Measuring travel emissions

Flights

We first identify the most common round-trip flight routes to a destination (including stop overs) starting from different regions throughout the US. We then apply emission factors per passenger for those flights, using data published by ICAO (the International Civil Aviation Organization). Finally, we apply the widely accepted radiative forcing (RF) factor of 1.9, to account for additional climate impact made when greenhouse gases are emitted into the atmosphere at high altitudes.

Driving

We consider only tailpipe emissions, and do not include well-to-tank (WTT) emissions, which come from extracting, refining and delivering fuel to a point of sale (gas station). Per EPA published data, a gallon of gasoline emits approximately 20 pounds CO2e when burned. 2019 EPA data puts the average mpg for light duty passenger vehicles in the US at approximately 25mpg–our approach is more conservative in consideration of SUVs and larger vehicles being popular among travelers, so we use a factor of 20 mpg.

Hotel Nights:

We use the hospitality industry’s leading tool for hotel carbon foot printing (Cornell Hotel Sustainability Benchmark Index), which aggregates data from 20,000+ global hotel properties. Emissions per hotel room night stay are based on the HCMI Rooms Footprint Per Occupied Room (kgCO2e) data set, upper quartile. If there is no data available for the geography where a property is located (city or state), we use the US all hotels average.