What does that mean for future number of humans? It may surprize you that it can lead to that the human population on our planet grows very fast.
It is all in the math. Growth in the long term is exponential.
Think of doubling something. Compare that with halving.
Look at about absolute sizes. Doubling will grow very quickly. But halving does not change that much.
We can use that simple fact to roughly estimate population growth under our assumption. I hope this page can help you think about it.
Here we only look at long term growth. In the near time population "pyramid" has a big effect. However we do not have sufficient data for the "pyramids" to include that. And after a generation the exponential growth is all that matters. (If you want a closer look at near term growth you can look at World Population History.)
The only purpose of this page is to make it easier to think about population growth in long term. I would say that this is very easy for anyone with a good understanding of math. So those people does not need this page. This page might be useful for you. Or not. But I would be glad to make this page better. Maybe I should try to explain more at the page below?