Making flying carbon neutral

Sustainable aviation fuel, electrification vie for the future of air travel

When you don masks to risk air travel these days, the least of your worries is the carbon footprint left in the plane’s wake. But someday, hopefully soon, COVID-induced stay-at-home-itis will come to an end and aviation’s contribution to global warming will begin to influence your travel plans.

Air travel contributes an estimated 3% of greenhouse emissions worldwide and 4% in the U.S. Unlike automobiles and trucks, aircraft pollution remains largely unregulated even though the Environmental Protection Agency has deemed its greenhouse gas emissions a threat to the public’s health and safety.

Unless governments around the world act, commercial and cargo flights’ share of total emissions will grow substantially over the next few decades. A growing global population is expanding its use of air travel and shipping while the other large sources of greenhouse gas emissions – electricity generation and ground transportation – are shrinking their use of carbon-based fuels. Vehicle electrification and green power generation is advancing at a rapid pace.

Electricity-driven aircraft, on the other hand, have not advanced much beyond the experimental stage. The electric planes offered by the few companies investing in the technology are small with limited range (See here, here and here, for instance). Industry giants Boeing and Airbus say commercial-sized electric aircraft are decades away and most likely will only be suitable for shorter flights carrying relatively few passengers.

Battery requirements are the biggest stumbling block. Automotive engineers have figured out how to get 300-plus miles out of a thousand-pound car battery pack. But given the current state of battery technology, it would take the equivalent of eight 747s to carry enough batteries to power a single large plane on a cross-country flight.

Biofuels: Big hope or bridge to nowhere?

This conundrum has given new impetus to the biofuels industry, which is positioning itself as the bridge to a future when batteries have advanced to the point where they can power commercial-sized aircraft. Earlier this month, the Biden administration and the airline industry set a goal of fully switching air travel to sustainable aviation fuel by 2050, with an interim goal of 10% by 2030.

But biofuel production faces its own technological hurdles. Jet fuel is similar to diesel fuel and can be produced by the same refineries. But refining biodiesel from biomass (municipal garbage, yard waste, vegetable oils, trees, corn stalks, whatever) costs at least twice as much as producing jet fuel from oil, and possibly a lot more unless done on a massive scale. As a result, sustainable fuels currently supply just 1% of global aviation industry demand.

Moreover, plans to switch to sustainable aviation fuel are drawing criticism from skeptical environmentalists. They say encouraging a switch to biofuels will only serve to retard the pace of electrifying air travel.

“The problem with a bridge is that it slows the rate at which you get to the other side,” said Clare Lakewood, a senior attorney with the Center for Biological Diversity. Last December, the group sued to prevent implementation of a Trump administration rule backed by the airline industry that would have created an aircraft emission standard that the current jet fleet already meets.

“If you have an incentive, the technology evolves very quickly,” she said. “But as long as you rely on biofuels, you’re not going to have that same pressure. You don’t get to the other side because you wind up with a lot of people who have a vested interest in producing biofuels.”

The next ethanol scam?

Many scientists remain concerned about the greenhouse gas emissions associated with current methods of biofuel production, which rely on crops like corn and soybeans. Cutting down forests for cropland to produce the fuel increases carbon emissions. To avoid that scenario, the administration’s proposal would require a 50% reduction in emissions before earning the proposed fuel tax credit that would make sustainable aviation fuel affordable.

Biofuel producers including the American Farm Bureau Federation, the National Corn Growers Association and the National Farmers Union are already lobbying to influence how those emission reductions will be measured. In early August they wrote a letter to leaders of the Senate Finance and House Ways and Means committees claiming the EPA’s assessment of biofuel emissions was out of date. They want the Department of Energy to do the calculations, claiming its scientists are more conversant with current methods of producing less-polluting sustainable aviation fuel.

New technologies for producing greener biofuels are coming online because a handful of states have already enacted tougher standards. As with auto mileage standards, California is leading the way.

Its 2010 law provided tax credits for any transportation fuel that reduces greenhouse gas emissions by at least 20% by 2030. Aircraft refueling stations at San Francisco and Los Angeles airports have begun implementing programs to take advantage of the credits.

That has fueled a small boom in sustainable aviation fuel production using the latest technologies for converting municipal waste into biodiesel. Start-up Fulcrum BioEnergy, for instance, recently opened its first waste-to-fuel biodiesel plant outside Reno, Nevada, which will produce 11 million gallons of “zero carbon” fuel annually.

The company’s plans include building eight plants three times that size in other cities, including one in Gary, Indiana, to serve airports in the Chicago region – the nation’s largest air transportation hub. Its partners include British Petroleum, United Airlines, Cathay Pacific and Japan Airlines. Shell Oil this week announced plans to produce ten times the current annual worldwide production of sustainable aviation fuel by 2025.  

Recognizing that the existing fleet will be around for decades, some environmental groups have begun pushing for shorter timelines for increasing the share of fuel coming from sustainable sources. Others want airlines to post emissions estimates so consumers can compare carbon footprints as well as prices when choosing flights. They also say the government should discourage air travel by ending frequent flyer programs and investing more in high-speed rail.

Lakewood, the Center for Biological Diversity attorney, argues the surest path to lower air travel carbon emissions is a simple performance-based standard that drives technological change. “A lot of airlines are making a big push for biofuels. It’s greenwash to avoid actual regulation,” she said. “The government should set an airline emission cap and let them meet it however they see fit.”