The Seductive Vision Of Green Aviation 

Air travel is profoundly bad for the environment but one of the hardest industries to decarbonize. Can green technologies make a difference before it’s too late?

Gretta Johnson for Noema Magazine

Henry Wismayer is a writer based in London.

Picture yourself in an airship pushing into the northern latitudes. From the vantage of a barstool in the center of a luxurious lounge, you look through panoramic windows to see an Arctic vista scroll past. The ride is as smooth as a cruise liner cutting through a mirror sea. Above you is a white canopy, the base of the great bladder of gas keeping you airborne. Down below, a huge oval shadow glides across the pack ice.

I disembarked from this flight of fancy and came back to reality in an industrial estate on the outskirts of the town of Bedford, a couple hours north of London. For now, the airship of my imagination sat disassembled in front of me — an engine, the top section of a tail fin, a salubrious sample cabin.

Hybrid Air Vehicles calls it the Airlander: a colossal, state-of-the-art dirigible that was originally conceived as a military surveillance platform for the U.S. Air Force. That idea was scrapped as America de-escalated its operations in Afghanistan, but by then a new application for airships was emerging. Aviation is the most energy-intensive form of transport, and in recent years the industry has come under intense scrutiny for its environmental footprint. Unlike a passenger airplane, a passenger airship — buoyant and slow — doesn’t have to burn much fuel to stay in the air. 

“We’ve completely normalized flying in an aluminum tube at 500 miles an hour, but I think we’ve got some big changes coming,” said Tom Grundy, an aerospace engineer and HAV’s CEO, who was showing me around the research facility.

Many of the scientific principles behind Grundy’s airship are a throwback to a bygone age, when Goodyears and Zeppelins carried affluent clientele around America and Europe and occasionally between the two. Other aspects are cutting-edge. The cambered twin hulls will be inflated with 1.2 million cubic feet of inert helium, not flammable hydrogen like most of the Airlander’s interwar forebears. The skin, a composite of tenacious, space-age materials, is barely a tenth of an inch thick but so strong that there is no need for any internal skeleton. Grundy handed me a handkerchief-sized off-cut. “You could probably hang an SUV off that,” he said. When it goes into production later this year, it will be the world’s largest commercial airliner: around 300 feet long, nearly the length of a soccer field.

But arguably its key selling point — the reason HAV resuscitated a mode of aerial transport once thought to have gone down in flames with the Hindenburg — is that it’s green. Even powered by today’s kerosene-based jet fuel, the total emissions per kilometer from its four vectored engines will be 75% less than a conventional narrow-bodied jet covering the same distance. The Airlander of course is much slower. A maximum velocity of under 100mph means that it’s never going to compete directly with jet airliners. “We tend to think of it as sitting between the air and ground markets — a railway carriage for the skies,” Grundy told me.

“When it enters service, perhaps as soon as 2026, the Airlander will offer premium, multi-day cruises to hard-to-reach places like the Arctic Circle.”

A 100-seat cabin designed for regional travel has already attracted orders from carriers in Spain and Scotland. The prototype we were sitting in, with a futuristic carbon-fiber profile and wine glasses dangling above a wraparound bar, is the central section of another configuration called the “expedition payload module.” When it enters service, perhaps as soon as 2026, it will offer premium, multi-day cruises to hard-to-reach places like the Arctic Circle. Behind the communal lounge, a central corridor will lead to eight double ensuite bedrooms. “You’ll even be able to open the windows,” Grundy said. 

Earlier, I’d joined David Burns, a former British Airways pilot, on a simulator flight. He explained how the vehicle could stay low over wilderness areas, soaring slowly past redwood forests in California or desert dunes in the Sahara. Near cities, it would stay a little higher, around 1,500 feet, about as far up as the blimps above American football games. “It’s a big beast,” Burns said. “You don’t want to scare the bejeezus out of people!” When he took an early prototype for its maiden flight near Bedford in 2016, half the town turned out to see it, their necks craned toward the sky as a white leviathan cruised slowly overhead.

What the Airlander really brought home is the range of variables at play when you attempt to clean up arguably the hardest of all industries to decarbonize. Vital to the modern way of life, air travel requires vast amounts of ground infrastructure and careful coordination between armies of employees and software. So many aspects of aircraft design influence its commercial viability and environmental impact: materials, speed, payload, costs. A slower vehicle means more hours in the air. But Grundy claimed that it also means less risk to mitigate and therefore less time-consuming boarding protocols. Constructing an airport for today’s hub-and-spoke air-route system necessitates the razing of a vast area. The Airlander, with its vertical takeoff and landing, requires just an acre of clear land — or water. The retractable studs can set down on both.

This hangar is part of a growing ecosystem of enterprises, from small, garden-shed startups to governments and aeronautical giants, which are all wrestling with similar trade-offs in an effort to sever aviation’s dependence on fossil fuels. There are chemists trying to refine jet fuel with algae, aerospace engineers revolutionizing wing configurations and physicists squeezing more and more energy out of advanced batteries. 

“There’s a chance,” writes the journalist Christopher de Bellaigue in his new book “Flying Green,” “that the cumbersome, needy, petulant, change-averse behemoth that is modern aviation is starting to rediscover the fearlessness and zest of [the first aviators], and that in saving itself it will help save the world.”

For this generation of innovators, steering the business of flight toward a sustainable future might be one of the great technological challenges of the age. But then flight, by its very nature, has always been about defying gravity.

On a clear late summer day in 1911, a celebrated reporter named Richard Harding Davis stood on a polo field outside Aiken, South Carolina, and cast a skeptical eye over another prototypical aircraft. The plane was a Wright Model B, an evolution of the Wright Brothers’ pioneering flyer, which eight years earlier had achieved the first sustained flight of a heavy aircraft — 12 momentous seconds above the sand of Kitty Hawk, in North Carolina. The Model B’s twin wings, one atop the other, were made from muslin fabric pulled tight over a spruce frame. Two pairs of bicycle wheels comprised the landing gear.

Davis climbed into a space for a single passenger next to the pilot, Frank Coffyn, both of them perched on the front edge of the lower wing. “My toes rested on a thin steel crossbar,” Davis later wrote. “It was like balancing in a child’s swing hung up from a tree.” Behind their heads, the plane’s twin propellers were “thrashing the air like a mowing machine.” 

Coffyn pushed forward on a long lever and the contraption skittered along the grass. By the time they reached the edge of the field, a terrified Davis was surprised to discover that they were already airborne. “And then a wonderful thing happened,” he wrote. “The polo field and then the high board fence around it, and a tangle of telegraph wires, and the tops of the highest pine trees suddenly sank beneath us.”

Davis’s description of his flight was a breathless hymn to a new mode of human experience. “What lures them,” he wrote of flight’s pioneering generation, “is the call of a new world waiting to be conquered, the sense of power, of detachment from everything humdrum, or even human, the thrill that makes all other sensations stale and vapid, the exhilaration that for the moment makes each one of them a king.”

Coffyn’s Model B had whirred above the countryside for just six miles. “But we had gone much further than that,” Davis wrote. “And how much farther we still will go no man can tell.”

It would be decades before the general public could be convinced to follow Davis into the air. Early passenger carriers were vomit rockets. Unpressurized cabins restricted them to lower and more turbulent altitudes. The first air stewards employed by the predecessor of United Airlines were conscripted from the nursing sector to manage the anxiety, vertigo and air sickness passengers experienced aboard.

Aviation’s quantum leap came after the Second World War with two inventions forged in the battle for aerial supremacy. The first was radar, which enabled air traffic controllers to choreograph congested skies. The second was the jet engine. The first truly successful passenger plane, the Boeing 707, was a jet tanker designed to refuel bombers in midair refitted to carry 181 people. Its cruising speed of 550 mph was almost three times faster than its propeller-driven antecedents. 

“Someone flying economy from London to Sydney uses up a fifth of their personal carbon budget on a single round-trip flight. In a first-class seat, they would deplete 60%.”

In the ensuing decades, market-based competition between carriers and manufacturers has ensured that the evolution of aeronautic technology continued. Through deregulation and economies of scale, the invisible hand has made flights faster, more convenient — and much cheaper. “In 1960, a one-way flight between New York and London would have cost you around $300,” writes de Bellaigue. “If you shop around now, you can travel the same route for the same price, despite the fact that inflation has depreciated your $300 by 900 percent.”

All this growth has also overseen an exponential rise in the jet engine’s corollary: ton after metric ton of greenhouse gases. 

The genius of a jet engine is its simplicity. When set in motion, rotating titanium blades suck in air at a tremendous rate: over a ton per second during take-off, the engine’s most active phase. Much of this air is then fed into a series of fans of decreasing blade size known as a compressor. The compressed, superheated air enters a central chamber where it is combined with jet fuel — most commonly Jet A-1, a highly refined kerosene — at an air-fuel ratio of approximately 50:1. When ignited with an electrical spark, this mixture combusts, reaching temperatures of almost 5,500 degrees Fahrenheit. This controlled explosion drives a turbine before being released through a rear outlet, generating huge amounts of thrust. 

The process is elegant and powerful but unavoidably pollutive. The fumes that emanate from this exothermic reaction are a combination of carbon dioxide, nitrous oxide, sulfates, water vapor, soot, contrails and other aerosols. Efforts to quantify how this cocktail of fumes contributes to anthropogenic climate change tend to focus on CO2 because it is by far the most abundant greenhouse gas — 76% of global emissions. In 2018, civil aviation produced an estimated 896 million tons of CO2 — 2.4% of the global footprint.

But most of the other components of a jet engine’s exhaust fumes are also heat-trapping. The best metric to track the prodigious emission of these particulates, which are especially damaging to the atmosphere because of the high altitude of their release, is called “effective radiative forcing.” This is the extent by which a given human activity alters the energy balance of the atmosphere. By this measure, aviation is responsible for 3.5% of human activity’s total “warming impact.”

According to a recent study, the world has already burned through half of the “carbon budget” — the limit of what the atmosphere can handle and still stay beneath 1.5 degrees Celsius of warming — that was set during the 2015 Paris Agreement. The remaining budget, around 250 billion metric tons, equates to a lifetime allowance of around 31 metric tons of CO2 per person. Someone flying economy from London to Sydney uses up a fifth of that quota on a single round-trip flight. In a first-class seat, which has a bigger carbon footprint owing to the additional space it takes up on a plane, they would deplete 60%.

“The decreases in emissions that have resulted from incremental technological efficiencies have been swallowed by the growth in air traffic.”

For many years, the response of airlines to the calcifying international consensus about greenhouse gas emissions and climate change has been sluggish, characterized by foot-dragging, dispensations and greenwashing. 

Aviation has always been a precarious business, vulnerable to economic shocks. Profits tend to be razor-thin. Ethical considerations cause friction with the imperatives that have shaped the industry for decades: to keep expanding the number of planes and passengers in the air for as competitive a price as possible. 

However, the industry is also viewed as an indispensable infrastructural resource. Jet fuel is not taxed like gasoline for cars. Carbon emissions are not priced into the cost of flight tickets, which also tend to be exempt from any form of sales tax. During Covid, as global air traffic dropped by 94%, the American government approved a $25 billion bail-out package for the U.S. airline industry within days of the first lockdown. Traditionally, these forces in concert have ensured that the question of sustainability was relegated to an afterthought or paid lip-service with half-measures like opt-in emissions-offsetting schemes. 

The kind of innovations that feature on the newest airliners like the wide-bodied A350, Airbus’s latest flagship, are often promoted as an environmental boon. Progress in fuel efficiency, aerodynamics and lighter composite materials has made jet-fueled aircraft much more efficient. A flight today produces half as much CO2 as it did in 1990. 

But whatever gains have resulted from incremental efficiencies have been swallowed by the growth in air traffic. Between 1990 and 2019, the number of passengers traveling by air globally rose from 1 billion to 4.5 billion. The International Air Transport Association predicts that these numbers, driven by burgeoning commercial markets in Africa and the Asia-Pacific region, will breach 10 billion by 2050. As the decarbonization of other industries accelerates, some forecasts estimate that aviation’s share of global emissions could balloon to 27% over the same period. 

In spite of this, the aviation industry has thus far avoided the kind of environmental regulation that is precipitating reform in other sectors. Borderless by definition, aviation is exempt from the terms of the Paris Agreement primarily because its international nature convolutes the easy apportioning of responsibility. If Emirates runs a route from Paris to Mumbai across the airspace of a dozen other countries, who owns the emissions?

Nevertheless, as the accounting has grown starker, so, too, has the mood begun to shift. In October 2021, at an IATA conference in Boston, signatories pledged to make the aviation industry net zero by 2050. A year later, the International Civil Aviation Organization, the U.N. body that defines industry standards, adopted “a long-term global aspirational goal” to achieve the same. But if “long-term aspirational goal” seems mealy-mouthed and noncommittal, it is because every option is fraught with drawbacks and difficulty.

The bedrock of most industry blueprints for reaching net zero by 2050 is “sustainable aviation fuel.” SAFs can be derived from a variety of sources including household waste, agricultural residues and non-food crops. Although using them to power an aircraft still entails combustion and a pollutive exhaust, they generate fewer greenhouse gases over the course of their lifecycle: A flight fueled by SAFs can claim to have produced 80% less CO2 than one fueled by traditional jet fuel.

Arguably the most compelling business case for transitioning to SAFs is that they are a “drop-in” technology. The hardware involved in its transport and utilization is little different from the kerosene-compatible equipment it would replace. You still have a flammable liquid that is moved around by truck and pipeline, stored in silos and combusted in conventional jet engines. Theoretically, it could be rolled out quickly, with a relatively minor overhaul to existing fleets and ground infrastructure. And its efficacy as a substitute for kerosene is proven. Last March, Airbus took its A380 super-jumbo for a three-hour flight powered by fuel refined primarily from used cooking oil.

For planes like the A380, the world’s largest passenger airline — nearly 240 feet long, with a take-off weight of 617 tons — most observers agree that SAFs are the only pathway to reducing emissions. Even the most starry-eyed proponents of alternative technologies concede that no other technology looks likely to decarbonize long-haul flight, certainly in the near term. The IATA’s net zero blueprint envisions that SAFs will provide 65% of aircraft propulsion by midcentury. 

Spurred by such projections, governments are starting to mandate and incentivize SAF use and production. In April, the European Parliament agreed to a new raft of laws and subsidies that will require fuel suppliers and airlines to introduce an ever-increasing proportion of SAF to their aviation fuel mix, starting from 2% in 2025 and rising to 70% by 2050. 

Concurrently, the U.S. government is rolling out its “SAF grand challenge,” which will use tax credits and grants to ramp up SAF production to 3 billion gallons a year, around 10% of national demand, by 2030. The Energy Department aspires to see SAFs replace conventional fuel wholesale by 2050, an ambition that, according to Energy Secretary Jennifer Granholm, “will help American companies corner the market on a valuable emerging industry.” 

Where things get sticky is in producing the biomass, or feedstock, from which SAFs are refined in the first place. The world’s most popular vegetable oil is palm oil. In the mid-2000s, as Western governments incentivized fuel suppliers to increase the production of biofuels, the net result was an unintended catastrophe, the extent of which is still not fully known: In the rush to meet demand, Indonesian farmers cut down millions of acres of mostly untouched rainforest, replacing it with a sprawling monoculture of oil palms. So much methane escaped from Borneo’s freshly exposed peatlands that observers began characterizing it as a “carbon bomb.” Research from NASA subsequently found that, during the peak of its slash-and-burn frenzy, Indonesia was producing more CO2 than all of Europe.

Hoping to avoid a repeat of such devastation, both EU and U.S. initiatives include stipulations about the sustainability of the feedstocks that can be used in SAF production. A handful of companies are researching the potential of fuel derived from algae or yeast, both of which are abundant. United Airlines has invested in a company that is trying forest windfall and agricultural waste. But the practicalities are daunting. A February report from the Royal Society found that switching all U.K.-based airliners to SAFs derived from homegrown rapeseed would require the conversion of 68% of the country’s existing agricultural land.

If SAFs seem problematic, the more radical alternatives, which the industry tends to bundle together in the basket of “new” or “clean-sheet” technologies, are arguably more so. Electrofuels (or e-fuels), in which CO2 is extracted from the air and synthesized into a liquid hydrocarbon, look promising on paper — they effectively close the carbon loop, recycling CO2 that is already in the atmosphere. The world’s largest airplane manufacturer, Airbus, is betting big on hydrogen, which releases zero CO2 when combusted and has an astonishing energy density — almost three times that of kerosene. But farming and storing the constituent gases for either option remains prohibitively expensive. With current technology, isolating hydrogen from the molecules in which it naturally occurs consumes 30% more energy than it generates.

The stark reality is that no one has yet conceived of a product or menu of products that can realistically scale to match demand. For now, the promises look flimsy and the roadmap formidable. Only four years ago, global SAF production accounted for less than 0.1% of global jet fuel consumption. 

“For now, the promises for alternative aviation fuels look flimsy and the roadmap formidable.”

In a spotless hangar at an ex-military airport northwest of Gothenburg, Sweden’s second-largest city, Guilherme Albuquerque invited me to sit at the controls of an ES-30, a 30-seater electric plane. In front of us was an array of buttons, switches and instrument panels, and behind was an open skeleton of aluminum and electrical wiring. The view through the cockpit windows was a simple 3D rendering of London’s City Airport.

Albuquerque issued some instructions: Push forward on the thrust levers. Depress a small button on the central console to release the breaks. When the speedometer hits 80, pull back on the joystick. 

Airborne, the four rotating discs on the wings accelerated to a blur. It was all quite serene, drifting back and forth above the Thames, until Albuquerque asked me to land. I came in at a suicidal angle of around 40 degrees, perspiration beading on my forehead, the plane coming to rest on the grass beside the runway. Looking over my shoulder, Heart’s chief engineer, Markus Kochs-Kämper, said my performance made him “feel sick.” The avionics worked seamlessly. 

The life-size simulation model that sits in the “Integrated Test Facility” of Heart Aerospace, a Swedish start-up founded in 2018, is some way from taking to the skies, but it still exudes an atmosphere of clinical, state-of-the-art potential. A sepia portrait of Amelia Earhart, the first woman to fly solo across the Atlantic, hangs in the break room, a nod to the polluting era of flight that the company hopes to revolutionize. Heart has more than 200 employees who hail from 28 different nations. Their Promethean mission: To prove the commercial viability of battery-powered flight. 

Heart’s initial prototype was the ES-19, so named for the number of passengers it could hold. Pieces of the old design — an engine, a composite nose — now ornament the periphery of the hangar. The ES-30 borrows much from its predecessor’s design, but its larger capacity takes it into a different category of certification, commonly known by its FAA designation “Type 25.” This means that it will be held to the same standards of airworthiness as today’s jets. 

The increase in the size of the airframe has necessitated some compromises. In place of the ES-19’s pure electric assemblage, its larger sibling will operate with a “reserve hybrid” system. The finished plane, which should be ready for its first test flights by 2026, will have four electric motors and a large undercarriage containing five metric tons of batteries. Using extant technology, Heart says those batteries will be able to carry the ES-30 over distances of 200 kilometers (124 miles). Its most obvious applications would be to fly routes that are currently underserved by on-the-ground infrastructure like roads and rail — or as “puddle-jumpers,” small aircraft designed to hop between islands (or, this being Scandinavia, across fjords). 

In order to pass certification, commercial airliners must have a reserve energy capacity. Any plane you’ve taken recently probably carried 50% more fuel than it needed in case it was forced to reroute or stay in a holding pattern above the destination airport. In the ES-30, this backup power will come from a gas turbine housed in the tail assembly. The fuel to power it, whether kerosene or SAF, will be stored in the wings. In order to augment this heavy wingspan, diagonal struts run from the underside of each wing to the base of the fuselage. 

To a purist dreaming of clinical engineering and space-age aesthetics, these might seem like unwieldy concessions. But if sleekness is nice, achieving proof-of-concept is better. 

The Tesla precedent — a private company defying the naysayers to prove a green technology’s viability, and in so doing reshape the very concept of transport — is a lodestar for advocates of electric aviation. The skepticism surrounding its potential echoes the same that dogged early electric cars: Electric could never rival combustion; V8s forever. Fast forward a decade, and Tesla’s latest Model S has a top speed of 200mph and a range of 390 miles. 

It is of course a different proposition when you need to get the machine off the ground. Five hundred years after Leonardo da Vinci sketched experimental “ornithopters” in a Florentine workshop, the work of getting and keeping something aloft boils down to the same ineluctable physics. Power and weight. Lift and drag. Out of all the technologies in the solution pipeline, full electrification offers by far the lowest energy density. A kilogram of lithium-ion battery provides around 2-3% of that supplied by a kilogram of kerosene. And batteries, unlike liquid fuel, don’t expend their weight. 

But if the ES-30’s long-term potential is contingent on breakthroughs that are anticipated rather than actual, each month seems to bring fresh encouragement. In April, the Chinese company CATL announced that it had successfully developed a condensed battery with an energy density of 500 watt-hours per kilogram, a significant increase in capability. (For comparison, Tesla’s most advanced batteries have less than 300 Wh/kg.) In May, Scandinavian Airlines released a batch of tickets for seats on the ES-30s it has on order, which are due to go into service in 2028. They sold out within 24 hours. 

“Out of all the technologies in the solution pipeline, full electrification offers by far the lowest energy density. And batteries, unlike liquid fuel, don’t expend their weight.”

It is hard to resist being swept up in the romance and crusading optimism of such endeavors. Flight has captivated people since we first looked up and felt envy for the birds. Supplementing that fascination with moral purpose makes for an intoxicating combination. For skeptics, however, the imaginative power of what Davis described as the “new world waiting to be conquered” risks blinding consumers to their limitations. 

Some of the buzziest projects under development in electric aviation are not passenger planes but autonomous urban air taxis. Also known as eVTOLs (for electric vertical takeoff and landing), with cute names like “Joby” and “Cityhawk,” these vehicles are essentially scaled-up iterations of drone technology: multi-rotor, driverless limousines. Critics say they are seeking to disrupt a sector (urban transport) that already has a clear road map to decarbonization, and that they merely replicate short journeys already being done cheaply and easily on the ground using a fraction of the energy.

“It’s a dangerous combination — technophilia plus investment bubbles,” Richard Aboulafia, the managing director of Aerodynamic Advisory, told me. He noted that eVTOLs travel more or less the same distance as a family car, electric versions of which are rapidly being adopted by consumers. While sustainable mass-transit aviation screams for investment, terawatts of brainpower and billions of dollars in venture capital are being expended to fulfill the sci-fi fantasy of a flying car. Aboulafia calls it “the greatest recarbonization scheme the industry has ever seen.”

Back in the U.K., I spoke to Finlay Asher of the advocacy organization Safe Landing. An engineer, Asher previously worked at Rolls Royce, the world’s third-largest aircraft engine manufacturer. The prototype engines he worked on — with lightweight carbon-fiber fans and smaller compressors — made small gains in power-to-weight ratios that would equate to marginal emissions reductions. But over time, Asher became concerned about the dissonance between the aviation industry’s environmental PR and its determined pursuit of scale. If these new jet engines required 10 to 15 years of exhaustive R&D and certification, the idea that transformative new technologies could come online and scale in time to fulfill net-zero pledges by 2050 seemed fanciful. 

This calculus wasn’t being reflected by a sense of urgency within the industry. In 2019, Greta Thunberg captured headlines by sailing across the Atlantic to attend a climate summit in New York, and the Swedish concept of flygskam, or “flight shame,” gained traction. In response, Rolls Royce’s sustainability team circulated charts illustrating the way its engines had grown more efficient over time. Asher asked to see data that showed the total fuel being burned in the growing number of engines being brought to market, but was met with silence. When he did the calculations himself, it was a diagonal line shooting ever upward. 

“While sustainable mass-transit aviation screams for investment, terawatts of brainpower and billions of dollars in venture capital are being expended to fulfill the sci-fi fantasy of a flying car.”

That same year, at the Paris Airshow, chief technology officers from a group of aerospace giants issued a joint statement emphasizing the indispensability of their businesses, while reassuring the public that the net-zero transition was well underway. Asher found himself disagreeing with every word.

“It felt like sleight of hand,” he told me. “The industry is going: ‘Look at these shiny electric aircraft over here.’ Meanwhile, we’re continuing to massively expand the number of aircraft powered by jet fuel.”

After founding Safe Landing alongside a group of fellow industry malcontents, Asher sought to voice a litany of reservations about nascent eco-friendly flight technologies: SAFs are unscalable, hydrogen is decades away, batteries will never develop enough energy intensity to cope with long-haul. The insuperable enemy is time. 

But he’s also keen to emphasize a more holistic point: that in a global race to decarbonize all energy consumption, throwing huge quantities of renewable energy into a utility as uniquely wasteful as aviation is counterproductive. Based on current technology, for example, an e-fuel derived from renewables ends up converting just 10% of the energy used in its production and combustion into actual thrust. That same energy put into the grid uses 100%. 

Neither do the more optimistic projections account for the fact that the efficacy of any new energy source depends on the sustainability of the wider lifecycle. If the power used to liquefy hydrogen or charge lithium-ion batteries comes from an unsustainable source, or if hectares of rainforest are denuded to mine a battery’s constituent materials, any ecological gains will be negated.

“In a global race to decarbonize all energy consumption, throwing huge quantities of renewable energy into a utility as uniquely wasteful as aviation is counterproductive.”

Thinking about aviation in this way exposes the hidden drawbacks of so much of what is going on in the innovation space. In Greensboro, North Carolina, Boom Supersonic is in the process of developing a needlepoint supersonic plane that will cut flight times in half. Designed to be run on e-fuels, it is being marketed as a flagship of carbon-neutral flight. But the amount of energy it consumes will be five times that deployed on an ordinary jet airliner flying the same route. While major aerospace corporations extol their investment in green technologies, private jet sales are through the roof.

Aboulafia worries that the industry is indulging in “the triumph of appearance over reality.” As he told me: “It’s out of sight, out of mind. You don’t see the massive petrochemical facilities that have to make the stuff we’re talking about. You just see this sleek, cool thing.”

What’s required above all else, according to Asher, is to put a price on emissions. At present, subsidies and tax exemptions make flying “artificially cheap,” he told me. Adding an emissions surcharge to the price of airfare and directing that money toward abatement strategies like offsets, direct-air capture or sustainable innovation is the only way to mend the cleavage between the ecological ramifications of flying and the marketplace.

Such proposals tend to raise egalitarian hackles. For Western governments to slap a tariff on flying just as millions of people in less economically developed nations might be interested in trying such a luxury for the first time is a hard, hypocritical sell. Only 20% of people around the world have ever been on a plane. And the majority of flight tickets are purchased by a sliver of frequent flyers, around 1% of the global population. A recent study published by the International Council on Clean Transportation found that a progressively distributed “frequent flyer levy,” in which a tariff increases in proportion to the number of times a person flies in a given year, would raise 98% of its revenue from the richest 20% around the world. The introduction of such a levy would invert the current perverse paradigm, which sees the most prodigious polluters rewarded through air miles and “frequent flyer” programs.

“We don’t need technology, we need policy,” Asher said. “Get the policy right and the technological solutions will follow. It’s inevitable that the cost of flying is going to increase. The questions are: Do you want to drive over a cliff edge, or do you plan for it now? Is it going to be early design or late disaster?”

There is, of course, another option. In technological terms, it is the least nettlesome. It is a strategy that could be implemented overnight with the right amount of public and political will. Psychologically and culturally, however, it presents an almighty challenge. People could decide to fly less. 

Perhaps the most intriguing dynamic in the conversation around flight and the environment is one that is rarely countenanced and that most of us who fly would rather ignore. In the majority of cases, flying is inessential. In “Flying Green,” de Bellaigue notes that aviation “has a strong claim to be the most damaging leisure activity in the world.” 

By taming distance, the plane opened up the world. In so doing, it reshaped our expectations of what constitutes a fulfilling life. It’s why air travel and the foreign holidays it facilitates are always marketed in the language of freedom. That annual trip to Mexico or Greece or Thailand has come to be seen as the ultimate dividend for the drudgery that brackets it. And while a growing cohort of people have started to forsake flying for ethical reasons, poll after poll (not to mention passenger numbers) suggests that it’s one indulgence most people are unwilling to relinquish for the sake of the climate, even though it is among the most consequential. 

One recent British survey found that 48% of respondents were unprepared to reduce the amount they fly for leisure. In another, 96% said that an annual overseas holiday was important to their mental health. Several older polls revealed that Green Party members and voters are more likely to fly long-haul than supporters of other political parties.

This reluctance to translate environmental consciousness into personal self-sacrifice points to the underlying impasse that is thwarting a head-on reckoning with our addiction to the air. No one wants to be first to act. 

The unpalatable truth is that any objective appraisal of green aviation’s potential remains clouded by denial. If enthusiasm for new technologies is deceptive, it is a masquerade in which much of the flying public is all too happy to collude. We are all Icarus now, mesmerized by our wings, soaring too close to the sun.

“The reluctance to translate environmental consciousness into personal self-sacrifice points to the underlying impasse that is thwarting a head-on reckoning with our addiction to the air.”

In May, after I finished demonstrating my ineptitude on the Heart Aerospace simulator, I went underground and back in time. A few minutes from Heart’s facility is an old Swedish Air Force base. Early in the Cold War, the military dug hangars into these granite hills, a network of concrete-lined tunnels designed to withstand a nuclear attack. When it was decommissioned in 1998, an enterprising squadron commander transformed it into a museum.

I entered the “Aeroseum” through a small door and walked into a cavern that descended past ranks of jet fighters and helicopters, some of the cockpits occupied by vintage mannequins. The ominous strains of Gustav Holst’s “Mars, the Bringer of War” rumbled from wall-mounted speakers. At the base of the slope, the space opened into a series of side tunnels, each one full of aging aircraft and engines. On one wall, heroes and milestones in the evolution of flight — the Wright Brothers, Charles Lindbergh, the first jets, the debut of the Boeing 747 — were memorialized in a timeline of placards.

Transitioning from Heart’s dustless modernity to this dim-lit mausoleum of extreme combustion was a dizzying experience. What struck me as I walked was the sheer speed of the technological evolution the museum chronicled. We went from Davis clinging to Frank Coffyn’s arm for dear life as a rickety biplane wheeled for a few brief minutes over South Carolina fields to a million air passengers a day in a little over a single century. And how much farther we still will go no man can tell.

It was tempting to imagine that the planes polluting the skies today would be the relics of tomorrow. Perhaps, on some distant future date, an Airbus A350 and a Boeing Dreamliner would find themselves parked here, wingtip to wingtip, monuments to aviation’s dirtier past, while overhead a new generation of planes — and even the odd airship — transported passengers through a troposphere without contrails. 

It was a seductive vision. But it couldn’t overcome my wider misgivings. Successful flight cannot only be measured in how high and how fast you soar, but in whether you make it back to Earth in one piece. It doesn’t just require thrust. It requires brakes.