Air Emissions Compared
Air Emissions
The world of flight carbon offset calculations alone is not a simple one. Calculating carbon emissions from flying involves many factors. From direct CO2 emissions to contrail-forming, all factors have an environmental impact in their own way.
Europe Aviation Traffic - March 2019 vs 2020
Credit: Eamonn Brennan @eurocontrolDG
Air Emissions Compared
When calculating a selection of return economy class trips for one (1) traveller, the following examples highlight the vast differences in carbon emission calculations.
Amsterdam (AMS) to New York City (JFK)
3,643 mi | 5863 km | 3166 nm
 | |
Organisation | Methodology | CO2 (tonnes) |
|---|---|
0.692 | |
0.95 | |
1.72 | |
1.9 | |
1.75 | |
Kudos with Thrust Carbon | 0.822 |
New York City (JFK) to San Francisco (SFO)
2586 mi | 4162 km | 2247 nm
 | |
Organisation | Methodology | CO2 (tonnes) |
|---|---|
0.594 | |
0.80 | |
1.22 | |
1.4 | |
1.24 | |
Kudos with Thrust Carbon | 0.584 |
Los Angeles (LAX) to Hong Kong (HKG)
7260 mi | 11684 km | 6309 nm
 | |
Organisation | Methodology | CO2 (tonnes) |
|---|---|
0.882 | |
1.88 | |
3.43 | |
3.9 | |
3.49 | |
Kudos with Thrust Carbon | 1.640 |
Sydney (SYD) to Melbourne (MEL)
439 mi | 706 km | 381 nm
 | |
Organisation | Methodology | CO2 (tonnes) |
|---|---|
0.141 | |
0.22 | |
0.28 | |
0.350 | |
0.22 | |
Kudos with Thrust Carbon | 0.106 |
Other factors such as airline and aircraft type if included, may impact the results
DEFRA - Department for Environment, Food & Rural Affairs (UK Government)
What is Radiative Forcing (RF) for air travel?
Radiative Forcing (RF) is a change in the balance of solar and terrestrial radiation in the Earth’s atmosphere (ICAO). Aviation contributes to climate change by increasing atmospheric radiative forcing through the emission of gases and aerosols and changing cloud abundance. This has a higher impact than only emitting CO2 from the ground. This is why a multiplier needs to be taken into account.
DEFRA states “Organisations should include the influence of radiative forcing RF in air travel emissions to capture the maximum climate impact of their travel habits. However, it should be noted that there is very significant scientific uncertainty around the magnitude of the additional environmental impacts of aviation.”.
Conclusion
While it is disappointing that carbon emission calculations vary currently with the lack of one (1) standard in addition to a less mature state for non-air (e.g. hotels, car rentals), our partnership with Thrust Carbon aims to provide data that is as accurate and fair for the environment as possible.
Limitations of Data
Not all fleets are homogenous
These calculations are probably most valid for airlines with a modern fleet of aircraft. These might be less accurate for airlines that have an older fleet and thus have higher offset factors.
Incorrect RF
There is uncertainty about the right radiative factor. Depending on the study reviewed, a Radiative Forcing Index (RFI) of anywhere between 1.2 and 4.7 is appropriate. The RFI for aviation emissions was estimated by the Intergovernmental Panel on Climate Change (IPCC) to be 2.7 with an uncertainty of ±1.5 (1999). In other words, the IPCC estimated that the total RF of aviation was 2.7 times that of just CO2 emissions from aviation. When the IPCC estimates were updated, RFI was calculated to be approximately 2 (Sausen et al., 2005). This estimate is in the same order as the UK Government (DEFRA).
Direct flights that actually aren’t
A flight such as Amsterdam (AMS) to Jakarta (CGK) while presented as a direct flight does make a stop for refuelling in Singapore (SIN). This divides the overall flight into long-haul and short-haul flights that can impact the carbon emission factor. Since we are limited to having data about such “direct” flights with stops, this factor is not yet fully accurate.