Could the world be on the brink of a new, cleaner era of aviation? That’s certainly what you might think from the way some people are talking.
Mandates for blending so-called Sustainable Aviation Fuel into jet kerosene form one plank of the European Union’s recently announced plans to reduce emissions 55% by 2030. The technology will be key to airlines’ ambitions to get to net zero by mid-century, according to a study by the World Economic Forum. Airbus SE has released dazzling concept designs for three zero-emission aircraft, and plans to devote five years to studying the idea before deciding whether to spend money developing a commercial version.
The feeling of progress toward eliminating air travel’s carbon footprint is no doubt valuable to the sorts of affluent, globally aware customers on whom the industry depends. There’s a reason airlines were some of the earliest and most important sellers of carbon offsets to consumers — though the environmental benefits from such products are often patchy at best.
Unfortunately, the truth is that mitigating emissions from aircraft is one of the most challenging areas the world will face over the coming decades. In power generation, road transport, steel, chemicals and shipping, there are genuine breakthrough technologies such as wind, solar, batteries and green hydrogen which could sharply reduce or even eliminate carbon. Aviation’s best alternative technologies are far more incremental, and each have substantial barriers to adoption.
Take Sustainable Aviation Fuel, or SAF. The vegetable oils that we use in cooking and cosmetics are chemically not all that different from the hydrocarbon chains derived from petroleum. Blending a mix of up to 50% biofuel into an aircraft’s tanks doesn’t even normally require any change in the basic technology. SAFs already comprise about 0.1% of the jet fuel market, and data providers S&P Global Platts and Argus Media last year started publishing regular prices.
However, it’s hard to see how SAFs will more than nibble at the edges of the aviation industry’s emissions. For one thing, they’re four or five times more expensive, and fuel already comprises about a quarter of airlines’ costs. That’s quite different from renewables and electric vehicles, which are at or below cost parity with conventional alternatives.
Supply is a further problem. The world’s agricultural land is struggling to meet burgeoning demand for household fats as it is, with palm oil prices rising to a record of 4,506 Malaysian ringgit ($1,066) per metric ton in May. To meet half of 2019’s 300 million tons of jet fuel demand with palm (by far the cheapest as well as most productive commercial vegetable oil, in terms of tons per hectare) would require nearly three times the present area planted for large-scale cultivation. It’ll be even harder in the future: Aviation fuel demand is likely to rise threefold by 2050.
Finally, there’s the question of how much carbon such measures really mitigate. Once you account for processing and the effects of turning virgin land into farms, biofuel produced from Southeast Asian palm oil and US corn often has a larger footprint than the fossil-based equivalent, according to a study by the International Council on Clean Transportation. Some other biofuels offer more substantial benefits, but none are close to being commercialized on a sufficient scale. Under the aviation industry’s standard for SAF, a product only needs to offer a 10% improvement in emissions relative to petroleum for it to count as sustainable. That's not all that much better than the savings of 5% or so you'd get from reducing drag with improved wingtips.
There are other technologies on the horizon, too, but it’s unclear whether any will be viable. Kerosene stores more than 40 times as much energy per kilogram as the best lithium-ion cells, so a battery sufficient to provide the same power as the fuel tank on seven-seater jets like the Cessna Citation M2 would weigh about as much as a 180-seat Airbus A320 fully laden with fuel and passengers. 1 That’s unlikely to work in anything other than niche applications.
Hydrogen easily outperforms kerosene in terms of mass density, but it takes up a lot of space, too. Current models of aircraft would need to be completely redesigned, with fuel going in the fuselage instead of the wings, meaning less space for passengers and cargo and a wholesale rethink of the economics of the plane. There’s also the issue of customer acceptance: The paired concepts of “aviation” and “hydrogen” inevitably evoke images of the Hindenburg airship exploding over New Jersey in 1937.
To be sure, it’s possible that all or a combination of these will be able to chip away at the edges. Batteries may not have the power to manage take-off and landing, but a hybrid plane using electrical power in cruising flight might reduce the carbon footprint somewhat. Hydrogen’s weight savings could make it attractive enough to be worth going back to the drawing board on aircraft design — but it can take three decades just to develop a new conventional jet engine, so we’re not likely to see that sort of change until many years into the future.
That’s not reassuring. For all that the airline industry wants to hold out the promise of a pathway to net zero, it has no real idea of how it’s going to get there. Mitigation options at the moment offer no more than marginal benefits, which will be overwhelmed by the enormous growth in demand as more of the world becomes affluent enough to fly.
The current desperate state of aviation — hobbled by border closures and with much of the industry teetering on the edge of insolvency — is almost certainly the best it will be in climate terms for a generation. The way to make your air travel habit more sustainable once lockdown ends is brutally simple: Fly less, and hope others do the same.
Bloomberg
