The sky got very crowded last year with over 3 billion people travelling by air, according to preliminary figures from the International Civil Aviation Organization (ICAO). The world's 3 billion travelers took off on 33 million fights, beating the previous year's total by a million.
But with extra trips come extra carbon emissions.
In the Netherlands, one of the world's biggest airlines, KLM, is attempting to lessen the environmental impact of air travel by investing in ideas that could help aircraft fly using biofuels alongside conventional fossil fuels.
In May 2014 the airline launched a series of transatlantic flights from Amsterdam to Aruba and Bonaire. During these flights, an Airbus A330-200 was powered by a mixture of fossil fuels and sustainable biofuel.
"We started in May, and we started two series of 10 biofuel flights on a weekly basis," Inka Pieter, Director of Corporate Social Responsibility & Environmental Strategy at KLM, told CNBC's Sustainable Energy.
KLM's biofuel planes use a truck to refuel. "With this truck, I fill the plane with a blend of biofuel and fossil fuel," Leo Drost, a Fuel Operator for KLM, said.
"My colleague on the other side of the plane is standing on the dispenser. He will fill the left side of the plane only with fossil fuel," Drost added. When the plane is airborne, the fuels are mixed and burnt normally.