With Betrand Piccard, Swiss, at the helm of Solar Impulse I and II, history was made in the early 21st Century with around-the-World travel in a solar-based heavier-than-air-craft.
We must reduce and eventually ban carbon and fossil fuel-based flight. The effect on the atmosphere is even greater with high altitude flight.
ALL carbon or bio-based fuel must eventually be eliminated with equity. All flight must eventually be solar/electric/instantly renewable.
Solar Impulse has support of airmen and some aircraft companies. Only a beginning in around-the-world flight. Still, we must uphold reduction in a region’s/culture’s/country’s emissions as per Paris Agreement and IPCC findings. This is the basis of the student strikes and other actions.
We can think beyond this. Science must think beyond this.
Many regions do not have developed train or rapid transit. Our Earth is diverse. If we do not want to destroy habitat by building more steel tracks or boring tunnels through mountains, we must consider other means of transport.
In some ways, the less-developed South American continent is very similar to the seat of Empire, the USA in this. Both have more or less untouched mountain ranges crossing the continents. The Andes. The Rockies. We do not want to increase our footprint by building more rapid transit on the ground.
Same maybe true of Africa, as well. River basins; jungle; savanna. We do not want this disturbed, so lighter-than-air and solar flight seem – at present – the best options.
Africa, South and North America have airport infrastructure in place.