Space travel is fundamental to the human species living sustainably in the long term. Correcting greenhouse gasses doesn't help us if the next day we find a planet-killer asteroid is a few weeks away.

In this regard, the comment about CO2 is actually much more pertinent than it seems at first. If we manage to screw up the climate in this century (which seems very likely these days), inundating every coastal cities in the world, "sustainable space colony" will have to wait a bit longer. Much longer. If you're worried that an asteroid might hit us 500 years from now, you might want to rethink your priority.

Advancing chemical rockets now is important, but compared to the scale of space colony, it feels somewhat like producing better vacuum tubes to make sure (say) the US is the first to create strong AI. Any sane 50s US leader would have understood that "trying not to have a nuclear war with Soviet" is a much more important goal anyway: you can't fund AI research if your country is a radioactive wasteland.

We went from not flying anything heavier than air to going to the Moon in 66 years. If we really really wanted to, we could go to Mars in thirty. This is a problem of priorities, not technologies (although the technological problems are real, they are not insurmountable).

CO2 is a direct and immediate threat.

Unless the lead time is 50-100 years, years might as well be tomorrow, it's going to kill us all either way. Even that might be stretching it.

> Humans as a species will survive CO2

Maybe, personally I believe humans will cause their own extinction. I'm just not sure yet if we're going to take all life with us or not. Dealing with CO2 is a toss up between making the planet uninhabitable or completely inhospitable to life.

So... what, we just halt development of all vehicles, globally, period? Bye-bye trains, planes, cars, bicycles, and buses?

You can't develop the future of transportation or the future of propulsion systems if you literally shut down global commerce.

Besides, an airplane (for example) is not wedded to the engine. Developments in prop planes carried over directly to jet planes, once the jet engine matured. Any future propulsion system that can replace jet engines will probably not be hard to work into many plane designs of the day.

Better to make incremental progress on poverty, without constraining the innovators to work on problems that don't interest them, or that seem even more intractable than e.g. space travel or AI.

Those same < 10 000 people probably doesn't know nor have the ability to fix all the problems on Earth, but they might be able to get to Mars.

Parent: See that little blue dot in the night sky? That’s Earth.

Child: What is Earth?

Parent: Earth was the planet of our ancestors, before people came to Mars.

Child: Who lives on Earth now?

Parent: Nobody. It’s a dead planet. The actions of rich, selfish people destroyed it.

Child: How did the rich, selfish people destroy Earth?

Parent: They burned it up as fuel, getting to Mars.

That proverbial man who plants trees knowing he will never sit in their shade is proverbial for a reason.. it's an amazing and heartwarming little saying because it's a contrast to how we generally behave, as individuals as well as organizations and masses. We learn from repeated catastrophe.. sometimes, maybe. But this problem is not one we can have a lot of attempts at solving. Right now we are still moving into the wrong direction, and probably even accelerating.. sure, hitting a wall can make people change their direction, but not if it breaks their neck, so to speak.

I'm not enormously optimistic. I'm just saying that compared to interstellar travel, avoiding fossil fuels seems like a fairly small problem.

The biggest lever we've got right now is computation, so yeah maybe it would be more efficient to develop AI / IA first and then mass space travel, but we can't be sure.

Also, fundamentally we can accept a few billion deaths. That sounds and is grotesque, but it wouldn't be the end of humanity. I don't see how climate change kills us all in the next 100-500 years.