Four Routes to Lower Aviation Emissions, Ranked by Timescale
Aviation decarbonisation is usually discussed one technology at a time, which makes it hard to see how they relate. Put side by side, they sort into a clear order — and the ordering is by timescale rather than by ambition.
Efficiency: available now, limited ceiling
Newer engines and airframes, better routing, higher load factors, weight reduction, single-engine taxi. All of it works today, all of it saves money as well as carbon, and because combustion CO2 is fixed per kilogram of fuel, every percentage of fuel saved is a percentage of emissions saved.
The ceiling is the problem. These are incremental gains against traffic growth, and efficiency improvements have historically been outpaced by demand.
SAF: available now, constrained by supply
Drop-in fuel, no new aircraft, no new infrastructure. The constraints are production volume, cost, and the arithmetic of blending: the saving is blend percentage times lifecycle reduction, so a 2% mandate saves about 1.4% and a 50% blend at a 70% pathway saves 35%.
The SAF calculator makes that ceiling visible. It is the largest near-term lever available and it is not, on its own, a solution.
Electric: real, and short-range
Batteries carry about 0.9 MJ/kg against kerosene's 43 — a gap of roughly 48 to 1, only partly offset by an electric drivetrain's much better efficiency. The range calculator puts ten tonnes of battery at about 2,700 km against 57,300 for the same mass of Jet A on the same aircraft.
That makes electric flight a trainer, commuter and short regional technology rather than a narrowbody one, and it is genuinely useful there. Hybrid configurations extend the reach somewhat.
Hydrogen: favourable physics, hard engineering
Nearly three times kerosene's energy per kilogram and no CO2 at the engine, against a quarter of the energy per litre, cryogenic storage at minus 253 °C, tanks that will not fit in a wing, and an airport fuel system that does not exist.
It also depends entirely on clean hydrogen production, and its water emissions at altitude are a genuine open question. Credible programmes are aimed at regional aircraft on a decades-long timescale.
What the ordering implies
Efficiency and SAF are what can move this decade. Electric addresses the short end. Hydrogen is a long-horizon bet on the medium end. Nothing on the list replaces long-haul kerosene in the near term, and no honest account of the subject says otherwise.
That is not an argument for doing nothing. It is an argument for being precise about which lever operates on which timescale, since the alternative is treating a 2% blend mandate and a hydrogen aircraft programme as though they were competing answers to the same question.
The part the numbers leave out
Everything above concerns CO2. Aviation's non-CO2 effects — contrails, induced cirrus, nitrogen oxides at altitude — are a substantial and uncertain part of its total climate impact, and they respond to different interventions: routing to avoid contrail-forming conditions is a live area of research with no fuel change required at all.
A CO2 calculation is a floor on the impact and a well-defined one. It is not the whole account, and any tool that produces a single number, including the ones on this site, should be read that way.