Humanity is not essential for the survival of the universe, says physicist Stephen Hawking.
Professor Hawking, the author of the best-selling A Brief History of Time, cautioned that the human race will not survive another millennium if the greenhouse effect becomes irreversible.
Hawking is calling for stronger public reaction and is urging people to look after the planet.
"We are just a chemical scum on a minor planet," he said.
He is also warning that a nuclear calamity could be triggered by an accident or by terrorists capturing nuclear weapons.
"We now have good evidence that the world is getting warmer. I'm worried that the greenhouse may become irreversible and the atmosphere might become like that of Venus, raining boiling sulphuric acid," Hawking said .
"Russia and the United States are no longer so trigger happy, but they still have enough bombs to destroy everyone on the planet," Professor Hawking told a press conference in Bombay, India's financial and film capital, where he attended a week-long international scientific conference.
"Nuclear war is a danger we would have rather forgotten," he said and added that the risk increased with more countries acquiring nuclear weapons. Suppose there's an accident or terrorists get hold of them," he said.
In May 1998, India and Pakistan conducted a series of nuclear tests, joining the United States, Russia, Britain, France and China as the only countries that have openly declared their nuclear weapons status.
Hawking is in Bombay for a conference on the string theory - the so-called Theory of Everything - that the British physicist and others feel could provide answers to conflicting theories on the origin and fate of the universe.