What are the low-carbon alternatives for long-distance travel? For overland travel, I guess we already know the answer: High speed electric trains and electric

What are the low-carbon alternatives for long-distance travel? For overland travel, I guess we already know the answer: High speed electric trains and electric cars / buses (which will eventually become self-driving), with the power being generated by renewables/nuclear. For travelling over oceans, it's much more difficult. Are there any realistic concepts out there? A new generation of sailing ships? It's really disappointing to see the lack of political leadership on this stuff. Nobody in politics is saying: "we're going to have to stop flying one day, it might be a good idea to start funding the alternatives"