Irish Times, June 6th 2024 - link

After a brief hiatus during the pandemic, flying is back with a bang. Nearly 40 million people used Irish airports in 2023, the highest number on record, causing Ireland’s consumption of jet kerosene to soar by 15 per cent. This brings its annual greenhouse gas emissions back to the historically high levels seen just before the pandemic.

Since 1990 Ireland’s population has grown by 44 per cent but emissions from aviation increased by 500 per cent.

Flying is one of the most carbon-intensive activities. It takes an enormous amount of jet kerosene to lift an aeroplane 10km into the air and propel it across countries, oceans and continents. A jumbo jet burns more than 10 tonnes of fuel each hour. One return transatlantic flight can wipe out the entire carbon savings someone might have made from making their diet or transport habits more sustainable.

Aviation accounts for 2.5 per cent of global carbon dioxide emissions, a figure that rises to 4 per cent when the warming impact of contrails and other factors are accounted for. The responsibility is highly unequal: Only 1 per cent of the global population is estimated to cause half of its emissions, as a very small share of people fly regularly. One study estimated that only 11 per cent of the global population flew in 2018, and only 4 per cent flew internationally. But this figure is set to rise with the growing global appetite for flying.

Ireland is no exception. DAA, the commercial semistate company that owns and operates Dublin Airport and Cork Airport, is leading the call for expanding airport capacity. Its annual report paints an optimistic picture for sustainability: carbon emissions in DAA airports fell by 22 per cent against the baseline values across 2016-2018, which contradicts the trend suggested by jet fuel consumption

Moreover, in response to a sit-in by group Mothers’ Rebellion protesting the climate impact of planned airport expansion, DAA listed its investments in sustainability initiatives and highlighted its target to reduce its carbon emissions by 51 per cent by 2030.

The tension lies in the fact that DAA is only counting emissions from ground operations, not from burning jet fuel in the planes themselves. But the vast majority of aviation’s climate impact is from the plane, not the airport. DAA’s own planning documents show that lifting the passenger cap will increase emissions by 22 per cent by 2031, around 750,000 tonnes. Sustainability initiatives at the airport can’t come close to offsetting this.

Claims that emissions can fall while flights grow is not backed by evidence. New technological solutions to replace jet kerosene are still far off and are likely to come at a very high cost. Aviation is considered one of the most difficult and costly sectors to decarbonise.

Sustainable aviation fuel (SAF), a potential replacement for jet kerosene, could either be made from biofuels, such as crops or waste, or so-called e-fuels, where carbon captured from the atmosphere is reacted with hydrogen generated from renewable electricity, such as from wind power and solar farms. But both options come with significant downsides.

A report by the Royal Society calculated that more than half of the UK’s agricultural land area would be required to grow crops to replace all its jet fuel, which is clearly not feasible. Much attention has been paid to the prospect of converting waste cooking oil to jet fuel, which is appealing in theory. But the same report estimates that only 0.6 per cent of jet fuel could be replaced by this resource.

Converting renewable electricity to an e-fuel would be extremely energy intensive. According to the Royal Society report, between five and eight times the UK’s renewable capacity in 2020 would be necessary to generate enough electricity.

Any of these options will significantly increase the cost of flying. A new paper by my colleagues in UCC and others shows that e-fuels would add hundreds of euro to the ticket price of intercontinental flights for economy seating, and several thousand for premium seats.

The crux of the issue is that the climate cost of flying is not factored into the ticket price, making it artificially cheap. Jet kerosene is not even subject to excise duty or VAT. If the price of flying did factor in these costs, it is highly unlikely that the demand for flights would grow to the extent forecasted by airlines and airports.

What would flying look like if we really took climate action seriously? I expect that travel would become slower and more conscious. Now, 26 per cent of trips from Dublin Airport are for three nights or less. Rail and sail options could certainly be improved: one-third of passengers fly to the UK.

Solutions to decarbonise aviation may emerge but they will likely come with a high cost. Expanding airports on the basis that the era of cheap flying will last forever is severely misguided.