Stephen Hawking has once again warned that humanity could wipe itself out before it has a chance to establish far-flung space colonies.

At a recent talk in England, the famed physicist singled out nuclear war, genetically engineered viruses and global warming as likely culprits. According to Hawking, the odds of a planetary disaster in the next millennia are high.

"Although the chance of a disaster to planet Earth in a given year may be quite low, it adds up over time, and becomes a near certainty in the next thousand or 10 thousand years," Hawking told the audience in a public Q&A session after this year's BBC Reith lecture in England. [9 Real Ways the World Could End]

Humans could survive if they have colonized other planets and stars before disaster strikes, he said.

But we're now entering a particularly perilous period, as humans haven't established a cosmic backup plan, as of yet, he added.

"We will not establish self-sustaining colonies in space for at least the next hundred years, so we have to be very careful in this period," Hawking said.

Repeated warnings

This isn't the first time the theoretical physicist has warned of planetary doom. Early last year, Hawking warned that human aggression threatened to wipe us all out. He's also spoken out about the potential for nonhuman threats, and has expressed concern that artificial intelligence could "spell the end for the human race." Both Hawking and billionaire entrepreneur Elon Musk have warned of the dangers of killer robots, and they both co-signed a public letter last year urging world leaders to ban killer robots.

Yet despite his gloomy prognostications, Hawking doesn't believe catastrophe is inevitable. Though he believes danger looms on the horizon, he said he is an "optimist" who believes humanity can overcome the risks facing it.

And Hawking, who has done groundbreaking work on black holes, string theory and other theoretical physics topics, has a positively cheery outlook on his own life and time.

"From my own perspective, it has been a glorious time to be alive and doing research in theoretical physics. There is nothing like the eureka moment of discovering something that no one knew before," Hawking said.

Listeners can hear Hawking's Reith lectures online on BBC Radio 4 on Jan. 26 and Feb. 2.

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