Exciting news: soon we will be flying sustainably. Visits to snowy Northern Hemisphere mountains and glaciers could be possible without the sickening sense that we’ve hastened their melting.
Slow down. Aviation still burns a lot of oil. Despite recent news of funding to scrutinise the feasibility of Kiwi-made sustainable aviation fuel, guilt-free flying is far from imminent. That’s according to recent publications co-authored by Robert McLachlan, an applied mathematician at Massey University who specialises in mathematical modelling.
The international aviation industry is aiming for net-zero greenhouse gas emissions by 2050 and last year published Making Net-Zero Aviation Possible, An industry-backed, 1.5°C-aligned transition strategy. It offers mostly techno-fixes: fuel efficiency, sustainable aviation fuel and aircraft powered by batteries or hydrogen.
Rousing publicity accompanies the prospect of electric and hydrogen-powered planes even though they’re predicted to account for only 11% of the 2050 goal. They scarcely feature until 2040 and only tiny electric planes yet exist.
That accords with Sounds Air’s experience. In 2021, it signed a letter of intent to buy three 19-seat e-planes from Heart Aerospace to fly across Cook Strait. None were built. As McLachlan’s calculations revealed, the battery wouldn’t supply enough real-life range.
Sounds Air now awaits hybrid-electric planes. “Who knows where it will end up, but you have to start somewhere and we want to be part of it,” says managing director Andrew Crawford.
Batteries are too heavy to store sufficient energy for large planes. Long-range hydrogen-fuelled planes are promised eventually: Airbus has pushed out delivery of these to 2050. “There are many engineering challenges to solve,” says McLachlan.
The lion’s share of decarbonising is posited to come from sustainable aviation fuels. The most thrilling is e-fuel, created with hydrogen drawn from water and carbon from air. It can replace liquid fossil fuels directly. Building of the first full-scale e-fuel plant will begin next year in Norway.
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But making e-fuel requires double the electricity needed to make hydrogen fuel, which is three times more hungry than charging batteries. McLachlan calculates New Zealand would need 14 (for hydrogen) or 28 times (for e-fuel) the renewable electricity we generate now to produce the required fuel for aviation alone.
Biofuels could help. These are made mostly from materials that could otherwise be food for people or animals, and may eventually be made from woody waste. Aviation has huge energy needs, so even when truly sustainable biofuels come, the cost and huge volume needed for anything but minimal dilution of aviation gas mean it’s at most a partial solution, says McLachlan.
Aeroplane efficiency improvements are likely, but these can be realised only with new planes. But fleets are updated infrequently. What’s more, he says, “efficiency gains have always been swamped by passenger growth”.
Plans for sky-high passenger growth are his main concern, because that’s likely to increase emissions well before solutions materialise. The 2050 strategy envisions passenger numbers doubling. New Zealand’s major airports and airline plan to expand – meaning more planes – and a new Central Otago airport is proposed.
To slow demand for flights, the Parliamentary Commissioner for the Environment recommended a distance-based departure tax. That wouldn’t dent the pockets of the richest 1% of people who create half the aviation emissions globally, but it might prod their consciences – as could replacing frequent-flyer rewards with levies.
A good start, says McLachlan, would be government oversight of airport expansions, and bringing international aviation into the Zero Carbon Act, carbon budgets and the Emissions Trading Scheme. It’s easy to shirk this while international aviation is excluded from global emissions accounting requirements, but that exclusion may soon end.
Another issue that’s shirked by all aviation mitigation policies is aeroplanes’ non-CO₂ warming. This is short-lived warming caused by contrails, and the release of nitrous oxides that alter the upper-atmosphere chemistry of ozone, methane and water vapour in a heat-trapping manner. Including these effects triples the climate effect of flying as it’s now practised.