Carbon conversion factors

Carbon conversion factors are used to calculate the amount of CO2 emissions resulting from burning fuel for electricity, heating or transport. To calculate the emissions caused by a certain activity, just multiply the amount of it (in the units shown) by the appropriate conversion factor. These factors all provide emissions in units of kgCO2eq (carbon dioxide equivalent, used to account for greenhouse gases apart from CO2).

Note that this is a work in progress. It contains some omissions and errors, and isn’t yet properly sourced.

See also: the CRAGs worksheet or spreadsheet: both make it easier to calculate your total footprint.

Heating

Heating factors are straightforward because a known quantity of fuel is generally burnt directly in a boiler or stove.

Electricity

Electricity factors depend on the fuel mix your supplier uses to feed your supply into the National Grid. Gas, coal, nuclear and renewables (wind, wave etc.) all have characteristic carbon outputs and combine to give the overall fuel mix for each supplier. However, the situation is complicated by the market in renewable obligations certificates (or ROCs) that power companies trade between themselves to meet government obligations for the proportion of renewable supply.

Discussion: 'green tariff' electricity (cragcentral message#219)

Here, we give an average figure for normal (“brown”) electricity, and a discounted figure for green tarriffs which retire ROCs: but this is still under debate.

Travel

Car

Car travel factors can use either the amount of fuel burnt (most accurate), or the mileage (less accurate, but more convenient). Diesel produces less carbon and more energy per unit volume than petrol.

Discussion: recording car emissions (cragcentral #241) & other car threads

by fuel use

by mileage

Mileage is recorded on MOTs and the odometer, but many different factors influence how much carbon is emitted per mile, including: make and model of car (engine efficiency, aerodynamics), driving style and tyre pressures.

These are approximate figures for typical classes of car. You can look up the factor for your specific car at http://www.vcacarfueldata.org.uk/search/search.asp .

Plane

Planes affect climate in several different ways, over and above the CO2 released when aviation fuel (kerosene) is burnt. However, the magnitude of these effects is scientifically uncertain, ranging from 2-times to 4-times emissions from fuel alone. Planes also vary in efficiency. Fuel use is usually unknown, so we rely on mileage for flight emission calculations.

Discussion: Our CO2 from flying – in case you were wondering (cragcentral message#85)

These represent an average plane efficiency, and assume a 2.7-times multiplier due to other effects on climate. You can find out the mileage between airports at http://www.webflyer.com/travel/milemarker/ .

Ferry

Conversion factors for ferries are uncertain as fuel use figures are hard to come by. However, probably due to the large mass of car ferries and cruise liners, they are surprisingly high. Factors for hovercraft and catamarans are not known.

Discussion: Air miles vs sea miles.

External links

• Defra conversion factors at http://www.defra.gov.uk/environment/business/envrp/pdf/conversion-factor…