What you don’t know can hurt you: European vacation edition

In our recent transatlantic airline fuel efficiency study update, we compared the fuel efficiency of 20 airlines with routes between the United States and Europe. Most of the transatlantic routes in the study originated from the East Coast. But, how about us on the West Coast?

While there are nonstop flights between Europe and cities like San Francisco (SFO), San Jose (SJC), and Oakland (OAK), more often than not your flight will have at least one layover, meaning you likely won’t be on the same model of plane for your entire journey. How does this impact the overall carbon intensity of these transatlantic trips? To find out, we modeled different airlines and aircraft over non-stop and one-stop routings using PIANO 5 to determine the least carbon intensive ways to get from the San Francisco Bay Area to various European destinations.


If you are looking to drop by Buckingham Palace and pay a visit to the Royal Family, there are plenty of options. The overall least carbon intensive option is a non-stop flight from Oakland to London-Gatwick on Norwegian. However, these flights are only offered three times a week, and those living in the San Jose area may find the airport inconvenient.  (If so, they only need wait until April of next year to get flights direct from SFO to London-Gatwick.)

The combination of aircraft on any given itinerary results in a wide variation in carbon intensity. The least carbon intensive option from San Francisco is with KLM when the flight to Amsterdam is on a Boeing 787-9 aircraft. When combined with a flight to London-Heathrow, this route emits 4% more CO2 than the Norwegian non-stop. While KLM offers daily service between SFO and Amsterdam, the Dreamliner is not used on all flights. Older, less fuel-efficient, Boeing 777-200s and 747-400s emit an estimated 23% and 43% more CO2 per passenger than the 787-9 on the route, respectively.  This illustrates the importance of the aircraft operated on a given route as a driver of fuel efficiency.

For non-stop flights, Virgin Atlantic and its Boeing 787-9 from San Francisco emit an estimated 1,164 kg of CO2 per passenger round trip, while British Airways uses the same aircraft from San Jose and emits an estimated 1,334 kg of CO2 per passenger. Virgin’s higher load factors and denser seating makes the difference here.  The Boeing 787-9 was one of the most fuel-efficient aircraft in our transatlantic rankings, so it’s no surprise to see them in the least carbon intensive options.

Regardless of which Bay Area airport you choose to fly out of, the most carbon intensive flight option includes a British Airways flight on a Boeing 747-400, which results in between 79% and 96% more CO2 per passenger than the least carbon intensive options.  To put this into perspective, choosing KLM’s 787-9 flight through Amsterdam would save over 1 tonne of carbon emissions per passenger round trip to London compared to the American (A321) and British Airways (B747-400) flight through JFK. Assuming a family vacation for four, that’s equivalent to the amount of carbon dioxide emitted in order to power the average American home for approximately 8 months.

British Airways stated that its lower seating capacity, or higher number of first and business class seats, caused its lower fuel efficiency per passenger. But the quad engine aircraft itself burns a lot of fuel regardless of how many seats you put on it.


Like London, a KLM flight on the Dreamliner is one of your best options for reducing your carbon footprint to take in the City of Light. Two American flights also offer low-carbon intensive trips through Chicago and Dallas-Forth Worth, with both emitting just over 1,300 kg CO2 / passenger.

While United’s flight through Chicago ranks somewhere in the middle in carbon intensity, the same can’t be said for the United flight that connects with its partner airline, Lufthansa, in Frankfurt. That route’s intensity is a whopping 2,186 kg CO2 / passenger, almost twice as much as the most efficient KLM flight.

Trying to avoid a layover? Norwegian offers a non-stop flight to Paris’s Orly Airport. However, despite the flight being on a Dreamliner, the route’s lower than average passenger load factor hurts its fuel efficiency, making it below average in carbon intensity.


Besides San Francisco, the ICCT also has an office in Berlin. If I were to visit this office, the least carbon intensive option would be to take KLM’s Dreamliner flight from SFO. Flying any of Norwegian’s Dreamliners out of Oakland is a more carbon friendly option than flying British Airways’ Dreamliner out of San Jose due to the higher seating density of Norwegian’s aircraft and BA’s lower load factor.

While the Boeing 777-300ER tends to be one of the most fuel-efficient aircraft in our rankings, the United flight between San Francisco and London produces a higher than anticipated amount of CO2 per passenger due to extremely low passenger load factor (50%).


Travelers who want to choose the lowest carbon flight for a specific trip, as opposed to choosing the most fuel-efficient carrier generally, need to pay attention to the individual aircraft servicing their flights. While Norwegian was overall most fuel-efficient for transatlantic flights, and American below average, we could find examples of where the latter carrier operated less carbon intensitive flights from the San Francisco Bay Area.

For the three European destinations analyzed, KLM was the most fuel-efficient option out of San Francisco International Airport. However, the exact amount of carbon emissions for a KLM itinerary depends on the aircraft flown on between San Francisco and Amsterdam. Compared to the Boeing Dreamliner, the other aircraft models that KLM operates emit between 116 and 476 kg more carbon dioxide per passenger round trip – or equivalent to powering an average home between 3.5 and 15 weeks.

Until there’s an easy way of comparing carbon impacts of flight options, a quick rule of thumb is that the least carbon intensive international flight options tend to include new twinjet aircraft (e.g. Boeing 787 Dreamliner, Airbus A350), while the most carbon intensive options tend to include quad-engine aircraft (e.g. Boeing 747 and Airbus A380). The good news is that European airlines that still use “The Queen of the Skies” – British Airways, KLM, Lufthansa, and Virgin Atlantic – have all announced the retirement of the quad engine 747 by the end of the next decade.

Knowledge is power, and perhaps fewer carbon emissions.