Don’t Drive - Flying By Plane Is Greener Way To Travel

Posted on 15. Jun, 2009 by Ross in Energy News, Transport

Despite airlines now talking about carbon-neutral growth and bio-fuels, they already have a green feather in their cap: flying by plane causes less carbon emissions than driving a car.

A study (PDF) from the University of Berkeley, California found that the carbon footprint of flying, generally held to be the most environmentally polluting form of transport, is actually much lower per passenger than for cars and is comparable to travel by train when the vehicle life-cycle and associated travel infrastructure costs are taken into account.

There was some good news for the car industry: cars were only the second most polluting travel option in the study, with the most-polluting being a urban diesel bus running off-peak. The bad news is that the same bus running during peak hours became the greenest mode of transport, leaving cars languishing below aircraft at the bottom of the table.

Flying by plane benefited in this analysis primarily because air travel enjoys high occupancy rates - the data for large aircraft involved the planes being on average over 80% full. This is of course a direct result of the economics of flying: lower passenger numbers would make flights more uneconomical unless charges were massively increased, and the phenomenon of cheap flights has driven passenger numbers up over the last couple of decades. In contrast, the train lines in the ran on average at as little as 25% full, whilst the average car contained 1.58 people.

Emissions per person is a metric usually condemned by the car industry. The relative efficiency of motorbikes is often rubbished by some car fans who respond by pointing out that you can’t fit 5 people on a motorbike. However, the reality is that most cars are driven around far below their capacity, especially during commuting hours, rendering them more polluting. It is worth pointing out, however, that even with an average of 3 people in the car is would still perform worse than a significantly under-capacity train.

Where aircraft also came out on top compared to everything else was in infrastructure costs. The carbon cost of building new roads, railways and bridges was a massive additional cost to the life-cycle emissions of cars and trains. By comparison, new airport construction paled into insignificance. Additional factors such as infrastructure, vehicle production, maintenance and fuel production added another 50% onto the carbon emissions cost of a family car.
Graph of relative emissions from different transport modes over their entire life-cycle
The nature of air travel’s advantages over cars signals trouble for future improvements. Minimising unnecessary road construction, car-sharing, lighter/smaller vehicle bodies, regenerative breaking and new electric/fuel-cell/hybrid engine technologies can all make significant and largely immediate impacts upon car travel. Many of the same points can be made for rail travel too, as well as greening the electricity supply more with a greater proportion of energy generated by renewable sources.

Aircraft, unlike cars, have always been designed to be as light as possible in order to minimise fuel costs. Other than the now-retired Concorde, where speed and luxury was the primary goal, passenger aircraft are geared towards transporting as many people as possible as cheaply as possible. Infrastructure carbon costs are already small, passenger numbers are consistently high and little progress has been made towards new energy sources for aircraft. Progress on fuels has largely been towards the now-controversial field of bio-fuels: batteries and fuel-cell fuels don’t have the same energy density as oil, meaning planes would have to carry heavier loads of fuel, whilst hydrogen-powered planes has the additional unfortunate first thought of ‘Look what happened to the Hindenburg!’

That’s not to say the airlines are doing nothing. Despite a 70% improvement in energy efficiency over the past 50 years largely through higher cruising altitudes, the Intergovernmental Panel on Climate Change expects a further 20% reduction on top of that by 2015 and a further 20-30% by 2050. The International Air Transport Association last week committed to achieve carbon-neutral growth by 2020, following earlier announcements by more environmentally ambitious airlines like Virgin Atlantic. Everything from landing control software to wing surface design is being tested to try to leverage even the smallest gains in efficiency.

The stakes are high for the airline industry. As well as making flying cheaper and/or more profitable, airlines are a perennial scapegoat for rising atmospheric carbon dioxide levels. With the Copenhagen conference fast approaching, industry leaders are fearful of externally-mandated emission cap-and-trade schemes and are aware of being an easy target in the minds of politicians and the public.

Image by bensonkua @ Flickr