[Stratos]

"Now, is this a good thing or a bad thing."
There have to be a certain population increase if the pension system should work but, of course, a population explosion is not good either. Countries with a population growth like that will have problems supporting it´s citizens. More people being born will eventually lead to more elderly which will require more people to be born to support them.

"Also, at what point will Europes voice in the United nations end up being one vote, one voice? If Europe are a united nation with a combined foreign policy, combined economy and all the other benefits of being a single nation, why should they keep the many votes that belong to a seperate nations?..."
Parts of Europe already has a somewhat combined economy in shape of the Euro but a common foreign policy might prove to be more difficult to achive, the War on Iraq thing shows that well. I don't see Europe as one single nation for a long time, but a federation of states isn't impossible. There are after all a federalist movement in Europe. On the other hand we Europeans are a diverse lot who have waged war against each other since the beginning of time and have different cultures and languages so a single nation will be difficult to create. European countries will probably want to stick with their votes in the UN, they are after all not that united.

"Now, if the population sizes proportionally change, what will this mean? As Asia ends up vastly outnumbering Europe, will geopolitical power shift to recognise these changes, or will Europe hold onto world power, like an aging Emperor."
Perhaps, but that would require them to be more modern and efficient. Europe, USA, Australia, New Zeeland, and Japan makes up less than 1/6 of Mankind yet we have a more or less complete economic dominance. And these countries are not likely to let go of their power that easy. Most of the population explosion takes place in more or less poor countries that have little power themselves. But China have a great potential to become very powerful.