Cars get a lot of the blame for poor air quality and causing greenhouse gasses. They're everywhere, we all use them to some extent - usually as a luxury - so it makes sense that we examine their role in our environment.
But what about planes? Hong Kong has one of the world's busiest airports. Last year, it handled nearly 280,000 flights, 3.35 million tonnes of cargo and 46 million passengers.
According to Greenpeace, transportation contributes about 13 per cent of global greenhouse gas emissions, of which two thirds comes from road transport with the rest coming from ships, trains and aircraft.
Other sources say air traffic contributes 2 per cent of all emissions of carbon dioxide, one of the most common gasses blamed for global warming.
The numbers are not exact, but emissions from aviation contribute far less to climate change than cars and trucks.
Still, aviation is becoming increasingly popular, particularly in a country such as China, where many people can now afford to fly.
Not all airliners boast the same fuel efficiency. The US government has calculated that the average airliner can fly one seat 27 kilometres per litre of fuel. This is about the same as driving a big SUV with four passengers.
