Elon Musk has warned humans could “self-extinguish” before his firm SpaceX is able to colonize Mars.
The Tesla CEO said his plans could also be scuppered by a supervolcano, a comet strike, or a “giant war”.
If World War Three broke out, there was a “low” chance of building a self-sustaining city on Mars afterward, he added.
The billionaire, 49, has said he wants to set up a self-sustaining Martian civilization, which he described as a “great adventure”.
Speaking at the 2020 Mars Society Virtual Convention, he said: “I think it’s helpful to have as the objective the creation of a self-sustaining city on Mars.
“This has to be the objective, not simply a few people or a base, but a self-sustaining city.
“The acid test really is if the ships from Earth stop coming for any reason, does Mars die out?”
He continued: “Are we going to be able to create a self-sustaining city on Mars before or after World War 3?
“Hopefully there is never a World War 3, but the probability of launching after World War 3 is low.
“We should try to make this city self-sustaining before any possible World War 3.”
He continued: “Really we just face a series of probabilities. There’s some chance we could have a giant war, a supervolcano, or a comet-strike – or we might just self-extinguish.
“Quite frankly, right now, civilization’s not looking super strong, you know, we’re looking a little rickety right now.”
But he warned it’s “not an escape vehicle” unless Mars is made self-sustaining, which will “probably not happen in my lifetime”, the Express reports.
The tech mogul recently set himself the goal of sending humans to the Red Planet by 2026 – seven years before NASA aims to land astronauts there.
SpaceX is currently developing the Starship rocket, which aims to carry up to 100 people and equipment to Mars.
But a second full test flight of the company’s latest Starship prototype crashed last Tuesday in Texas, US.
Bosses recently announced plans to offer the “first all-civilian” flight into the Earth’s orbit during the fourth quarter of 2021.