The Climate Footprint of Airtravel

Airplane Window

The aviation section of the CORE website highlights the key factors that have to be taken into account when calculating air travel emissions for the purpose of climate footprint and offset calculations.

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How should the effect on climate change from air travel be calculated so that an individual or a company can accurately calculate the climate footprint of their current air travel?

Companies and individuals are increasingly interested in calculating and minimizing their climate footprint*.  Although aviation emissions are small** when compared to other sectors of the economy, air travel can contribute a significant proportion of an individual’s climate footprint.

For example, the average European emits about 11 tons of CO2 per year. If a European takes one transatlantic round-trip flight, say from Frankfurt to New York, they will add 0.8 – 2 metric tons*** of CO2 (excluding non-CO2 effects) to their climate footprint.

It is important to have an accurate metric to calculate the climate impacts of air travel. Yet calculating air travel’s impact on climate change is a complex task, and the currently available air travel calculator estimates can vary by up to a factor of three. There are two separate issues that have to be taken into account when calculating the climate footprint of an individual air passenger:

1. Total Climate Effects from Aviation:

In order to estimate the full effect of aviation on climate change, it is necessary to account for CO2 as well as for all other, non-CO2 warming effects.

The non-CO2 warming effects of aviation are most commonly accounted for in emissions calculators through a Radiative Forcing Index (RFI) or a multiplier. These terms refer to a dimensionless factor which is multiplied by the calculated CO2 emissions in order to account for all warming effects.

The multipliers used by different calculators lie between 1 (i.e. not accounting for non-CO2 warming effects) and 3 (i.e. the total warming effect is calculated at three times that of the CO2 emissions alone). These numbers are usually chosen in reference to the IPCC special report on aviation (IPCC, 1999). Unfortunately, these multipliers are often scientifically flawed. These webpages seeks to explain why.

The first few section of this site explain to a non-technical audience what these non-CO2 warming effects are, how they can be measured and incorporated into aviation climate calculators: First, we explain in a general way how scientists measure climate impacts. Then we introduce all the different greenhouse gases due to air travel that contribute to climate change. We then discuss the advantages and the short comings of several metrics that have been used to account for the full climate impact of air travel. We conclude with our recommendations.

These sections are closely based on the SEI Discussion Paper:
Carbon Offsetting & Air Travel Part 2: Non-CO2 Emissions Calculations (pdf)
All references have been removed from the webpages and can be found in the paper.

2. Flight Parameters:

In order to assign to each passenger the CO2 emissions they are responsible for, the aircraft parameters that are needed to calculate CO2 emissions on a per person basis have to be examined.

The flight parameter section the website looks at the following parameters: Aircraft Model, Flight Profile and Flight Distance, Cargo on Passenger Flights, Seat Occupancy Rate (Load Factor), Seat Class.

These sections are closely based on the SEI Discussion Paper:
Carbon Offsetting & Air Travel Part 1: CO2-Emissions Calculations (pdf)
All references have been removed from the webpages and can be found in the paper.

For an excellent but more technical update on the various scientific issues involving aviation and climate change, please see the US Federal Aviation Administration's Aviation Climate Change Research Initiative (ACCRI) papers.

For more resources and links, go here.

This website is maintained by the Stockholm Environment's CORE team. Learn more about CORE. We welcome comments and input:

We would like to thank Dietrich Brockhagen, Robert Elleman, David Fahey, Melanie Fitzpatrick, Jan Fuglestvedt, Sivan Kartha, Eric Kemp-Benedict, Dorothy Koch, Jessica Lane, Karen Marais, John Putnam, Thomas Tomosky, Andrew Tron, Mary Vigilante, and Ian Waitz for their comments, edits and suggestions.

*Climate footprint: Usually an individual’s or a company’s contribution to climate change is called their ‘carbon footprint.’ This is slightly misleading because, as we discuss in this paper, carbon dioxide (CO2) is just one of many greenhouse gases that have an impact on the climate.  To include the impact of all greenhouse gases, we use the term ‘climate footprint.’

**Aviation emissions: Aviation currently accounts for approximately 2-5% of total carbon dioxide (CO2) emissions and approximately 13% of all transportation related CO2 emissions (IPCC, 1999). If non-CO2 warming effects are included, the contribution of aviation to global climate change is even larger. Yet civil aviation is growing rapidly at 5.9% per year (IPCC 2007: Mitigation of Climate Change, p. 334; ICAO, 2007). This is faster than any other mode of transportation (WBCSD 2002), and the sector’s contribution to climate change will therefore continue to increase.

***Return Flight Frankfurt to New York: Estimated emissions depend on among other things on the type of airplane, occupancy rate and seat class. See our first paper for details.