Stephen Hawking expressed concern that life on Earth is at risk from a sudden nuclear war, a genetically engineered virus, global warming, or other dangers humans have not yet thought of. Hawking stated: “I regard it as almost inevitable that either a nuclear confrontation or environmental catastrophe will cripple the Earth at some point in the next 1,000 years”, and considered an “asteroid collision” to be the biggest threat to the planet. Such a planet-wide disaster need not result in human extinction if the human race were to be able to colonize additional planets before the disaster. Hawking viewed spaceflight and the colonization of space as necessary for the future of humanity.