Future Flying

Although carbon dioxide emissions from aviation account for less than 2% of the total contribution to global warming, the overall climate impact of flying is considerably larger. Aviation produced roughly 2.14% of total global CO₂ emissions in 2024 ^A,B (just under a billion metric tons), but aircraft also emit water vapor, nitrogen oxides, soot, and other particles and aerosols at high altitudes, where they interact with atmospheric chemistry and cloud formation in ways that trap both incoming solar radiation and re-emitted longwave radiation from the Earth which stops it from escaping, both of which amplify warming. Contrails and contrail-induced cirrus clouds, in particular, enhance the greenhouse effect by trapping infrared radiation (see reference note below for [17,18]), while nitrogen oxides lead to ozone formation, another greenhouse gas. When these non-CO₂ effects are combined with direct CO₂ emissions, the total radiative forcing from aviation is estimated to be about 3.4-4% of human-driven warming, making aviation’s climate footprint roughly double what its carbon dioxide emissions alone would suggest.

Contrails are ice-crystal clouds formed by aircraft at cruising altitude, made out of condensation trails of water vapor (from fuel combustion and the surrounding atmosphere). Water vapor can condense onto aircraft aerosol emissions, such as soot (carbon) particles. These clouds are short-lived, but the colder and more humid the air is, the longer they persist.

These clouds can influence Earth’s energy balance in two opposing ways. During the day, their bright, reflective surfaces can scatter and reflect a portion of incoming solar radiation back into space, exerting a short-lived cooling effect by reducing the amount of sunlight that reaches the surface. At the same time, however, contrails act like thin cirrus clouds, efficiently absorbing and re-emitting longwave infrared radiation emitted from Earth’s surface. This process traps heat within the lower atmosphere, producing a net warming influence that is particularly pronounced at night, when the absence of incoming solar radiation means only the heat-trapping effect remains. Overall, the warming effect of contrails tends to outweigh their reflective cooling effect. However, the mechanisms behind this effect are still poorly understood, and research is constantly being conducted to further quantify the overall impact and the conditions required.

The cited 15-25% figures generally describe the fuel-efficiency improvement of newer-generation aircraft and engine combinations over the aircraft they replace, rather than changing only the engine on an existing airframe. Results vary by aircraft class, route and operating conditions ^{[11,22,36,37]}.

The “50 times” comparison contrasts energy stored per unit mass of current batteries with the chemical energy contained in jet fuel per kilogram. It is a useful raw fuel-mass comparison, rather than a complete propulsion-system comparison: electric motors are substantially more efficient than turbine engines, while battery packs also require casing and thermal management and retain their mass after discharge. The relative mass can therefore vary, although batteries still store far less usable energy for their weight, which remains the central limitation ^[74-79].

Flight tests of prototype electric aircraft have been conducted in several locations, notably in the UK, USA, and China. These tests involved short flight durations between airfields in close proximity, or longer flights that involved laps of airfields, under carefully controlled airspaces. These tests were conducted by private companies or respective air forces, displaying the capabilities of electric aircraft. However, fully electric commercial aircraft are still under development, with plans to go airborne within the decade. These will be regional flights of less than 500km, with minimal passenger capacity, as shown in [89-93]. Electric medium and long-haul flights (from international flights up to intercontinental and trans-Atlantic distances) are projected to be commercially viable by the 2090s ^{[14,74,75,94]}. However, some industry and academic experts have suggested that is a very optimistic estimate, and some believe that electric aircraft over long-haul distances will never be commercially viable.

Sustainable aviation fuel still releases CO₂ when burned. Its potential climate benefit is primarily assessed across the fuel’s lifecycle, because biogenic carbon or carbon captured from the air can replace the release of newly extracted fossil carbon. However, actual emissions savings depend on the type of feedstock used to produce the fuel, land-use changes involved, energy used in production and transport, additionality (whether claimed indirect savings would have happened anyway) and the proportion blended with conventional fossil fuel. Different SAF pathways can therefore deliver markedly different levels of emissions reduction ^{[95-100,135,136]}.

CORRECTION: Around 55% of European airlines’ publicly announced SAF commitments and supply agreements are expected to come from used oils and fats, including animal fats, used cooking and other waste oils. This describes agreements and planned contracts, rather than fuel already in use as implied in the video.

Hydrogen contains no carbon, so hydrogen fuel cells only produce water at the point of use. Hydrogen combustion produces water vapor and can also cause nitrogen and oxygen in the air to react and form nitrogen oxides.

The approximate 86% NOₓ reduction reported by [124] applies to its specified aircraft configuration and is not a universal reduction rate.

Overall lifecycle emissions (and thereby emissions savings relative to conventional jet fuel) associated with hydrogen fuel depend on renewable-powered hydrogen production in place of carbon-intensive methods, plus indirect emissions from the energy and infrastructure required to produce, cool, compress, transport and store the hydrogen as well ^[122-126].

Estimates have been made for when the first hydrogen-powered aircraft will be commercially available. Early industry and government scenarios placed entry into service at around 2035-2040 ^[131-133]: McKinsey & Company ^[133] estimated that in an optimistic scenario, hydrogen planes could be available from 2035, but Business-as-Usual and Prudent scenarios suggested a later market entry of 2040. This optimism was shared by Heathrow Airport and the UK Government ^[131] who suggested that this aircraft could be used domestically from 2035, regionally by 2040. However, these are projections rather than confirmed delivery schedules. The UK source itself is now archived, raising questions about whether more recent updates have rendered these predictions unlikely.

Airbus’ ZEROe program ^[132] has aimed to introduce a hydrogen-powered aircraft into service by 2035, but in February 2025, announced that this project had been postponed, citing that the technology was developing slower than anticipated, indicating a delay of 5-10 years ^[134]. Several months later, they had still not indicated a clear timeline for their first hydrogen-powered aircraft, cutting the budget for the project.

The 3:1 figure describes the chemical ratio between molecules, rather than their relative weight or volume. In simplified terms, producing e-SAF requires roughly three hydrogen molecules for every molecule of captured carbon dioxide. The precise balance varies somewhat with the production process and final fuel. For example, [136] gives an H₂-to-CO feed ratio of approximately 2:1 - captured CO₂ may first be converted to CO, which consumes additional hydrogen. No single input ratio applies to every production route, but 3:1 provides a useful guide to the underlying chemistry.

The Project SkyPower figure is a forward-looking industry projection based on e-SAF expanding rapidly with sufficient investment and policy support. It is not an established market forecast or guarantee. The outcome will depend on how quickly production scales, but the projection illustrates the substantial role e-SAF is expected to play by 2050.