A closer look at the role of Sustainable Aviation Fuels (SAFs) in decarbonizing aviation.
As airlines are actively seeking ways to cut down on carbon emissions, they are placing a growing emphasis on alternative fuel technolgoies. While batteries and hydrogen hold much promise, their widespread use for commercial aviation is decades away. However, adopting sustainable aviation fuels (SAFs) is a quickly available means to carbon reduction. The aviation industry has committed to achieving net-zero by 2050, meaning the industry aims to remove as much CO2 from the atmosphere as it emits. Climate advocates and industry insiders are promoting SAFs as a practical means of quickly attaining this ambitious target.
The aviation industry is currently responsible for 2.5 percent of global CO2 emissions, and it’s betting that SAFs are a quick means to pare that percentage down. SAFs are an alternative to traditional petroleum-based jet fuel, and are typically composed of organic materials or waste leftover from other production processes. While other technologies such as batteries and hydrogen can provide even great carbon reduction, those technologies require major aircraft redesign and re-certification challenges: new technologies must comply with Aerospace Recommended Practice ARP4761A which great increases cost and deployment times.
Biofuels used to power aircraft are often produced via oils extracted from crops, such as soybean and corn, but they can also come from household and municipal waste. However, the sources and processes that go into producing SAFs are not necessarily sustainable themselves, which means developing these fuels can still contribute to climate change.
While airlines are touting SAFs as a way to rein in aviation emissions, the estimates that they provide for reductions are anything but precise: somewhere between 40 to 90 percent. Moreover, SAFs are rather expensive and production thus far is limited. With such wildly variable estimates, it seems there is still a long way to go with scaling and understanding SAFs. The feasibility of SAFs as a climate change panacea remains to be seen.
For years, we’ve heard that carbon offsets were the way of the future. Instead of investing actively in decarbonization technologies, airlines essentially took a relatively passive approach, trying to maintain their current level of emissions while compensating for it elsewhere.
Under carbon offsetting schemes, for every ton of CO2 that airlines emit, they pay to preserve a piece of rainforest or stop a form of pollution that theoretically “offsets” the emissions. The idea is basically: you pollute here, but you plant there, and one cancels out the other. However, it’s becoming increasingly clear that carbon offsets are ineffective at best and an outright scam at worst.
So now, airlines are pursuing alternatives for decarbonizing and reaching net-zero emissions. However, the process will not come cheap. McKinsey estimated that decarbonizing aviation would require $175 billion in investments – each year – until 2050, which is almost $5 trillion in total. The study also found that bringing aviation on a path to net-zero emissions by 2050 requires a doubling of current aircraft fuel efficiency gains and a unworkably rapid roll-out of SAFs.
So, it seems that SAFs are going to be too expensive and too difficult to produce to achieve the kind of reduction that the airlines are hoping for.
Are SAFs Really Sustainable?
The sustainability of SAFs depends on how land and resources are used to cultivate feedstocks – the raw materials used to create SAFs. Environmental advocates warn that SAFs may potentially contribute to biodiversity loss and deforestation if large areas of land are dedicated to feedstock production, such as growing corn to be used as a biofuel. Fortunately, SAFs are similar enough to regular aviation fuel that total recertification of aircraft engines is not required; this means redesigning engines per ARP4754B is not required.
Growing, producing, and transporting SAFs all has an environmental impact, though the overall carbon footprint is still significantly lower than that of fossil fuels. However, even if the feedstocks are grown or produced sustainably, the conversion process of organic matter into biofuels is inefficient and energetically costly. All of this is why scientists often refer to ”lifecycle emissions” to assess the complete impact of SAFs. This calculates all the resources and emissions associated with the production, transport, and burning of SAFs.
It’s also important to note that, when SAFs are actually used as fuel, they have comparable emissions to fossil fuels. Consequently, aircraft are still burning organic matter and releasing CO2. Since the emissions from the combustion of SAFs are similar to fossil-based jet fuels, the majority of the reductions in greenhouse gas savings originate from the production process, which, again, are limited. But again, despite concerns over deforestation and biodiversity loss associated with agriculture, SAFs have a marginal production impact compared to the extraction and refinement of fossil fuels.
So while SAFs have the potential to reduce the carbon footprint of aviation, careful reconsideration of feedstock selection, production processes, and adherence to sustainability criteria is essential to realize their environmental benefits.
Because of the limitation of SAFs, aviation innovators are also putting forward other solutions to decarbonizing the sector. Electric vertical takeoff and landing (eVTOL) aircraft, which are electric-powered as opposed to fuel-based, are one proposed alternative. However, batteries are not particularly sustainable either, relying on precious metals often sourced from conflict zones. Moreover, eVTOL aircraft won’t be able to fly long haul for at least another decade or so.
In reality, there is no perfect solution to decarbonizing aviation. It will take myriad solutions including advances in technology, more fuel-efficient aircraft, and political will to meaningfully reduce emissions. Otherwise, net-zero 2050 will remain a pipe dream.
About the Author
Hilderman has trained over 31,000 engineers in over 700 aviation companies and 30+ countries. His intellectual property is in use by 70% of the world’s top 300 aviation and systems developers worldwide, and he has employed and personally presided over 500 of the world’s foremost aviation engineers on 300+ projects the past thirty-five years.
AFuzion’s solutions are on 90% of the aircraft developed over the past three decades. His latest book, Aviation Development Ecosystem, debuted at #1 on the Aviation category best-seller list.