By Olivia Chang, Life of the Land intern and a fossil fuel divestment organizer with Olin Climate Justice.

Aviation accounts for at least a quarter of Hawaii’s emissions, and more if we account for emissions from international and military flights. The aviation industry is relying heavily on alternative jet fuel (AJF)—what it likes to call “sustainable aviation fuel”—to reach net zero in the next few decades. The industry often claims that AJF can reduce emissions by up to 80%. In reality, emissions vary greatly by feedstock and measurement method, with the most technologically credible alternative jet fuels providing little to no reductions compared to fossil jet fuel.

Most alternative jet fuel is currently produced from first-generation fats, oils, and greases, such as soybean, rapeseed, and palm oil, which—on paper—appear to cut emissions almost in half compared to fossil jet fuel. Cultivating these crops, however, has resulted in devastating environmental, biodiversity, and health impacts. Palm oil production, for example, is associated with numerous human rights abuses and has been a huge driver of deforestation in Indonesia and Malaysia. When high carbon-stock forests, natural lands, or pastures are converted to agriculture to grow energy crops, the disturbed biomass and soil creates indirect emissions, a process known as induced land use change.

Once induced land use change emissions are taken into account, using alternative jet fuel made from virgin fats, oils, and greases provides barely reduces emissions, and actually sometimes even increases emissions compared to fossil fuels. This is not particularly surprising, given that efforts to replace fossil diesel in cars with first-generation biodiesel has only increased overall transport emissions in Europe.

But lifecycle analyses don’t always factor in the emissions caused by induced land use change, and when they do, they often underestimate them. That’s partially because it is difficult to estimate precisely, with emissions generally being estimated through high-uncertainty economic models that estimate changes in global land use in response to increased biofuel demand. Many lifecycle analyses use the GREET emissions model, which has been criticized for relying on a single induced land use change model that assumes some land types sequester (instead of release) carbon when converted to cropland, thus consistently underestimating induced land use change emissions compared to other models [1]. Researchers at the International Council for Clean Transportation have argued that GREET’s use of a single economic model does not reflect the high uncertainty in calculating induced use change emissions. (GREET is, of course, generally preferred by the aviation and biofuels industry).

And lifecycle analysis models do not take into account displacement emissions—when the use of low-supply feedstocks for AJF diverts supply from other sectors, forcing those sectors to use alternative sources in their place. For example, lifecycle analysis models generally treat palm fatty acid distillates (PFAD), a byproduct of palm oil production, as a waste, and therefore assume zero upstream emissions prior to its collection. However, supply of PFAD is limited and is used by the oleochemical industry to produce candles, soap, and animal feed. If the supply of PFAD was diverted to produce alternative jet fuel, the oleochemical industry would be forced to use palm oil as a replacement for PFAD, meaning that emissions would simply move from one sector to the other.

Other biofuels are inherently limited in supply

Possibly in recognition of the social license risk of palm oil, airlines have instead advertised jet fuel made from waste streams (2nd-generation biofuels), such as used cooking oil, forestry residues, and municipal solid waste. Since feedstocks that are truly wastes do not have upstream emissions associated with their production, these biofuels have some of the highest emission reductions—for example, used cooking oil reduces emissions 84% compared to fossil jet fuel.

Municipal solid waste is particularly popular because it could be, theoretically, have negative displacement emissions—municipal solid waste diverted from landfills avoids methane leakage from anaerobic digestion.  In practice, efforts to scale up production have not been fruitful. And refining plastics found in landfills could, according to the EPA “emit air pollution that is so toxic, one out of four people exposed to it over a lifetime could get cancer”.

Of waste feedstocks, the only process that can produce 2nd generation alternative jet fuels at a commercial scale uses waste oils. Unfortunately, there is a very limited quantity of sustainable waste available to produce 2nd-generation biofuels, and demand from other sectors, such as ground transport, outstrips supply. As a result, regulations meant to limit the use of 1st-generation biofuels and promote the production of 2nd-generation biofuels, such as those in the EU, have resulted in schemes where fresh palm oil is passed off as used cooking oil for tax credits.

Moreover, the supply of waste feedstock is inherently limited: there is only so much used cooking oil, or sewage sludge, or crop cuttings, to go around. And attempting to scale the supply of waste means that—by definition—it is no longer waste.

Other biofuel feedstocks deemed promising include cellulosic energy crops, like switchgrass and miscanthus, and cover crops like carinata and camelina. While they provide meaningful emission reductions, they are extremely energy inefficient to produce, and have not demonstrated commercial viability. One kilogram of sugarcane oil yields just 4.04 MJ of jet fuel, whereas the same amount of palm oil yields 5 times that amount. Growing energy crops also uses up arable land, in competition with other applications such as feeding a growing global population.

In the realm of non-biogenic feedstocks, synthetic fuels or “e-fuels”—produced from hydrogen and carbon dioxide—are widely touted because they approach carbon-neutrality when produced with renewable electricity, Like other “promising” jet fuels, however, synthetic fuels will remain in “exceptionally” limited supply for at least the next decade, and are enormously energy intensive. If produced from grid-standard electricity, they have higher CO₂ emissions than petroleum. And if all jet fuel used today were replaced by synthetic fuels, its production would require two-and-a-half times the renewable electricity currently available globally.

Magical thinking

Alaska Airlines summarizes it succinctly: “much of what’s needed to decarbonize requires aviation new technologies that don’t exist yet—or aren’t available with enough supply and at a sustainable cost”. One would therefore be forgiven for assuming that serious proposals to combat the climate crisis would not gamble on AJF. Instead, both the state energy office and HECO’s decarbonization plans depend almost entirely on alternative jet fuel, along with some electrified aircraft [2] and efficiency improvements [3], to achieve zero emissions from the aviation sector by 2045.

The HSEO is relying on alternative jet fuel to scale exponentially to 10% of Hawai’i’s jet fuel in 2030, in six years; that number quadruples to 40% in 2045. The 2030 assumption, more than double the EU’s goal of 5% by 2030, is based on Hawaiian Airlines’ stated commitment to scaling up AJF [4]. And the industry has routinely failed to meet its AJF goals: fifteen years ago, the International Air Transport Association predicted biofuels would be 10% of jet fuel in 2017, and in 2011, Air Transport Action Group promised it was “striving to practically replace 6% of our fuel in 2020 with biofuel. We hope this figure can be higher”. It is worth nothing that AJF’s current share of jet fuel, one sixth of one percent, is so low that reports from the International Energy Agency simply round down to zero.

Even more vexingly, the HSEO report assumes that all biofuels have zero emissions, meaning that even with large scale adoption of AJF, future emissions from aviation are likely to be many orders of magnitude greater than the report predicts.

As alternative jet fuels are currently anywhere between 2 to 8 times more expensive than fossil jet fuel, widespread adoption will not happen without substantial government subsidies. There are bills moving through the legislature that incentivize import and production [5] of any biofuel as long as its lifecycle emissions are lower than fossil fuels. An alternative jet fuel that only provides 10%—or even 1%—emissions reduction would thus be eligible for tax credits.

If these bills pass and Hawai’i incentivizes alternative jet fuel without emissions reductions standards, it’s all too likely we end up with planes marketed as “sustainable” while flying on palm oil. If Hawai’i does implement meaningful emission standards and even explicitly bans palm oil [6], given the limited supply and viability of 2nd-generation biofuels it is unclear that alternative jet fuel would ever scale up to the quantities desired.

But let’s put that aside for a moment and assume we are able to bypass issues in scaling up production, and by 2045 there is a ready supply of alternative jet fuel. At the moment, alternative jet fuel must still be blended with fossil jet fuel to be compatible with aircraft, meaning planes that “run on sustainable aviation fuel” are also running on vast quantities of fossil fuel. And even if we were to achieve 100% AJF blends, most of aviation’s global warming effect from flying comes from non-CO₂ emissions, and only some of this can be addressed by biofuels.

So while alternative jet fuel may not be a credible decarbonization solution, it is a great greenwashing strategy. Promote “promising” jet fuel technologies while conveniently ignoring the fact they are several decades away from real commercial viability; overemphasize the low-emission biofuels that have limited ability to scale while forgetting to mention that the vast majority of “sustainable” aviation fuel barely reduces emissions. The myth of soon-to-be-sustainable aviation is both a convenient narrative and a dangerous one, lulling us into a false sense that aviation can continue growing at its rapid pace.

A real climate solution

On the other hand, there is a method to reliably, effectively, and quickly curb aviation’s emissions: fly less.

I have no doubt you reacted to this proposal with a mixture of skepticism and derision. Flying is so deeply embedded in Hawai’i—two thousand miles from nothing, with a near-complete dependence on tourism—that flying less may seem so farfetched as to be impossible. And indeed, our systems have been set up in such a way that aviation is critical to Hawai’i’s social, political, and economic structures—that much is self-evident.

Curtailing aviation is seen as so politically tenuous that the state energy office takes an enormously convoluted path to avoid saying it outright. Scenario 2 of the HSEO decarbonization plan requires a “10% reduction in flight miles by 2030”, which is achieved by “working with” hotels to incentivize longer visitor stays. The report assumes this would increase the average trip length from 9 days to 10 days, and therefore “reduce emissions from air travel without impacting the economic benefit tourism brings”.

Putting aside doubts about whether this scheme would achieve the intended outcome [7], nowhere does it mention that the emissions reductions come from fewer tourists, and therefore fewer flights—because, of course, we can reduce emissions, but never, ever, at the expense of continued growth [8], that basic tenet which rules all. Maintain air travel at all costs, call tourism “sustainable” so we can feel good about it, and do anything to avoid saying the words “fly less”.

But for most of the world, flying less—or not at all—is the reality. While airlines tout their relatively low contribution to global emissions [9], this is only because very, very few people—less than 5% of the global population—have ever taken a flight. For those of us who aren’t heads of state or fossil fuel executives, taking a flight is possibly the fastest way to heat the planet. One round-trip flight from Honolulu to SFO emits more carbon than, say, three people in Kiribati will emit in an entire year, and yet it is Kiribati that may be underwater in just 26 years. The great injustice at the heart of this crisis is that climate change will most affect those who have done the least to cause it.

We need policies that curtail aviation quickly, and equitably—and we can’t allow technological wishful thinking to get in the way. I am not promising it will be easy. In fact, our task ahead is nothing short of Herculean: redesigning our economic systems so that everyone in Hawai’i can meet their needs, irrespective of visitor arrival numbers, will require nothing less than a fundamental paradigm shift. And because government and industry has stalled on climate action for so long, we have even less time to do it.

But there is what is politically “possible”, and there is the scientific reality. As Adrienne Buller notes, “one of those is going to have to give, and only one of them can give.”

A clean and healthful environment is a right. Flying is not. We can continue contorting into climate “solutions” that sacrifice the rest of the world to dubious biofuel schemes so that a privileged few in the Global North can jetset with a little less guilt. Or we can ask ourselves: if the basic proposition of endless aviation growth is incompatible with decarbonization, if to continue with business as usual in a climate crisis is to enable vast, avoidable suffering, and if we believe everyone is entitled to a clean, healthy, and sustainable environment—then what do we need to do?

Author’s Note: I felt a lot of hesitation at publishing this article. I attend a college far away from home, so I fly a lot more than the vast majority of people both globally and in the US. I am in that privileged few. You would be correct to note the hypocrisy in me calling for fewer flights while I continue to fly across the country. I don’t publish this article in an attempt to launder guilt; I generally believe that focus on individual action cannot come at the expense of systemic change, and I also think that change must also happen at the scale of individuals, and that if we are to address the climate crisis, the overconsumption associated with affluent lifestyles in the Global North will need to end. I don’t know what to do with all of that, other than personally flying less in the future and continuing to organize for climate justice with all that I have in me.

Endnotes

1. There are two prevailing models for calculating induced land use change emissions: Global Trade Analysis Project (GTAP-BIO) and Global Biosphere Management Model (GLOBIOM). Because GTAP-BIO makes certain assumptions around land use, such as the assumption that some land types sequester (rather than release) carbon when converted to cropland, it consistently estimates lower land use change emissions compared to GLOBIOM. As the merits of each model are currently the subject of significant academic debate, the lifecycle analysis model developed by the International Civil Aviation Organization, CORSIA, estimates induced land use change emissions by harmonizing the two models.
2. The HSEO report assumes that just 0.2% of current inter-island aviation could be electrified by 2045. Even so, Airlines4America writes that “technological readiness for electric power aviation necessary for inter-island aviation is still immature and it is unclear whether technology will mature sufficiently by 2040 to meet the ambition of the HSEO Decarbonization Strategy”.
3. Emissions reductions achieved by increased aircraft efficiency improvements are outstripped by aviation growth, which is unsurprising given that efficiency improvements are usually accompanied by increased resource use. From 2010 to 2019, average fuel efficiency improved by 1.8% per year, while global air freight has been increasing at more than three times that rate.
4. The airline qualifies this “commitment” as a “forward-looking statement” in which “risks, uncertainties and assumptions relating to the Company’s operations and business environment […] may cause the Company’s actual results to be materially different from any future results”.
5. As Island Energy Services notes: “Producing in-state biofuels will likely be very limited. […] Reliance on dedicated in-state energy crops will require a tremendous amount of land. For example, energy grass is a higher yielding crop that can produce 7.5 barrels of biodiesel per acre annually.1 In order to produce 10,000 barrels per day of biofuel (or less than 10% of Hawai’i’s current fossil fuel demand), nearly 500,000 acres of land is required. For reference, Oahu totals 386,000 acres”.
6. Whether emission standards can even address the negative impacts of biofuel is a matter of debate. Biofuelwatch argues there are no credible ways of addressing major indirect impacts of bioenergy through standards, and no regulatory mechanism for monitoring/enforcing compliance with standards. Standards can’t address “sustainability of demand”. For example, excessive demand for agricultural products and wood has led to deforestation; incentivizing SAF production will increase demand for aviation. Moreover, the WTO and trade agreements exert strong pressures against genuinely meaningful standards.
7. Would creating incentives for longer hotel stays change the average trip length, and would that reduce the number of people flying in and out? There are two core assumptions here: first, that length of stay is only influenced by total cost of accommodations. But a longer stay increases the cost of other expenses beyond accommodation, driving up total trip cost. And even if longer trips were cheaper, how many people can take additional time off work or school? Second, the assumption that all hotels are always 100% occupied, such that travelers will cancel their trips because they cannot find lodging. This assumption obviously does not hold in low season, but even in high season, is it ever the case that every accommodation in Hawai’i is fully booked? Even during the most crowded times of year, if a traveler’s preferred hotel is not available, they can simply find another hotel.
8. Airlines4America says as much, quite candidly, in its comments on the HSEO’s decarbonization report: “policies aimed at air travel demand reduction could have adverse and unintended consequences of reducing overall economic activity. The focus of Hawaii’s decarbonization strategy should be to reduce carbon emissions in the most cost-effective manner without impacting economic activity”.
9. Flying accounts for 2.5% of global emissions and 3.5% of human-caused warming. The EESI finds that “[b]y 2050, commercial aircraft emissions could triple given the projected growth of passenger air travel and freight”. As other industries decarbonize, aviation is poised to eat up an increasingly large share of the carbon budget.