Humans must leave Earth in the next 200 years if we want to survive.

That was the stark warning issued by Professor Stephen Hawking in the months before his death at the age of 76.

The legendary physicist believed that life on Earth could be wiped out by a disaster such as an asteroid strike, AI or an alien invasion, the Daily Mail reported.

He also warned over-population, human aggression and climate change could cause humanity to self-destruct.

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He believed, if our species had any hope of survival, future generations would need to forge a new life in space.

Climate change

One of Hawking's main fears for the planet was global warming.

"Our physical resources are being drained, at an alarming rate. We have given our planet the disastrous gift of climate change," Hawking warned in July.

"Rising temperatures, reduction of the polar ice caps, deforestation, and decimation of animal species. We can be an ignorant, unthinking lot."

Stephen Hawking warned over-population, human aggression and climate change could cause humanity to self-destruct. Photo / AP
Stephen Hawking warned over-population, human aggression and climate change could cause humanity to self-destruct. Photo / AP

Hawking said that Earth will one day look like the 460°C (860°F) planet Venus if we don't cut greenhouse gas emissions.

"Next time you meet a climate change denier, tell them to take a trip to Venus. I will pay the fare," Hawking quipped.

The physicist also believed President Donald Trump's decision to withdraw from the Paris Climate Agreement has doomed our planet.

He warned Trump's decision would caused avoidable damage to our "beautiful planet" for generations to come.

"Next time you meet a climate change denier, tell them to take a trip to Venus. I will pay the fare," Hawking once said.

"We are close to the tipping point where global warming becomes irreversible," the celebrated scientist told BBC last year.

Asteroid strikes

If global warming doesn't wipe us out, Hawking believed Earth would be destroyed by an asteroid strike.

"This is not science fiction. It is guaranteed by the laws of physics and probability," he said.

"To stay risks being annihilated.

"Spreading out into space will completely change the future of humanity. It may also determine whether we have any future at all."

Hawking believed Earth would be destroyed by an asteroid strike. Photo / 123RF
Hawking believed Earth would be destroyed by an asteroid strike. Photo / 123RF

Hawking was working with Russian billionaire Yuri Milner's Breakthrough Starshot project to send a fleet of tiny "nanocraft" carrying light sails on a four light-year journey to Alpha Centauri, the nearest star system to Earth.

"If we succeed we will send a probe to Alpha Centauri within the lifetime of some of you alive today," he said.

Astronomers estimate that there is a reasonable chance of an Earth-like planet existing in the "habitable zones" of Alpha Centauri's three-star system.

"It is clear we are entering a new space age. We are standing at the threshold of a new era," Hawking said.

"Human colonisation and other planets is no longer science fiction, it can be science fact."

Hawking believed that In the long run the human race should not have all its eggs in one basket, or on one planet.

"I just hope we can avoid dropping the basket until then," he said.

AI could replace humans

Hawking claimed that AI will soon reach a level where it will be a "new form of life that will outperform humans".

He even went so far as to say that AI may replace humans altogether, although he didn't specify a timeline for his predictions.

The chilling comments during a recent interview with Wired.

He said: "The genie is out of the bottle. I fear that AI may replace humans altogether.

"If people design computer viruses, someone will design AI that improves and replicates itself.

"This will be a new form of life that outperforms humans."

He also he said the AI apocalypse was impending and "some form of government" would be needed to control the technology.

During the interview, Hawking also urged more people to take an interest in science, claiming that there would be "serious consequences" if this didn't happen.

Stephen Hawking's pearls of wisdom

• On the reason the universe exists:

"If we find the answer to that, it would be the ultimate triumph of human reason - for then we would know the mind of God" - A Brief History Of Time, published 1988.

• On being diagnosed with motor neurone disease: "My expectations were reduced to zero when I was 21. Everything since then has been a bonus" - Interview in The New York Times, December 2004.

• On black holes: "Einstein was wrong when he said, 'God does not play dice'. Consideration of black holes suggests, not only that God does play dice, but that he sometimes confuses us by throwing them where they can't be seen" - The Nature Of Space And Time, published 1996.

• On God: "It is not necessary to invoke God to light the blue touch paper and set the universe going" - The Grand Design, published 2010.

• On commercial success: "I want my books sold on airport bookstalls" - Interview in The New York Times, December 2004.

• On fame: "The downside of my celebrity is that I cannot go anywhere in the world without being recognised. It is not enough for me to wear dark sunglasses and a wig. The wheelchair gives me away" - Interview on Israeli TV, December 2006.

• On an imperfect world: "Without imperfection, you or I would not exist" - In Into The Universe With Stephen Hawking, The Discovery Channel, 2010.

• On euthanasia: "The victim should have the right to end his life, if he wants. But I think it would be a great mistake. However bad life may seem, there is always something you can do, and succeed at. While there's life, there is hope" - Quoted in People's Daily Online, June 2006.

• On intellectual showboating: "People who boast about their IQ are losers" - Interview in The New York Times, December 2004.

• On the possibility of contact between humans and aliens: "I think it would be a disaster. The extraterrestrials would probably be far in advance of us. The history of advanced races meeting more primitive people on this planet is not very happy, and they were the same species. I think we should keep our heads low" - In Naked Science: Alien Contact, The National Geographic Channel, 2004.

• On the importance of having a sense of humour: "Life would be tragic if it weren't funny" - Interview in The New York Times, December 2004.

• On death: "I have lived with the prospect of an early death for the last 49 years. I'm not afraid of death, but I'm in no hurry to die. I have so much I want to do first" - Interview in The Guardian, May 2011.