Last month, a navy blue, six-seater aircraft took off at Cranfield Airport in England. Usually, a 15-minute, 20-mile flight wouldn't be noteworthy -- but this was the world's first hydrogen fuel-cell-powered flight for a commercial-size aircraft.

The plane's powertrain -- the mechanism which drives the plane, including fuel tanks and engine -- was built by ZeroAvia, a US and UK-based company developing hydrogen-electric engines. Using liquid hydrogen to feed fuel cells, the technology eliminates carbon emissions during the flight.

A conventional flight today produces half the CO2 generated by flights in 1990, largely thanks to an increase in fuel efficiency. However, due to record traffic growth, driven by increasing passenger numbers and trade volume, the aviation industry is creating more emissions than ever before -- accounting for 2% of global manmade carbon emissions. This percentage is set to increase says Bobby Sethi, a senior lecturer in aviation at Cranfield University: other industries, like road transport, are "decarbonizing at a faster rate" he says, while aviation is lagging behind.