It's been the pretext of many a science fiction novel.
The world is in peril.
It's an asteroid!
It's Global Warming, urhh Cooling, uhh Change!
Change! (That's the ticket!)
The nations must unite!
A Global Legislative Body must be created.
Oh! How convenient!
We already have a corrupt international legislative body: the U.N.!
If you want people to unite you must give them a cause common to them to fight.
A common enemy.
If you want to create a global government and you cannot get aliens to invade the earth, then you must find some other major global impending disaster to unite the nations under your political control.
Thus global climate change.
Just ignore all the data, buy off some politicians with foreign aid and foundation donations, buy off some scientists with grants and have politicians pontificate on a subject they have no understanding of and throw an international party that everyone can charge off the expense of (put it in Paris, that'll guarantee a crowd) to talk about it.