ROI calculator assumptions

Emmissions Data

The carbon data in this table is based upon the official 2009 guidelines from the Department Environment Food and Rural Affairs, originally published in 2001. Emissions for other fuels can be found on Defra’s Environmental Reporting page. Figures have been updated to include the July 2009 data where applicable. This table only gives some of the main conversion factors, and CO2 equivalents are given on a Gross Calorific Value basis: Defra intends to move to a net CV basis in the near future which will slightly increase emission factors from natural gas and LPG.

The car mileage figure is based upon an average UK family car returning 29mpg. If your car fleet returns better figures on average, (or you driving a smaller car achieving (say) 40mpg, or regularly share a car) then you could adjust the mileage accordingly to estimate CO2 emissions. In choosing a figure, it’s worth bearing in mind that official published fuel consumption figures are calculated under ideal conditions (a warmed up engine, no sharp braking or accelerating) and can be at least 10-15% better than achieved by most drivers in real life.

Aeroplane emissions are very hard to estimate. The figure above is based upon short-haul (European) flights in economy class of 1500 miles – add up to 50% for business class travel with lower seat densities. However there is some evidence that there is at least as much Global Warming effect again from other aircraft emissions in the upper atmosphere, such as ozone created from NOx or condensation trails, than solely from the CO2 emitted on the journey. Please go tol Carbon Workout which allows you to estimate emissions from specific journeys, using a database of over 500 airports served by UK flights.