In 2009 2.5 billion journeys were taken in aircraft.
Evened out across the global population, every third person on earth took a flight. In reality it is the wealthiest proportion of the 1 billion people in western economies who took most of the journeys.
The projection is that by 2014 there will be 3.3 billion journeys taken.
This represents a 32% increase in 5 years.
Mobility is an inevitable consequence of affluence. As more and more people have disposable income, many will want to use some of those funds to travel. As economies grow, more business is done and so travel to buy, sell and negotiate also increases.
In the mid 1960’s the first Boeing 737s carried 100 passengers up to 2775 km. This was quite a revolution at the time.
The latest Boeing 737-800s carry twice the number of people over 5,500 km and use 23% less fuel.
Suppose it were possible to replace all the aircraft flying in 2009 with the latest fuel efficient models. It would be possible to absorb almost all of the 5 year increase in passenger volume to 2014 through fuel efficiencies that these more efficient vehicles bring.
Future aircraft construction materials that are lighter and still strong enough will see even greater fuel efficiencies. Aircraft built in the next decade or two might only use a third of the fuel guzzled by the earliest models.
Replace all the 737-800s with aircraft of composite material designs and 13 years of growth in passenger numbers could be accommodated without increasing fuel use above that used in 2009.
But even if all these replacements were possible by the mid-2020s, less than a generation from now, fuel use in air travel would begin to increase over 2009 levels.
In half the time since those first Boeing 737 aircraft began flying all the fuel efficiencies would have been used up by the increased volume of traffic.
Clearly instant replacement with the best technology is impossible.
Some of those fuel hungry early models are still in the air on the more remote routes operated by obscure airlines. And it is these cheaper fare options that will be responsible for much of the growth in passenger numbers. The fuel efficiencies will arrive incrementally.
In the absence of some remarkable technology that can replace jet engines running on aviation fuel, greenhouse gas emissions from or air travel will grow along with the airline industry.
There is talk of a jet-rocket vehicle that would travel in the stratosphere, have no emissions because it flies above the atmosphere on hydrogen fuel and could reduce the travel time from Sydney to London to a few hours. Commercial flights might happen by 2040.
By then there will be close to 10 billion journeys per year.