Fuel usage (l) * fuel CO2 emissions factor (kg/l) / no. of people in car
-(CO2 emissions per litre of EU fuel: diesel = 2.617 Kg/l, petrol = 2.329 Kg/l, taken from https://www.forestresearch.gov.uk/tools-and-resources/fthr/biomass-energy-resources/reference-biomass/facts-figures/carbon-emissions-of-different-fuels/ +
(CO2 emissions per litre of EU fuel: diesel = 2.617 kg/l, petrol = 2.329 kg/l, taken from https://www.forestresearch.gov.uk/tools-and-resources/fthr/biomass-energy-resources/reference-biomass/facts-figures/carbon-emissions-of-different-fuels/ )
Ferries/chunnel not accounted initially due to lack of data. See if that has changed. DFDS now (2024) have their own carbon insetting program - ask if ticket-buyers used that, to avoid double-counting.