We need global democratic government. It's the only solution to everything from climate change to tax evasion and worldwide inequality. Is it possible? Yes. Is it probable? Less and less likely every day. We need to have a forceful push for this, or else we're going to be in a very bad state in the next 50 years.
The biggest obstacle to global governance is communication. How can the will of the people and that of a governing body be made intelligible to the masses if a country is large in size? Until recently, it wouldn't have been possible, but with the advent of the internet, it seems more and more feasible that we might one day see a centralized governing body for the entire world. A mediating force would be necessary to account for the differing social norms across the globe, but it seems logical that technology will eventually mitigate language and communication difficulties, and that the world will be so well-connected (commercially and culturally) that national divisions will begin to seem arbitrary.
Global governance may not happen for the next few decades or even when we are no longer alive to see it. There are people who may not want global governance to occur. Not everyone will agree when it comes to making decisions for their country or the world. There will always be someone who opposes the decision if it does not benefit them. People around the world have their own agenda, and I am certain they would not want to follow after someone else. Also, I believe that a single governing system is impossible. People will refuse to follow leaders that do not meet their concerns. Having a single system does not seem reasonable, a back-up system is needed in case that one single system fails. With the internet, people have more ways of knowing what goes on in the world, and who is doing what. This gives people access to making their opinions known to the world so to speak. This can spark disagreements between people or groups on the internet, and it can lead us to nowhere. These few reasons are why I believe global governance is very unlikely.
Global governance may be possible but it does not sound likely at least for the next few decades. There are people out there who may not desire or want global governance to occur. There is also the issue of conflicting relationships between countries and nations around the world. Unless people can band together or act neutral towards each other, global governance is not going to happen at all. One system can not control or regulate the entire world, it is not possible and not reasonable to have only one system in place. A back-up system may be needed in case all else fails. There is also the fact that even if global governance does happen, leaders of nations have their own agenda that benefits them and their country regardless of what others want.
If you think about it, with the current global leaders it is not possible because countries do not get along and will continue to not get along. Just because we have internet does not mean global governance will be achieved. Miscommunication is inevitable, but so is disagreement. Even if something seems miscommunicated to someone, that same person might not agree with what the communicator is actually trying to say. I highly doubt that more connection will make it more possible to have global governance. Also, I highly doubt that we would be able to convince the world to have one mediating force to basically rule the world.