1. electricity is based on a figure of 0.35 kg of carbon emissions per kilowatt hour generated by a natural gas fired power station. Averages for Europe based on ISPRA report on carbon dioxide emissions number 172/2012
2. Tree offset calculation is based on a tree planted in the humid tropics absorbing on average 22 kg of carbon dioxide annually over 40 years – each tree will absorb 1 ton of CO2 over its lifetime; but as trees grow, they compete for resources and some may die or be destroyed – not all will achieve their full carbon sequestration potential. This calculator assumes that 5 trees should be planted to ensure that at least one lives to 40 years or that their combined sequestration equals 1 ton.