Global Aviation CO₂ Emissions

Introduction

Fig. 1: Commercial aviation. (Source: Wikimedia Commons)

Aviation (pictured in Fig. 1) represents a significant global economic activity that fills the societal need for mobility. [1] At the same time, its CO₂ emissions contribute to anthropogenic climate change. [2] This issue has motivated the development of policies seeking to lessen the severity of aviation's climate effects. [2,3] In order to make more informed policy decisions that achieve this goal, we must quantitatively understand aviation's global CO₂ emissions, which this report will clarify.

Analysis

We will start by calculating the total fuel consumption from global aviation. To do this, we will multiply the number of passenger-kilometers from global aviation by the average fuel consumption per passenger-kilometer of a jet. The number of passenger-kilometers from global aviation in 2018 has been reported as 8.3 trillion. [4] The average fuel consumption (in MJ) per passenger- kilometer of a jet has been estimated as 1.59, 1.58, and 1.55, so we will round this value to 1.6 MJ per passenger-kilometer for our calculation. [5-7] Given these two numbers, we find that the total fuel consumption in 2018 equals 1.33 × 10¹⁹ J. To convert this to amount of CO₂ emitted, we divide total fuel consumption by the energy density of jet fuel, 4.2 × 10⁷ J/kg, and then multiply the resulting quantity by 44/14 (the ratio of the molar mass of CO₂ to that of oil). Thus, we find that 9.94 × 10¹¹ kg (994 Mt) of CO₂ was emitted in 2018.

In parallel with this calculation, let us perform a cross check on the amount of fuel used per passenger-kilometer. Specifically, we will divide the total amount of kerosene consumed in the United States by the total number of passenger-kilometers in the U.S. According to the Energy Information Administration (EIA), 6.23 × 10⁸ barrels of kerosene-type jet fuel were supplied in 2018. [8] To express this quantity in energy units, we convert to kilograms at 136 kg/bbl and then multiply by the jet fuel energy density of 4.2 × 10⁷ J/kg. We find that 3.36 × 10¹⁸ J of jet fuel was consumed in 2018 in the United States. We then divide this value by 1.16 × 10¹² passenger-kilometers, which is the total number of passenger-kilometers from 2018 U.S. aviation. [9] This gives us 2.9 MJ per passenger-kilometer. With this value, which disagrees with the reported average fuel consumption values mentioned earlier by about a factor of 2, we find that around 1800 Mt of CO₂ was emitted in 2018.

Finally, let us take an alternative approach in determining global aviation CO₂ emissions by computing the ratio of the amount of jet fuel delivered per year to the amount of oil consumed per year in the U.S. and then applying this ratio to the global oil budget. Based on EIA data, this ratio is equal to 623,061 (thousand barrels of jet fuel) divided by 7,484,140 (thousand barrels of oil), or 0.083. [8] The oil part of the 2018 world energy budget is 1.9 × 10²⁰ J. [10] So, we obtain a global jet fuel consumption of 1.6 × 10¹⁹ J in 2018, or equivalently, we find that global CO₂ emissions in 2018 roughly equal 1200 Mt.

Conclusion

We have employed several different approaches to calculate multiple values of global aviation's 2018 CO₂ emissions: 994 Mt, 1800 Mt, and 1200 Mt. It is worth noting that the value reported in references [2,3] is 1034 Mt, which falls in the range of total emissions we have found.

© Ajay Ravi. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] V. Grewe et al., "Evaluating the Climate Impact of Aviation Emission Scenarios Towards the Paris Agreement Including COVID-19 Effects," Nat. Commun. 12, 3841 (2021).

[2] D. S. Lee et al., "The Contribution of Global Aviation to Anthropogenic Climate Forcing for 2000 to 2018," Atmos. Environ. 244, 117834 (2021).

[3] S. Gössling and A. Humpe, "The Global Scale, Distribution and Growth of Aviation: Implications for Climate Change," Glob. Environ. Change 65, 102194 (2020).

[4] L. Zhang et al., "Measuring Imported Case Risk of COVID-19 From Inbound International Flights - A Case Study on China," J. Air Transp. Manag. 89, 101918 (2020).

[5] B. Cushman-Roisin and B. T. Cremonini, Data, Statistics, and Useful Numbers for Environmental Sustainability: Bringing the Numbers to Life (Elsevier, 2021).

[6] K. Forinash, Physics and the Environment (IOP Concise Physics, 2017).

[7] A. Benito and G. Alonso, Energy Efficiency in Air Transportation, 1st Ed. (Butterworth-Heinemann, 2018).

[8] "Petroleum Supply Annual, Vol. 1," U.S. Energy Information Administration, August 2022, Table 1.

[9] "National Transportation Statistics 2021," U.S. Bureau of Transportation, 2021, Table 1-40.

[10] "BP Statistical Review of World Energy 2022," British Petroleum, June 2022.