Aviation’s present-day contribution to human-induced global warming is 4% and is likely to increase over the next 30 years
It is possible that, though the global heating impact of aviation so far has been about 4%, this could make up about one-sixth (about 16%) of the remaining temperature budget required to limit global warming to 1.5˚C by 2050. A recently published article, by a number of well recognised academics, suggests that emissions produced by the aviation industry must be reduced each year if the sector’s emissions are not to increase warming further. The authors show that the only way to ‘freeze’ the temperature increase from the sector is to cut its CO2 emissions by about 2.5% per year. The industry plans extensive growth over coming decades, but the academics say “there is little chance for the aviation industry to meet any climate target if it aims for a return to normal.” There are hopes the low carbon fuels could be found, and also that the non-CO2 impacts of burning jet fuel at high altitude could be cut, by using different fuels, emitting less water.
Aviation’s present-day contribution to human-induced global warming is 4% and will increase over the next 30 years
NOVEMBER 4, 2021
by Institute of Physics
Warming stripes of aviation, showing the percentage contribution to global warming from 1980 to 2021.
Credit: Developed as part of ongoing collaboration with the European Aviation Safety Agency’s environmental work (e.g. ec.europa.eu/transport/sites/default/files/2019-aviation-environmental-report.pdf )
Aviation is responsible for more global warming than implied by its carbon footprint alone. According to new research published today, aviation could consume up one-sixth of the remaining temperature budget required to limit warming to 1.5˚C by 2050.
The article, published in Environmental Research Letters, suggests that emissions produced by the aviation industry must be reduced each year if the sector’s emissions are not to increase warming further.
Given that aviation is widely recognized as a sector which is challenging to decarbonise, this research aims to inform the discussion about aviation’s ‘fair share’ of future warming.
The researchers behind the study, based at the University of Oxford, Manchester Metropolitan University, and the NERC National Centre for Earth Observation, developed a simple technique for quantifying the temperature contribution of historical aviation emissions, including both CO2 and non-CO2 impacts. It also projects future warming due to aviation based on a range of possible solutions to the climate crisis.
Milan Klöwer, lead author of the study said: “Our results show that aviation’s contribution to warming so far is approximately 4% and is increasing. COVID reduced the amount people fly, but there is little chance for the aviation industry to meet any climate target if it aims for a return to normal.”
The authors show that the only way to ‘freeze’ the temperature increase from the sector is to strongly decline CO2 emissions by about 2.5% per year; however, there is room for optimism as they also show that ensuring a 90% mix of low carbon sustainable fuels by 2050 would achieve a similar outcome, with no further temperature increase from the sector. But this relies on a sustainable production chain of low-carbon fuels that does not exist yet, as Milan Klöwer points out. “The aviation industry has to come up with a credible plan for a 1.5˚C world.”
“Any growth in aviation emissions has a disproportionate impact, causing lots of warming”, says Professor Myles Allen, co-author of the study. “But any decline also has a disproportionate impact in the other direction. So the good news is that we don’t actually need to all stop flying immediately to stop aviation from causing further global warming—but we do clearly need a fundamental change in direction now, and radical innovation in the future.”
Co-Author Professor David Lee, Manchester Metropolitan University, adds, “These are important results that show stylized pathways of how we can get to where we need to be with aviation emissions, robustly showing the different roles of CO2 and non-CO2 impacts. One of the important nuances is that the non-CO2 impacts, like the formation of contrails and cloudiness, have been thought to dominate the total impact: this is true at present, but it’s not widely understood in the stakeholder community that if you take care of CO2, the non-CO2 fraction decreases in importance, even more so with sustainable alternative fuels that generate fewer contrails. [Which fuels?] This emphasizes the importance of tackling aviation’s CO2 emissions.”
The aviation industry has only recently begun to tackle the warming effect of flying, and this study is timely for quantifying that impact. The solutions discussed in this study, such as moving to alternative fuels, present a clear pathway to minimizing warming but these will take time to implement. In the short-term, there are actions that the industry can take right now.
Dr. Simon Proud, of the National Centre for Earth Observation and RAL Space, suggests, “A ban on fuel tankering—where aircraft carry more fuel than they need, and hence burn extra fuel, to save the cost of refueling at the destination—would reduce CO2 emissions in Europe alone by almost one million tonnes.” Other solutions, such as more efficient air traffic control and minimizing holding patterns at airports would also reduce emissions and help keep future warming minimal.
Global aviation carbon emissions
There is other data at https://ourworldindata.org/co2-emissions-from-aviation
Global aviation (including domestic and international; passenger and freight) accounts for:
- 1.9% of greenhouse gas emissions (which includes all greenhouse gases, not only CO2)
- 2.5% of CO2 emissions
- 3.5% of ‘effective radiative forcing’ – a closer measure of its impact on warming.
The latter two numbers refer to 2018, and the first to 2016, the latest year for which such data are available.
If the non-CO2 forcing effects are twice those of the CO2 alone, aviation would contribute 5% of the total global heating impact. It is likely to be even higher than this, with a multiplier of more than two.
UK aviation CO2 was 9.4% of UK’s total territorial emissions in 2019
UK aviation CO2 emissions in 2019 were 38.5m tonnes out of total UK CO2 emissions of 409.6m tonnes (including international aviation and shipping) so aviation = 9.4%.
See official Government (BEIS) statistics at 2019 UK Greenhouse Gas Emissions, Final Figures (publishing.service.gov.uk) and final-greenhouse-gas-emissions-tables-2019.xlsx (live.com), Table 1.1 and Table 6.1.
Atmospheric changes from aircraft emissions result from three types of processes:
(i) Direct emission of substances which have a Radiative Forcing (‘RF’) effect (e.g. CO2);
(ii) Emissions that produce or destroy radiatively active substances (e.g. NOx); and
(iii) Emissions that cause aerosol particles and contrails.