Photo: Flickr, CC
Same Flight, 450% Difference in CO2 Emissions Between Airlines...
According to 700-page Stern Report on the economics of climate change, CO2 emissions from aviation are about 600-700 megatonnes per year, or about 2-3% of total global CO2 emissions. The single digit percentage might not seem like much, but there are aggravating factors: Aviation is currently the fastest-growing source of CO2, and is expected to keep growing rapidly in the next 20 years. Also, those emissions are not spread evenly across world population. For some people, flying might represent a huge portion of their individual carbon footprint (do you recognize yourself?), and so any improvement can have a big impact. Get ready to green your flying: Let's look at what makes a difference!
Photo: Franco Folini, CC
Before we start, the most important point: Nothing can make as big a difference as stopping flying. If you don't have to fly, don't. If you can cut back, do it. The rest is mitigation... It's important, but in a 'lesser evil' kind of way.
So How Big a Difference Can I Make Without Stopping Flying?Not All Airline Tickets Get You the Same Deal The first thing to know is that the fuel efficiency of airplanes - and thus CO2 emissions - are not a static thing. Efficiency has been changing over time as technology gets better, and it varies between plane models and types of planes.
For example, according to the IPCC (see 7.2.4) there was a 70% aircraft fuel efficiency improvement (30% coming from airframes and 40% from propulsion) over the 1950-1997 period, and a further 40-50% improvement is expected for the 1997-2050 period (about 25% airframe and 20% propulsion).
So there are definitely significant differences between older and more recent planes. No airline is still flying planes from the 1950s, so the range won't be that big, but some have more "legacy" planes than others.
Hugh Somerville, from the aviation industry's environmental taskforce Greener by Design, says: "Newer airlines have younger fleets, and they also operate with more than 90% load factors." So the carbon footprint per passenger is far less than that of a plane with only half a load.
However, it's not quite so simple. The growth of inexpensive no-frills airlines has also increased the total number of flights, so while they might be relatively more fuel efficient, they also add to the total. It's not a net good, just a lesser evil if you must choose between two airlines that have different planes.
Like a fuel efficient car, we must remember that it is not "good" for the environment, just "less bad." Thinking that it is "good" because it is relatively better can lead us to the Jevons paradox: "the proposition that technological progress that increases the efficiency with which a resource is used, tends to increase (rather than decrease) the rate of consumption of that resource."
According to the International Air Transport Association (IATA), "modern aircraft achieve fuel efficiencies of 3.5 litres per 100 passenger km". This might sound good at first, but there are a few things to remember: First, that number depends on their assumption and methodology (sometimes on paper they use 100% of seats filled, and underestimate how much luggage there's on the plane), and in the real-world it can often be higher. Second, this fuel consumption figure is per passenger. A fuel-efficient car might get 6 liters per 100 km on the highway, but if you have 4 people in the car, that's 1.5 liter per passenger 100 km. Third, and that's something we'll talk more about a bit later, is where the plane emissions occur. That's where radiative forcing comes into play and can make a big difference (even if you use a conservative modifier).