Tragedy of the commons regulation for global shared stocks/sinks – e.g. there’s a single shared global atmosphere that we’re collectively not managing very well.
I don’t believe world government “would” necessarily solve this, but it might help.
Another question might be “what are the issues that a world government might cause”.
E.g. there isn’t a guarantee that world government is going to be representative, care about interests other than its own, not be repressive. At least with smaller scope governments it is in principle easier to flee.
Perhaps another question would be: why would member states / individuals voluntarily join a world government and choose to stay part of it? How would that be a good tradeoff for them?