For many companies, air travel is one of the largest sources of emissions. At the same time, the methods for calculating the climate impact of air travel are often complex and can vary. We are therefore sharing a guide with our best recommendations so that you can make robust calculations that can be compared over time.

Why is aviation's climate impact more than CO₂?

Air travel not only causes carbon dioxide emissions, but also nitrogen oxides, water vapor, soot particles, and contrails, which contribute to global warming. Research shows that as much as two-thirds of aviation's total climate impact is due to factors other than carbon dioxide emissions.

If these other factors are omitted when calculating emissions from your flights, there is a risk of obtaining misleading values, thereby providing you with a weaker basis for reducing your climate impact.  

What does RFI mean?

RFI stands for Radiative Forcing Index and is often referred to as the "high altitude effect." In short, it means that emissions from aviation increase significantly at high altitudes compared to emissions at ground level. According to the Swedish Environmental Protection Agency, emissions from fossil fuels at high altitudes can lead to a doubling of emissions.

The high-altitude effect – the climate impact of emissions at high altitudes can be as much as twice as large as if they had occurred at ground level.

How to calculate emissions from flights – ZeroMission's recommendations

Here are our key recommendations for accurately calculating your company's climate impact:

1. Include upstream emissions

The entire life cycle of aviation fuel – from extraction to distribution – accounts for approximately 20 percent of the total climate impact. We therefore always recommend that these emissions be taken into account in your calculations, even though this is not a requirement under the GHG Protocol (Greenhouse Gas Protocol).

2. Expect an RFI factor of 1.7 or higher

To capture the total climate impact of aviation, an RFI value of at least 1.7 should be used. This means multiplying the direct emissions (which occur in the air, known as "tank to wheel") by 1.7. This is an established and well-documented value that we believe provides a realistic result. For clarity, we also recommend that you openly disclose which factor is used.

Be sure not to include upstream emissions ("well to wheel") when multiplying by the RFI factor of 1.7, as only emissions occurring in the air are affected by the altitude effect. For example, if you receive emissions data for your flights from a travel agency, you can ask whether upstream emissions are included in the total value and what proportion of the total value they represent.

3. Be precise in your calculations

It may sound obvious, but we would still like to emphasize that you use data that reflects reality. Standard values risk significantly underestimating emissions from, for example, business class. Always include data that is as accurate as possible, such as passenger kilometers, flight class, and load factor.

4. Be transparent in your reporting

We recommend that you always report:

• carbon dioxide emissions and emissions that also include nitrogen oxides, water vapor, soot particles, and contrails,
• which RFI factor is used,
• what assumptions have been made,
• which parts of the value chain are included.

This creates credibility and shows that your company takes its sustainability reporting seriously.

5. Choose your travel agency carefully

Many suppliers report without any RFI factor or upstream emissions. Therefore, your own calculations should be made where possible – or additions made where data is missing.

ZeroMission guides you when more details are needed

For strategic decisions, such as optimizing travel policies or comparing airlines, more detailed data sources may be needed. ZeroMission is happy to ZeroMission choose the right method and quality-assure your calculations.

Making accurate climate calculations for aviation is not difficult – but it does require a conscious approach. With the right support, the results will be both reliable and useful for governance and goal setting.

Get in touch if you would like us to help you further!