The number of people who flew to the summit in private aircraft has drawn criticism. According to the International Air Transport Association, about 2% of global carbon emissions are caused by aviation. It also creates non-CO2 emissions high above the ground, which can have an additional warming effect. A return economy class flight from London to New York will emit 0.67 tonnes of carbon dioxide per passenger. This is equivalent to 11% of annual UK emissions, and about the same amount as the CO2 produced by Ghanaians over the course of a year.