Methodology library

Travel emissions methodologies

What each SQUAKE methodology calculates, what it includes, what data it uses and where the factors come from.

Flight

From distance-band averages to flight-specific models, with or without non-CO₂ effects.

Compare flight methodologies

Hotel

Footprints per occupied room-night, by country, city or hotel class.

Compare hotel methodologies

Car

Rental categories, national averages, a specific model or your own data.

Compare car methodologies

Train

National averages, operator data and station-to-station values.

Compare train methodologies

Terms used on these pages

CO₂e: Carbon dioxide equivalent. All greenhouse gases expressed as the amount of CO₂ with the same warming effect, usually over 100 years.
Well-to-wheel (WTW): Producing and delivering the fuel or electricity, plus using it in the vehicle. For flights it is also called well-to-wake.
Tank-to-wheel (TTW): Using the energy in the vehicle, such as the fuel burned. For electricity, publishers differ: some count power plant emissions here, others count them upstream. For flights it is also called tank-to-wake.
Well-to-tank (WTT): The upstream part of well-to-wheel: extracting, refining and delivering fuel, and the supply chain of electricity.
Non-CO₂ effects: Extra warming caused by aircraft at cruising altitude, mainly through contrails and nitrogen oxides. Methods add it with a multiplier (often called a radiative forcing multiplier or index), report it separately, or leave it out.
Passenger-km: One passenger travelling one kilometre. Most flight and rail factors are given per passenger-km.
Room-night: One occupied hotel room for one night. The hotel methods here work in room-nights; HCMI can also use floor area.
Emission factor: Emissions per unit of activity, for example grams of CO₂e per passenger-km.
Factor year: The edition of a publisher's factors. Where you can set it, pin it so that results stay reproducible.
Great-circle distance: The shortest distance between two points on the globe. Flight methods start from it, and some add a correction for detours.