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.
But the problem is that very often big cars carry only one or two passengers. In that case, an airliner is much more fuel efficient than a car.
However, a passenger taking a round-trip flight from London to Sydney consumes roughly the same amount of fuel as driving a small sedan 50 kilometres a day for 18 months.
Because fuel prices has risen sharply in the past decade, airlines now do whatever they can to improve fuel economy.
The newest jets are the most fuel efficient, but older jets are being retrofitted in lighter materials such as carbon fibre.
Longer flights are generally more fuel efficient than shorter ones because jets burn a lot of fuel during takeoff. In a short flight, takeoff accounts for a bigger percentage of the entire trip than on a longer flight.
Jumping on a plane to fly to another country has become an ordinary part of our lives. But like driving a car instead of taking a bus or train, air travel is often an indulgence.
And it is our luxuries and over-consumption that has led to our present climate change problem.