Carbon emission oddities - the effect of COVID-19 on business travel emissions

In most cases, COVID-19 led to an increase in carbon emissions per-passenger when flying, the effect of which is only being understood now.

As emissions experts, we use the latest data-sources to ensure clients see a true reflection of their emissions. In ‘normal’ times, emissions vary up to 20% between different airlines. During COVID-19, it was an entirely different situation, with emissions varying by hundreds or even thousands of kilograms of CO2e.

The effect of this is only just becoming known. There is a long lag before some data-sources used for calculations are reported . This in itself is normal, but the impact of the pandemic means there is far more flux in some of these data sources than usual (e.g. load-factor data for airlines in APAC is still only known up until December 2021). We explore how emission factors change and how to handle them in one of our deep-dives into changing carbon emissions.

What are the main factors affecting carbon calculations that changed during COVID-19?

Many factors are taken into account when conducting a carbon calculation, but three areas stand out that caused wild swings in emission calculations during COVID-19:

  1. The aircraft type in operation - different aircraft types have different fuel burns, with newer planes typically having a lower fuel burn than older planes that are designed for the same distance.
  2. The passenger load factor* - this is the percentage of passengers on the aircraft compared to empty seats. Ultimately the carbon emissions are divided between the number of passengers, so more empty seats means the emissions are shared between fewer people.
  3. The freight to passenger ratio - passengers are not responsible for the freight held on an aircraft, so the ratio of passengers to freight is also very important. More freight means fewer emissions allocated to the passengers.

COVID-19 had a fascinating effect on all three of these major computation points, with inefficient aircraft being phased out of service at the start of the pandemic, a huge reduction in the number of passengers flying, and a remarkable increase in air freight during the same period.

* We are sometimes asked if this effect is offset by the lower fuel needed on an emptier plane. While it’s true that planes are fueled based on the weight they carry, aircrafts are heavy, and the physics of flight requires a lot of energy, so the difference in fuel between an empty and full aircraft is only 5-20%.

On average, this caused large increases in per-passenger emissions

During the height of regional lockdowns, some airlines kept flights operating for essential reasons, even though those flights were largely empty. If we take a major flag carrier for example:

January 2019 Factors

January 2021 Factors

% Change

83.9% passenger load factor

9% passenger load factor

-89.3% decrease in passenger load-factor

66:34 passenger to freight ratio

14:86 passenger to freight ratio

-91.61% decrease in emissions attributable to passengers

Both of these factors will play off against each other. While the amount of freight relative to passengers increased, it was not enough to offset the huge fall in passengers. The end result is an increase in emissions of around 100% per passenger.

We have found these examples to be common across regions with strict lockdowns.

There are some examples of vastly lower emissions

Interestingly, due to the same factors as before, some regions actually experienced decreased per-passenger emissions where the transition to freight was high enough. Let’s look at another major flag carrier:

January 2019 Factors

January 2021 Factors

% Change

88.8% passenger load factor

16.6% passenger load factor

81.3% decrease in passenger load-factor

41:59 passenger to freight ratio

<1:99 passenger to freight ratio

98.7% decrease in emissions attributable to passengers

The changes in ratio lead to a fascinating emission calculation, where almost all the emissions are attributed to the airline’s freight in 2021. As a result, long-haul flights on this carrier have emissions in 2021 that are as much as 95% lower than in 2019.

We must emphasise while this is an interesting example, it is a rare exception to the rule. Across the industry, emissions were far higher on a per-passenger basis in 2020 and 2021.

Not all carbon methodologies are equal

We are big fans of ‘simpler’ carbon methodologies since they enable many businesses to get started calculating their footprint with ease. Examples include the straightforward DEFRA methodology. However, the 2020, 2021, and 2022 DEFRA methodologies apply passenger load factors and freight ratios from 2018, which does not give you a true picture of your emissions. In many cases, this would under-report your emissions during COVID by 200% or more.

Even some newer methodologies, such as the Google methodology, still use passenger load factors and freight data from 2019 for many flights.

We suggest looking for a methodology that uses data that is as recent as possible. The Thrust Carbon air methodology is one of those methodologies enabling you to have a far more accurate picture of your emissions.

These numbers will still be debated for some years to come

Some airlines are still overdue publishing data, and many flight operations were more efficient during covid (e.g. there was less air traffic congestion). In many cases, we will not know the true carbon emissions of flights during COVID-19 for years. What we should all do in the meantime is ensure we are using the most recent data possible, plugged into the best methodologies for the given data available.

This uncertainty is part of carbon science and is supported under standard carbon accounting guidelines. We suggest reading this deep-dive into the nature of changing carbon calculations to learn more.

Want to get started exploring your numbers in more depth?

The Thrust Calculator and our Thrust Advisory services can help you explore your carbon emissions in detail, using the most up-to-date methodologies. Understand your programme’s current status-quo, and explore intelligence to learn what changes your business needs to make in order to reach net-zero.

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