Learning to Fly Green

Let's start with an uncomfortable and increasingly important truth: flying is pretty tough on the environment. Sure, today's aircraft are some 70% more fuel efficient than planes operating in 1970. But passenger numbers are soaring: the industry expects to fly 2.2 billion people this year, 10% more than in 2005. The result? Aviation's share of global CO2 emissions, now around 2%, is expected to hit 3% by 2050.

Problem is, flying is often the only way to go. Four-fifths of airline-related emissions come from journeys over 1,500 km, for which there's no real alternative (Moscow to Beijing by...