.
2.
Lifts you get from other people
For this section we use average data for different classes of car and then allocate a share of emissions to
you for the lift you get.
Table CF5 uses national averages for different classes of car These are as reported in the DEFRA GHG
Conversion figures 2010, and include a 15% real world uplift.
The final figure, that for the car sharing scheme, streetcar is based on the manufacturer’s g per km
emission data for the west oxford streetcar – which is a VW golf Diesel 2.0tdi (129g) plus a 15% real
world uplift.
Personal transport emission factors
Small Car, up to 1.4l petrol engine
Medium Car 1.4-2l petrol engine
Large car above 2l petrol engine
Small car up to 1.7l diesel engine
Medium Car 1.7-2l diesel engine
Large Car above 2l diesel engine
Medium petrol hybrid car
Large petrol hybrid car
Medium LPG car
Large LPG car
Streetcar
kgCO2/vehicle mile
0.28020
0.34762
0.48362
0.23640
0.29399
0.39778
0.19344
0.35140
0.31377
0.43618
kgCO2/vehicle km
0.17411
0.21600
0.30051
0.14689
0.18268
0.24717
.12020
.21835
.19497
.27103
0.14835
Calculations Table 2 then calculates the annual emissions relating to each journey by calculating the
annual total mileage for each journey and multiplying it by the appropriate conversion factor.
Finally, this is shared by the total number of occupants in the car.
Commuting using public transport
We used the following conversion factors for each different type of public transport, which are taken from
the DEFRA GHG Conversion factors Update 2010
Transport
from passenger km
to
national rail
Km
kg C02
0.05651
regular taxi
Km
kg C02
0.15352
black cab
Km
kg C02
0.20034
local bus
Km
kg C02
0.15874
london bus
Km
kg C02
0.08912
Coach
Km
kg C02
0.03065
Eurostar
Km
kg C02
0.01512
European Rail*
km
Kg CO2
0.04488
london underground
Km
kg C02
0.07462
foot passenger ferry
Km
kg C02
0.01928
car passenger ferry
Km
kg C02
0.13322
multiplier
* figure from 2009
Source: http://www.eea.europa.eu/data-and-maps/figures/specific-co2-emissions-per-passenger-1
In Table Calc 3: Commuting – regular
We calculate the total annual mileage for each regular commuting journey, then multiply it by the
relevant conversion factor from above.
C. Other travel
1. Using your own Vehicle
In table 4 we calculate the overall social mileage remaining for each vehicle by subtracting the total
mileage already allocated to commuting from the total annual mileage by that vehicle.
Lifts you give people
We then offload a share of this mileage to anyone you give a lift to for any key journeys.
Table Calc 5 uses the data inputted into travel questionnaire table “Lifts you give people” to calculate
what share of your vehicles emissions to allocate to others, thereby reducing your personal travel related
emissions.
First we calculate the annual mileage for the journey, then using the conversion factor for the relevant
vehicle, calculate the total emissions associated with that journey. Finally we calculate which share
should be attributed to non household members, which is then removed from your household’s carbon
footprint.
2. Lifts you get from other people
Methodology as for commuting lifts.
3. Public Transport
We use the same methodology as described for commuting journeys using public transport to work out
emissions relating to social mileage for regular and one-off significant journeys.
D. Flights
Calculation:
To calculate the CO2 emissions for each flight:
Take the direct distance between departure and destination in Km.
Times by the relevant emission factor to convert to CO2
Times by the radiative forcing factor of 1.9
Key Methodology and sources behind the flight calculation:
Direct Distance
We use the website www.webflyer.com to source distances.
The following conversion factors are taken from DEFRA Conversion Figures 2010 and include the Great
Circle Distance uplift factor of 9% and CORINAIR uplift factor of 10-12%.
Air Passenger Transport Conversion Factors10
Passeng
er kms
travelled
(pkm)
Method of travel
Flight type14
Cabin class
Domestic14
Short-haul international
14
Long-haul international14
x
km
uplift
factor
x
CO2
kg CO2
per
pkm 13
12
CH4
kg
CO2e
per
pkm
Scope 3
Total
Direct
N2O
GHG
kg
kg
CO2e
CO2e
per
per
pkm
pkm
11
Average
x
109%
x
0.17147
0.00013
0.00169
0.17328
Average
x
109%
x
0.09700
0.00001
0.00095
0.09797
Economy class
x
109%
x
0.09245
0.00001
0.00091
0.09336
Business class
x
109%
x
0.13867
0.00001
0.00136
0.14004
Average
x
109%
x
0.11319
0.00001
0.00111
0.11431
Economy class
x
109%
x
0.08263
0.00000
0.00081
0.08345
Premium economy class
x
109%
x
0.13221
0.00001
0.00130
0.13352
Business class
x
109%
x
0.23963
0.00001
0.00236
0.24200
First class
x
109%
x
0.33052
0.00002
0.00325
0.33380
Great Circle Distance Uplift Factor
An additional 9% is added to take into account the fact that airplanes do not fly directly from one point on
the globe to another (The Great Circle Distance), rather journeys can take indirect routes and involve
circling after take off or before landing, and account for delays.
CORNAIR Uplift
The provisional evidence to date suggests an uplift in the region of 10-12% to climb/cruise/descent
factors derived by the CORINAIR approach is appropriate in order to ensure consistency with estimated
UK aviation emissions as reported in line with the UN Framework on Climate Change, covering UK
domestic flights and departing international flights
Source: http://www.defra.gov.uk/environment/business/reporting/pdf/100805-guidelines-ghgconversion-factors.pdf p 23
Radiative Forcing Factor
The IPCC defines radiative forcing as a measure of the influence a factor has in altering the balance of
incoming and outgoing energy in the Earth-atmosphere system and is an index of the importance of the
factor as a potential climate change mechanism.
The website Treehugger explains what this means in terms of climate change and flights as follows:
“Flying Has More Impact Than Just Carbon Emissions
In terms of aviation those climate change mechanisms are not just carbon emissions, but other
emissions from burning fuel as well, plus soot, contrails (which can help form cirrus clouds) and other
factors as well. These factors magnify the warming effect beyond what just the effect of carbon dioxide.
And since you're pumping them directly into the upper atmosphere the effect is still greater.
Radiative Forcing Takes Into Account More Than a Single Flight
It's important to note that when talking about radiative forcing, the impact does not take into account
the influence of a particular flight from one place to another; instead, it figures in the historic impact
over time. It's not that your particular flight has this impact, but aviation in general does.
This is unlike how carbon emissions from a flight are calculated, even those these too are a bit of an
abstraction: Certain assumptions are made regarding the planes used on a given route, by particular
airlines, how full the plane is (generally about 75%), et cetera, to come up with the emissions for a
route that are a good representation of the flight.
How Much Greater an Impact Does Radiative Forcing Create?
In figuring how much greater an impact radiative forcing causes, a radiative forcing index is used as a
multiplier. No one doubts that radiative forcing has an impact, but in calculating how large an RFI to
use is where the real debate starts.
Depending on the particular study you look at an RFI of anywhere between 1.2 and 4.7 is appropriate.
As of a 2000 report, the IPCC considers a good RFI figure to be 2.7. However, a more recent study
indicates that a lower figure of 1.9 is probably a better estimate of radiative forcing's impact.”
We use a Radiative Forcing Factor of 1.9 in our calculations. Some other calculators such as Act on CO2
do not, so you will get very different flight related carbon footprints using these different calculators.
Section 4: Your Lifestyle
Introduction
This final section moves on to the emissions that we are indirectly responsible for – through the food we
eat, our choice of pets and spending habits. Because of the huge diversity of carbon footprint associated
with even nominally identical consumables, the purpose of this section is primarily to give a sense of the
relative impact of different consumption choices. It has been hard to find comprehensive primary data,
so it is important to view the results of this section as illustrative of the relative possible impact of
different choices, rather than absolute.
A. Food
This section of the calculator was originally based on figures quoted by George Marshall in his very
readable “Carbon Detox” p213, which in turn is based on a carbon calculator developed by Laurie
Michalis of the Quaker Living Witness project. In subsequent versions, we have refined the questions
where possible based on other referenced sources.
The figures aim to reflect all the CO2 and greenhouse gas missions used in agriculture, fertilizers, food
transport, processing, storage, shops and catering. It also factors in the methane and nitrous oxide from
animals, animal wastes and agricultural soil.
1. Diet
The calculation starts by selecting a base figure (Table 1) for each member of your household, depending
on your choice of diet.
Table 1: Base Diet
Annual
Emissions (kg)
2000
2250
1750
1500
Typical British diet (38% nutrition is animal based)
Serious meat diet (50% animal based)
Light meat diet (a little meat once a day or less)
Vegetarian/vegan diet
Lamb & Beef
We then take into account the impact of eating lamb and beef.
Lamb &
Beef
Nothing
Eat lamb and beef
From Carbon Detox
minus 10%
Do not eat lamb or beef
From Carbon Detox (200kg – we changed this to 10% to
allow for difference sized diets)
Nothing
We are all
vegan/vegetarian
From Carbon Detox
Nb no sources are cited for this in Carbon Detox. However, if you compare these figures to those in
Chris Goodall’s informative book “How to Live a low carbon life” they seem roughly comparable.
Of the 130 million tonnes of CO2 that Chris Goodall estimates as resulting from the UK food chain, 19
million come from methane from animals or slurry – or 15%. The majority of this will come from cows
and sheep. Some of this can be attributed to milk production, but much will be due to lamb and beef
production. Add to this the foodstuffs grown to feed livestock, much of which will also require inputs
and energy, and the inefficient conversion rates of grain into meat protein, and the 10% impact doesn’t
look unreasonable.
Milk Products
Milk, the other key product from cattle, can play a significant factor in food related emissions. In “How
Bad are Bananas” Mike Berners Lee gives the following estimates for the emissions associated with key
milk products:
1 kg cheese - 12 kg co2
1 pint milk - 723g kg co2 (or 1272 g CO2 per litre)
According to the Dairy Farming Information Council, the average weekly consumption for key dairy
products is as follows
Average consumption per person per week (2009)
Liquid Milk (ml)
1,568
Yogurt and Fromage Frais (ml)
203
Cheese (g)
116
Butter (g)
39
Cream (ml)
23
Dairy Desserts (not frozen) (ml)
44
Equivalent CO2
1994g
1392g
Source: http://www.dairyco.org.uk/datum/consumer/uk-dairy-consumption/uk-dairy-consumption.aspx)
This gives 3.4 kg for milk and cheese. Assuming an extra 0.6kg for other dairy products that’s a total 4
kg a week or around 200 kg a year pp – or 10% of the average food footprint.
Using this as a rough base link, we scale up the base diet accordingly: no milk products (and minus 7%)
Dairy
Option
none
low
average
above average
high
Impact pp
- 10%
- 5%
0%
+ 5%
+ 10%
2. Food choices
We then factor in the likely impact of a number of factors associated with food sourcing and choices,
which raise or lower the initial base diet emission as outlined in the table below. The calculation is made
on the basis that the entire household takes this food choice. As this section is only indicative - the
precise CO2 impact of your food choices being dependent on so many factors - the impact of these
choices is calculated at broad household, rather than individual level. When in doubt I have gone back to
the core principle for quicksilver which is rewarding behaviour which results in a lower carbon footprint,
even if the precise reduction can be debated.
Category
Organic
Impact per
person
Reduce by
14.5%
Reduce by 11%
Reduce by 7%
Reduce by 3.5%
Nothing
Ready
Meals
add 60 kg or 3%
Nothing
Options
All our food is
organic
Most of our food
is organic
Around half our
food is organic
Some of our
food is organic
Rarely buy
organic food
We eat ready
meals once or
more a week
We eat ready
Source
See below “organic”
See below “ready meals”
minus 50 kg or
3%
Grow
your own
Nothing
Minus 10kg or
0.5%
Minus 25kg or
1.25%
Minus 50kg or
2.5%
Seasonal
minus 50kg or
2.5%
Nothing
Plus 50kg or
2.5%
Airfreight
Minus 50 kg or
2.5%
Nothing
Plus 50 kg or
2.5%
Kitchen
Waste
Nothing
minus 150kg
or 7.5%
Minus 215kg or
11%
meals less than
once a week
We never eat
ready meals
We do not
grow our own
food
We grow some
of our own veg
in the summer
We grow most
of our own veg
in the summer
We grow
almost most of
our own veg
We only eat
fruit and veg
that’s in
season locally
We sometimes
eat out of
season food
We regularly
eat out of
season food
We never eat
air freighted
goods
We sometimes
eat air
freighted
goods
We often eat
air freighted
goods
We do not
compost our
kitchen waste
We compost
some of our
kitchen waste
We compost
all of our
kitchen waste
Jury is out on specific savings, but
http://www.bbc.co.uk/bloom/actions/growyourown.shtml suggests up to
50kg pp due to reduction in food transport.
Although we cover airfreight separately, householders who are avoiding
out of season fruit and veg will be reducing transport and storage related
emissions. The 50kg is purely speculative.
CG estimates 3 million tonnes a year from air freighted food. – That’s
50kg per person
See calculations below in “Kitchen waste”
Organic Foods
The jury is out on the impact of organic food on climate change. Discussions about the reduction due to
reduced carbon emissions because of reduced chemical inputs, and increased carbon sequestration by
organic farming methods are countered by others claiming the origin of food and claims of increased land
mass needed for organic production resulting in deforestation.
For this calculator, we will assume that there are no increases in transportation when an organic diet is
chosen as this is covered in another question. We will also assume there is no increased deforestation.
Key reductions come from two areas:

Increased Sequestration
Soil association estimates that switching all UK agriculture to organic would offset 23% of the
UK agriculture’s current GHG emissions.
Soil carbon and organic farming, Soil Association.
http://www.soilassociation.org/LinkClick.aspx?fileticket=BVTfaXnaQYc%3d&tabid=574
UK’s agriculture emissions are 47.6MtCO2e
Source: 18 September 2007 Market Mechanisms for Reducing GHG Emissions from Agriculture,
Forestry and Land Management, Department for Environment, Food and Rural Affairs
http://www.defra.gov.uk/evidence/economics/foodfarm/reports/ghgemissions/wholerep.pdf
which, based on a population of 61million equates to 780 kg pp. 23% of this is 180kg pp

Reduced Chemical Inputs
According to http://www.sustainablefood.com/guide/nitrogenissue.html
Manufacturing and transport of fertiliser are estimated at 6.7 tonnes CO2e for each tonne of
Nitrogen fertiliser. Thus as 850,000 tonnes used in UK, this = 5.7mt CO2e. Out of a total
UK GHGs of about 180 mtonnes, this = about 3%. Most N fertiliser production is abroad (East
Europe), with about 800,000 tonnes imported.
5.7mt CO2 equates to 110 kg CO2e per person..
180kg (sequestration) plus 110kg (reduced fertilizers) is a total of 290kg pp – or 14.5% of the 2000kg for
an average diet.
Nb Chris Goodall comes up with a slightly greater figure, estimating that fertilizer manufacture, transport
and use result in 36 of the total 130 tonnes of CO2e he attributes to agriculture – 36%. I very much hope
this to be the case, but given that the debate still rages regarding the impact of organic farming in climate
change terms, I’ll stick with our more conservative figure.
Processed foods:
In Carbon Detox, George Marshall gives a figure of +200kg for processed and imported food, and minus
400kg for very little of imported and processed food. I wanted to unpack this a little.
Chris Goodall, in How to lead a low-carbon life (2nd Edition) estimates
(8.5%) 11 million tonnes from food and drink manufacturing and processing plus
(8 %) 10 million tonnes for packaging,
(3%)
4 million tonnes for rotting packaging
(4.6%) 6 million tonnes for retail store operations.
This makes a total of 31 out of the 130 million tonnes total (24%.)
Although most foods require some processing, storage and packaging, the amount will be significantly
higher in products such as chilled ready meals.
Ready Meals make up £2.7 billion food sales.4 Sales of total food made up around £65 billion, so ready
meals accounts for around 4% of all food purchases 5 For these the vast majority are either chilled (53%
of the value of retail sales) or frozen (40%).6
Although it very hard to make accurate calculations, I believe it is fair to assume that ready meals, will be
responsible for more than their fair share of emissions, than their market share would be indicated based
purely on their share of the market. This because of the additional processing, packaging and chilling
required in their manufacture and storage.
Lets then assume they are three times more carbon intense that other foods, so are responsible for 12% of
the 31 tonnes Chris Goodall identifies above – 3.1 tonnes or 60kg a person. A household with a higher
than average consumption of ready meals should have this reflected in their food footprint, and
correspondingly those, who do not purchase them to have a similar sum removed from their footprint.
4
http://oxygen.mintel.com/sinatra/oxygen/display/id=480766 viewed 26/1/11
http://www.defra.gov.uk/evidence/statistics/foodfarm/food/pocketstats/documents/foodpocketbook2010.pdf
6
Mintel 2003
5
According to the Food Standards Agency, quoting a Mintel Report from 2003, ready meals are used by
77% of households and of those that use ready meals, 28% use them more than once a week, 26% once a
week and 44% three times a month or less frequently.
This brings us to defining a “high user” as once or more a week (54% of those that purchase them – or
42% of all households) a medium user as less than once a week, and low users as those who never
purchase them (23%).
http://www.food.gov.uk/news/newsarchive/2003/jun/readymealsmarket
Kitchen Waste
In “How to Live a Low Carbon Life” Chris Goodall (based on figures from www.wasteonline.org.uk)
states that on average we are each responsible for generating 85kg kitchen waste, which in turn results in
27kg methane and 71kg CO2. Taking into account the fact that landfill operators capture most of the
methane released in landfill, he calculates this translates into 215kg CO2 GHG equivalent. A poorly
managed compost heap can also generate CO2 and worms are accused of being a source of nitrous oxide –
but I admit I have not factored these into the calculator as these factors were too variable and frankly,
life’s too short.
B. Pets
The main source of CO2 associated with pets is due to their high meat diets (although the poop they
produce doesn’t help on the greenhouse gas front either).
Figures specifically relating to pets are hard to source – so we’ve had to do some calculations to get an
approximation. We know that a high meat human diet generates 2250kg a year CO2, and involves eating
2250 kilocalories a day, which neatly equates to 1 kg of CO2 a year, for every kilocalorie eaten a day.
Using this, and recommended daily calorie intake for different size cats and doges, we arrive at the
following approximation.
Animal
Cat
Dog – 10 lb (4.5kg)
Dog – 30 lb (13.5kg)
Dog – 50 lb (23kg)
Dog – 70 lb (32kg)
Dog – 90 lb (41kg)
Daily intake KCalories = kg CO2 a year
175
366
609
1222
1574
1901
The statistics for dogs represents an averaging of data available at this site
http://dels.nas.edu/dels/rpt_briefs/dog_nutrition_final.pdf
size
inactive
active
young adult
older active
10lb
(4.5kg)
296
404
436
327
365.75
30lb
13.6kg)
674
922
93
745
608.5
50lb
(22.7kg)
989
1353
1451
1093
1221.5
70lb
(31.8kg)
1272
1740
1876
1407
1573.75
90lb
40.9kg)
1540
2100
2264
1700
1901
No I know I haven’t factored in for kittens, pregnant animals, goldfish, hamsters…. but the key purpose
of this section is to highlight that all members of your household – including the four legged ones – have
an impact in terms of your greenhouse gas emissions, rather than the advocating the extreme measure
suggested in the title of Robert and Brenda Vale’s book "Time To Eat The Dog."
C. Goods & Services
So far we have looked at carbon emissions relating to fuel to heat and power our house, our transport
needs and food. The two key outstanding areas are government services delivered on our behalf (eg
health, defence education) and the carbon relating to all the other goods and services we buy.
In the Carbon Trust document CTC603 “The Carbon Emissions in all that we consume”, researchers at
the University of Surrey used a carbon attribution model to assign carbon to a number of different
domestic functions.
The study calculated to total carbon of emissions of the UK to be 176.4 C(Mt), which equates to 646.8 Mt
of CO2. We have already accounted for a number of activities listed in other sections of the calculator. If
we take these away from the total sum, we are left with the remaining carbon we have yet to account for.
Estimating CO2 emissions associated with discretionary spend
a) Excluding emissions already covered in quicksilver:
Appendix A shows the breakdown linked to the most carbon intensive activities. Of these, the
following have already been accounted for in our calculator:
Categories already accounted for
domestic fuel use
domestic electricity
domestic private transport
hotel, catering, pubs
motor vehicle production
meat processing
agriculture
dairy products
fish and fruit processing
Subtotal
c (Mt)
25.3
22.0
18.3
8.3
7.1
2.3
1.6
1.3
1.3
87.5
co2
92.8
80.7
67.1
30.5
26.0
8.3
5.7
4.8
4.8
320.7
b) Excluding UK government and infrastructure overheads
Some of the remaining emissions can’t really be considered linked to discretionary spend, rather they
are to do with government service and other services operated on our behalf. In this category I have
included insurance and pension funds as we ask people to exclude this from their discretionary spend
calculations. Additionally there are a number of categories which would be hard to pinpoint to an
individual’s discretionary spend. I have therefore also lumped them together to be shared equally on a
per capita basis.
Govt Services, Infrastructure & Misc
health & vet. Services
Education
letting of dwellings
other land transport
social work activities
insurance & pension funds
public administration & defence
Construction
Telecommunications
renting of machinery etc
fuel production & delivery
total
6.09
3.8
3.19
2.77
2.34
2.17
2.13
1.72
1.52
1.21
6.23
33.17
22.33
13.93
11.70
10.16
8.58
7.96
7.81
6.31
5.57
4.44
22.84
121.62
This equates to 1.968 tonnes of CO2 per person. (but see below for final figure).
Finally, we are left with the following categories.
Other areas of consumption
soap and toilet preparations
Furniture
printing/publishing
water transport
alcoholic beverages
wearing apparel
recreational services
1.19
1.58
2.05
2.17
2.39
2.57
2.88
14.8
4.36
5.79
7.52
7.96
8.76
9.42
10.56
54.37
c) dealing with the remaining categories
There are two key remaining categories that need to be accounted for within the footprint.
First, the data provided only covers the top 25 categories, but there are another 109.27 Mt CO2 from other
categories. Without further information as to the nature of these categories it is hard to assign them
accurately. The best I was able to do was to propose a split based on the relative proportions of known
emissions relating to government/infrastructure to other areas of consumption.
Government/infrastructure:
Other consumption:
known
121.62
54.37
69%
31%
69% of 109.27 = 75.40 Mt
31% of 109.27 = 33.87 Mt
-----------------
175.99
Finally, we need to apportion shares of aviation fuel emissions. Aviation fuel is responsible for 40.33
tonnes in the Carbon Trust calculations. However, we are factoring in radiative forcing to our model, so
need to multiply this by 1.9 to take this into account. This results in 76.63 Mt CO2 that we need to
allocate.
Less than 3% of commercial air travel is purely cargo planes, so for the sake of simplicity we can divide
aviation fuel emissions based on the proportion of leisure to business travel passengers. 60% of air
passenger travel is for leisure purposes.7 This equates to 45.98 Mt CO2. Which we have already included
in the travel calculations. The remaining 30.65mT has yet to be accounted for.
In Summary we reach the following figures:
Government & Infrastructure:
121.62 + 75.4 = 17.02 Mt CO2 or 3.18 tonnes a head
Other consumption
54.37 + 33.87 + 30.65 = 118.89 Mt CO2 or 1.92 tonnes a head.
Give we are dealing with such crude estimates, for ease of communication I will approximate these to 3
tonnes a head from infrastructure and government services, and 2 tonnes a head from goods and services.
Apportioning emissions from consumption of goods and services to households.
So, we now have very crude figure of an average of 2 tonnes per person, or 4.8 tonnes per average
household for consumption of goods and services.
Initial work with households quickly indicated that the vast majority of people have very little detailed
knowledge about their household spend. However, most people were able to estimate their household
income. I therefore decided to use Gross Domestic Household Income, GDHI as a proxy indicator for
estimating the base emissions likely to result from household spend.
GDHI is the amount of money that have available for spending or saving. This is money left after
expenditure associated with income, eg taxes and social contributions, income from property ownership
7
CAA 2005 publication “Demand for Outbound Leisure Air Travel and its Key Drivers”
and provision for future pension income. The gross disposable household income for the UK was
£14,872 a head, or £35,692 for the average household.
Source: Office of National Statistics Press Release, 31 March 2010: Variations in household income per head in UK regions.
If we use GDHI as a rough indicator of consumption of other goods and services, dividing the 2 tonnes of
CO2 per person relating to other products and services, this equates to 135kg per £1000 of spend.
Once again I should stress that this shouldn’t be viewed as an accurate reflection of CO2 per £ of spend,
not least as GDHI includes spend on food, fuel etc which we have discounted above, but this does provide
a rough sliding scale for estimating the element of a household’s indirect footprint relating to goods and
services.
Calculating CO2 emissions linked to discretionary spend.
First calculate the base household footprint relating to discretionary spend by using GDHI to get the
starting point. We also offer less specific options for people not willing or able to disclose figures.
In testing early versions of the calculator many householders felt that it was unfair to include money that
they saved as part of their overall spend, in this version they are able to net this off. We also allow for
additional spent of old savings or loans. We also give the option to net off any money invested in
supporting environmental charities or other green investments.
Some individuals had asked if they could net off mortgage or rental costs, but this could be viewed as a
contribution towards the embodied energy in the homes we occupy, so is included.
We have a higher than average household income
We have an average household income
We have a lower than average household income
Under £10,000
£10,000 -£20,000
£20,000 - £30,000
£30,000 - £40,000
£40,000 - £50,000
£50,000 - £60,000
£60,000 - £70,000
Over £70,000
Increase total by 25%
6 tonnes
4.8 tonnes
Decrease total by 25%
3.6 tonnes
0.7 tonnes
2 tonnes
3.4 tonnes
4.7 tonnes
6 tonnes
7.4 tonnes
8.8 tonnes
10.2 tonnes
There were important
for people who do not
know, or do not wish to
disclose their
Household income..
Calculated at 135 kg
per £1000, using the
midpoint of each range.
Used 75,757 for over
£70k and £5k for under
£10k
Using this as a base figure, the resulting emissions can be adjusted according to the spend patterns and
waste management strategies undertaken by the individual households. Quicksilver has been developed
with a key aim of influencing household behaviour to encourage activity which results in a lower carbon
footprint.
As with the food section, we wanted to “reward” certain consumption behaviours with a reduction in
carbon footprint. The exact impact of any one action is pure conjecture, so the results for this section
should be viewed purely as indicative.
For example, it is fair to assume that a household who purchases second hand goods, avoids generating
overly packaged products and always recycles what packaging is generated will have a lower footprint
than one that does not.
The categories we have chosen to highlight are picked either because estimated figures for their impact
were available, or because they are an area that have been singled out for their potentially high footprint.
Products:
Although the make up of every household’s shopping basket will vary enormously, making it impossible
to accurately reflect their differing carbon footprints, there are a number of products known to have a
higher or lower carbon footprint than others. A trawl of various sources indicate that amongst the highest
contributors to our carbon footprint are electronics, clothing and textiles, paper whereas spend on second
hand, hand crafted good or labour based services tend to have a lower carbon footprint.
The percentage changes shifts in each of each of these are harder to calculate. For example in Chris
Goodall’s “How to live a low carbon life”. P238 Second edition he gives the following figures.
Clothing:
Paper
Cement
Computer/mobile
910kg per person a year
365 kg
150kg
135kg Other sources give different figures.
Computers and mobiles only account for £2.30 of the total £15 weekly spend on electronic and electrical
equipment8, bringing the total electronics figure to more like 880kg, making electrical equipment and
clothing the stand out big carbon items to focus on.
With this in mind, we use the following questions are designed to give a very rough indication of people’s
spending patterns in relation to these high carbon items and so reflect this very approximately in their
overall footprint - the highest consumption cost being penalised with an increased footprint, and the lower
consumption option with a reduction.
Electronic & Electrical
+5%
We regularly upgrade our household technology
0
We replace electronic and electrical items when they break
- 5%
We don't have many electrical or electronic items
Clothing
+5%
We like to keep up with the latest fashions and buy new clothes every week
0
We buy new clothes to replace worn out items or for special occasions
-5%
We rarely buy new clothes
We also included questions focusing on low carbon spend – recycled and second hand goods. The exact
impact is extremely hard to measure so the figures are purely illustrative.
Recycled goods
1%
0
-1%
We never buy recycled products
we sometimes buy recycled products
we always buy recycled products
Second hand
5%
0
-5%
8
We never buy second hand items
We sometimes buy second hand items
Whenever possible we buy second hand items
ONS, Family Spending 2009,
Waste:
According to WRAP9, each household is responsible for around 20-25kg of household waste a week – or
year just over a tonne a year. As well as the embodied energy in the materials we through away, organic
matter sent to landfill can rot to produce methane.
The average person sends 330kg to landfill or incineration and recycles just 170kg. Overall this results in
230kge per person.10 In this source, kitchen waste is attributed with being responsible for around 65kg
CO2e (somewhat lower than the 215kge we use in our food calculations, but possibly because it takes
into account the fact that the average household already composts much of its kitchen waste.) Leaving
165kg pp – around 8% of the 2 tonnes associated with consumption.
This can be reduced in two ways – either by recycling more OR by generating less in the first place. As
indicators for this we use the following questions:
How much do the following statements match your household’s approach to waste reduction?
(6 completely – 0 not at all)
We never use disposable or “single use” items eg nappies, bags,
We always buy products with the minimum possible packaging
We recycle all our glass, tins, paper, card and plastics
We recycle or pass on all our unwanted clothes and textiles
We always mend broken items rather than replace them
For each question we scale the discretionary spend base accordingly, enabling a very waste conscious
household to have up to a 7.5% reduction in its overall footprint.
Answer
0
1
2
3
4
5
6
Percentage change
+1.5%
+1 %
0.5%
0
-.5%
-1%
-1.5%
Once again, I should stress that for this section of the calculator the results should be viewed as very
approximate. Data for the carbon footprint associated with goods and services is sparse and highly
variable. We have had to fall back on our principle of rewarding lower carbon behaviour with a reduced
carbon footprint when developing this final section. The resulting figure should be good enough to help
householders see an impact of shifts in the purchasing and waste management strategies, but should not
be taken as absolute.
9
http://www.wrap.org.uk/downloads/Environmental_benefits_of_recycling_2010_update.9c655a62.8816.pdf
How Bad are Bananas, Mike Berners-Lee p61
10
Results Page
Overall Householder’s Results
These are drawn from the relevant questionnaire summary tables. The column for overall household
emissions includes all emissions resulting from the activity and fuel consumption indicated in the
questionnaire. This includes the full emissions relating to powering the home.
Individual Results
This is calculated by dividing the overall household’s carbon footprint by the total number of occupants
in the house.
When a householder has indicated that there are other residents in the household eg lodgers that they wish
to exclude from calculations, a share of the emissions relating to powering the home is allocated to those
people, and the remaining emissions shared equally amongst the core household.
National Averages
Our national averages for direct emissions are based (with heartfelt thanks) on Chris Goodall’s
calculations from his book How to Live A Low Carbon Life (2nd Edition). There are a couple of
modifications made to his figures to make them consistent with our methodology.
Estimates for indirect emissions are based on the calculations described earlier based on the Carbon
Trusts Report “The carbon emissions generated in all that we consume”.
lighting and appliances
space and water heating
car travel
public transport
1.0
1.5
1.2
0.1
CG's figures plus cooking p34
CG's figures plus cooking p34
CG's figures p34
CG's figures p34
Car ownership
0.2
See below
Flights
subtotal for direct emissions
Food
1.2
5.2
2.1
CG's figures
Pets
Goods & services
0.2
2.0
based on my calculations below
As calculated in lifestyle section
Subtotal indirect emissions
4.3
Subtotal
9.5
UK infrastructure
Grand total
CG's figures
3
As calculated in lifestyle section
12.5
Average: car ownership
In section 3 we calculated that for each year of an average car’s life, there is an associated emission of
0.37 tonnes. From the Dept of Transport Fact sheets there are 28.2 million private cars. This works out
as an average of 0.46 cars for each of the. 61.8 million people in the UK. Therefore an “average” share,
per person is just under 0.17 tonnes relating to car ownership or 0.2 to one decimal point.
Average: Pets
There are 27 million pets in the UK with dogs and cats being the animal of choice for pet lovers with over
7.3 and 7.2 million across the UK respectively. (Source: National Pet Month 2008). Using the average
figures from our pet table calculation, and dividing by average population we reach this average figure.
[(7.3million x 1134) + (7.2 million x175)]/61 million = 0.156 tonnes, or 0.2 to one decimal point.