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Not all carbon measurement methodologies are created equal

October 07, 2022


By Mark Corbett
Founder, Thrust Carbon

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CWT partner Thrust Carbon applies a granular emissions calculation methodology that not only gives you an extremely accurate measure of your carbon footprint but that, as a result, maximises your ability to measurably reduce it.

In this guest blog Thrust Carbon Founder and Director Mark Corbett, explores the ins and outs of measuring carbon emissions.

Methodology… I seem to hear that word a lot

That’s not surprising. Businesses are under shareholder, consumer and employee pressure to decarbonise. To measure progress, they need to measure both a “baseline” (the starting carbon footprint) and progress from that baseline towards a target (“50% reduction by 2030” for example). The methodology is the umbrella term for how we get and manipulate input data to arrive at the carbon footprint number. 

Why the noise?

When measuring carbon footprint from any business activity, the methodology needs to be consistent. The decisions we make when we do those measurements greatly impact the number we end up with. 

For example, if you’re measuring the emissions from a fleet of trucks, do you just measure their direct emissions from burning diesel? Or do you also measure the emissions from extracting and transporting the oil? How about the carbon footprint of manufacturing the new trucks you bought this year?

So as you can see, the devil is in the details! That’s why the noise - not everyone agrees on those key details.

OK, how does this apply to travel?

What makes a good methodology for air travel emissions?

Again, the devil is in the details. A good methodology, like the one that Thrust Carbon uses, should account for differences in the following factors:

  • Class of travel: A bigger seat means putting more planes in the air to transport the same number of passengers, increasing carbon footprint.
  • Flight distance: The further a plane travels, the more fuel it has to burn.
  • Aircraft type: Different generations of aircraft create leaps in aerospace technology that boost fuel efficiency.
  • Seating layouts: “Business” or “First” class on a short-haul flight look very different to a long-haul flight and the methodology needs to reflect that.
  • Occupancy (often called “load factor”): The more full a plane is, the lower will be the emissions per passenger.
  • The split between passenger and freight load: The more freight is on the plane, the lower the share of emissions accounted for by the passengers and their baggage. It’s more efficient to put as much payload (freight and passenger) as possible on a single flight, so a low passenger-to-freight ratio will result in a lower per-passenger emission level.
  • Radiative Forcing (the higher impact that greenhouse gas emissions have when emitted at higher altitudes)

What difference do those factors make?

Let’s take the Aircraft Type to illustrate this. A newer generation of aircraft can mean a double-digit percent reduction in per-seat emissions. If you can promote two carriers to your travellers on a key route - one flying second-generation and one flying third-generation craft - you probably want to promote the one with the newer model. But for that to deliver a measurable reduction, you need to capture that aircraft type data point and account for it in your reporting.

This stuff seems to be pretty controversial…

Indeed it is. Let’s take a recent story from the BBC about the methodology that Google Flights applies (Thrust Carbon’s Kit Brennan provided his expertise to demystify this one). A barely-announced change to how they account for non-carbon greenhouse gas emissions cut their estimates in half - they removed radiative forcing from consideration.

OK, so I’ve got my checklist. Anything else I should know?

Even the same methodology applied differently can give different results. Whereas Thrust Carbon updates occupancy estimates monthly, if a calculation uses an older estimate it wouldn’t account for the much higher occupancy levels the industry has seen as travel has surged in 2022. For example, the UK government’s published emission factors (commonly referred to as “the DEFRA factors”) are still calculated using 2018 load factor statistics.

Got it! Getting the right methodology from the right place sets me up for success

That’s right. Not all methodologies are created equal - they need to be precise enough that your real-world actions deliver the measurable results your customers and other stakeholders want to see.

If you want to find out more - speak to your CWT account manager today.



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