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There is growing interest, and concern, in the aviation industry about pollution and emissions. With an industry target to reach net-zero carbon by 2050, this is understandable. Much more needs to be done in many areas. One area that stands out is carbon dioxide (and other pollutant) emissions and quantification. This concept has been around a long time, and in use by many, but there is no standard way to measure or report it yet.

Measuring carbon dioxide

We have been calculating carbon dioxide emissions for some time now. This has become increasingly important as more governments, businesses, and individuals need ways to quantify emissions. For governments and corporations, this is increasingly part of policies, reduction targets, and reporting requirements. For individuals, there is a rising green consciousness, and a desire to pay to offset emissions.

Carbon calculators are used to do this. However, many governments, environmental agencies, NGOs, and trade bodies, as well as airlines and carbon offset service companies create these, with differing results.

The principle is straightforward, but the implementation and data used can (and does) differ between calculators. While it may become standard in some areas or countries to use one particular calculator, it becomes hard to compare different estimates. In such a global industry, this is worrying.

Calculating the emissions

It is, of course, highly impractical to measure actual aircraft emissions (even on an experimental scale, this has been very limited). Instead, calculations are made using inputs that are known. The focus is on calculating the expected emissions for a flight. The actual emissions for each flight will of course differ depending on many factors – including the prevailing winds and effect, weather conditions, the actual flight length with diversions or holding, and the exact number of passengers.

Calculators generally work by looking at the following:

  • Distance of the flight. This is, of course, the main factor that differs between flights.
  • The fuel burn for the aircraft type. To work out the amount of fuel consumed for a flight, you need to know the flight distance and the fuel burn for the aircraft type operating the flight. It is important to take account of more efficient aircraft, particularly for airlines and corporate users. The International Civil Aviation Organisation (ICAO) makes such data for aircraft types available, but again different models can source different data.
  • Carbon dioxide produced from fuel burn. Once you have the total fuel consumed, it has to be converted into actual carbon dioxide emissions. ICAO suggests a factor of 3.16 for this.
  • Number of passengers. There are differences whether you want to know emissions per flight or emissions per passenger. Assumptions need to be made about economy or premium cabins, and occupancy of commercial flights.

Looking at other emissions

Carbon dioxide is not the only emission of concern. Other pollutants, including nitrous oxides and water vapour can be worse in their effect on global warming. This is especially the case when looking at aviation emissions at altitude, rather than ground-based transportation emissions.

Most calculations will take account of these emissions, but again, methods vary. Some attempt to calculate these, while others will make use of a multiplication factor based on the calculated carbon dioxide emissions. Others may ignore it and only consider carbon dioxide.

Using an evidence-based multiplication factor makes sense, and there has been plenty of research work carried out in this area. This has resulted in some standardisation, such as the GWP (Global Warming Potential) index, which suggests using a factor of 2 times carbon dioxide emissions. Different calculators can use different amounts though. In a study into such calculations by the Environmental Change Institute at Oxford University, factors ranging from 1 (no effect) up to 4 were found to be in use.

The UK calls for standardisation

So far there has been little standardisation of calculations. The ICAO does produce a methodology for such calculations, and has an online tool itself that will produce emissions numbers based on this. This is, of course, not used by everyone.

Calls for formal standardisation are increasing in many countries. As just one example looking at these differences between calculations, the Oxford University study found that two considered models differed by 100%, for carbon dioxide calculations for the same transatlantic flight.

In the UK, the CAA took action at the start of 2023 following media reports of differing practices in calculations, and differing results being presented to passengers. The first step in this is a call for information/evidence from the industry until April 2023. Explaining the benefits of this, the Head of Strategy for the CAA said:

“Better understanding the most effective type, format, and communication of environmental information will help us achieve the goal of supporting the government’s net zero aviation target. I encourage everyone to help inform the way passengers are provided access to accurate and relevant information about the environmental impact of their flights… providing trustworthy data enables more sustainable choices.”

This is specifically focussed on the environmental and emissions information presented to passengers when researching and buying flight tickets. However, it is part of the wider CAA Environmental Sustainability Strategy, and the government’s net-zero by 2050 plans.

Final Thoughts

Given the global nature of the industry, and the rapid increase in interest in emissions from more parties (including individuals whenever buying flights), it is understandable that new calculators and methods have developed. There has been some work to standardise this, including from ICAO, but this has yet to be fully adopted. Individual countries taking action to legislate will likely be the next steps.

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