The worst of the pandemic may be over for airlines, but the industry faces another looming crisis: an accounting over its contribution to climate change.

The industry is under increasing pressure to do something to reduce and eventually eliminate emissions from travel, but it won’t be easy. Some solutions, like hydrogen fuel cells, are promising, but it’s unclear when they will be available, if ever. That leaves companies with few options: They can make tweaks to squeeze out efficiencies, wait for technology to improve or invest today to help make viable options for the future.

“It’s a big crisis, it’s a pressing crisis — a lot needs to be done soon,” said Jagoda Egeland, an aviation policy expert at the International Transport Forum, a unit of the Organization for Economic Cooperation and Development. “It’s a hard-to-abate sector. It will always emit some carbon.”

Experts say commercial air travel accounts for about 3% to 4% of total U.S. greenhouse gas emissions. And while planes become more efficient with each new model, growing demand for flights is outpacing those advancements. The United Nations expects airplane emissions of carbon dioxide, a major greenhouse gas, to triple by 2050. Researchers at the International Council on Clean Transportation say emissions may grow even faster.

Before the pandemic, a “flying shame” movement, which aims to discourage air travel in favor of greener options like rail, was gaining ground globally thanks to Greta Thunberg, a Swedish climate activist. There were early signs that it may have reduced air travel in Germany and Sweden. Now French lawmakers are considering a ban on short flights that can be replaced by train travel.

Investors are pushing businesses to disclose more about their efforts to lobby lawmakers on climate issues, too. And some large corporations, whose employees crisscross the globe and fill plush business class seats, are reviewing travel budgets to reduce expenses and emissions.

The urgency isn’t lost on the industry. Scott Kirby, CEO of United Airlines, speaks often about the need to address climate change, but even he acknowledges that it will be difficult for the industry to clean up its act. He wants United and other airlines to try different things and see what works.

“It is the biggest long-term issue that our generation faces. It is the biggest risk to the globe,” Kirby said in a recent interview. “There are plenty of things we can compete on, but we all ought to be trying to make a difference on climate change.”

There are efforts to electrify small planes for short flights — including one backed by United — but doing the same for longer, larger flights will be tough, maybe impossible. Commercial planes like the Boeing 787 and Airbus A320, which can carry a few hundred passengers, require an immense amount of energy to reach cruising altitude — more energy than modern batteries can efficiently supply.

Someday, hydrogen fuel cells and synthetic jet fuel could help to decarbonize the industry, and pilot projects have already begun, mainly in Europe, where Airbus says it plans to build a zero-emission aircraft by 2035. Boeing has put its emphasis on developing more fuel-efficient planes and is committed to ensuring that all of its commercial planes can fly exclusively on “sustainable” jet fuel made from waste, plants and other organic matter.

At a petrochemical plant outside Houston, Neste U.S. and Texmark Chemicals are converting imported undistilled diesel into renewable jet fuels. The undistilled diesel is made from used cooking oil and waste from vegetable and animal processing plants.

Neste, a Finnish company, is the world’s largest producer of renewable jet fuel. Its U.S. customers include American Airlines, JetBlue and Delta Air Lines.

United, which buys renewable jet fuel from Fulcrum BioEnergy and World Energy, recently announced a deal with more than a dozen major corporate customers, including Deloitte, HP and Nike, that will result in the airline’s buying about 3.4 million gallons of sustainable fuel this year. American has an agreement to buy 9 million gallons of such fuel over several years, and Delta says it plans to replace one-tenth of its jet fuel with sustainable alternatives by 2030.

“There is huge growth potential for sustainable aviation fuel,” said Jeremy Baines, president of Neste U.S. “It’s a niche market today, but it’s growing very rapidly. Between today and 2023 we are going to increase our production at least 15-fold.”

Neste produces 35 million gallons of renewable aviation fuel and hopes to reach 515 million gallons annually by the end of 2023 by ramping up production at refineries in Singapore and Rotterdam, the Netherlands. That is enough to fuel close to 40,000 flights by wide-body aircraft between New York and London, or well over a year’s worth of pre-pandemic air travel between the two cities.

But it is important to put those numbers in perspective. U.S. airlines used more than 18 billion gallons of fuel in 2019, and the country as a whole consumes more than 100 billion gallons of petroleum products annually.

‘A Real Stretch’

Rystad Energy, a Norwegian consulting firm, predicts that renewable fuels will become increasingly economical after 2030 and supply 30% of all aviation fuel by 2050. But IHS Markit, a U.S. consulting firm, estimates that sustainable jet fuel will make up only 15% of all jet fuel by 2050.

Renewable jet fuel has its limits, too. The fuel reduces carbon emissions by only 30% to 50% compared with conventional jet fuel, according to Daniel Evans, global head of refining and marketing at IHS Markit. What’s more, production of the fuel can cause deforestation when the raw materials are farmed.

Some companies want to get around those problems by avoiding agricultural crops. Fulcrum, in which United is invested, is planning to build a plant in Britain to produce jet fuel out of waste from landfills and other trash. Red Rock Biofuels, a Colorado company, hopes to use waste woody biomass.

But development of renewable fuels from waste or substances like fast-growing algae and switch grass has been frustratingly slow.

“It’s going to be a real stretch,” Evans said. “Even if you are burning 100% biofuel, it’s still not going to be getting you to carbon neutral.”

Biofuels are also about 50% more expensive to make than conventional fuel, according to Michael E. Webber, chief science and technology officer of Engie, a French utility working on advanced jet fuels.

Hydrogen offers another possibility, although probably not for several decades. Instead of batteries or fuel engines, the potential hydrogen-powered aircraft of the future would operate with hydrogen tanks and fuel cells, though the technology would need to be advanced to reduce the size of the tanks and cells. The hydrogen could be made with renewable power sources like the wind and sun to reduce planet-warming emissions. But such fuels cost two to three times more than conventional fuel, experts say.

Several European countries also require refiners to produce and blend renewable jet fuel. The European Union is financially supporting Airbus’ development of a hydrogen-fueled aircraft, and the French government is encouraging Air France to research a synthetic jet fuel.

In the United States, federal support is minimal, so far. Renewable jet fuel producers receive a $1 per gallon subsidy under existing federal tax credits for biodiesel, but a bill introduced last month in the House would provide a tax credit starting at $1.50 per gallon. A tax on carbon emissions could help make alternative fuels more competitive against conventional jet fuel in the future.

Store Carbon or Buy Offsets?

Another option that many airlines have turned to is carbon offsets. By buying an offset, a company or individual effectively pays somebody else to plant or not cut trees or to take other steps to reduce greenhouse gases.

But the benefits of some offsets are difficult to measure — it’s hard to know, for example, whether landowners would have cut down trees had they not been paid to preserve woods, a common type of offset. Kirby, the United CEO, is skeptical that such offsets are effective.

“Traditional carbon offsets are a marketing initiative; they’re greenwashing,” he said. “Even in the few cases where they are real and are making a difference, they’re just so small that they can’t scale to solve the global problem.”

United helps passengers and corporate customers buy offsets, but Kirby said the company was focusing more on sustainable fuel and removing and storing carbon in perpetuity.

In December, the airline said it was investing in 1PointFive, a joint venture between Occidental Petroleum and a private equity firm that plans to build plants that suck carbon dioxide from the air and store the gas deep underground. This approach would theoretically allow United and other airlines to remove as much carbon from the atmosphere as their planes put into it.

“It’s the only solution I know of that can help get us as a globe to zero, because the others, if you understand the math, they just don’t work,” Kirby said.

Such efforts had long been dismissed as impractical, but corporations are increasingly pouring money into them as investors and activists pressure businesses to decarbonize. Kirby said such investments would help to drive down costs. But some experts warn that while direct air capture can help industries that are difficult to decarbonize, the ultimate aim should be to attack the problem at the source.

“If you can avoid the emissions in the first place, it’s so much cheaper and easier than having to pull it back out,” said Jennifer Wilcox, an Energy Department official and expert on direct air capture.

Despite the formidable challenges, Kirby is optimistic that investments in alternative fuels and carbon capture technology will yield a breakthrough.

“In the near term, it’s about getting them to work economically,” he said. “Once you cross that threshold, you will have an exponential increase.”

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