Beware! "Zero-emission" is never possible; not for aircraft, not for animals/humans. Coming quite close to it with an aircraft is possible if you understand how! It is possible already with aircraft flying TODAY [1], if those responsible only want. Do they?

Airbus: "By 2035, the world’s first zero-emission commercial aircraft could [or could not] take to the skies. To bring this vision to reality, Airbus is exploring [not: developing and building] game-changing concept aircraft – known as ZEROe – powered by hydrogen, a disruptive zero-emission technology [note: the technology is zero-emission not the aircraft] with the potential to reduce aircraft emissions by up to 50%. [2]
What is meant? "zero-emission aircraft" or only "reduce aircraft emission by up to 50%"?
What is meant? "zero-emission aircraft" or only "zero-emission technology"?

"At Airbus, we are convinced that carbon-neutral aviation is ... achievable." [3]
When? What is "carbon-neutral aviation"? Is it "carbon-neutral growth (CNG)"? This is due in 2020, but is not achieved (or only due to the Corona pandemic). So it must be "no carbon" or "a closed carbon cycle" making carbon (CO2) emissions "neutral".

"... it is estimated that hydrogen has the potential to reduce aviation’s CO2 emissions by up to 50%." [4]
Why only 50%? "50%" is not "carbon-neutral aviation". How to achieve "carbon-neutral aviation", if 50% CO2 is still emitted?

Please compare with the first statement: "reduce aircraft emissions by up to 50%" versus "reduce aviation’s CO2 emissions by up to 50%". "aircraft emissions" or "aviation's emissions"? "emissions; 50%" or "CO2 emissions; 50%"?

"This is why we have the ambition to develop the world's first zero-emission commercial aircraft by 2035." [3]
"Zero-emission" by only reducing CO2 by 50%? Aviation's emissions are more than only CO2. We do not have a CO2 problem. We have a water problem!

"All three ZEROe [zero-emission] concepts are ... powered by hydrogen combustion." [5]

The logic here is difficult to grasp.

Facts are:

1. Hydrogen combustion emits 2.6 times more water per energy than kerosene.
2. This leads to contrails forming already at lower altitudes and hence more often.
3. Hydrogen is an energy carrier that is responsible for as much CO2 as its production has emitted.
4. If hydrogen is produced from electricity, the energy mix has to be accounted for. No one can claim only the "clean portion" of the electricity and leave the "dirty portion" to others.
5. Aviation's emissions contributing to global warming are much more than CO2! They include also NOx.
6. A large contribution to global warming is from Aircraft-Induced Cloudiness (AIC). See Figure 1 in [6].

It is not only about emissions, it is also about depletion of resources and primary energy consumption. The primary energy factor of electricity is about 2.6. A Life Cycle Analysis (LCA) sums it all up. Did Airbus do it? No, not that we would know of.

Nevertheless, hydrogen has a potential in aviation! But it needs to be discussed fully and done right!

[1] CAERS, Brecht; SCHOLZ, Dieter, 2020. Conditions for Passenger Aircraft Minimum Fuel Consumption, Direct Operating Costs and Environmental Impact. Deutscher Luft- und Raumfahrtkongress 2020 (DLRK 2020), Online, 01.-03.09.2020. Available from: https://doi.org/10.5281/zenodo.4068135
[2] https://www.airbus.com/newsroom/stories/these-new-Airbus-concept-aircraft-have-one-thing-in-common.html
[3] https://www.airbus.com/company/sustainability/environment/decarbonisation.html
[4] https://www.airbus.com/innovation/zero-emission/hydrogen.html
[5] https://www.airbus.com/innovation/zero-emission/hydrogen/zeroe.html
[6] KÄRCHER, Bernd, 2018. Formation and Radiative Forcing of Contrail Cirrus. In: Nature Communications, Vol. 9, Article Number: 1824. Available from: https://doi.org/10.1038%2Fs41467-018-04068-0