Our policy is not to fly for the purposes of our work.
Why don’t we fly?
Firstly, it is a highly energy intensive way of moving people and things around – it takes a lot of energy to overcome gravity and keep a plane ‘up’ and to move it through the air.
Secondly, in terms of global warming potential the exhaust gases from aircraft are more potent than the exhaust gases from other forms of transport due to the chemical reactions which take place when emitted at altitude, and the physical effects of condensation trails.
This means that one kilogram of carbon dioxide emitted from a plane (at altitude) is equivalent to two to three kilograms emitted on the ground.
Flying – how much energy does it take?
Long-haul
A Boeing 747-400 with 240,000 litres of fuel carries 146 passengers about 8,800 miles (14,200 km). The energy cost of one full-distance round-trip on such a plane is:
(2 X 240,000 litre)/416 passengers X 10 kWh/litre = 12,000 kWh per passenger. (The 10 kWh/litre refers to the calorific value of the fuel).
Making one such trip a year would give an average energy consumption of:
12,000 kWh/365 days = 33 kWh/day
To put this in perspective a single return trip requires more energy per passenger than running a one bar electric fire 24 hours per day, 365 days per year.
Short-haul
In 2007, the most efficient airlines delivered transportation at a cost of 37 kWh per 100 p-km (passenger km). Other airlines are probably in the order of 73 kWh per 100 p-km.
So a return trip from London to Rome (1430 km) will have an energy cost of approx 1060 kWh with the most efficient airlines and about 2090 kWh with the least efficient.
Flying and greenhouse gas emissions
Flying creates other greenhouse gases in addition to CO2. These include water, ozone and nitrous oxides. The exhaust also creates clouds (visible on a cool clear day) which can enhance the warming effect, particularly at night.
Because of these effects (known as Radiative Forcing), the consensus amongst climate scientists is that green house gas emission figures for aviation need to be ‘uplifted’ by a factor of between 2 and 4. (The Tyndall Centre (2005) suggested an uplift factor of 2.7). We currently use a figure of 3 in our calculations.
So the return flight on the Boeing 747-400 (as set out above) would emit:
12,000 kWh X 0.24 kg CO2 per kWh (assumed carbon emission factor for aviation fuel) x 3 (uplift) = 8600 kg
And a return trip to Rome would emit between approx 760 kg and 1500 kg CO2 depending on the efficiency of the airline.
Sources:
Sustainable Energy – without the hot air. MacKay, David J.C. UIT Cambridge, 2008. ISBN 978-0-9544529-3-3. Available free on-line from www.withouthotair.com
Carbon factor for aviation fuel. Assumed to be equivalent to that of petrol (excluding up-lift), figure from Carbon Trust publication CTL018.PDF available from here
