My Turn

By Christopher Eliot

In a previous Lincoln Squirrel article, I explained why “sustainable” aviation fuel (SAF) is unlikely to make aviation climate-friendly, barring one or more significant technological breakthroughs.

If SAF will not make aviation climate friendly, what should be done? Unfortunately, this is a very hard question to answer. I do not have an ideal solution any more than the aviation industry, but I believe my truthful admission is better than industry propaganda. It requires a lot of energy to fight the law of gravity. Currently, aircraft use the energy reservoir of millions of years of fossil fuel. It is unclear what renewable energy sources can practically be used to support aviation. It is more unclear if we can produce enough renewable energy for basic electrical needs and aviation too.

Expanding aviation is clearly wrong: we don’t want to make a hard problem bigger. We need to constrain the growth of aviation, starting with private jets which are the worst part of the problem as explained by Alex Chatfield on February 23 (“My Turn: Proposed private-jet Hanscom expansion is a climate bomb in sheep’s clothing“).

Existing aircraft can be made somewhat more efficient, thus reducing their environmental impact. Unfortunately, crowded seating, while loathsome for passengers, does reduce the fuel consumption per passenger mile. Scheduling that reduces empty seats is beneficial to the airlines and to the environment. Flying directly to a destination under 3,000 miles away is almost always more environmentally friendly than flights with layovers. Further efficiencies are possible but will only produce some percentage of improvement, easily outweighed by increases in travel.

Spending a trillion dollars to support production of SAF does not seem like a good use of resources or a path to a solution. Spending a trillion dollars on high-speed rail is much more likely to succeed and have a much better impact on climate considerations.

The single most impactful proposal is the development of blended wing aircraft. Fundamentally altering the shape of an airplane to generate much more lift will significantly reduce fuel consumption, and climate impact. JetZero claims the design can reduce emissions by up to 50%. However, more independent estimates predict more conservative benefits of 20-30%. Furthermore, the development of a new aircraft with associated production, servicing, and operational infrastructure is exceedingly challenging from a technical perspective, and maintaining the investment interest for the long development period is excruciatingly hard. The safety issues associated with a new design are immense. One or two fatal crashes could easily end production of an otherwise promising technology.

Jet contrails, while short-lived, turn out to have a massive effect on global warming and may account for 50% of the climate impact of aviation. Modifying flight paths to avoid the conditions where contrails form could substantially reduce this effect, although this has not been proven.

Electric aircraft are being tested and may soon become operational but it is not certain this technology will prove to be economically feasible. Several promising companies including Eviation and Lilium that have attempted to develop electric aircraft have recently failed. The industry wants to focus on electric vertical takeoff and landing (eVtol) instead of the simpler electric conventional takeoff and landing (eCtol) form of electric aircraft. From an environmental perspective, eVtol is probably bad and eCtol is probably good. All forms of electric aviation are technically difficult and have an uncertain future.

EVtol would create a whole new aviation industry providing a fast way to commute from cities to suburbs. Vertical takeoff and landing requires a prodigious expenditure of energy, likely limiting range to 25-50 miles. It is likely that eVtol will be a form of luxury travel unavailable to most people. It will probably be an expensive replacement for bus and automobile service to those who have the means. It will place a further drain on limited green energy sources, create new sources of overhead noise and confusion while reducing the environmental impact of nothing.

ECtol, on the other hand, could replace a certain number of short range flights (200-300 miles), including trips to The Cape and Islands. While this is a limited benefit, it is certainly better for the environment than using private jets to fly those same routes. Approximately half of all air travel is under 593 miles. More than 90% of high-traffic scheduled flights are less than 1,500 nautical miles. Current battery technology cannot produce electric aircraft that address a large percentage of the aviation problem. Increasing battery efficiency by at least a factor of three might allow electric aircraft to replace almost half of the current passenger miles. Electric aircraft do not have to cross oceans to dramatically reduce the climate impact of aviation.

My best plan for aviation requires (hopefully) addressing 10-30% of the problem with electric aircraft, 20-50% through the development of blended wing aircraft, 10-30% by reduction in contrails, 20-30% of the problem with high-speed rail, 10-20% of the problem with SAF, 10% from incremental optimization of engines, and remaining reductions due to remote meetings, more local vacationing, and some reductions in the use of air travel. The technological improvements are all uncertain; reduction in air travel is the only proven way to reduce aviation’s impact on the climate. However, while uncertain, the various engineering proposals (other than SAF) could greatly reduce the climate problem of aviation. Moving slowly toward this goal will be better for the aviation industry than following the false promise of SAF and being forced to drastically scale back operations when the scale of the climate crisis becomes inescapable.

What can you do?

The most direct action is to reduce your air travel slightly, maybe by 10%. Perhaps you can combine two trips into one (longer) trip or convert an in-person meeting to an online meeting. You can support groups opposed to private jet expansion and write to your government representatives.

Eliot, a Lincoln resident, is the former chair of the Hanscom Field Advisory Commission.

“My Turn” is a forum for readers to offer their letters to the editor or views on any subject of interest to other Lincolnites. Submissions must be signed with the writer’s name and street address and sent via email to lincolnsquirrelnews@gmail.com. Items will be edited for punctuation, spelling, style, etc., and will be published at the discretion of the editor. Submissions containing personal attacks, errors of fact, or other inappropriate material will not be published.