Professor Hawking said people need to work together to tackle the issues
These include environmental threats like climate change and diseases
He also mentioned the dangers of people losing jobs to AI and robots
The physicist said we have technology capable of destroying the planet
[Note] - World government is not really something he is advocating. Rather, it is the lesser of two evils. Constructing a world government that will not eventually fall prey to corporate control, tyranny, classism / racism / and the continuing division between rich and poor, will be virtually impossible, imo. More importantly, the emergence of technology, AI, robots, computerisation, GMO, etc., all make it both easier for the control by groups at the top, and also makes it more likely that technocracy will overtake the entire globe.
Before we move towards a dangerous world government, we NEED to work out a completely new economics, invested in the ecology and in humanity. Things are already so out of control that, I am certain, technocrats are already working on ways to cull billions of people. Always, these plans arise in secrecy.