[mikro2nd]

I suspect that the only way for long-distance, heavy-lift aviation (and military aviation) to continue operating in a political/economic climate that demands CO2 reduction/elimination will be via biodiesel. Batteries ain't gonna do it. Zeppelins might be way forward for freight traffic where slow doesn't (often) matter as much, but for large scale passenger transport (again: assuming it's to survive) I don't see anything approaching the specific-energy embodied in diesel. Fischer-Tropsch (sp?) is well understood and can be made to work with pretty-much any feedstock.

[dieortin]

What about hydrogen?

[mikro2nd]

I've been advocating Hydrogen for energy storage/transport for decades, but I don't think it works for planes. Specific energy (energy per kg) is against it, I'm afraid. It's not the H2 that weighs much, but it's such a sneaky/leaky gas that containment vessels end up weighing quite a lot. (Maybe there have been improvements in the past decade or so - it's been about that long since I looked.) Hydride storage can't deliver the H2 fast enough for aircraft (again, unless there've been some advances) and we'll not even speak of the flammability issue ;)

[benhurmarcel]

Many large companies in the aviation industry are investing hard on it though. For example: https://www.airbus.com/innovation/zero-emission/hydrogen/zer...