Williams College Air Travel Greenhouse Gas Emissions Information & Reduction Program

Travel is an important part of our lives. It connects us with people and places and allows us to conduct our work more productively and meaningfully. Globally, travel is on track to recover from COVID-19 declines, and if it were a country, it would rank among the top 10 carbon emitters. Thus, to avoid the worst effects of climate change, travel needs to become less carbon-intensive.

At Williams, travel emissions’ share in total greenhouse gas (GHG) emissions is rising. College-sponsored travel now constitutes the second-largest emissions source after emissions from the central heating and power plant.  This growth is due to the college’s purchase of 100% green electricity, thereby removing a large source of emissions, as well as an expansion in travel itself, pandemic-induced reductions notwithstanding. 

Williams remains committed to reducing carbon emissions with goals to cut direct campus and electricity-related emissions, pursue energy efficiency and sustainable building methods, improve the fuel economy of college vehicles and reduce travel related emissions. The college also continues to purchase carbon offsets to neutralize the remaining emissions.

Informed travel planning can help with avoiding some emissions and seeking out less carbon-intensive travel options. That is the reasoning behind the Williams College Air Travel Greenhouse Gas Emissions Information & Reduction Program. 

This page offers information on the program, on the climate impacts of air travel, and shares tips for reducing them. Please don’t hesitate to reach out to the Zilkha Center at [email protected] with questions or to let us know how we can support you with your travel-related decision making.

  • Although travelers cannot easily change airline practices, there are a few things each of us can do to reduce our travel carbon footprint, nudge airlines to do their part, and encourage others to do the same. Here are some tips for greener flying:

    Learn about Flight Emissions

    Greenhouse gas emissions can be difficult to put into the context of our daily lives. We, therefore, used a carbon emissions equivalency calculator developed by the EPA to provide some points of comparison for flights between Boston and destinations around the world (all flights are direct roundtrip journeys in economy class).

    GHG Emissions of a roundtrip between Boston and ... San Francisco London Nairobi Rio de Janeiro Beijing Sydney

    CO2e emitted


    metric tons



















    Equivalent to ... Using 137 gallons of gasoline Switching 58.7 light bulbs to LEDs Driving 8,067 miles by car Recycling 94.8 bags of trash Carbon sequestered by 3.6 acres of forest 57.6% of average annual home energy use

    Things to Consider when Planning Your Trip

    • When booking flights, consider carbon emissions as one decision criterion. The college's travel booking platform Egencia and Google Flights both calculate the carbon emissions of flights and help users choose less carbon intensive travel while they browse for flights. They also include the estimated emissions associated with the trip in the booking confirmation email.  Alternatively, flight carbon calculators (there are many, such as this one) can be used to determine the average carbon emissions between two places and inform the choice alternatives to flying. (Note: each provider of carbon emissions information makes decisions on how to calculate them, thus, results may differ.)

    How to Fly Greener

    • Direct flights are generally less carbon intensive than flights with multiple legs (takeoffs and landings consume more fuel and hence emit more GHG). So if possible, book direct, non-stop flights.
    • Bundle trips. If you have to travel to multiple destinations within a short period of time, consider bundling them into a single trip, especially if this saves flight legs and reduces distance flown, which can translate into GHG savings.
    • The class of service flown impacts the GHG emissions, i.e., business class is more carbon-intensive than economy, and first class more so than business class. This is because of the differences in space and weight allowances made for premium cabin fliers compared with economy class ticket holders. When possible, consider switching to a less carbon intensive service class.  
    • In most cases, regional travel (say less than 300 miles) by car or train is less carbon intensive than flying to those destinations and still doable in terms of time and convenience. For car travel it is even better if the car in question is an electric or hybrid vehicle and the grid used to charge the battery is not predominantly powered by coal or oil.
    • Choose airlines that actively work to reduce their carbon footprint. A growing number of airlines have made commitments to greening their operations, including reducing GHG emissions. Check out a recent article on these airlines and how they are doing it. For U.S. carriers, Airlines for America, a U.S. airline trade association announced in 2021 that its members have committed to achieving net-zero emissions by 2050. You can find the member airlines here.

    Alternatives to Traveling in Person

    • Virtual travel! Reviewing travel needs and policies may offer ways to keep a portion or all of it in the virtual realm. This could include opting to bring a speaker to campus virtually or zooming into a meeting instead of flying (or traveling by other means). Encouraging conference or meeting organizers to offer a hybrid format for their gatherings can help staying connected with peers while reducing travel needs for others as well. 
  • Informed by the work and consultations conducted by the Campus Environmental Advisory Committee (CEAC), the program aims to provide travelers who undertake college-sponsored air travel (i.e., paid for using college funds) with information on the greenhouse gas emissions of their trips and opportunities for reducing them.

    As an informational program, we will begin with monthly emails to air travelers (or those making travel reservations) containing the following information:

    • The estimated GHG emissions of each flight,
    • The estimated climate damages associated with the GHG emissions using established Social Cost of Carbon (SCC) estimates, and
    • Information on opportunities for reducing flight-related GHG emissions.

    The Social Cost of Carbon concept represents a monetary estimate of the damages incurred by releasing an additional metric tonne of carbon dioxide equivalent. It raises awareness of the growing magnitude of climate change damages and their disproportionate impact on vulnerable populations. The program uses two SCC estimates, the first is the Obama Administration's estimated SCC of $52 per metric tonne of CO2, while the second corresponds to a more comprehensive and updated estimate of $185 per metric tonne CO2.

    Data Use & Privacy: The data for the informational program comes from our internal financial reporting systems for purchasing cards, accounts payable and bookings made through the travel platform Egencia. To estimate flight emissions we only use airport (origin, destination) information and annually updated emissions factors from the UK's Department for Environment, Food & Rural Affairs (DEFRA). The email is only sent to the person associated with the trip and identifying information is not shared with any other party. Reports on travel related emissions use aggregate data at the departmental and college level without identifying information. Please note that not all college-sponsored travel might be included in the data and some data limitations exist that could result in a misclassification of a flight-related expense such as luggage fees. If you believe that you have received a message by mistake or the message contains errors, please contact the Zilkha Center at [email protected].

  • The charts below track the monthly and cumulative total GHG Emissions from college-sponsored air travel for fiscal year 2023 (beginning with the program's launch in October 2022) and fiscal year 2024.

    A chart showing the monthly air travel CO2e emissions as bars and the cumulative total as a line, both in metric tons of CO2e, for fiscal year 2023
    Monthly and Cumulative CO2e Emissions from Air Travel in Fiscal Year 2023 [metric tons]
    A combined bar and line chart showing the monthly (bar) and cumulative (line) air travel emissions in metric tons of CO2e for Williams College.
    Monthly and cumulative CO2e emissions for July 2023 - May 2024
    Bar chart of monthly CO2e Emissions from college-sponsored air travel in fiscal years 2023 and 2024.
    Monthly CO2e Emissions for FY23 and FY24
    Line chart of monthly cumulative CO2 emissions from college-sponsored air travel in fiscal years 2023 and 2024.
    Cumulative CO2e emissions in FY23 and FY24


  • The main sources of institutional GHG emissions are on-campus, direct fuel combustion (central plant and vehicle fleet), indirect emissions from purchased electricity, and indirect emissions from activities such as employee and student transportation (employee commutes and college-sponsored travel).

    The college has eliminated emissions from purchased electricity through the Farmington, ME solar PV project and additional Renewable Energy Certificate (REC) purchases. It is also working on a plan to substantially reduce on-campus fossil fuel combustion.

    As a result, reducing transportation related emissions is the next big emissions source that we hope to tackle, although we are also working on other indirect emission sources such as food, procurement and waste. Air travel is among the most carbon-intensive ways to travel. Our most recent GHG emissions report estimated air travel emissions of 695 metric tonnes of carbon dioxide equivalent, amounting to 5.5% of total emissions. However, travel has been heavily impacted by the COVID-19 pandemic and has already begun to rebound to pre-pandemic levels. For comparison, the college’s most recent pre-pandemic air travel emissions in FY19 amounted to 4,799 metric tonnes CO2e, or more than a fifth of the college’s total GHG emissions.

    It is thus imperative that we increase our efforts to reduce transportation related emissions, including in particular air travel GHG emissions. The informational campaign aims to build awareness and share insights with travelers on the climate impacts of air travel as well as the opportunities for greener travel.