In our new Synergy column, Cosmos writers explore how we’re dealing with the urgent issues of climate change.
In 2019, Greta Thunberg crossed the Atlantic by boat to attend a climate summit in New York, her action bringing the Swedish concept flygskam or ‘flight shame’ into the mainstream.
Instead of a 9-hour flight, the activist opted for a 2-week journey, in sometimes choppy seas, by solar and wind-powered yacht to avoid the greenhouse emissions caused when airplanes burn jet fuel.
That same year, environmentalist David Suzuki renounced all flying for similar reasons, except in cases of family emergency. Now when he speaks to overseas audiences, he joins via digital conferencing platform from his cabin on a small island in British Columbia.
Flying is an energy and emission-intensive way to travel.
Globally, domestic and international aviation contributes about a gigatonne of global greenhouse gas emissions (based on pre-COVID figures) – roughly double Australia’s national emissions.
Despite a fleeting pandemic drop, flights (and their accompanying emissions) have already rebounded to about 80% of their pre-COVID levels.
Passenger transport – business trips and tourism (which Imma Perfetto recently explored) – makes up 81% of aviation emissions, according to the US-based Environmental and Energy Study Institute. Air lifting freight contributes the remainder.
But does reducing fossil fuels really demand giving up on business travel and international jaunts? Or, can emerging zero emission technologies lift off in time to keep aviation afloat?
Signs of turbulence ahead
The International Energy Agency (IEA) has mapped future scenarios for technology uptake and behaviour changes needed to reach net zero emissions by 2050, in line with climate targets.
One of its energy modellers, Apostolos Petropoulos, says “aviation, while contributing a relatively small share of global emissions, presents significant challenges for decarbonisation”.
Aviation presents significant challenges for decarbonisationApostolos Petropoulos, IEA energy modeller
The IEA’s modelling highlights the difficulty of tackling aviation emissions, particularly as demand for flights – for business, leisure and freight – continues to grow.
Other sectors like electricity and land-based transport reduce their emissions with greater ease thanks to competitive, off-the-shelf technologies – renewable energy, energy efficiency, electrification and energy storage.
Meanwhile, aviation’s contribution to global energy-related emissions is expected to lift from about 2% today to 4% by 2030. By 2050, air travel is expected to make up nearly a third of remaining energy-related carbon dioxide (CO2) emissions, Petropoulos says.
Unfortunately for frequent fliers, aviation’s climate impact isn’t limited to the CO2 produced by burning jet fuel.
While up in the air, planes also emit sulphate and soot particles, water vapour, nitrous oxides and contrails at high altitudes. According to the International Panel on Climate Change (IPCC), these other pollutants also affect planetary warming and cooling by tinkering with aerosols, clouds and the atmosphere.
Overall, the combination of these effects results in more bad news: the IPCC estimates the added warming effect, called radiative forcing, non-CO2 emissions cause could more than double the climate impact of aviation’s CO2 emissions alone.
Nations are grounding their emissions
The IEA views behaviour changes – like some are considering – as a crucial lever to reduce aviation activity and emissions.
“This includes a reduction of short-haul flights when a direct high-speed train connection is available, a reduction of a part of business long-haul flights with teleconferencing, and a reduction of leisure flights due to a frequent flyer levy, the latter one being the measure having the biggest impact,” Petropoulos says.
Flying is an energy and emission-intensive way to travel.
Achieving net zero emissions, under the IEA’s scenario, means replacing flights with train trips and capping business flights (which today make up a quarter of air travel) and long-haul leisure flights at 2019 levels.
Petropoulos says behavioural change can lead to a reduction of over 20% in total aviation activity in 2050 and some countries are already making moves in that direction.
Last year France became the first place to ban flights between cities in favour of regular, fast and efficient train services, on routes where a suitable intercity rail service exists.
Professor Peter Newman, coordinating IPCC lead author for transport and an expert in transport and sustainability at Curtin University, believes other countries will soon follow France’s lead, with a second rail revolution underway; China, India and Europe have been choofing ahead modernising and expanding their rail systems as well.
The chase for electric dreams
Aviation isn’t just about moving people. Parcels and goods get moved as well.
And whether for human mobility or commerce, some hope electrified aviation, the light aircraft and battery-based copters that some colloquially call ‘flying cars’ or ‘air taxis’, will take off.
The Australian Government anticipates emerging aviation technologies like drones could triple aircraft movements in urban areas.
Professor Rico Merkert, an expert in transport economics at the University of Sydney, says in short haul and regional applications electrifying aircraft might be a viable option, and one Australian regional airline Rex will begin trialling this year.
Batteries are very heavyProfessor Rico Mercert, University of Sydney
Merkert says electric aviation, whether in the form of drones, electric vertical take-off and landing (eVTOL) or electric short take-off and landing (eSTOL) craft could also be a good thing in terms of climate change, provided they use renewable energy.
But it remains to be seen if the technology can slash emissions, given many air taxi proposals are targeted at replacing land-based transport options or adding a new travel mode into the mix, rather than serving as an alternative to jet-fuelled aircraft.
And proponents are also dealing with real world concerns of regulation, planning, safety, noise and community expectations. RMIT researchers publishing in Drones say companies need to navigate greater turbulence and collision risks caused by high-rise buildings and infrastructure in urban environments.
A complete fuel switch is essential for the future
Sadly, those holding out hope for electrified long-haul flights will need to pair that with a healthy dose of reality. Electric-powered flight is unlikely to be an alternative any time soon. The main reason, says Merkert, is a mundane one.
“Those batteries are very heavy.”
So, do we all need swear off flying like Thunburg and resign ourselves to our cabins like Suzuki?
While battery-powered flights might be a long shot for interstate or international trips, there is some hope in sustainable aviation fuels made from non-fossil fuel feedstocks – food and organic wastes, agricultural or forestry residues, biomass and other sources.
Do we all need swear off flying like Thunburg and resign ourselves to our cabins like Suzuki?
Right now, the IEA says these sustainable fuels constitute less than 0.01% of aviation energy use, but the sector will rely on biofuels or synthetic fuels to meet climate goals.
To be on the flight path to net zero, the IEA says half of jet fuels in 2040 need to be low emission alternatives, rising to almost 80% by 2050.
Although some airlines have started mixing small percentages into their jet fuel, it’s not at levels to meaningfully dent emissions. It’s also expensive – at least 3 times more expensive than conventional carbon-based fuels, Merkert says.
He adds that green hydrogen, an energy intensive fuel made using large amounts of renewable electricity, still has numerous engineering challenges to overcome, though it might be an option in the longer term.
While there are some viable options on the runway – alternative travel by land, sea or online, emerging aircraft technologies and new fuels – solving aviation emissions is likely to require long haul effort at scale to counter the expected surge in aviation demand.
Businesses and individuals can already choose to stay grounded. But the flight path to net zero will also require restraints and incentives to curb frequent flying, along with policies to increase the production of sustainable fuels, as these are the two most promising options.