Analysis: while planes are getting more fuel-efficient, the carbon associated with your seat on a plane is very, very high

By James CarrollTrinity College Dublin

There's a wonderful line in book The Martian. Alone and facing certain death, Mark Watney (the hero) decides "I’m going to have to science the shit out of this". The EU's 2050 "almost-zero-carbon" journey probably needs a similar slogan. Our scientists, engineers and entrepreneurs, whether motivated by the public good or private profit, are our Carbon Heroes. But getting firms and households to buy-in to lower-carbon living over the next 31 years is a different matter and one of the drivers is that these decisions are very confusing.

A major grey area is "upstream carbon", the carbon embedded in our products. For example, we tend to think buying locally-grown potatoes directly from the farmer is more environmentally friendly than, say, buying Vietnamese rice in the supermarket (and we’re probably right). But a precise carbon comparison would need to include the emissions associated with every step of the production process and also the carbon embedded in every single manufacturing input. Then we’d need to do this all again for every single step in the distribution chain.

If you’re interested in such comparisons, great – Science Needs You – but we need to be realistic in our expectations of household decision-making. Yes, boycotting products with clear and certain high upstream emissions will send a very important signal to firms. But in the absence of accurate Life-Cycle Assessment labels for every product, busy families cannot be expected to make these calculations and comparisons themselves. Modern worldwide supply-chains are as intricate, interlinked and interdependent as the flora and fauna in a prehistoric jungle.  

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A household only has complete control of one carbon impact – its own downstream emissions, the carbon that comes out of your chimney, flue and/or tailpipe, and your share of emissions from electricity generation. The rest - the emissions from firms, government and generators - is really someone else’s area of control and responsibility (and they’re on it).

Back to that local spud vs Vietnamese rice comparison. A household can only really control the carbon associated with shopping (the carbon associated with collecting one item from a local farmer is higher than buying everything in a single trip to the supermarket) and cooking (boiling potatoes can take an hour of energy, while cooking rice can take just 10 minutes).

In terms of our "leisure", there is good news. Much of what makes life enjoyable is already fairly low on downstream carbon. Take, for example, the mobile phone. The electricity cost of an entire year of calls, messaging, streaming, and internet is about €2. And a modern TV? In terms of energy consumption, it’s basically fit for an eco-warrior. Furthermore, meeting friends in a pub, café or cinema can also a relatively green activity, depending on how you get there and back.

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However, there is one aspect of our leisure and identity which is problematic: flying. The carbon associated with your seat on a plane is very high. For example, my wife and I flew to the Canaries earlier this year. Our two return economy seats on the Boeing 737-800 had a carbon footprint of 2,146kg. To put this into perspective, our entire year of driving (16,000 km in a modern diesel car) has a carbon footprint of 1,704kg.

Planes are certainly getting more fuel efficient, but frankly these improvements are akin to lighting a scented candle in a sewer. While the contribution by airlines towards total global carbon emission is indeed very small (2%), this low share is due to the fact that most people in the world do not fly. Most of my downstream carbon last year was associated with flights. 

However, not all planes are equal. Take, for example, a flight between Dublin and London Heathrow. You’ll probably find yourself on either an Airbus A320 emitting 173kg carbon (one economy seat return) or a Boeing 737-800 emitting 170kg. However, you could also end up on a turboprop (i.e. propeller) plane which emits considerably less. For example, the Bombardier Dash 8 emits 105kg and the ATR 72 emits just 75kg. In summary, comparing the best with the worst, you can reduce your flight carbon by almost 60% by choosing airlines that operate these aircraft, if the destination is within range (turboprop is not suitable for longer distances).

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If you have the time for it, switching to ground transport, where possible, reduces your carbon impact further. For example, I travelled to Paris by "Rail and Sail" to research this article. The carbon associated with the ferry plus train was 64% lower than the jet engine alternative.

The obvious downside is time: I left the house in Dublin at 7am and checked-in to my hotel in Paris at 11pm, so it took 16 hours door to door. Also, at the time of booking, this low-carbon alternative cost €60 more. On the plus side, I had a serious fry-up on the ferry, a pie and pint in a London pub between trains and saw lots of dramatic seascapes and landscapes along the way. I returned by air to compare the "hassle" factor and, by some strange twist of fate, my flight was cancelled. In the end, it took over 24 hours to get home, but it would have taken just five on a normal day. 

For longer flights, the carbon-minimising household has one option. The offsetting concept is fairly straightforward: just think of your household’s lifetime carbon as a big bucket, but with a hole in the bottom. Your annual energy consumption fills the bucket at a rate which depends on your household’s energy efficiency (your insulation and boiler, for example). But you can increase the size of the hole at the bottom by either sucking carbon out of the air (by planting trees or, in the near future, by mechanical means) or by reducing the current/future emissions of others (by investing in their energy-related technologies).

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Offsetting can be simple and you can even DIY. For example, you could donate LED lightbulbs to a household who can’t afford them, or buy a share of an electric car with some friends and donate it to someone who will make the largest carbon savings, such as a taxi driver in Cairo. More formally, you can invest in projects that install renewables in developing countries. However, there’s one rule to offsetting: "additionality". That is, don’t plant a tree in a place where one would have grown anyway a few years later through natural processes.

Ideologically, many are uncomfortable with offsetting. Are we just offloading our carbon-reducing responsibilities to others? Well, there’s a growing market for that and offsetting is currently extremely cheap.

Like planting trees, offsetting will likely play a role in the world’s transition to a low-carbon economy. If regulated and priced correctly, it could also improve living standards in developing countries. But these foreign carbon-saving opportunities will dry-up eventually and, sooner or later, we will all have to get our own house in order.

Carbon-saving opportunities will dry-up eventually and, sooner or later, we will all have to get our own house in order

However, unlike nearly every other household technology, there is no low-carbon alternative for travelling extremely long distances. While battery weight-to-capacity ratios are continuously improving, they still have a long way to go if electric planes are to fly more than a few hundred miles. Until then, carbon-neutral flight can only be achieved through offsetting.

Dr James Carroll is a postdoctoral research fellow in energy economics at Trinity College Dublin


The views expressed here are those of the author and do not represent or reflect the views of RTÉ