The other answer here gets the main answer right but made some mistakes along the way. tl;dr: There's no answer to this question or The answer is completely unknowable, depending on a couple factors. Here's why:
There's no scientific definition of what a language is. That is to say, there is absolutely 100% no objective distinction between what is a language and what is just a dialect or variety. The distinction, when made, is done on sociopolitical grounds and not linguistic ones. The other commenter made the point that it's problematic to determine. I'm saying it's not a scientific reality that such a determination can be made.
We don't know what the actual linguistic diversity of the world is. There are many under-documented languages in the world. There are even languages which no one in the world has ever heard except those who speak it.
As a related point, we have absolutely no idea what languages existed in the past. Europe had other language that were lost before written records were kept, for example. Basque is the last descendent of these, and it itself not Indo-European. But what were its neighbours in the past before Indo-European spread? We can't know.
We don't know how language came about. There are guesses, but we just don't know. We don't even know if all modern languages share a common ancestor or not. If they did or if they didn't, the answer to this drastically changes the number of possibilities.
If the question were answerable at all, there are far too many unknowns to be able to do so. In actuality, it's just not answerable.
Answering your question would require determining at what point a dialect becomes a completely different language. For one example, take modern American versus British English: they're pretty clearly the same language. But, what about something like Hawaiian Pidgin English? I can understand it based on my knowledge of English, but it's obviously got its own grammar and (restricted) vocabulary. Spanish and Portuguese might be a little further separated than this: based on studying Spanish for a couple years in high school, I can sometimes understand Portuguese.
This was a much more significant issue before modern communications such as the printing press standardized languages. In the ancient world and the Middle Ages, you couldn't point to any large region and say "This speaks Parisian French"; rather, there'd be a continuum where every few villages would have a somewhat-changed dialect until, by the Mediterranean coast, they'd be speaking full Occitan or Italian. English is somewhat unique in that it never had a significant continuum due to its speakers being on an island, and French influence from the Norman Conquest diverging Old English from its continental relative West Frisian. But even so, Lowland Scots is either a far-diverged dialect of English or a closely related separate language.
What's more, even aside from this confusion of definitions, you can add widespread blind spots in our historical knowledge: even if we could settle what was a language and what was a dialect, we know next to nothing about what languages and dialects were spoken across (for example) 1000 AD South America.
So, unfortunately, your question can't be answered. Linguistic diversity has certainly decreased since the invention of printing, and probably even more since the global economy came to prominence, but any attempt at a specific answer would demand impossible precision.