Iran Air aircraft

Aviation could consume one-sixth of remaining ‘temperature budget’

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A major new study has found that aviation’s present contribution to anthropogenic global warming is 4 per cent and is set to increase to 2050, should pre-pandemic growth resume, potentially consuming up to one-sixth of the remaining temperature budget to limit warming to 1.5°C.

The study suggests that emissions produced by the aviation industry must be reduced every year if the sector’s emissions are not to aggravate warming further.

Aviation is widely recognised as a hard to abate sector, along with shipping, construction and steelmaking. Although research efforts are underway to develop sustainable aviation fuels (SAFs), hydrogen-powered aircraft and electric aircraft, these all remain in early stages and it is highly unlikely that the sector will be able to reduce emissions as quickly as other sectors. The study set out to inform the discussion about aviation’s 'fair share' of future warming.

Researchers from 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 historic aviation emissions, including both CO2 and non-CO2 impacts. It also forecasts future warming due to the sector, based on a range of possible responses to climate change.

The aviation industry has only recently begun to tackle the warming effect of flying; this study is timely for quantifying that impact. The solutions discussed, such as moving to alternative fuels, present a clear pathway to minimising 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 tinkering - where aircraft carry more fuel than they need, and hence burn extra fuel, to save the cost of refuelling 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 minimising holding patterns at airports would also reduce emissions and help keep future warming minimal.

The study concluded that, when accounting for more than just its carbon footprint, it could consume up to a sixth of the remaining temperature budget required to limit warming to 1.5˚C by 2050, in line with the 2015 Paris Agreement.

“Our results show that aviation’s contribution to warming so far is approximately four per cent and is increasing,” said PhD candidate Milan Klöwer, lead author of the study. “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 study found that the only way the sector can 'freeze' its contribution to warming is to strongly cut its CO2 emissions by 2.5 per cent yearly. Ensuring a 90 per cent mix of low-carbon SAF by 2050 would achieve something close to this, with no further temperature increases from the sector. However, this relies on a sustainable production chain of SAF that does not yet exist. “The aviation industry has to come up with a credible plan for a 1.5°C world,” said Klöwer.

The University of Oxford’s Professor Myles Allen, co-author of the study, said: “Any growth in aviation emissions has a disproportionate impact, causing lots of warming, but any decline also has a disproportionate impact in the other direction. The good news is that we don’t actually need to stop all 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.”

Professor David Lee of Manchester Metropolitan University, another co-author of the study, added: “These are important results that show stylised 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 SAFs that generate fewer contrails. This emphasises the importance of tackling aviation’s CO2 emissions.”

In September, Royal Dutch Shell announced its intention to produce two million tonnes of sustainable aviation fuel (SAF) by 2025, which would mark a ten-fold increase from current global output of SAF. 

The research paper - 'Quantifying aviation's contribution to global warming' - has been published in the journal Environment Research Letters.

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