The late physicist, who died in March this year at the age of 76, penned his worries about the future in his last book Brief Answers to the Big Questions.
In his conclusive work, Professor Stephen Hawking warned of rising global temperatures, asteroids, the threat of nuclear war and the rise of artificial intelligence.
He wrote: “The Earth is under threat from so many areas that it is difficult for me to be positive. The threats are too big and too numerous.”
First, the physicist argued the Earth is far too small to sustain the rapid growth of its indigenous human population.
Professor Hawking said humans are “draining” the planet of its resources faster than it can replenish them.
As a result, global warming and climate change have become major threats to the planet’s stability and survivability.
The scientist wrote: “Global warming is caused by all of us. We want cars, travel and a better standard of living.
“The trouble is, by the time people realise what is happening, it may already be too late.
“As we stand on the edge of a Second Nuclear Age and a period of unprecedented climate change, scientists have a special responsibility, once again, to inform the public and to advise leaders about the perils that humanity faces.”
I am convinced that humans need to leave Earth. If we stay, we risk being annihilated
Professor Hawking said climate change threatens to kill off the Amazon rainforest, decimate the polar caps and pump the atmosphere full of Carbon dioxide.
But the biggest threat in his estimate is the possibility of nuclear war, which he feared humans have forgotten about.
The professor said Cold War animosity between the US and Russia may no longer be the catalyst for war, but raised the possibilty of terrorists getting ahold of nuclear material and building dirty bombs.
He argued the risk of this happening grows with each country that realises its nuclear potential.
In one way or another, Professor Hawking said it is “inevitable” a nuclear or environmental cataclysm “cripples” the planet.
But if this happens and the planet is irreversibly damaged – could we find shelter among the stars?
Not necessarily, according to Professor Hawking, due to the “violent nature” of space.
The scientist said space is full of black holes, powerful radiation and rogue asteroids – another source of potential destruction on Earth.
Still, he argued the only solution is to abandon the sinking ship and set course for new worlds where humans might not replicate their mistakes.
Professor Hawking said: “We can be an ignorant, unthinking lot. When we have reached similar crises in our history, there has usually been somewhere to colonise.
“Columbus did it in 1492 when he discovered the New World. But now there is no new world. No Utopia around the corner.
“We are running out of space and the only places to go to are other worlds.”
In the long run, Professor Hawking urged humans to cast a wide net throughout space and successfully settle as many new worlds as possible.
Doing so will ensure the survival of the human race even if its demise is accelerated by its own hands.
He said: “I am convinced that humans need to leave Earth. If we stay, we risk being annihilated.”