They supplied us with arrival data for the largest U.S.-based airlines for the last three holiday seasons, which we define as Nov. 20-Dec. 1 for Thanksgiving and Dec. 20-Jan. 6 for the winter holiday. (We examined only arrivals because departure delays can often be offset once a plane is airborne.) The U.S. Department of Transportation also tracks flight information for the holiday season, but FlightStats' list of airlines is more comprehensive.
Meanwhile, Downing Street has revealed the carbon dioxide emissions from the prime minister's plane will be "offset" by making an investment in "energy-saving technology" in the developing world.