He think that the nuclear warheards in USA and Russia are enough to destroy the earth several times,so the biggest danger people are facing is nuclear war.In addition,climate change will also threat human's surviving environment.So Hawkin suggest that we move to other planets.However,I think that even though there are many nuclear warheads in the earth,leaders of these countries can sit down to have a talk and they will be aware of the danger of using nuclear weapons and stop using them.Also,if all people can start to use less energy,the climate will be sure to turn back into how it was like before.