The argument is that focusing on space exploration deflects from facing the realities of climate change on our planet. If people start to think that space exploration could yield a solution to an increasingly uninhabitable climate on Earth, it could create a scenario where we spend even more on space exploration and less on addressing Earth's climate.
Once we are dealing with scenarios where hundreds of millions of humans are dying, it becomes harder to rule out the possibility of some desperate political or military leader resorting to using nuclear weapons. From there it is a small step to full nuclear war and the deaths of billions of humans.
Perhaps the "optimistic" scenarios are ones in which the hundreds of millions of humans that die are located far away from any nuclear armed countries, or at least those countries aren't destabilised by the economic and migration consequences of those deaths. I can, unfortunately, imagine militaries being routinely used this century for wiping out the remaining civilian populations of failed states.
This thinking seems backwards. How can we learn to take a totally dead planet and make it living when we can't even figure out how to keep this one healthy?
Mars and Venus are, as far as every experiment has shown, dead as doornails. Using them as a testbed for experiments that are too dangerous to do on Earth without first practicing is a good use for them.
To give two examples among many:
SpaceX's next major goal after making Starship capable of flying to Mars is to develop the infrastructure to refuel Starship on Mars. They plan to manufacture their fuel using the Sabatier process, which is also a form of carbon sequestration.
Research and development into Martian food production pushes the envelope in many agricultural research areas like vertical farming, high efficiency production with few inputs, et cetera.
Furthermore, cheap space travel does solve global warming because it makes the solution of orbital sun blocking feasible, which unlike currently available geoengineering tech, is instantly reversible.
Both is more than one.
Does it? It's not an either/or proposition.
Researching and developing technologies to allow humans to live in space in a sustainable way seems like it would almost certainly also create applications of such technology that can benefit us on Earth.
Whether that's methods to scrub the atmosphere of a space-based habitat of toxins/pollutants, utilize waste in productive ways and a raft of other stuff would be incredibly useful on Earth.
As an aside, I'd point out that even if we start colonizing space habitats, other planets and/or even planets around other stars, there are no technologies available or imagined that could transport colonists from the Earth faster than birth rates would replace them and continue population growth.
Yeah, you should avoid needing that but it is certainly not impossible given high enough tech level & in-space infrastructure. Launch loops and orbital elevators should have more than enough capacity to enable that.
For a science-fiction-backed-by-real-science account of it might go, see this Orions Arm article: https://www.orionsarm.com/eg-article/49b46fd2198ed
Much bigger problem actually is where to put those billions once you have to move them in a hurry off a planet.
I think you're underestimating the effort, resources and logistics something like this would require.
In 2016, there were ~256 live births per minute[0]. That works out to ~369,000/day.
Even multiple space elevators couldn't hope to come anywhere close to that, but perhaps with launch loops as well we might be able to approach that.
But even if we could, how much of global production of, well everything, would need to be dedicated to getting even 350,000 people and the stuff they need off the earth every single day?
>Much bigger problem actually is where to put those billions once you have to move them in a hurry off a planet.
An excellent point. Even if you didn't need to hurry, the resources required just to stage such a migration are staggering and would likely exceed the production capabilities of the planet.
But as you point out, we don't really have any place to send all those "colonists" so the point is moot.
In order to make this argument, you have to first figure out what percentage of NASA's budget is spent on space exploration versus things like GPS systems, weather satellites, climate monitoring, solar monitoring, physics experiments, etc etc, which have direct or indirect benefits to things happening here on earth.
NASA's budget for entire actual space exploration would be more-or-less a rounding error on our defense budget which routinely has $5b projects which benefits very few people and arguably makes the quality of life worse on our planet.
Space exploration is more though, because not only is space exploration an investment in a back-up plan, it brings very real benefits home to earth. The whole point of exploration is that you don't know what you are going to find or what the repercussions of what you find will be.
In the early 70's, physicist Gerard K. O'Neil asked the question "Is the surface of a planet really the right place for an expanding technological civilization?" [0]
You would seem to answer this question with 'Yes.' Why?
As far as we know, we are the only part of the universe that is capable of consciousness. The argument is that it is worth going to great lengths to insure against species-wide disasters (e.g. runaway global warming, giant meteor, World War 3)
Its macro-level thinking versus micro-level.
But they have. Bezos has invested heavily into Rivian, and Musk into Tesla.
And as you've mentioned it helps create new technology opportunities which also generate efficiency/value/taxes like space internet and in the longer term mining without destroying our planet.
There are plenty of benefits to society. Although there will always be a contingent who thinks everything not an altruistic social giveout = bad use of excess capital.
And what exactly is "addressing Earth's climate" ?
This naive hope that green parties keep pushing "if we cut carbon emissions it's all going to go back to the way it was" ?
Carbon levels have already risen and climate change is already happening - nobody can realistically predict the specifics or the time scale. All existing predictions I've seen have been way out of error margins - and stuff like thawing ice and releasing trapped methane etc. can have huge non-linear contributions.
Saying that X% cut in emissions is going to reduce temperature increase by Y on Z timescale is just wishful thinking, and we don't even have mechanisms to enforce X% cut across the world.
Investing in technology that could help settle Mars is a way to protect from the inescapable negative climate effects we will have to live with, the sooner we start to deal with those the better (eg. start building for hurricanes/floods/large temperature differences, etc.)