Sustainable Aviation

Why Aviation Is Hard to Decarbonize

Flying is one of the more difficult sectors to clean up, and the reason comes down to physics. Batteries store far less energy per kilogram than jet fuel does — even the best lithium-ion cells hold roughly a fortieth of the energy density of kerosene by weight. An aircraft that has to climb to cruising altitude and stay aloft for hours cannot afford to carry a power source that heavy without giving up most of its payload and range. That is why battery-electric flight today is realistic only for very small aircraft on very short hops, not for the widebody jets that carry most passengers and cargo across long distances.

The second obstacle is time. Airplanes are not like cars, replaced every few years — a commercial jet typically flies for 20 to 25 years or more before retirement, and airlines order new aircraft years in advance. That means the fleet flying today will still be largely in service in the 2040s. Even if every manufacturer stopped producing anything but a hypothetical zero-emission aircraft tomorrow, it would take decades for the existing fleet to turn over — and global air travel demand keeps growing in the meantime, unlike, say, electricity generation, where a single power plant can sometimes be swapped out much faster than an entire aircraft fleet.

Sustainable Aviation Fuel: The Nearest-Term Lever

Given those constraints, the industry's biggest near-term tool is not a new kind of airplane — it is a new kind of fuel. Sustainable Aviation Fuel, or SAF, is a drop-in replacement for conventional jet fuel, meaning it can be blended with standard kerosene and used in existing engines, fuel systems, and airport infrastructure without modification. It is made from renewable or waste feedstocks — used cooking oil, animal fats, agricultural residues, municipal waste, and increasingly synthetic pathways that combine captured carbon dioxide with hydrogen — rather than from crude oil.

SAF does not eliminate emissions at the point of combustion; burning it still produces carbon dioxide in flight. What makes it "sustainable" is the lifecycle math: the feedstocks either recycle carbon that was already going to be released, such as waste products, or were grown by absorbing carbon dioxide from the atmosphere, so the net addition of new fossil carbon is lower than pumping and burning crude oil. Approved SAF blends today are typically certified up to about 50 percent of the fuel mix on a given flight, though the actual industry-wide share is usually much lower — global SAF production remains a small fraction of total jet fuel demand.

The Industry's Net-Zero Commitment

In 2022, at its 41st Assembly, the International Civil Aviation Organization — the United Nations body that sets global standards for international aviation — saw its member states adopt a long-term aspirational goal of net-zero carbon dioxide emissions from international aviation by 2050. This mirrored a similar commitment the airline industry itself, through the International Air Transport Association, had already adopted the year before. It is described as "aspirational" because it is not a binding treaty obligation forcing any single state to hit specific numbers, but it does frame how governments, manufacturers, fuel producers, and airlines are expected to coordinate: through a mix of SAF scale-up, new aircraft technology, operational efficiency, and market-based measures to cover what cannot yet be eliminated directly.

CORSIA: Offsetting What Can't Yet Be Eliminated

One of those market-based measures is CORSIA — the Carbon Offsetting and Reduction Scheme for International Aviation, also administered through ICAO. The basic idea is straightforward: international airlines are expected to keep the carbon dioxide emissions from their international flights from growing beyond an agreed baseline. For emissions above that baseline, airlines can purchase verified carbon offsets — credits representing emissions reductions or removals achieved elsewhere, such as reforestation or renewable energy projects — to balance out the excess. CORSIA began with a voluntary pilot phase in the early 2020s and is scheduled to become mandatory for most participating states from 2027 onward.

Beyond Fuel: Fleet, Operations, and Airports

SAF and offsets are not the only levers. Airlines continually renew their fleets with newer aircraft that burn meaningfully less fuel per seat, thanks to more efficient engines and lighter airframe materials. On the operations side, small changes add up at scale: flying more direct routings instead of longer paths dictated by congested airspace, descending more smoothly instead of in fuel-burning step-downs, and taxiing on a single engine rather than two on the ground. Airports contribute too, by electrifying ground support equipment — the tugs, belt loaders, and baggage carts that used to run on diesel — and by supplying aircraft with ground power and pre-conditioned air at the gate so they don't need to run their own engines or auxiliary power units while parked.

The Honest Challenges

None of this is solved yet, and the industry itself is generally careful not to claim otherwise. SAF production is a small fraction of what aviation would eventually need, feedstock supply is limited, and it typically costs several times more than conventional jet fuel — costs that show up somewhere in the system, whether absorbed by airlines, supported by government incentives, or passed to passengers. Offsets carry their own credibility questions: a credit representing a reduction that would have happened anyway is not a real net benefit, and offsetting is generally understood as a bridge for what cannot yet be avoided, not a substitute for reducing emissions at the source. The honest summary most of the industry converges on is that reaching net-zero by 2050 requires progress on every lever at once, with SAF scale-up as the most consequential piece over the next two decades.