The Problem With Planes
Aviation is a critical part of the modern world, but how emissions-intensive is it really, and why?
1. Packing Your Carbon Suitcase
Imagine getting off the plane after a 7 hour flight between London and New York City and picking up your suitcase. If it’s a bit on the heavy side, it might weigh about 20 kg. How much would the carbon dioxide emissions of that single flight weigh per passenger?
The Calculation: It’s about 5500 km from London to NYC (one-way). A typical person and their bags might weigh about 100 kg in total. A typical plane emits about about 0.1 kg of CO2 per km travelled, per 100 kg of payload. So the flight would emit about 550 kg of CO2 per passenger. What about a return flight? Well, it’s double the distance, so about 1100 kg of CO2 per passenger.
So you get back from your return trip to New York and go to pick up your 20 kg suitcase, which feels heavy - but having been responsible for the pouring of over a tonne of CO2 into the upper atmosphere, you can be very glad you’re not carrying the other 55 suitcases that would account for.
That’s not even the worst of it. There are two other big problems we need to consider:
Firstly, we’ve so far only been considering one greenhouse gas: carbon dioxide, whereas a significant percentage of an aircraft’s global warming potential actually comes from other greenhouse gases
Secondly, the high altitude at which aeroplanes cruise means that Secondary Effects further increase the aircraft’s global warming effect. These are explained in Section 2.
The contribution of these other gases and effects is very difficult to quantify, but estimates typically put their contribution to the flight’s total global warming potential between about 45% and 75% (reference WIP).
Bringing these factors together, and using the estimate (reference WIP) that non-CO2 emissions are responsible for about 50% of the journey’s total global warming potential, that’s equivalent to the climate impact of about 2200 kg of CO2, or about 110 suitcases of CO2. In that case…
What about Other Modes of Transport?
Okay, 110 suitcases sounds like a lot. But people need to go places, so how does flying compare with other modes of transport? The key parameter we use to assess this is the amount of emissions that a mode of transport produces per passenger, per km travelled.
This relative emissions of several key modes of transport are shown in Figure 1, made by the BBC2. Clearly, air travel is the most emissions intensive per passenger per km, and it’s even worse if we consider that the planes typically fly far greater distances than other travel methods. It is therefore critical that we find ways to drastically increase the sustainability of aviation if it is to have a future.
2. Secondary Effects
This section is a Work in Progress! Come back next week for more.