Background guide #2
Transport emissions
How green is our transport?
The overwhelming majority of the world's vehicles are powered by oil, either in the form of petrol (most cars), diesel (most trucks) or kerosene (most planes). Even those trains and cars powered by electricity usually rely on fossil fuels being burned in power stations.
All told, transport accounts for around 14% of human-created greenhouse emissions - and that's excluding the manufacture of vehicles. Most transport emissions take the form of CO2, created when carbon in the fuel is burned in an engine and combines with oxygen in the air.
Quick Jump
Total impact of our emissions
In terms of total impact on climate change, driving is thought to release around six times more CO2 emissions than flying and seven times more than ships and boats. Cars alone create nearly half of our total transport emissions.
But how about choosing a form of transport for individual journeys? How does driving from, say, London to Edinburgh compare with going there by air, train or bus?
Gas guzzlers
Comparing the emissions of various modes of transport is tricky, since there are so many variables to consider. For example, some trains run on electricity while others run on diesel. Some cars are fuel efficient while others are gas guzzlers. Similarly, short flights are more polluting per mile than long ones (since take-off accounts for a larger amount of fuel use), but less polluting overall.
There's also the question of how to factor in the occupancy rates of the vehicles. Driving a car containing four people saves more energy per passenger than solo driving. But taking an extra passenger doesn't actually reduce the total impact of the trip. If anything, it increases it, due to the extra weight being carried. With these caveats in mind, it is possible to calculate typical figures for per passenger emissions of various forms of transport. The figures for flights are multiplied by three to account for the non-CO2 greenhouse impacts of planes.
| Transport type | Emissions per passenger |
|---|---|
| Short haul flight | 130g/km |
| Long haul flight | 105g/km |
| Ford Mondeo 1.8i (driver plus 1 passenger) | 93g/km |
| Toyota Prius (driver plus 1 passenger) | 52g/km |
| Bus | 89 g/km |
| Train | 60g/km |
| Coach | 20g/km |
It's all about distance
The total climate impact of a trip depends not just on the emissions per passenger kilometre, but also on the distance travelled. This is why flying can add so much to a person's carbon footprint. Planes let us travel vast distances in just a few hours - something that simply isn't possible any other way.
Added pollution
Aside from climate change, motor vehicles also emit particles and gases (such as sulphur dioxide and carbon monoxide) that can be harmful to human health. Things have improved thanks to catalytic converters and unleaded petrol, but the problem is still very real.
The World Health Organisation estimates that around 800,000 people a year die prematurely due to air pollution, most of it related to vehicles. Even in the UK, the figure is more than 30,000.
Diesel vehicles tend to be better than petrol vehicles in terms of greenhouse emissions, but worse in terms of local air pollution. Against this backdrop, it is hardly surprising that engine manufacturers across the world are increasingly focusing their attention on developing cleaner technologies.
These guides have been reproduced from BBC Green, part of BBC Worldwide.
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